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Return To 

SfflK AND TECHNOLOGY 

Library of Congress 




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SEP 21«60 

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' 















SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 



of 


By 





This document contains information affecting the national defense of the 
United States within the meaning of the Espionage Act, 50 U. S. C., 31 and 32, 
as amended. Its transmission or the revelation of its contents in any manner 
to an unauthorized person is prohibited by law. 

This volume is classified SECRET in accordance with security regulations 
of the War and Navy Departments because certain chapters contain materials 
which was SECRET at the date of printing. Other chapters may have had a 
lower classification or none. The reader is advised to consult the War and 
Navy agencies listed on the reverse of this page for the current classification 
of any material. 






Manuscript and illustrations for this volume were prepared for 
publication by the Summary Reports Group of the Columbia 
University Division of War Research under contract OEMsr-1131 
with the Office of Scientific Research and Development. This vol¬ 
ume was printed and bound by the Columbia University Press. 


Distribution of the Summary Technical Report of NDRC has been 
made by the War and Navy Departments. Inquiries concerning the 
availability and distribution of the Summary Technical Report 
volumes and microfilmed and other reference material should be 
addressed to the War Department Library, Room 1A-522, The 
Pentagon, Washington 25, D. C., or to the Office of Naval Re¬ 
search, Navy Department, Attention: Reports and Documents 
Section, Washington 25, D. C. 


3V 


xyECUN 

oriW 


S'* 


't^YD 




■taty 


of 


Copy No. 

238 


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This volume','liL the seventy others of the Summary Technical 
Report of Nf$8D, has been written, edited, and printed under 
great pressure. Inevitably there are errors which have slipped past 
Division readers and proofreaders. There may be errors of fact not 
known at time of printing. The author has not been able to follow 
through his writing to the final page proof. 

Please report errors to: 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports atid sent 
to recipients of the volume. Your help will mako this book more 
useful to other readers and will be of greatr^rhlue in preparing any 
revisions. 

. 31 




A 


\ 








SUMMARY TECHNICAL REPORT OF DIVISION 10, NDRC 


VOLUME 1 


MILITARY PROBLEMS 
WITH AEROSOLS AND 
NONPERSISTENT GASES 


^REGULATION: BEFORE SERVICING 
«R REPRODUCING ANY PART OF THIS 
MSCUMENT, ALL CLASSIFICATION 
1BKI NGS MUST BE CANCETYFiT 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 
VANNEVAR BUSH, DIRECTOR 


NATIONAL DEFENSE RESEARCHDIummi i ill * 


JAMES B. CONANT, C 




DIVISION 10 


SEP 21 «60 


W. A. NOYES, JR., CHIEF \ uffUSt i960 

Defense memo 2 Aug 

UBBAEV « CO***- 


WASHINGTON, D. C., 1046 






NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative 1 

Frank B. Jewett Navy Representative 2 

Karl T. Compton Commissioner of Patents 3 

Irvin Stewart, Executive Secretary 


l Army representatives in order of service: 


2 Navy representatives in order of service: 


Maj. Gen. G. V. Strong 
Maj. Gen. R. C. Moore 
Maj. Gen. C. C. Williams 
Brig. Gen. W. A. Wood, Jr. 


Col. L. A. Denson 
Col. P. R. Faymonville 
Brig. Gen. E. A. Regnier 
Col. M. M. Irvine 


Col. E. A. Routheau 


Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 

Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 

Commodore H. A. Schade 
* Commissioners of Patents in order of service: 

Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suitable 
projects and research programs on the instrumentalities of 
warfare, together with contract facilities for carrying out 
these projects and programs, and (2|4 <g fy$£)uster the tech¬ 
nical and scientific work o^tM phntracks. Mcji^ specifically, 
NDRC functioned by jAitiating research projects on re¬ 
quests from the Army (^jffeONkvy, or on requests from an 
allied government Kpansmitted through _thf\Liaison Office 
of OSRD, or on its own considered initiative as a result of 
the experience of its members. Proposals prepared9^ the 
Division, Panel, or Committee for research contracts for 
performance of the work Involved in such pro^jec^sSwere 
first reviewed by Nl^l^C^and if approved, recommended to 
the Director of OSRD. Kgen^pproval of a proposal by the 
Director, a contractvpmnitting maximum flexibility of 
scientific effort was arranged. The business aspects of the 
contract, including such matters as materials, clearances, 
vouchers, patents, priorities, legal matters, and administra¬ 
tion of patent matters were handled by the Executive Sec¬ 
retary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were: 

Division A — Armor and Ordnance 

Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


iv 


Library of Congress 




In a reorganization in the fall of 1942, twenty-three ad¬ 
ministrative divisions, panels, or committees were created, 
each with a chief selected on the basis of his outstanding 
work in the particular field. The NDRC members then be¬ 
came a reviewing and advisory group to the Director of 
OSRD. The final organization was as follows: 


Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub-Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 



2015 


460887 


























NDRC FOREWORD 


A s events ol the years preceding 1940 revealed 
more and more clearly the seriousness of the 
world situation, many scientists in this country came 
to realize the need of organizing scientific research 
for service in a national emergency. Recommenda¬ 
tions which they made to the White House were given 
careful and sympathetic attention, and as a result the 
National Defense Research Committee [NDRC] 
was formed by Executive Order of the President in 
the summer of 1940. The members of NDRC, ap¬ 
pointed by the President, were instructed to supple¬ 
ment the work of the Army and the Navy in the de¬ 
velopment of the instrumentalities of war. A year 
later, upon the establishment of the Office of Scien¬ 
tific Research and Development [OSRD], NDRC 
became one of its units. 

The Summary Technical Report of NDRC is a 
conscientious effort on the part of NDRC to sum¬ 


sampling inspection by the Applied Mathematics 
Panel. Since the material treated in them is not dupli¬ 
cated in the Summary Technical Report of NDRC, 
the monographs are an important part of the story 
of these aspects of NDRC research. 

In contrast to the information on radar, which is 
of widespread interest and much of which is released 
to the public, the research on subsurface warfare is 
largely classified and is of general interest to a more 
restricted group. As a consequence, the report of 
Division 6 is found almost entirely in its Summary 
Technical Report, which runs to over twenty vol¬ 
umes. The extent of the work of a Division cannot 
therefore be judged solely by the number of volumes 
devoted to it in the Summary Technical Report of 
NDRC: account must be taken of the monographs 
and available reports published elsewhere. 

The varied activities of Division 10, under the 


marize and evaluate its work and to presenfy^g^^g^fdpfst^p of W. A. Noyes, Jr., included the study 
useful and permanent form. It comprises - some ' arid deyelopment of gas mask filters and absorbents, 
seventy volumes broken into groups screening smokes, chemical warfare munitions, offen- 

to the NDRC Divisions, Panels, and Committees. sive chemical warfare dispersal of insecticides, and 

The Summary Technical Report of each Digi^^h,2 fr496(i>roblems related to these fields. Perhaps one 
Panel, or Committee is an integral survey of the of the most notable achievements of NDRC was the 
work of that group. The first volume of^f^^awqaiaao Di&lMWS &S§@lopment of smoke generators which 
report contains a summary of the report, gating the^yw^^^o^ screening strategic targets in all the- 


problems presented and the philosophy! 
them, and summarizing the results of the research, 
development, and training activities undertaken. 
Some volumes may be “state of the art” treatises 
covering subjects to which various research groups 
have contributed information. Others may contain 
descriptions of devices developed in the laboratories. 
A master index of all these divisional, panel, and 
committee reports which together constitute the 
Summary Technical Report of NDRC is contained 
in a separate volume, which also includes the index 
of a microfilm record of pertinent technical labora¬ 
tory reports and reference material. 

Some of the NDRC-sponsored researches which 
had been declassified by the end of 1945 were of suf¬ 
ficient popular interest that it was found desirable to 
report them in the form of monographs, such as the 
series on radar by Division 14 and the monograph on 


aters of war. 

The Division’s contributions not only greatly aided 
the Allied war effort and saved both military and 
civilian lives, but will continue to benefit mankind in 
peacetime. The Summary Technical Report of Di¬ 
vision 10, prepared under the direction of the Divi¬ 
sion Chief and authorized by him for publication, 
presents the methods and results of the widely varied 
research and development programs carried out by 
the very able personnel of the Division and its con¬ 
tractors. For their invaluable achievements, we join 
the Nation in expressing our grateful appreciation. 

Vannevar Bush, Director 
Office of Scientific Research and Development 

J. B. Conant, Chairman 
National Defense Research Committee 




























































































































































































































































































FOREWORD 


I n presenting the Summary Technical Report of 
Division 10 of the National Defense Research 
Committee, the Chief of the Division desires espe¬ 
cially to thank those who have contributed of their 
time and energy to its preparation. In particular, 
Dr. W. C. Pierce has accepted full responsibility for 
obtaining the manuscript from the various authors 
and for editing it into final form for publication. 
This task has been a long and arduous one which has 
maintained Dr. Pierce’s contacts with defense work 
for many months after the close of the war. He de¬ 
serves special thanks for his efforts. However, his 
efforts would have been fruitless without the active 
cooperation of all of those who prepared the various 
chapters. The names of these men are too numerous 
to mention in this foreword, but they deserve out- 
real gratitude for putting in clear, concise form the 
results of nearly six years of effort on military re¬ 
search. Without the work they have done, the task 
of reviewing and utilizing the vast amount of infor¬ 
mation accumulated would have been superhuman 
for those who might engage in this work in the future. 

Division 10 was formed from Section B-5 and B-6 
of old Division B of the National Defense Research 
Committee. At the time of its formation, the Chiefs 
of these two Sections were Dr. W. H. Rodebush, of 


the University of Illinois, and Dr. D. M. Yost, of 
the California Institute of Technology. These two 
men deserve much credit foi; organizing the scientific 
work which later was incorporated in Division 10. 

Finally, it should be stated that the work of the 
Division was in a very real sense a cooperative ven¬ 
ture. The Summary Technical Report makes no 
attempt to allocate credit either to individuals or to 
contractors. From a purely scientific point of view, 
this is best. From the standpoint of feeling of satis¬ 
faction which may be gained by individuals who have 
contributed to a worthy cause, the personal credit 
side is emphasized in the volume entitled “Chemis¬ 
try in World War II.” In that volume, an effort is 
made, inadequate as that effort may be, to give the 
names of those who have done the work. 

Finally, the Division Chief feels that in addition to 
those who have edited and written this volume, his 
sincere thanks are due to all of those who contrib¬ 
uted to the work in the laboratory and in the field. 
Without the efforts of these people, the work of the 
Division could not have been carried out. 


W. A. Noyes, Jr. ' 
Chief, Division 10 * 


DECL ASSIFIED 
Ey authority Secretary of 


SEP 2 11960 

Defense memo 2 Augns 1 I960 
LIBRARY OF CONGREod 







































































































































































































* • 



































PREFACE 


D uring World War II, Division 10, in common 
with other Divisions of NDRC, issued volumi¬ 
nous reports. These were widely distributed, but even 
so, there are few complete files available today. A 
future worker could, by access to a complete file, 
reconstruct quite accurately the picture as of today. 
This would, however, be very tedious and time con¬ 
suming because of the large volume of reports and 
because these reports were written for current use 
and often dealt with fragmentary phases of the 
work; quite often the conclusions were changed dur¬ 
ing the progress of the work. 

The purpose of this volume is: 

1. To summarize the work done during World 
War II. 

2. To present final conclusions drawn from this 
work, from a critical point of view. 

3. To suggest further work which according to the 
judgment of today might be profitable. 

In compiling this volume an account is given of 
most of the activities of the Division, as enumerated 
in the Non-Technical Summary, above. One major 
activity of the Division, namely the field testing of 
gases, is largely omitted because this work was per¬ 
formed jointly with CWS and is adequately reported 
in the publications from San Jose, Dugway Proving 
Ground, and Project Coordination Staff. An account 
of NDRC participation in these activities is given in 
the History. 

The technical work of Division 10 and its pred¬ 
ecessors Sections B5 and B6 was described in a 
series of different reports, each of which had different 
circulations and were intended for different purposes. 
Complete files of the more important series, the 
NDRC and OSRD reports, are reproduced in the 
microfilms. Since other series of reports were of an 
ephemeral nature they were not completely repro¬ 
duced, but copies are available in the Division files. 
The following reports were issued: 

1. OSRD. These are formal reports, each pre¬ 
sumably covering some completed phase of work. 
Distribution was through the OSRD office and, in 
general, these reports were not circulated to indi¬ 
vidual contractors. Serial numbers were chronologi¬ 
cal, without reference to the Division from which the 
report originated. A list of titles of OSRD reports 
from Division 10 is given in the Bibliography. 

2. B6 NDRC Reports. This series, designated by 
roman numerals, was started in 1941 as a means of 


disseminating information among the contractors 
of the Section. Much of the material in these reports 
is also given in the OSRD reports. The B6 series was 
discontinued with the formation of Division 10. A 
list of titles is given in the Bibliography. 

3. Division 10 Informal Reports. This series was a 
continuation of the B6 series, for interchange of in¬ 
formation among the Division contractors. A separ¬ 
ate series was published for each of the sections of 
Division 10, each with its own serial number. 
Designations are 10.1-1, etc. The series was con¬ 
tinued to the end of the war. A list of titles is given 
in the Bibliography. 

4. Contractor’s Reports. At the conclusion of a 
contract a final report was required. In addition some 
contractors submitted special reports upon request, 
or periodically. These reports are to be found only in 
the Division files. In a few instances they are in¬ 
cluded in the microfilms. 

5. Monthly Summary Report. This was a monthly 
report of the “news letter” type designed for distri¬ 
bution only among the contractors of Sections 10.1 
and 10.5. It started January 15, 1943, and continued 
until April 15, 1945. While all of the material given 
in this series was more formally reported in the 
OSRD s erMj ORA SffS RlfeP been included in the 

micrfgmg ut j, orit Secretary of, r „„ n 

6. Munitions Development Laboratory \_MDL] 


e This series was published 
945, for rapid dissemina¬ 
tion of information concerning developments in the 
i& 1 Hid ^miW&films. 

^ Mvision Chief. Bi¬ 
monthly the Division Chief prepared a summarizing 
report of activities, which was given a limited distri¬ 
bution in the upper echelon of OSRD and to the 
Services. Since all of the material of these reports is 
given firsthand elsewhere, they are not included in 
the microfilms. 


Monthly Prx 
from Januarfjr-1944 


ACKNOWLEDGMENTS 

The reports in this volume were for the most part 
written after the end of the war, by the men who had 
actively participated in the program. These authors, 
whose names appear in the various chapters, made 
personal sacrifices of time and energy to write the 
reports at a time when their major interests lay in 


IX 



X 


PREFACE 


other activities. The editor desires to acknowledge 
his indebtedness to all authors for the competent and 
authoritative summaries they have prepared. Par¬ 
ticular mention should be made of the assistance 
rendered by Dr. David Sinclair, of the Johns Man- 
ville Corporation, for serving as editor and advisor in 


the manuscript of the aerosol section, and by Dr. 
Jack G. Roof of the University of Oregon who 
served as editor and advisor for the section on 
M ic rometeorology. 

W. Conway Pierce 
Editor 


declared 

B y authority Secretary 

t;iro 2 1 '950 

/» rv, - ** ^ 

» efeIlS . 






CONTENTS 


CHAPTER PAGE 

Summary. 1 


PART I 

THE GAS MASK 


1 U. S. Gas Masks. 7 

2 Testing of Gas Mask Charcoal and Canisters.12 

3 Manufacture of Activated Charcoal.23 

4 Impregnation of Charcoal.40 

5 Surveillance of Impregnated Charcoal.88 

6 Adsorption and Pore Size Measurements on Charcoals and Whetlerites 97 

7 Mechanism of Chemical Removal of Gases.150 

8 The Adsorption Wave.169 

9 Canister Design.183 

10 The Aerosol Filter.. . CLASSIFIED 190 

11 Performance of U. S. and Foreign Gas Canister^ 4utJioi;ity Secretary olf94 

12 Protection against Carbon Monoxide.203 

13 Criticisms and Recommendations. SEP* 2* ! •IQftf). • 207 


Defense memo 2 August 1960 
PART II - 

MICROMETEOROLOGY AND TFrlMF# q^ONGRESS 
CHEMICAL WARFARE GAS CLOUDS 


14 General Meteorological Principles.213 

15 Micrometeorological Instruments.239 

16 Behavior of Gas Clouds.260 

17 Field Sampling Methods for Nonpersistent Gases.284 


PART III 
AEROSOLS 


18 General Properties of Aerosols.297 

19 Stability of Aerosols and Behavior of Aerosol Particles.301 

20 Formation of Aerosols.314 

21 Optical Properties of Aerosols .318 

22 Measurement of Particle Size and Size Distribution.334 

23 Filtration of Aerosols.354 

24 Methods of Testing Smoke Filters.360 

25 Smoke Screens.375 

26 Travel and Persistence of Aerosol Clouds.380 

27 Theory of Obscuration.389 


xi 
























CONTENTS 


xii 


PART IV 

NEW MUNITIONS FOR SMOKE AND TOXIC GASES 


CHAPTER PAGE 

28 Introduction.395 

29 Atomization of Liquids.398 

30 Thermal Generator Munitions.411 

31 Fuel Blocks for Thermal Generator Munitions.459 

32 New Screening Smoke Mixtures.485 

33 Exhaust Smoke Generator for Airplane Engines.507 

34 Munitions for Dispersal of Liquid Droplets.524 

35 Munitions for the Dispersal of Solid Particles.534 

36 Dispersion of Herbicides.546 

37 Plasticized White Phosphorus .551 


PART V 

MI SC ELL A NEO US TOPICS 

38 Insect Control — The Development of Equipment for the Dispersal 


of DDT.577 

39 Inorganic Toxic Gases.604 

40 The Preparation of Fluorine.610 

41 The Stabilization of Cyanogen Chloride.613 

42 Stabilization and Flame Inhibition of Hydrogen C}^anide.618 

43 Wind-Tunnel Studies of Fog Dispersal, Gas Diffusion, and Flow over 

Mountainous Terrain.621 

44 Radioactive Tracers.640 

Glossal.645 

Bibliography.647 

OSRD Personnel.696 

Contract Numbers.698 

Project Numbers.704 

Index.707 










■pei e 

l£&-" 






























Zc 


.^6lC 










SUMMARY 


By W. A. Noyes , Jr. 


absorbents. 

chemical warfare and 


re 

P 


D ivision 10 was formed from two sections which 
had been established in 1940 for studying the 
broad problems of aerosols and of gas mask absorbents 
respectively. By the end of the war, the activities 
of the Division had broadened to cover many sub¬ 
jects, some of which were totally unrelated to either 
of those assigned by the Services at the beginning. 
For the purposes of discussion, the work of the 
Division may be subdivided under the following 
headings: 

1 . Gas mask filters. J$— 

2 . Screening smokes. y %r &u J ch° 

3. Chemical warfare munitions (including smoke 
munitions). 

4. Gas mask 

5. Offensive 
problems. 

Certain miscellaneous activities do not fall*under 
one or another of the above headings. 

The work on the gas mask filter was necessitated 
by the threat of toxic aerosols set up by munitions. 
The U. S. Army gas mask filter of 1940 was satis¬ 
factory for many toxic smokes of the type first used 
by the Germans during World War I, but this filter 
proved to be vulnerable under certain climatic 
conditions particularly at high humidities. Moreover, 
solid agents of exceedingly high toxicity are known, 
and the possibility of their use made desirable an 
improvement in the protection afforded by the filter. 

The activities of the Division centered around 
improvement in the filter testing methods and im¬ 
provement in the filter itself. The use of radio¬ 
active tracers permitted quantitative measurements 
of filter penetration to be made, but optical methods 
were much better for penetrometers to be used in 
control of canister production. Several improve¬ 
ments were made in optical penetrometers and the 
devices in use by the Army and the Navy at the 
close of the war, had their origins in the work of 
Division 10. 


The theory of filtration developed by Section B-5 
indicated clearly that the fibers of a satisfactory 
filter must have diameters of the same order of 
magnitude as those of the particles to be removed. 
Since such particles may be only a few tenths of a 
micron in diameter, filter fibers of that size were 
demanded. 

While synthetic fibers were produced on a small 
scale by Division 10 contracts, the naturally occur- 
of high availability and with the right 
meter asbestos. The incorporation of 
cellulose paper together with 
methods of providing adequate tensile strength were 



_ Ahe> achievements of Division 10. Army and Navy 
" gas mask canisters during the last two years of the 
. , , war were eqtli^ea with paper filters developed under 

^ a. V Thfe screening of st 


A WY stahhfiing of strategic targets was one of the 
early important problems brought to the attention 
of Section B-5. A critical examination of the theory 
of screening was carried out on several contracts 
with the result that a white smoke with particles of 
such diameter as to give maximum scatter of wave 
lengths in the neighborhood of 5000 Angstrom units 
was shown to be best. Methods of producing such 
smokes were devised in the laboratory and carried 
forward to a practical scale by various contracts. 
Smoke generators using high boiling petroleum 
fractions were developed and used in large numbers 
by the Armed Services. This is one of the notable 
achievements of the NDRC in the war effort. 

The tactical use of smoke demands a different 
type of screening material than the strategic use. 
White phosphorus was the principal material used 
in bursting munitions, but it had the serious dis¬ 
advantage of short burning time and of “pillaring”. 
These disadvantages were overcome by producing 
a white phosphorus plasticized with synthetic 
rubber. 

The offensive use of chemical warfare had been 
confined mainly to the standard agents of the last 




2 


SUMMARY 


war in bursting munitions and in spray tanks. Di¬ 
vision 10 was assigned the problem of developing new 
devices particularly for those agents which are de¬ 
stroyed by heat and which may have toxicities 
considerably higher than those known previously 
such as mustard gas and phosgene. A thermal 
generator for setting up aerosol clouds of mustard 
gas was developed and showed promise in the tests 
carried out by the Chemical Warfare Service, al¬ 
though bombs based on this principle were not 
manufactured in quantity during the war. For 
thermolabile solids which are exceedingly toxic, 
a bomb was devised using gas pressure without 
burster. The main difficulty in using this type of 
agent is concerned with proper micronization of the 
solid material and the prevention of agglomeration 
at the time the bomb is burst. Satisfactory progress 
was made on these matters, but the impression is 
gained that the problem is far from solved. 

The gas mask absorbent in use by the United 
States Army in 1940 showed good protection against 
most agents when dry, but was vulnerable toward 
certain agents such as arsine and cyanogen chloride 
when wet. The work of Division 10 on gas mask 
absorbents concerned improvement in testing 
methods and improvement in the impregnation of 
charcoal. Related studies resulted in removal of 
soda lime from the canister filling, since this material 
is inert toward gases other than phosgene and 
hydrogen cyanide, the testing of gas mask absorb¬ 
ents by introduction of a simulated breathing ma¬ 
chine, the improvement in indicator solutions, and 
the full demonstration that absorbents should be 
tested in canisters rather than in tubes. 

The incorporation of silver and chromium along 
with copper for impregnating the charcoal was the 
main contribution of Division 10 to gas mask ab¬ 
sorbents. This impregnation gives well-balanced pro¬ 
tection against non-persistent agents under all con¬ 
ditions of humidity and temperature which might be 
encountered in the field. There is some instability 
in storage, and certain types of charcoal are better 
than others in this respect. Nevertheless, it was 
shown that for ordinary conditions of use, this type 
of impregnated charcoal is adequate. 

The contributions of the Division on offensive 
chemical warfare other than munitions, were con¬ 
cerned with improvement in field sampling devices, 
development of meteorological instruments, and aid 
to the Armed Services in carrying out an extensive 
program of field experimentation with chemical war¬ 


fare munitions and agents. The results of this pro¬ 
gram were imparted to the Armed Services and aided 
materially in changing the doctrine for the use of 
chemical warfare agents. Many men were involved at 
several different field stations in this country and 
overseas. 

The work of the Division on the dispersal of insec¬ 
ticides involved a demonstration that there is an 
optimum particle size which is materially greater 
than that of a good screening smoke. Since most in¬ 
secticides such as DDT cannot be volatilized without 
decomposition, the production of a satisfactory 
aerosol must be based on principles different from 
those used in screening smoke generators. It was 
shown that a frothing mixture made by oil solutions 
of DDT and water heated to the proper temperature 
in a rapid stream, produced products of controlled 
size several microns in diameter. It was demonstrated 
that particles of this size are most effective either for 
mosquitoes on the wing or for larvicide control. 
Several generators for setting up such aerosols from 
the ground were developed and exhaust smoke gener¬ 
ators for planes and for a jeep could be adapted to 
dispersion of DDT aerosols. The plane devices were 
adopted by TVA and by UNRRA and were used to 
some extent by the Armed Services. 

Some of the problems not related to any of the 
above subjects may be mentioned in passing: 

1. The dissipation of fog over airfield runways 
was deemed to be of vital importance due to plane 
losses in the United Kingdom. The British system of 
gasoline burners was expensive and probably could 
not have been used under conditions of high wind 
velocity. Various methods of setting up heated air 
curtains were studied by Division 10 and plans for 
installations on several Pacific islands were provided. 
A method of high-intensity sound precipitation of 
fogs was also studied, but while some favorable 
results were obtained, it is probable that this method 
would not have been practicable in actual use. 

2. The purification of certain inorganic com¬ 
pounds to be used by Division 16 in infrared viewing 
devices was undertaken by one contract in Division 
10. Extraordinarily high degrees of purity are 
essential for compounds to be used in this connection, 
and the work of Division 10 did show that some of 
these impurities are more important than others. 

3 . In some Pacific islands, such peculiar air cur¬ 
rents are encountered that the location of airfields 
must recognize this situation. Since it is impossible 
for detailed measurements of these air currents to 




SUMMARY 


3 


be made in actual practice, the Air Forces requested 
Division 10 to make model studies in a wind tunnel. 
This was done, and the results were of interest to the 
Air Forces in determining the locations for airfields. 

4. Since the Chemical Warfare Service requested 
a study of the vulnerability of the gas mask canister 
to be made, it was essential that new types of com¬ 
pounds be synthesized. Many new compounds were 
made, but most of them involved fluorine in one 
form or another. Consequently, attention was di¬ 
rected to improvement in fluorine generators and to 
methods of synthesis using elemental fluorine. These 
extensive investigations did not disclose any new war 
gases of unusual promise, but they did serve to 
eliminate certain ones from consideration. 

5. Cyanogen chloride as a war gas has some ad¬ 
vantages over phosgene, particularly in that pro¬ 
tection against it by most gas mask canisters is very 
poor indeed. In humid, tropical climates, the 
Japanese canisters gave almost zero protection. 
Since cyanogen chloride is not stable in ordinary 
steel containers for long periods of time, a careful 
investigation of means of increasing the stability was 
made. Many of the factors affecting the rate of 
polymerization were studied, and although the final 
stabilizer was proposed by Division 9, the contribu¬ 
tions of Division 10 to this subject were considerable. 

6 . Hydrogen cyanide is a quick-acting lethal agent 
of great promise, but it is inflammable, and, when 
used in most munitions, it is destroyed by a fair 
fraction of the bursts. Means of preventing inflam¬ 
mation of this agent were studied by Division 10, and 
it was found that the incorporation of small per¬ 
centages of certain hydrocarbons improved stability 


upon detonation markedly. It is believed, however, 
that the final solution of this problem has not yet 
been found. 

7. The oxygen rebreather developed by the Naval 
Research Laboratory using K0 2 had one serious dis¬ 
advantage due to the accumulations of nitrogen in 
the circulating system. The elimination of this 
nitrogen was the subject of a series of studies made 
by Division 10. A small, supplementary bellows which 
would flush out a small fraction of the gases during 
each breathing cycle was proposed and shown to be 
satisfactory, although it was not adopted. 

8 . At one time, it was proposed that the dis¬ 
semination of herbicides over enemy territory might 
destroy crops and aid materially in shortening 
the war. Means of disseminating these compounds 
were studied by Division 10 and a proposal was 
made which probably would have been adopted by 
the Army had the war lasted much longer. 

9. Smoke signals, particularly with colored 
smokes, were used either for target identification, for 
air attacks or for markers during submarine tests. 
Division 10 designed smoke floats and bombs for 
both of these purposes. 

10. The standard smoke pot used by the Army 
contained a mixture of hexachloroethane, zinc oxide, 
and some reducing agent, such as finely divided 
aluminum. Manufacture of these mixtures is dan¬ 
gerous, and the smoke from such pots is extremely 
toxic due to the zinc. Division 10 developed an oil 
smoke pot in which the oil is vaporized in a suitably 
designed Venturi by the hot gases from a burning- 
fuel block. This smoke pot would have been in pro¬ 
duction had the war lasted a few months longer. 











































































































































































/ 



PART I 

THE GAS MASK 


I N the period 194-1 to 194-5 there was very close co¬ 
operation between the National Defense Research 
Committee [iVZ)i?C] and the Services on all inatters 
pertaining to the gas mask. Problems of research and de¬ 
velopment were attacked jointly, often with interchange 
of personnel. It is, therefore, not possible or desirable to 
confine this report to that work which was done by the 
NDRC. Rather, for completeness, a resume of the en¬ 
tire field of gas mask development is given in Part I and 
consequently, no attempt is made to allocate credit, 
either to the various branches of the Services or to 
NDRC. 



RET 







_PECLASSIFTFn 
Ey authority Secretary of 

SEP 2 11960 

Defense memo 2 August I960 Chapter 1 


A? 


library of congress. GAS MASKS 3 


By W. Conway Pierce 


l.l INTRODUCTION 

he development of a military gas mask began 
with the first gas attack 1 which was made by the 
Germans on April 21, 1915, in which they released a 
cloud of chlorine for travel downwind. By May 3, 
1915, British troops had been issued cotton cloth 
pads soaked in a solution of sodium thiosulfate and 
sodium carbonate, which provided a measure of pro¬ 
tection. From April 1915 to the end of World War I, 
the race between offense and defense was close. In the 
offense, the use of chlorine was followed in turn by 
phosgene [CG], chloropicrin [PS], mustard gas [H], 
lacrimators, and irritant smokes. Concurrently, gas 
protection went through the stages of an impreg¬ 
nated pad, a series of helmets of impregnated cloth, 
and finally a box respirator. This respirator was the 
progenitor of today’s mask, consisting of a canister 
filled with chemicals for air purification and a face- 
piece. The efficiency of charcoal as an air purifier was 
recognized early and by April 1916, British troops 
were using a canister which contained charcoal, soda 
lime, and permanganate particles. 

When the United States entered World War I, an 
intensive research and development program was 
started on gas masks. The general design of the U. S. 
mask that grew out of this work was much like the 
British. The mask consisted of four major compo¬ 
nents: a facepiece, canister, hosetube, and carrier. 
While crude according to present standards, it gave 
adequate protection against the attainable field con¬ 
centrations of that time. The facepiece was con¬ 
structed of rubberized cloth and gave protection both 
to the eyes and to the respiratory tract. Breathing 
was through the mouth by means of a hard rubber 
bit held in the teeth, and nose-breathing was pre¬ 
vented by a clip to close the nostrils. The mask was 
very uncomfortable. It was, however, perhaps even 
safer than modern masks, because there was no pos¬ 
sible danger from leaks at the face seal. The canister 


contained about 680 ml of a 60-40 mixture of acti¬ 
vated coconut charcoal with soda lime granules. Pro¬ 
tection was poor against cyanogen chloride [CK] 
and arsine [SA], particularly when the charcoal was 
humidified, but neither of these gases was used dur¬ 
ing the war. Excellent protection was afforded against 
the gases then in use, such as CG, PS, H, and diphos¬ 
gene. Smoke protection was very poor, but was ap¬ 
parently adequate because there are no records of 
mask failure caused by smoke penetration. The car¬ 
rier was a knapsack slung on the chest when in use, 
but otherwise carried by a shoulder strap. 

Following World War I, a continuing program of 
gas mask research and development was maintained 
at Edge wood Arsenal. Although budgets were small 
and staffs limited, extensive progress was made and 
the masks in use at the start of World War II were 
much superior to those of 1918. Comfort was in¬ 
creased by use of Tissot-type facepieces which per¬ 
mit nasal breathing. Smoke protection was much 
better, with the use of a carbon-impregnated filter 
paper through which all inspired air was passed. Gas 
protection was increased by an improved design of 
canister and by the impregnation of the charcoal 
with cupric oxide which acts as an oxidizing and 
basic medium for retention of acid or reducing gases. 
Nevertheless, there were at the start of the war two 
serious defects: (1) gas protection was poor against 
CK, SA, and certain other gases when the charcoal 
had become partially saturated with water vapor by 
equilibration with air of high humidity, and (2) the 
smoke protection could be broken down by prolonged 
exposure to a smoke which contained liquid droplets. 
Both of these, as well as other problems, were solved 
during the 1940 to 1945 period. 

1.2 GAS MASKS OF WORLD WAR II 

Army Service gas masks 1-3 6 of 1940 to 1945 were 
of various types. 



7 






8 


U. S. GAS MASKS 


Service, Old Style, M2A1-1XA1-IV a 

As improvements were made, one or the other of 
the components was altered and Service masks were 
issued with MIA1, MIA2, M2A1, and M2A2 face- 
pieces, MIXA1 and M9A2 canisters, and Mill, 
MIIIA1, MIV, MIVA1 carriers. The mask was char¬ 
acterized by a flat-type carrier mounted beneath the 
left armpit, a Tissot-type facepiece connected by a 
long hosetube to the canister, and a large oval can¬ 
ister. The complete assembly weighed about 5J4 lb. 
The MIA1 and MIA2 facepieces were made of stock¬ 
inette covered rubber sheets, assembled with a seam 
beneath the chin. The eyelenses were of flat safety 
glass. All other facepieces were molded in one piece 
from natural, reclaimed, or synthetic rubber, and 
had curved plastic eyelenses. Several different types 
of head harness and outlet valves were used in the 
various models. All types of facepieces had Tissot 
tubes to direct incoming air across the eyelenses to 
prevent fogging. 

Service, Lightweight, M3-10A1-6 

The Service mask was developed in 1943 to replace 
the old-style Service mask. The name “lightweight” 
is somewhat misleading. As originally designed, the 
weight was about 3)4 lb but, before starting pro¬ 
duction, protective capes and ointment were added 
to the carrier, so that the resulting weight was 5J4 lb, 
the same as that of the old mask. The lightweight 
Service mask may have M2A1, M2A2, M3, or M4 
facepieces and M10 or M10A1 canisters. 

The differences between the old style and light¬ 
weight Service masks are chiefly in the canister and 
carrier. The latter is designed for use in various po¬ 
sitions, namely, chest, side, or back. The hosetube is 
shortened from 27 to 18 in. The M10 and M10A1 
canisters are cylindrical, measuring 3J^6 in. in diam¬ 
eter by 5)4 in. long. They differ only in the volumes 
of charcoal, which are respectively 275 and 340 ml. 
The M3 and M4 facepieces are equipped with nose- 
cups to keep exhaled air from contact with the eye¬ 
lenses as an aid in prevention of fogging. 


a The model numbers for the gas mask assembly refer 
respectively to facepiece, canister, and carrier. Designations 
are not given for the minor constituents such as hosetube, 
outlet valve, and head harness. Prior to 1942, model numbers 
of standard items were in roman numerals, but items 
standardized thereafter were given arabic model numbers. 
Thus, the MIXA1 canister was revised in 1943 to M9A2. 
Revisions of a basic model are denoted by the letter A fol¬ 
lowed by an arabic number. 


Combat or Assault M5-11-7 

The combat mask was developed in 1943 to pro¬ 
vide a lightweight compact mask without a hosetube 
for use by assault troops. Objectives in this develop¬ 
ment were: 

1. Light weight. 

2 . Waterproof carrier, so that mask is not soaked 
by immersion during an amphibian operation. 

3. Compactness. 

4. Elimination of hosetube. 

It was not required that this mask be as rugged as 
the Service mask. 

The mask, when developed, exceeded the proposed 
requirements in many respects. After various tests, it 
was decided to mount the canister on the left cheek 
as in the British light mask, and to make the canister 
interchangeable with the British mask. The Mil 
canister departs from previous practice in that the 
air flow is axial through a flat bed. The carrier M7 is 
constructed of rubberized cloth and is made so that 
the flap has a watertight seal which will withstand 
immersion for hours. The complete assembly without 
capes or ointment weighs about 3 lb. 

Diaphragm 

Diaphragm masks are the same as Service masks in 
all parts except the facepiece, which contains a dia¬ 
phragm for voice transmission. The diaphragm mask 
is classed as a limited standard. 

Optical 

Optical masks are made in two styles. Facepiece 
M2 is designed for use with the other components of 
a Service mask. Its distinguishing feature is the addi¬ 
tion of plane-adjustable eyepieces, and a diaphragm 
for voice transmission. Facepiece Ml is a special unit 
requiring its own canister, carrier, et cetera. It is pro¬ 
vided with optical eyelenses and a diaphragm. The 
canister is mounted on a clip at the rear of the head 
harness and is connected by two 8J^-in. hosetubes to 
the air inlet of the facepiece. It is about the same size 
as an M10 canister and gives about the same protec¬ 
tion. This model is no longer used by the Army. 

Training M2-1-1 

Optional parts of the training mask are M2A1, 
M2A2 facepieces and M1A1 canister. This mask was 
developed as a compact, lightweight, inexpensive 
mask for use in training, and was never intended for 
combat duty. Features are a standard Service face- 
piece with a small cylindrical canister directly at¬ 
tached at the air inlet of the facepiece so that the 




GAS MASK CANISTERS 


9 


canister is suspended beneath the chin. The carrier is 
a small canvas or duck sack which is attached to the 
belt or carried by a shoulder strap. The complete 
assembly weighs about 2 lb. 

Because of its light weight and compactness the 
training mask was used in 1942 and 1943 as a Service 
mask in some theaters, but this practice was discon¬ 
tinued after the introduction of the M3-10A1-6 mask. 
The weakness of the training mask is in the slight 
protection afforded by the canister and in the inter¬ 
ference which the swinging canister causes in strenu¬ 
ous exercise. 

Combat Mask — Chin Type 

In the spring of 1945, a reconversion program was 
organized to make use of natural rubber facepieces 
from old-style Service masks which had been replaced 
by the M3-10A1-6 assembly. At this time, no rubber 
was available for the manufacture of new face blanks, 
and it was believed that old rubber facepieces were 
superior to new ones made from neoprene, the only 
material available at the time. Part of the available 
old facepieces were converted to lightweight Service 
masks, and the remainder to a chin-type mask using 
the Mil canister. This was done by fitting the face- 
piece with a metal adapter so that an Mil canister 
could be mounted beneath the chin. This model had 
serious disadvantages but was considered serviceable. 
New face blanks for this mask were not planned and 
production was limited to conversion of old face 
blanks. 

Navy 

The Navy mask of World War II was like the old- 
type optical mask (with the canister mounted on the 
head harness) except that curved plastic eyelenses 
were used. The earlier canisters contained about 
275 ml charcoal, but later this was changed to about 
360 ml, thereby increasing the protection. 

1.3 GAS MASK CANISTERS 

The canisters used in World War II are described 
below. Typical performance data for new canisters 
are given in Table 1. 

MIXA1 

This is a radial-flow canister weighing about 
1,000 g. The outer body is of corrugated sheet metal, 
rectangular in cross section but with rounded lateral 


edges. The adsorbent b is held in an inner chemical 
container made of perforated metal sheet. Air enters 
the outer container through an inlet valve at the 
bottom and flows radially through the charcoal bed 
to a central inner tube which is attached to an elbow 
nozzle mounted on the top of the can. A thin felt bag 
covers the inner tube and seryes as a dust filter. The 
outer body measures about 3x 4% x 6j/£ in. 

The filling is of two types: (1) Type D mixture of 
copper impregnated charcoal and soda lime in the 
proportions 80 to 20, and (2) copper or copper-silver 
impregnated charcoal. The mesh size is 6-20 U. S. 
screen. The volume of adsorbent is about 650 ml. 
The aerosol filter consists of 10 plies of carbon im¬ 
pregnated paper wrapped about the outer surface of 
the chemical container. This paper is made by aspira¬ 
tion of soot from a smoky flame through a porous 
texture paper. Fine carbon filaments are trapped in 
the coarse network of the paper and serve as a filter 
for removal of aerosols. 

M9A2 

This canister is identical in construction with the 
MIXA1 but differs in the filter and adsorbent. To 
facilitate identification, it is marked by a yellow top. 
The filter is asbestos impregnated paper, depending 
upon the fine asbestos fibers for filtration. The ad¬ 
sorbent is Type ASC charcoal (copper-silver-chro¬ 
mium). The gas protection is the best of any known 
canister, because of the large volume of adsorbent. 
The design is not efficient for utilization of the char¬ 
coal because penetration occurs through sections 
where the layer depth is least and not all the ad¬ 
sorbent is effective. 

M10 

This canister is cylindrical, measuring 3J^6 in- in 
diameter by 53^ in. in height. The general principle is 
like that of the MIXA1 with radial air flow. The 
filter is asbestos impregnated paper. The adsorbent 
is 275 ml, 12-30 mesh, Type ASC whetlerite. The 
weight is about 465 g. 


b Throughout this section of the book there is some con¬ 
fusion in usage of the words adsorbent and absorbent. Strictly 
speaking, an adsorbent removes gas by physical adsorption 
on the surface while an absorbent removes gas by chemical 
reaction. The distinction is difficult to make in many in¬ 
stances since removal by chemical reaction in the gas mask 
canister is preceded by adsorption on the charcoal surface. 
Consequently, most of the authors speak of adsorption and 
adsorbents; the Chemical Warfare Service, on the other hand, 
prefers the terms absorbent and absorption. 




10 


U. S. GAS MASKS 


Table 1. Gas mask canister data.* 


Model 

Filling 

type 

Volume 

Layer 

depth 

cm 

Weight in grams of gast retained at break 

CK 

80-80 

CK 

0-80 

AC 

0-80 

AC 

80-80 

CG 

SA 

80-80 

PS 

80-80 

MIXA1 

A or D 

650 

2.5 

<0.5 

2 

8 

3 

50 

<0.5 

7 

M9A2 

ASC 

650 

2.5 

15.0 

20 

15 

15 

50 

>12.0 

7 

Ml 

A 

220 

1.6 

<0.2 

1 

3 

1 

10 

<0.2 

4 

Ml A1 

ASC 

220 

1.6 

1.0 

4 

4 

4 

10 

>5.0 

4 

M10 

ASC 

275 

1.6 

3.0 

7 

7 

7 

15 

>12.0 

7 

M10A1 

ASC 

340 

1.8 

10.0 

15 

10 

10 

25 

>12.0 

10 

Mil 

ASC 

250 

2.8 

3.0 

7 

7 

7 

15 

>12.0 

7 


* These are average values for production canisters tested at high flow rate to a break of physiological significance. The CG life is about the 
same for dry and humidified charcoal. 

t See Chapter 2 for conditions of the tests and meaning of the symbols. 


M10A1 

The outer size and general construction are the 
same as the M10, the only difference being in the size 
of the chemical container, which holds 340 ml ASC 
whetlerite. As shown by data in Table 1, the gas pro¬ 
tection is much greater than that of the M10. The 
weight is about 500 g. After introduction of the 
M10A1 model, no more M10 canisters were manu¬ 
factured. 

Ml 

The M1 training canister was the first of the cylin¬ 
drical radial-flow models to be developed. It was de¬ 
signed for attachment directly to the facepiece. Con¬ 
struction is exactly like the M10, the only difference 
being in the length, which is 4% in. The adsorbent is 
about 210 ml Type A whetlerite. The filter is carbon 
impregnated paper. In 1943 the Ml was replaced by 
the M1A1. 

M1A1 

This canister is identical with the Ml, except that 
the filling is ASC whetlerite and the filter is asbestos 
impregnated paper. 

Mil 

The design of the assault mask was made possible 
by the development of this lightweight axial-flow 
canister, the development of which depended upon 
perfecting an asbestos-bearing paper which could be 
folded to give a large area in a small space. The paper 
used now contains 5 to 10% asbestos fibers which are 
incorporated with the wood pulp in the paper manu¬ 
facture and which provide the network of fine strands 
responsible for filtration. A method for folding a 
single sheet of area 500 to 600 sq cm to give a fluted 
filter of low resistance which is mounted at the influ¬ 
ent side of the canister has been developed. Above 


the filter there is a charcoal bed 2.8 cm in depth by 
10 cm in diameter. The volume is 250 ml. Prior to 
May 1945, Mil canisters had steel parts and weighed 
about 350 g, but production of aluminum body can¬ 
isters weighing about 250 g was started later. The re¬ 
duction in weight makes the assault mask much more 
comfortable to wear, because this side-mounted can¬ 
ister exerts a marked torque on the left cheek. 

The Mil canister is more efficiently designed than 
the M10 and gives equal or slightly better protection 
with 25 ml less charcoal. It is, however, not nearly so 
rugged as the M10 or M10A1 canisters and must be 
replaced far more frequently. For the purpose origi¬ 
nally designed, that is, for use by assault troops, it is 
excellent. Only field experience in gas warfare will 
show whether the assault mask is better than the 
Service mask for use under all conditions. 

1.4 PROGRESS IN 1940 TO 1945 
PERIOD 5 

The improvements effected in gas protection dur¬ 
ing World War II are summarized below. 

1. High-quality domestic charcoals were devel¬ 
oped from both coal and wood. These can now be 
produced in any desired amount and are more eco¬ 
nomical and better than the coconut charcoal used 
prior to the war. The cost of production was lowered 
to less than 30 cents per pound for some types of 
activated charcoal. 

2. An improved impregnated charcoal known as 
Type ASC was developed and was produced exclu¬ 
sively after the spring of 1943. It was made by im¬ 
pregnating with a copper-silver-chromium solution 
and drying at 150 to 200 C. This adsorbent gave a 
much better balanced protection than the previously 
used Type A whetlerite. Protection was about the 



















STATUS IN 1945 


11 


same as that of Type A whetlerite for CG, H, and 
PS, but wa& much better against AC, CK, and SA, 
particularly when the charcoal was equilibrated with 
moist air. Canisters filled with ASC whetlerite pro¬ 
vided good protection against all known war gases, 
both wet and dry. For a comparison, see the per¬ 
formance data of MIXA1 and M9A2 canisters in 
Table 1. 

3. It was shown that carbon-impregnated filter 
paper broke down rapidly when exposed to a smoke 
containing droplets of liquid, such as an oil-screening 
smoke. This was attributed to action of the liquid 
droplets on the fine carbon filaments which were nec¬ 
essary for filtration. Processes were developed for im¬ 
pregnating paper with asbestos fibers, which gave 
very efficient filters that did not break down on ex¬ 
posure to liquid smokes. The filters used on M1A1, 
M9A2, M10, and M10A1 canisters were of this type. 

4. An asbestos-bearing, thick-sheet paper suitable 
for making folded filters of the German type was de¬ 
veloped. It was made by suitably incorporating as¬ 
bestos with wood fiber during the mixing of pulp in 
the paper mill. When a sheet 500 to 600 cm 2 in area 
after suitable folding was made into a filter, the pres¬ 
sure drop was low and the efficiency of filtration was 
very high. This type of filter, used on the Mil can¬ 
ister, was the best of any U. S. design. 

5. Two different methods were developed for fold¬ 
ing the single-sheet type of canister filter: one, like 
the German, by a special machine; the other by hand 
operation. Both types produced excellent filters. 

6. Methods were developed for waterproofing 
canisters of various masks so that accidental immer¬ 
sion during a landing operation would not spoil a 
canister. All these devices had the weakness that 
some time was required to prepare a waterproofed 
mask for use. A waterproofing treatment for canister 
filters was effective in preventing the entrance of 
water into the adsorbent section when the canister 
was subjected to a brief immersion. 

7. A good facepiece canister mask of the combat 
type was developed for use by troops requiring the 
utmost mobility. This mask was compact and light, 
weighing only 1.6 lb without the carrier. The water¬ 
proof carrier protected the mask very well, even from 
prolonged immersion while wading ashore, yet pro¬ 
vided instant accessibility to the mask. 


8. It was shown that with modern impregnated 
charcoal the use of soda lime as an additional ad¬ 
sorbent is neither necessary nor desirable. Conse¬ 
quently, the use of soda lime in the canister was dis¬ 
continued in 1942. 

9. Improved methods were developed for testing 
charcoal, canisters, and filters. 

10. Extensive studies were made of the humidifi¬ 
cation of canisters in field use and the effect of humid¬ 
ification on performance. Numerous field and labora¬ 
tory surveillance tests were made to determine the 
useful field life of canisters. 

11. Theoretical studies of the nature of the ad¬ 
sorption wave, the factors important in canister de¬ 
sign, the structure of activated charcoal, and the 
state of the impregnant on the charcoal have made 
possible a much better understanding of the factors 
which influence gas protection. 

12. Improvements were made in components of 
the facepiece, such as the eyelens and outlet valve. A 
nosecup was designed to reduce fogging of the eyelens 
in cold climates. Synthetic rubber was used to make 
facepieces of satisfactory performance except at low 
temperatures. 

1.5 STATUS IN 1945 

It was generally believed that the gas protection of 
U. S. troops was the best of any nation’s armies. The 
supply of lightweight and combat Service masks was 
large enough to provide several masks for each man 
in active theaters. All these masks had ASC-filled 
canisters with asbestos-type filters. The U. S. face- 
pieces compared favorably in comfort and vision 
with those of other nations. 

Although adequate protection was offered, it was 
felt that further improvements could and should be 
made. All the existing masks were very uncomfort¬ 
able for prolonged wear, particularly in tropical 
climates. Vision was far from perfect for any of the 
facepieces. All masks were, as carried, too bulky and 
heavy. Facepieces and hose tubes were subject to pen¬ 
etration by mustard gas and were difficult to decon¬ 
taminate. Detailed comments on these and other 
features of the masks are given in Chapter 13, to¬ 
gether with recommendations for further research 
and developments. 







Chapter 2 

TESTING OF GAS MASK CHARCOAL AND CANISTERS 

By W. Conway Pierce 


2.1 THEORY OF GAS PENETRATION 
TESTS 

W hen a gas-air mixture is passed through a 
layer of adsorbent, the total amount of gas 
taken up before the break point — a point at which 
penetration is noted — will depend upon two factors: 
the activity and the capacity 1 of the adsorbent 
toward the gas used, with other conditions such as 
concentration and flow rate being kept constant. By 
activity is meant a rate function of gas adsorption. 
It is an inverse function of the depth of layer which 
will just permit instantaneous penetration. Capacity 
is defined as the weight of gas restrained per unit 
volume of adsorbent (footnote b, Chapter 1) when 
saturation is reached at a given partial pressure of gas. 



Figure 1. Distribution of gas concentration in tube of 
adsorbent which is partially saturated. 


The effects of activity and capacity on gas life 
(time to the break point) are shown in Figures 1 
and 2. For an idealized case Figure 1 illustrates the 
distribution of gas concentration along a long tube of 
adsorbent at the time a break is reached. C a is the 
influent concentration, and C e the effluent. In the 
region AB the adsorbent is saturated or in equi¬ 
librium with gas at a partial pressure C 0 . In the 
region BC the adsorbent is progressively less satu¬ 
rated as the effluent end is approached. The total 
amount of gas restrained at the break time is de¬ 
termined mainly by the length of the saturated re¬ 


gion AB and the capacity N 0 of the adsorbent. The 
length of the saturated region in turn depends upon 
the activity, or the length of the unsaturated region 
BC. This length depends upon the probability that a 
gas molecule will collide with the adsorbent surface 
and, after collision, be retained. The probability of 
striking the surface is a function of velocity, particle 
size, temperature, and other factors. A more com¬ 
plete discussion of these is given in Chapter 8. 

Figure 2 illustrates the effects of activity and ca¬ 
pacity on break times for layers of varied depths of 



Figure 2. Life-thickness curve, showing effect of layer 
depth of adsorbent upon gas life. Adsorbents A and B 
have different activities and capacities. The intercept in 
the z-axis gives the critical depth and the slope gives 
the increase in life per centimeter of length of bed, 
which is related to the capacity, No of the adsorbent. 

two adsorbents with different characteristics. Curves 
such as these are experimentally obtained by de¬ 
termining and plotting gas lives for various layer 
depths. At bed depth m adsorbent B will have the 
longer life, but at bed depth n adsorbent A has the 
longer life. Adsorbent A has greater capacity but 
lower activity than B. 

Because of the separate effects of activity and ca¬ 
pacity on the test life, it is not possible to obtain a 
reliable index of adsorbent quality from a single test 
unless the test is made under the conditions at which 


12 









TEST CONDITIONS 


13 


the adsorbent is to be used. Therefore, while tube 
tests were used formerly as the basis for charcoal 
specifications, it is customary now to base the speci¬ 
fication tests upon performance in the canister for 
which the charcoal is procured, and to make the 
canister test at conditions simulating actual use. 

2.2 TEST GASES 

At the present time, both British and Americans 
evaluate adsorbent quality in terms of the canister 
protection afforded against five standard agents: AC, 
CK, CG, PS, and SA. In addition, there is a tube 
test used to determine the extent of activation of the 
charcoal. The U. S. test for this is known as the ac¬ 
celerated PS test, and the British test is called the 
volume activity [VA]. The latter is essentially a meas¬ 
urement of adsorptive power for carbon tetrachlo¬ 
ride 2 under specific conditions. 11 

The choice of the test gases used is based in part 
upon the expected hazards in gas warfare and in part 
on long established custom. CG, AC, and CK cer¬ 
tainly represent probable hazards. CG, moreover, 
can be considered as typical for the gases which 
hydrolize to give halogen acids. AC and CK are per¬ 
haps typical of cyanide-containing gases. The use of 
PS in testing dates back to 1918, when it was an im¬ 
portant war gas. Now it is not considered a good war 
gas but is retained in testing because it is the only one 
of the standard agents removed by physical adsorp¬ 
tion. SA does not seem to represent an actual hazard, 
since to date no good methods have been discovered 
for setting up high field concentrations. Its use in 
testing also dates back to 1918, when it was found to 
penetrate the existing canisters readily and was con¬ 
sidered as a potential hazard. Considerable thought 
has been given to use of additional test gases to eval¬ 
uate U. S. adsorbents. Extensive surveys have been 
made of charcoal protection for many different types 
of gases, but to date no new agent of high toxicity 
and ability to penetrate a canister has come to light, 
except agents of types represented in the CG and 
AC tests. 

It is noted that the list of standard test gases does 
not include the persistent agents such as mustard 
and the nitrogen mustards. These are omitted for 
two reasons: (1) adsorbent tests with persistent 


a An empirical correlation 3 between VA values and PS lives 
can be obtained by the relation VA X 2.5 = PS life. This is 
not exact but is sufficiently accurate to give the proper order 
of magnitude for the PS life. 


agents are experimentally very difficult because of 
the low vapor pressures (which limit the gas concen¬ 
tration) and the long lives obtained, and (2) experi¬ 
ence has shown that the persistent agents, which have 
high boiling points, are very effectively removed 
from air by physical adsorption on charcoal. Any 
canister which will protect against PS will protect 
against a dosage of mustard vapor many times 
greater than is needed for penetration of the face- 
piece (by solution in the rubber). Consequently, such 
tests are not made a part of charcoal specifications 
and are performed only occasionally. 14 

Each of the agents CG, CK, PS, and SA evaluates 
a different characteristic of the absorbent. (See Chap¬ 
ter 7.) The dry CG life depends upon the amount and 
state of the copper oxide impregnant. The wet SA 
life is a function of the silver impregnant; the CK 
life depends upon the state and amount of hexavalent 
chromium present as a Cu-Cr compound; and the 
PS life depends on the adsorptive power of the char¬ 
coal. All gas lives are highly dependent upon the 
quality of the activated charcoal used as the base for 
the impregnant. 

2.3 TEST CONDITIONS 

Humidity 

Prior to 1941 all gas tests were made either at 0-0 
or 0-50 RH. b About this time, work was begun on the 
development of impregnants to improve SA and CK 
protection, and emphasis began to be placed on tests 
of moist samples. Partly by chance, and partly by 
design, the practice of equilibrating test samples 
with air at 80% RH was begun and this figure soon 
became standard for wet tests. In retrospect, it is 
seen that the 80% RH was a good choice, because 
for most charcoals the water adsorption isotherms 
are somewhat flat in the region of 70 to 90% RH (see 
Chapter 6). Consequently, if equilibration is done at 
80% RH, an exact humidity control is not important, 
because a 5 to 10% variation will not greatly affect 
the amount of water taken up. Further, it now seems 
that canisters which have been in use in tropical 
climates have water contents approximately equal 
to that picked up on 80% equilibration. 

Several different humidity conditions are now used 


b The first figure represents the humidity of the air with 
which charcoal is equilibrated prior to testing, and the second, 
the humidity of the test air. Thus 80-50 would denote a 
sample equilibrated with 80% RH air and tested with air 
at 50% RH (relative humidity). 









14 


TESTING OF GAS MASK CHARCOAL AND CANISTERS 


in research and specification control testing. They 
are 0-0 (PS tube test), 0-50, 0-80, 80-80, and 80-50. 
The last is used only when hydrolysis of the gas in air 
causes difficulty at high humidity. 0-0 canister 
tests are not used chiefly because of the difficulty in 
drying large volumes of air. 


Table 1. Canister test conditions. 



Humidity 

Humidity Concentration 

Flow rate 

Gas 

charcoal 

air 

mg/1 

1pm 

CG 

AR 

50 

20 

32-steady 

PS 

AR 

50 

50 

32-steady 

AC 

AR 

50 

10 

32-steady 

CK 

E-80 

80 

4 

50-breather 

SA 

E-80 

80 

10 

50-breather 


In the present routine whetlerite inspection tests, 
the conditions listed in Table 1 are used. The symbol 
AR appearing in the table designates normally dry 
charcoal “as received.” In this case, the moisture 
content is less than 2% by weight. If necessary, the 
charcoal is dried at 150 C. E-80 indicates that the 
charcoal is equilibrated at 80% relative humidity 
before testing. CG is tested at 0-50 because per¬ 
formance is usually better at 80-50. AC gives about 
the same life at 0-80 or 80-80. CK and SA are tested 
at 80-80 because protection is lower at this condition 
than at 0-80. 

Humidifiers 

Humidification of charcoal for testing is a labori¬ 
ous task, because the adsorption of water vapor from 
an air stream is not so rapid a process as removal of 
most other gases. Rather, when humidified air is 
blown through a layer of charcoal, only a small frac¬ 
tion of the water is removed. At 80% RH and an air 
flow of 10 liters per minute (1pm), it may require as 
much as 2 to 4 days to equilibrate an M10A1 canister. 

In order to care for the large numbers of samples 
required in inspection testing, a special humidifier 
was designed at Edgewood Arsenal to handle 50 can¬ 
isters simultaneously, and several units were con¬ 
structed by the Carrier Corporation. Operation was 
very satisfactory and reliable; a single machine can, 
on continuous duty, equilibrate over 100 canisters 
per day. 

A number of designs for laboratory equilibrators 
have been developed. All operate on the same prin¬ 
ciple, that is, streams of dry and saturated air are 
mixed in the ratios to provide the desired humidity, 
then blown to a distributor manifold to which sample 
containers are attached. These outfits give satisfac¬ 


tory operation but lack the convenience and auto¬ 
matic control of the large Carrier unit. 

The rate of equilibration varies from one charcoal 
to another. It is customary, therefore, to continue 
the passage of moist air through a sample until the 
weight becomes constant. Most types of charcoal can 
be equilibrated in less than eight hours on the Carrier 
equilibrator. 

It is, fortunately, unnecessary to humidify samples 
at constant temperature. Adsorption isotherms made 
at various temperatures (see Chapter 6) have shown 
that the amount of water taken up by a sample de¬ 
pends upon the relative humidity of the air stream 
and not on the specific moisture content. All test 
samples are equilibrated, therefore, at room temper¬ 
ature. 

Flow Rate 5 

For many years it was conventional to make can¬ 
ister tests at a 32-lpm flow with occasional engineer¬ 
ing tests at 64 1pm or higher. The 32-lpm flow rate 
was established in 1918 as an average breathing rate 
for men at moderately heavy exercise. During World 
War I most tests were, for convenience, made at 
steady flow. Some experimental machines to simulate 
intermittent breathing were designed and tested. The 
results of these tests are not available today, but in 
the light of present knowledge it is deduced that in 
tests of 1918 canisters there was little difference in 
steady and intermittent flow lives. 0 Probably it was 
because of such findings that intermittent flow test¬ 
ing did not become established at that time. 

In 1942 it was found that man-tests under condi¬ 
tions of heavy exercise gave gas lives much shorter 
than the standard 32-lpm lives for thin-bed canisters 
such as the Ml and M10. Further investigation 
showed that the peak flow rates of men at heavy exer¬ 
cise were of the order of 150 to 200 1pm, with minute 
volumes of the order of 50 to 60 1pm. At these flow 
rates, the adsorbent bed depth of Ml and M10 can¬ 
isters is so near the critical depth that penetration 
occurs within a few minutes, and only a small frac¬ 
tion of the adsorbent is saturated at the break time. 
These studies led to the development of breather 
pumps 4 for use in canister testing, to simulate human 

c The basis for this deduction is that in the deep-bed 1918 
canister the unsaturated zone was probably but a fraction of 
the total bed depth. Consequently, in intermittent flow tests 
the increased flow rate did not markedly affect the amount 
of charcoal which was saturated at the break time. It is only 
in thin-bed canisters that large effects are produced by an 
increase in flow rate. 








TEST CONDITIONS 


15 


breathing. Experimentally, it was found that a 
motor-driven reciprocating pump would give canister 
lives in good agreement with those from man-tests 
when the pump was operated at a speed to give a vol¬ 
ume of 50 1pm. This pump, as first constructed, gave 
a sine-wave type of flow curve somewhat different 
from the flow curve of human breathing. Considera¬ 
tion was at first given to the idea of constructing a 
cam-driven pump which would duplicate the average 
human breathing rate curve, 15 but when it was found 
that the sine-wave pump gave test lives in agreement 
with man-tests the cam-drive design was abandoned. 
Subsequent experience with breather pump tests con¬ 
firms the conclusion that it is not necessary to make 
the flow curve for the pump conform to the curve for 
human subjects. 

When the breather pump was officially adopted 
for canister testing, the previously used 50 1pm flow 
rate was retained. This was a desirable choice, since 
this flow rate is also used in British tests, which are 
made at standard flow rates of 16 and 50 1pm. It is 
recognized that a 50-lpm flow does not represent the 
maximum value for men at heavy exercise, for whom 
values as high as 80-90 1pm, with peak flow near 
250 lpm, have been reported; but it is thought that 
this rate is as high as any rate of sustained breathing 
likely to be found. 

The peak instantaneous flow rate for a 50-lpm 
sine-wave pump is about 155 lpm. In the British 
50-lpm test, the peak is 100 lpm, the test being per¬ 
formed by an interrupted steady-flow, off-and-on 
50% of the time. In a number of comparisons, it has 
been found that if indicators are identical, the British 
test agrees with the U. S. test. Only in exceptional 
instances, where the thickness of adsorbent layer is 
near the critical depth, might it be expected that the 
British and U. S. tests would disagree. Then the U. S. 
test, because of the higher peak flow, might give con¬ 
siderably shorter lives. 

At the present time, whetlerite inspection tests are 
made by 32-lpm steady flow for PS, CG, and AC, and 
by 50-lpm intermittent flow for CK and SA. This use 
of both types developed at the time the breather 
pump was adopted, because of equipment shortage. 
Since this plan has worked out satisfactorily for in¬ 
spection testing, there is no reason for changing the 
CG and AC tests to the higher flow rate. The CK 
test suffices to disclose any whetlerite of low activity, 
and the 32-lpm tests for CG and AC provide indica¬ 
tions of the gas capacity and the quality of the im- 
pregnant. 


The flow rate used in charcoal tube tests was for 
many years standardized at 500 ml per min per 
sq cm or a linear velocity of 500 cm per min. (An 
exception was in the accelerated PS tube test which 
was made at 1,000 cm per min linear flow.) The origin 
of this rate is not known, but probably it was started 
in 1918 for the purpose of correlating tube and can¬ 
ister tests, since the linear flow in the 1918 canister 
was at about 500 qm per min for a total flow of 
32 lpm. 

In research tube testing, there is no a priori reason 
to employ any standard flow rate. However, a value 
of 500 cm per min is today most widely used because 
the apparatus was originally designed for this rate, 
and flowmeters are calibrated for this value. 

Indicators 

When a layer of adsorbent is traversed by a gas-air 
stream the initial concentration distribution through 
the absorbent may be represented by the curve of 
Figure 3A. Some gas penetrates instantly because 




INFLUENT END INFLUENT END 

Figure 3. Distribution of gas concentration in tube of 
adsorbent. (A) condition at start of exposure, (B) con¬ 
dition at break point. 

the distribution along the adsorbent layer is expo¬ 
nential with distance, but the penetrating concen¬ 
tration is much lower than the usual “break’ ’ con¬ 
centration except when very thin layers are used. As 
the test continues, the adsorbent at the influent side 
becomes saturated and the unsaturated region moves 
progressively toward the effluent end of the bed. The 
situation at time t b is as shown in Figure 3B. When 
the effluent concentration reaches the break concen¬ 
tration Cb, the adsorbent is considered to be ex¬ 
hausted and the time required for penetration to 
reach C b is taken as the test life t b . From these con¬ 
siderations one can see that the choice of test indi¬ 
cator has an important role in defining the adsorbent 
life. 11 - 12 If the indicator is exceedingly sensitive, pen¬ 
etration may be observed at zero time. On the other 
hand, if the indicator is insensitive, penetration may 







16 


TESTING OF GAS MASK CHARCOAL AND CANISTERS 


not be indicated until the effluent concentration be¬ 
comes large, when most of the bed is saturated. 

In practice, an effort is made to select an indicator 
of such sensitivity that it will show a break when the 
concentration of gas that penetrates is of physiologi¬ 
cal significance, that is, when the gas becomes notice¬ 
able by causing lacrimation or choking or when it 
approaches a concentration which may be dangerous 
if breathed for a short time. For gases such as CG 
or CK, which are detectable by smell or lacrimation 
at low concentrations, the indicator break point 
should coincide with human detection. In case of 
gases which are detected with difficulty, such as SA 
and AC, the indicator break point is fixed below the 
concentrations or dosages which are thought to be 
dangerous. 

A list of the break point conditions in use at the 
present time is given in Table 2, with source refer¬ 
ences for each. It will be noted that the SA indicator 


Table 2. Break point concentrations of test indicators. 


Agent 

Break point 
concentrations 
mg/1 

Physiological 

significance 

Source 

CG 

0.007 ± 0.001 

lacrimatory 

TDMR 753 


0.009 ± 0.002 

coughing 

NDRC 10.1-3 

AC 

0.004 

? 

EATR 251 

SA 

10 mg total 

dangerous 

TDMR 456 
NDRC 10.1-3 

PS 

0.01 + 0.003 

odor 

TDMR 456 

CK 

0.008 

lacrimatory 

NDRC 10.1-24 


responds to a total penetration of 10 mg, while all 
others are expressed on a gas concentration basis. 
This differentiation is made because the effects of 
SA are thought to be cumulative, while for the other 
gases there is a detoxification threshold below which 
the gas may be breathed without danger. 

It is apparent from the data of Table 2 that the 
test indicators show a break before the point is 
reached at which a lethal dosage penetrates. Some 
measurements have been made of the dosage re¬ 
quired to cause penetration of Japanese, German, 
and U. S. canisters in lethal amounts 13 for continued 
gas exposure and for gas exposure followed by de¬ 
sorption. These studies show that for U. S. canisters 
there is a considerable safety factor after penetration 
becomes detectable before it becomes dangerous. For 
gases such as CK, which are harassing, the penetra¬ 
tion will cause discomfort or perhaps panic at just 
about the time of the chemical break. 

Descriptions of the indicators now used are given 


in the references of Table 2. These indicators are so¬ 
lutions which contain a chemical that will react with 
the test gas, together with some substance which will 
show a color change. Effectively, there is a titration 
of the indicator chemical by the test gas. Thus, it is 
necessary to employ a measured volume of indicator 
solution and to obtain the color change within a pre¬ 
scribed time interval, usually 2 or 3 minutes. In a 
test, there is a series of indicator breaks at constantly 
diminishing time intervals until the point is reached 
at which a fresh solution will give a color change 
within the prescribed interval. Sometimes it is not 
easy to establish just where this point is reached, 
which causes some uncertainty in the test life. Nor¬ 
mally, however, the effluent concentration rises quite 
rapidly near the break point, and this point can be 
located quite accurately. 

Either physical or chemical break indicators may 
be employed in testing. In research work physical 
methods are preferred because they are generally 
more objective than chemical tests, which usually 
depend upon color changes in a solution. Further ad¬ 
vantages of physical methods are that they give an 
instantaneous rather than a cumulative concentra¬ 
tion value, and that physical method readings can 
usually be recorded automatically. Disadvantages 
are in their nonspecificity and in the complicated and 
expensive equipment required. Almost any type of 
physical measurement which applies to a binary sys¬ 
tem of known components may be applied. Among 
those instruments which have found wide applicabil¬ 
ity in adsorbent testing and gas detection are gas in¬ 
terferometers, ultraviolet, visible, and infrared ab¬ 
sorption photometers, bridges for measuring the con¬ 
ductivity of solutions containing the gas or heat con¬ 
ductivity from hot-wire meters, and pH measure¬ 
ments on solutions. Each of these methods has special 
fields of applicability. 

Concentration of Test Gas 

In World War I it was customary to test at a vol¬ 
ume concentration of 1,000 ppm except when this 
made service times too long; in such cases, concen¬ 
trations of 5,000 or 10,000 ppm were used. The Brit¬ 
ish still make many of their canister tests at a con¬ 
centration of 1 per 100 (1% by volume), but present 
U. S. practice is to express concentration as milli¬ 
grams gas per liter and to use a round number in¬ 
stead of working on a volume basis. Many tests are 
made at 4 mg per 1, particularly in research. When a 
higher concentration is needed to obtain lives of con- 











TUBE TESTS 


17 


venient length, the values are usually 10, 20, or 
50 mg per 1. 

The choice of test gas concentration is usually 
made on the basis of the life obtained. In canister 
tests it is convenient to have lives of 25 to 50 min. 
Longer lives are too time consuming and shorter ones 
are subject to too much error because of uncertainty 
in fixing the exact break point. Whenever possible, it 
is desirable to make gas tests at low concentrations 
(near 4 mg per 1) which correspond fairly well with 
average field concentrations, where values of 10 to 
50 mg per 1 are attained usually for only short peri¬ 
ods. Testing at high concentrations has two disad¬ 
vantages: (1) often a high concentration will cause 
large heat effects which tend to dry the canister and 
may also affect protection because of the temper¬ 
ature rise of the adsorbent; (2) if the test gas is re¬ 
moved by adsorption alone, a test at high concentra¬ 
tion may indicate a misleading amount of protection 
because the adsorbent at the influent side is satu¬ 
rated at a high partial pressure of gas. For example, 
it was found that in a test of non-impregnated char¬ 
coal with CK at high concentration (27 mg per 1) a 
dosage of about 135 mg per min per 1 was required 
for penetration. When the gas concentration was re¬ 
duced to 0.27 mg per 1, the protection was reduced to 
a dosage of 13. At the high concentration, the influent 
layers held a large amount of gas. In the 0.27 mg per 1 
test, the influent layers held little gas because of the 
low partial pressure, and the protection obtained was 
low. When the test gas is destroyed by chemical ac¬ 
tion, there is not such a great difference in the amount 
of protection afforded at high and low concentra¬ 
tions. U.S. ASC-filled canisters will restrain about 
the same weight of AC, CK, or CG at 4 or 20 mg per 1. 

Temperature 

In general, little has been done about temperature 
control in tube and canister testing. Customarily, 
such tests are made at the prevailing room temper¬ 
ature, because for most of the test gases, minor vari¬ 
ations in temperature do not cause large effect. 
Moreover, control of external temperature would 
not greatly affect temperatures within the canister 
because heat conductivity in the charcoal bed is 
low. 

The only control test made at constant tempera¬ 
ture is the SA tube test (now obsolete). In this test 
it has been found that a thermostatically controlled 
water jacket around the test tube will aid in attain¬ 
ing reproducible results. 


2.4 TUBE TESTS 

A tube test 6-9 is made by blowing a gas-air mix¬ 
ture through an adsorbent bed (of predetermined 
thickness) in a small tube until penetration occurs. 
Tests of this type are much more convenient and 
economical than canister testfe which require large 
air flows and large quantities of gas and charcoal. 
Originally, during W(orld War I, there was probably 
fair correlation 10 between tube test lives and can¬ 
ister tests on the same adsorbent, because at that 
time the canister construction was like that of a large 
tube, with axial flow through a thick bed of adsorb¬ 
ent. Later, as canisters were made with thin beds 
and low linear flow rates, a good correlation between 
tube and canister tests lives no longer existed. The 
use of tube tests for charcoal and whetlerite specifi¬ 
cations was discontinued in 1943, except for the PS 
test, and today all gas protection specifications are 
based upon performance in the canister for which the 
adsorbent is procured. Tube tests are still widely 
used in research studies because of their convenience, 
speed, and the small quantity of sample required. 
Properly interpreted, they yield much useful in¬ 
formation. 

The equipment required for tube testing is simple. 
A gas-air mixture is prepared by introducing a me¬ 
tered gas stream, or a gas-laden air stream from a 
bubbler tube, into a metered air stream. After passing 
through a mixing chamber the gas-air mixture is 
forced into a manifold to which the test samples are 
attached. The test tubes are uniform-bore glass cylin¬ 
ders, usually about 2 cm in diameter and contain near 
the lower end a flat, perforated plate acting as a sup¬ 
port for the layer of adsorbent. The test sample is 
loaded into the tube by gravity fall from a vibrator 
hopper, which gives a slow and uniform feed rate. 
The customary bed depth is 5 cm, which requires 
only about 15 ml of the sample. Flow is downward 
through the sample to avoid disturbance of the 
packing. The lower or effluent end of the tube is con¬ 
nected to a container for the indicator solution. 

The standard tube test line of 1945 is designed for 
very efficient and uniform operation. Many conven¬ 
iences have been developed to aid in keeping the de¬ 
sired gas concentration and uniform flow rates. The 
most recent models are of all glass construction with 
few rubber joints to become contaminated or develop 
leaks. Eight samples can be tested simultaneously. 
Complete descriptions are given in CWS Pamphlet 
Number 2. 







18 


TESTING OF GAS MASK CHARCOAL AND CANISTERS 


Gas for the test line is supplied either from a cylin¬ 
der (under pressure), by bubbling a dry air stream 
through a tube of the liquefied agent, or from a gas¬ 
ometer. The latter is the least convenient method and 
is used today only for arsine. CG is usually supplied 
from a cylinder, CK and AC are vaporized from a 
liquid or supplied from a pressure cylinder. PS is al¬ 
ways vaporized from the liquid because of the high 
boiling point. 

PS Test 

Since 1918, one of the specification tests for acti¬ 
vated charcoal has been the chloropicrin life, which 
is assumed to represent the adsorptive power of the 
charcoal for a non-reactive gas. This test is run on a 
10 cm layer of charcoal in a tube with an inside di¬ 
ameter of approximately 1.4 cm at a rate of flow of 
1 1 per min per sq cm of cross sectional area (1,000 cm 
per min linear flow). The gas concentration is 47 mg 
per 1. Humidity conditions are 0-0. The break-point 
indicator is a starch-potassium iodide solution 
through which the effluent gas is passed after pyroly¬ 
sis in a heated quartz tube. 

Despite its long established usage, the PS test does 
not provide a good criterion for evaluating activated 
charcoal. The following objections may be cited: 

1. The PS life does not correlate with the protec¬ 
tion that charcoal will afford for other non-persistent 
gases after impregnation. Following the discovery of 
the ASC process for whetlerization (Chapter 4) it was 
found that some of the charcoals with highest PS 
lives gave the poorest 80-80 CK protection. It is now 
known that the performance of impregnated charcoal 
is to some degree correlated with the presence of 
large pores which provide channels for gas molecules 
to penetrate rapidly into the granule and that this 
characteristic is not related to the PS life. 

2. The PS test is,carried out at high relative gas 
pressure, which corresponds to a point near satura¬ 
tion on the adsorption isotherm (see Chapter 6). The 
amount of gas taken up is not a measure of the sur¬ 
face available for adsorption but rather is a measure 
of the total volume of pores in the sizes that are filled 
with liquid at saturation. Of more importance is a 
knowledge of the amount of gas which is held at low 
partial pressures. 

3. The retentivity, or amount of gas held very 
tightly by adsorption, is not related to the PS life. 

It is believed that the PS test should be discontin¬ 
ued and some other test for the adsorptive power of 
charcoal should be substituted. Apparently it is de¬ 


sirable to work at a low relative pressure of gas corre¬ 
sponding to a low point on the isotherm where capil¬ 
lary condensation does not occur. This cannot be 
done conveniently with PS because the lives obtained 
would be too long. It has been suggested that a life 
test with ethyl chloride might be used and studies 
are now being made of the correlation of ethyl chlo¬ 
ride lives with degree of activation and retentivity of 
charcoal. If such a test is used, the gas should be non¬ 
reactive, of low boiling point, and easily detected by 
chemical methods. Ethyl chloride satisfies these con¬ 
ditions nicely. 

Modified Tube Tests 

Frequent reference is made in Chemical Warfare 
Service [CWS] and National Defense Research 
Committee [NDRC] reports to “modified tube 
tests.” These are tube tests made with layer 
depths and (sometimes) flow rates other than the 
standard conditions, for the purpose of correlating the 
service times with those for a specific canister. Such 
a correlation is purely empirical, because flow rates 
are not the same as in radial-flow canisters, but for a 
given type of charcoal it is possible to select a bed 
depth which will yield a tube life in fair agreement 
with an M10 or M10A1 canister. The only use for 
such tests is in experimental impregnation programs 
when there is not sufficient sample for regular can¬ 
ister tests. 

2.5 CANISTER TESTS 

Types 

As stated previously, canister tests in use today 
are of two types: steady flow at 32 1pm and intermit¬ 
tent flow at 50 1pm with a peak rate near 155 1pm. In 
addition, in research and investigation of enemy can¬ 
isters intermittent flow tests are used at various 
other rates, the more common of which are 25 and 
16 1pm. 

The basis for using these low flow rate tests is that 
the usual 50-lpm test gives the protection afforded 
for men at heavy exercise. In the field, it is probable 
that most people exposed to a gas attack may be oc¬ 
cupying a fixed position and not exercising heavily 
during the period of the attack. Such an inference can 
be drawn from the reports of gas officers in World 
War I. Consequently, it is desirable to know what 
protection an enemy canister will afford under opti¬ 
mum defensive conditions. Often the protection at 
low flow rates may be excellent, because of high ca- 



MAN TESTS 


19 


pacity, when penetration occurs very quickly at high 
flow rates. 

The general principles of canister testing are like 
those of tube testing; a gas-air stream is passed 
through the canister until tests of the effluent stream 
show penetration of gas at a predetermined concen¬ 
tration. In one important respect, canister tests used 
during World War II differ from tube tests. The gas 
is pulled through a canister by suction applied at the 
nozzle, while in tube tests gas is forced through the 
adsorbent bed by pressure. The difference is one of 
experimental convenience only. 

In steady-flow test outfits there is suction flow 
throughout the system, but the standard arrange¬ 
ment used in breather machine testing employs a 
combination of pressure and suction. In this arrange¬ 
ment the gas-air mixture is prepared in a pressure 
system and blown to the canister chamber where it 
envelops the canister at atmospheric pressure. This 
has two advantages: (1) changes may be made in the 
flow rate through the canister without changing the 
gas-air flow rate, which would require readjustment 
of all controls; (2) man tests may be made when de¬ 
sired by disconnecting the pump and attaching a gas 
mask facepiece through which the subject breathes. 

Details of steady and intermittent flow tests are 
given in current editions of CWS Pamphlet Num¬ 
ber 2. The most recent one describes the newest 
model intermittent flow machines, which accommo¬ 
date two canisters for simultaneous testing. These 
differ from the single canister model only in having 
two canister containers attached to a common gas 
manifold. It is necessary to double the rate of gas 
supply. The breather pump for two canisters has two 
cylinders with the pistons operated 180° out of phase, 
so that gas is drawn half of the time from each can¬ 
ister. 

Desorption Tests 

If a gas is removed by physical adsorption there is 
a definite vapor pressure of the adsorbate over the 
charcoal and passage of air through an exposed can¬ 
ister will lead to desorption of the gas. This may be 
serious in case of a gas of high volatility which is not 
destroyed by chemical reaction with water or with 
the imp regnant in the canister. For example, Type A 
whetlerite will desorb CK readily. Exposure to a 
small dosage followed by passage of air will cause 
penetration in amounts sufficient to cause discom¬ 
fort. The danger of desorption from U. S. canisters 
with ASC whetlerite is small for any of the known 


toxic agents; all of those which have high volatility 
react with the imp regnant and are destroyed (CG, 
CK, AC, and SA), while the agents of low volatility 
are so firmly held by physical adsorption that ex¬ 
posure to a large dosage is necessary before desorp¬ 
tion will occur in dangerous concentrations. 

Numerous desorption tests 13 have been made of 
CK and AC from German and Japanese canisters. A 
known dosage of gas is put into the canister by carry¬ 
ing on the test for a predetermined time. Then the 
gas is cut off while passage of pure air is continued at 
the usual test rate. A portion of the effluent air is 
passed through an absorbing solution and at regular 
intervals samples are titrated by a suitable reagent. 
In this way, data are obtained for the concentration 
of gas penetrating as a function of time. Data for 
such tests are shown in Chapter 10. 

2.6 MAN TESTS 

It is frequently desirable to determine canister per¬ 
formance by man tests. Extensive use was made of 
such tests in World War I, but in World War II they 
were made rarely. In World War I, large gas cham¬ 
bers were arranged so that canisters could be 
mounted in the gas atmosphere for testing while the 
subject remained outside the chamber and breathed 
through a gas mask hosetube. The present inter¬ 
mittent-flow canister test machine is designed to 
permit man tests without necessarily constructing 
special chambers. For such a test the pump is discon¬ 
nected and the subject breathes through a facepiece 
attached at the effluent connection to the canister. 

Man tests may be made with or without chemical 
indicators. If indicators are used, the subject is pro¬ 
tected by an auxiliary canister which adsorbs gas 
penetrating from the test canister. Often it is desired 
to check or confirm chemical indicator break points. 
Then the protective canister is removed and the gas 
is detected by its odor or lacrimatory effects. Such 
tests should never be made with SA, which is odor¬ 
less, d or with AC, which is insidious in its effects, but 
can be made with CG and CK, both of which are 
readily detected. Much useful information has been 
gained from a limited use of man tests. Any new or 
unexpected performance from an experimental model 
canister should be confirmed by a man test; occasion- 


d As ordinarily made there is a pronounced odor associated 
with SA, but apparently this material (probably a carbide) is 
removed by charcoal; and the gas which penetrates a canister 
has no odor. 










20 


TESTING OF GAS MASK CHARCOAL AND CANISTERS 


ally, it is desirable to recheck standard machine tests 
by man tests with the subjects at heavy exercise. 

2.7 MINICAN TESTS 

The name “minican tests” has been applied to 
special tube tests carried out under canister condi¬ 
tions ; that is, with depth of layer and linear flow rate 
made the same as in the canister. This type of test 
has not been widely used, because results are always 
questionable, but on occasion it has provided useful 
information. Examples are tests of enemy canisters 
when only one was available and tests of collective 
protector canisters. 

For an axial flow canister, a minican test is merely 
a tube test with proper flow rate and depth of layer. 
The minicans simulating radial flow canisters must, 
however, provide for a variation in flow rate from 
influent to effluent sides, since the flow rate in an an¬ 
nular layer of adsorbent varies inversely as the ra¬ 
dius. A fair approximation for canisters such as the 
M10 has been obtained by use of a funnel-shaped 
layer with the areas at top and bottom proportional 
respectively to the outer and inner areas of the 
canister. 

Sources of potential error in minican tests are the 
possibility of wall leakage because the surf ace-volume 
ratio is so much greater than in an actual canister, 
and the possibility of temperature effects vastly dif¬ 
ferent from those in the canister. 

2.8 FIELD TESTS OF CANISTERS 

In connection with field experiments on the travel 
of gas clouds, numerous tests have been made of the 
actual protection afforded by canisters under various 
conditions. Such tests contribute no information that 
could not be obtained in the laboratory by reproduc¬ 
ing the field concentration-time conditions, but they 
do provide vivid illustrations of the possibility for 
breaking canisters. 

Two types of field canister tests have been carried 
out, with live goats and with breather pumps. The 
pumps are specially designed to operate at low power 
consumption. A rubber bellows is driven by a 
small motor to give a flow of about 16 1pm with 
24 to 30 c. Effluent gas from the canister is passed 
either through a recording meter or through an ab¬ 
sorbing solution which is later titrated. The entire 
apparatus is housed in a gas-tight box to avoid leak¬ 
age effects while operating in a high gas concen¬ 
tration. 


2.9 LAYER DEPTH STUDIES 

A very useful tube test, known as a layer depth 
test, was used to some extent in 1918 but much more 
extensively during World War II. Measurements 
were made of tube test lives at varied depths of layer 
and the resulting lives plotted as in Figure 2. From 
the slope of the curves, the capacity N 0 is computed. 
The intercept of the linear or nearly linear portion 
with the depth axis is known as the critical depth Xc. 
There is no quantitative correlation of N 0 and Xc 
with canister performance, but qualitatively the re¬ 
lation is very good. In a thin bed canister Xc is the 
important factor, and in a thick bed N 0 is most im¬ 
portant. 

Layer depth studies were most useful in research 
for studying impregnation methods, aging, and 
mechanisms of gas removal. They are also useful in 
evaluating and interpreting canister performance be¬ 
cause a knowledge of N 0 gives an efficiency ratio for 
the canister. This efficiency ratio is defined by the 
equation 

__ . mg of gas restrained 

Efficiency = —— -—--- 

N o (in mg per ml) X volume 

2.10 OTHER TESTS 

In addition to the gas tests of adsorbents already 
discussed, numerous other tests are used in the manu¬ 
facture and development of adsorbents and gas mask 
canisters. These are not discussed in detail because 
complete directions are given in CWS specifications, 
but they are listed. 

Heat of Wetting 

Until recently one of the basic charcoal tests has 
been the heat of wetting, that is, the heat evolved 
per unit mass or unit volume of charcoal when im¬ 
mersed in benzene. To some extent the heat of wet¬ 
ting is a measure of the degree of activation, but it 
may also depend upon the pore volume. 

Formerly it was believed that heat of wetting was 
measured by the tightness with which an adsorbate 
is held on charcoal, 9 but recently there has been 
doubt as to the interpretation of heat of wetting data, 
and this test has been dropped from charcoal speci¬ 
fications. 

Hardness 

The standard hardness test is an empirical meas¬ 
ure of the amount lost when a specified sample is 
shaken in a sieve with steel balls (CWS Pamphlet 





DEFICIENCIES IN TEST METHODS 


21 


Number 2, Part II, Section L). The purpose of the 
test is to prevent the use of soft charcoal which may 
break into dust after loading into the canister, but it 
does not accurately evaluate the desired quality in a 
charcoal and some other testing method might be 
better. No improved method is available, however, 
and until it is, the present test will be retained. 

Screen Analysis 

Because the pressure drop and gas protection af¬ 
forded by a given volume of charcoal depend upon 
the size and size distribution of particles, all charcoal 
is procured under rigid screen analysis specifications. 
These are based upon U. S. standard screen sizes. 
Charcoal for Ml, 10, 10A1, and 11 canisters is 12-30 
mesh. The usual distribution is near 20% (12-16), 
50% (16-20), 30% (20-30) by weight, but consider¬ 
able deviation is permitted among the three sizes. 

Apparent Density 

The apparent density is the mass in grams per 
milliliter of charcoal as loaded by slow gravity fall 
into a glass cylinder. 

Rough Handling 

An essential property of a gas mask canister is its 
ability to withstand jolting and impacts in normal 
usage without becoming deformed, losing adsorbent, 
or developing a high resistance. Empirical rough¬ 
handling tests of various types have been used for 
different types of canisters. All subject the test can¬ 
ister to very drastic treatment, after which the re¬ 
sistance must not exceed a specified amount and the 
gas life must not be below a stated minimum. All 
these rough-handling tests, while admittedly em¬ 
pirical, are based upon treatment which the canister 
might receive in combat use. All employ the princi¬ 
ples of impact and of vibration. 

Filter Tests 

Filter tests are described in Chapter 24. 

2.11 DEFICIENCIES IN TEST 
METHODS 

Although adequate for specification testing and 
the usual demands of research programs, the char¬ 
coal testing methods now used have some deficien¬ 
cies. The most important of these are: 

1. Tube tests, as previously indicated, show poor 
correlation with the lives of thin-bed canisters. This 


may be illustrated by data from a surveillance pro¬ 
gram for an extruded coconut charcoal whetlerized 
by the ASC process (see Chapter 5 for a discussion of 
surveillance). 


Table 3. Comparison of tube and canister lives. 


Storage condition 

5 cnji tube life 

M10 canister life 

Freshly prepared 

180-200 

46 

75 days, dry, 25 C 

188-201 

30 

75 days, wet, 25 C 

88-122 

0-2 

75 days, wet, 50 C 

75 days, dry, 50 C 

142-159 

0-2 

177-204 

20 


2. Minican tests cannot be relied on for exact in¬ 
dications of canister lives. They do, however, agree 
much better than the standard tube tests. The chief 
weakness in the minican test is the danger of wall 
leakage, particularly for thin-bed canisters, because 
the wall-volume ratio is much greater for small vol¬ 
umes than for the canister. 

3. Mesh distribution must be very carefully con¬ 
trolled in all tests, whether tube or canister. Changes 
in mesh size distribution affect the critical depth Ac 
which is particularly important in tests of thin depths 
of adsorbent. Further, there is often a difference in 
the degree of activation of large and small particles. 

4. The reproducibility of breather pump canister 
tests is not so good as desired. Greatest difficulty is 
encountered in the CK 80-80 test, which in many of 
the research studies is the most critical test. In gen¬ 
eral, canisters of poor to ordinary quality give quite 
reproducible lives, provided loading is carefully done 
with well mixed samples. Fortunately, most of in¬ 
spection testing is confined to samples giving M10A1 
CK 80-80 lives of about 30 to 50 min. But with long 
lives ranging from 70 to 100 min, quite erratic test 
results are often obtained. The following reasons are 
suggested to account for poor test precision. 

a. The break occurs very slowly and it is difficult 
to fix the point at which the penetrating con¬ 
centration of gas is sufficient to change the in¬ 
dicator solution within the specified time in¬ 
terval. 

b. Because the break occurs slowly, the effect of 
leakage or channeling caused by variations in 
packing the adsorbent may affect the apparent 
life markedly. In a long-life sample a good 
fraction of the adsorbent lies in the saturated 
region. Any leakage of gas through this region 
causes more rapid penetration. 

c. A slight variation in the water content of the 











22 


TESTING OF GAS MASK CHARCOAL AND CANISTERS 


charcoal may exert considerable influence on 
the life of a slowly breaking sample. As gas is 
taken up in the saturated zone, water is driven 
off, and as the sample dries the critical depth 
progressively decreases. 

d. The CK indicator has a temperature coeffi¬ 


cient. The effect of this may become more 
pronounced as the life increases, particularly if 
the break occurs slowly and it is difficult to fix 
the exact time at which the break occurs. 

5. The PS test is not a good criterion of charcoal 
quality, as discussed above. 




Chapter 3 

MANUFACTURE OF ACTIVATED CHARCOAL 

i 

By Warren L. McCabe 


3.1 INTRODUCTION 

W hen gas warfare was introduced in 1915, it 
was immediately necessary to find a suitable 
defense against this weapon. This means of defense 
was a canister containing activated carbon through 
which the soldier breathed. Activated carbon, now 
treated with catalysts to destroy non-adsorbable 
toxics, is at present the universal filling for military 
gas mask canisters. 

Although a number of carbonaceous raw materials 
were used in World War I to make gas mask char¬ 
coal, the most satisfactory product was manufac¬ 
tured from coconut shells. For the physical adsorp¬ 
tion of high molecular weight toxics, coconut chars 
are satisfactory but have two deficiencies: (1) the 
raw materials are obtainable only in tropical regions 
and must be transported over long distances; (2) the 
usual coconut char does not possess the proper pore 
structure to function satisfactorily as a base for the 
metallic catalysts necessary to destroy chemically, 
especially under conditions of high humidity, those 
toxics which are not adsorbed physically. It is known 
now that the second deficiency can be corrected by 
proper processing, but it is still undesirable to rely on 
a charcoal made from an uncertain supply of a for¬ 
eign raw material if a satisfactory product can be 
made from domestic substances. During the last few 
years, therefore, considerable work has been done to 
develop from plentiful domestic raw materials a rela¬ 
tively inexpensive carbon which is both an active ad¬ 
sorbent and a suitable catalyst base and which is 
hard and strong enough to withstand rough handling 
in the canister without disintegrating. 

The effort has yielded satisfactory results. Carbons 
of excellent quality and moderate cost are being pro¬ 
duced in large quantity. They are impregnated with 
a whetlerizing solution and heat treated to produce a 
canister filling which provides balanced protection 
against all toxic agents appearing practicable as field 
agents. They function satisfactorily under wide vari¬ 


ations of humidity and temperature. The main raw 
materials are waste wood and bituminous coal, both 
of which are available in nearly unlimited quantities. 
Other raw materials, including some of synthetic 
rather than natural origins, yield reasonably satis¬ 
factory products, but are not used in commercial 
processes. 

Most of the important practical developments 
have come from empirical trial and error experiments 
conducted for the most part by charcoal manufactur¬ 
ing companies, rather than from scientific research. 
The manufacture of high grade gas mask carbons is 
an art rather than a science. Nevertheless, a fairly 
comprehensive understanding of what constitutes a 
good charcoal has been attained, and the important 
factors in the manufacturing process have been 
identified. 

Although the present state of charcoal manufac¬ 
ture is satisfactory, and the quality of the product is 
high enough to discourage the use of gas as a military 
weapon, the modern adsorbent has not been tested 
in an enemy gas attack, and until the product has 
met the test of actual combat, there is a definite 
chance that it may be deficient. Reliance must be 
placed on the resources of science to correct such a 
deficiency, if it appears. Primarily this chapter sum¬ 
marizes the present scientific and practical knowledge 
that can be drawn upon to solve future problems 
which might arise in the manufacture of charcoal for 
gas mask use. 

3.2 GENERAL METHODS OF MANU¬ 
FACTURE OF GAS MASK CARBON 

The manufacture of gas mask charcoal is a typical 
industrial process. In cojnmon with all such opera¬ 
tions, a charcoal plant receives raw materials and 
converts them by physical and chemical operations 
to products which function differently from the raw 
materials. The activated product from the modern 
manufacturing process possesses an internal pore 


24 


MANUFACTURE OF ACTIVATED CHARCOAL 


structure of an extent and character that renders the 
charcoal a remarkab y active adsorbent for high 
molecular weight air-borne molecules. In its early 
use, the action of the material as a physical adsorbent 
was its mportant characteristic. Since World War I, 
activated charcoal has been used as the raw material 
for the process of whetlerization, in which the carbon 
is impregnated with metallic catalysts which are in¬ 
timately incorporated with the granule and which 
are active in destroying those low molecular weight 
toxics that are not adsorbed physically. 

Whetlerization processes are described in Chap¬ 
ter 4. This chapter treats only of the manufacture of 
charcoal suitable for whetlerization. 

Charcoal making processes are of two main types, 
which are differentiated by the method of activation. 
The first method is activation by hot gases, usually 
containing steam, and the second method is activa¬ 
tion by chemicals. 

The manufacture of gas-activated carbon usually 
includes the following steps: 

1. Crushing, grinding, and briquetting a car¬ 
bonaceous raw material. 

2. Crushing the briquettes and sizing the crushed 
material. 

3. Devolatilization of the crushed material. 

4. Gas activation by hot gases, usually containing 
steam. 

5. Screening the activated material to meet size 
specifications. 

Not all processes include all the steps, nor do they 
operate the steps in the same order. Certain processes 
have additional steps. For example, in the manufac¬ 
ture of charcoal from compressed wood, a high tem¬ 
perature calcination treatment is used between the 
carbonization and activation steps. 

The manufacture of charcoal by chemical activa¬ 
tion is a more specialized process that has but little 
in common with gas activation. It is described later 
in this chapter. 

In the preparation of charcoal by gas activation, 
the preliminary crushing and grinding is usually 
necessary to establish the preliminary structure for 
the system of macropores (see Chapter 6), which are 
necessary in the final product to give, under high 
humidity conditions, a good CK life. The briquetting 
step in the process is necessary to construct a struc¬ 
ture that will withstand subsequent crushing and 
processing and remain strong and hard enough for 
practical use in a canister. 

The briquettes are crushed to form a convenient 


size of granule for carbonization and activation. In 
at least one process, the final size of the finished gran¬ 
ules is established by carefully sizing the crushed, 
briquetted material before carbonization and acti¬ 
vation. 

Most raw materials contain quantities of water, 
hydrocarbons, oxygen compounds, and other volatile 
matter that must be removed before an active carbon 
can be prepared. A devolatilization process is re¬ 
quired, which consists of a low temperature carbon¬ 
ization. The devolatilization must be conducted in 
such a manner that the volatile matter will be disen¬ 
gaged from the residue without puffing or caking the 
particle and ruining its density and strength. 

Activation is the term applied to the step of devel- 
ing adsorptive rate and capacity in a carbonized and 
devolatilized material. During this step, additional 
devolatilization is accomplished, and the pore system 
is completed. 

Final screening to meet definite size specification is 
necessary. If the average particle size is too large, the 
rate of reaction between charcoal and toxic will be 
reduced and the canister life, especially in thin beds, 
will be too low. If the particle size is too small, or the 
range of sizes too great, the resistance to breathing 
will be excessive. Ideally, regular geometric particles 
of a single uniform size are desired, but practical 
manufacturing operations require that a reasonably 
wide spectrum of sizes be allowed, and because of 
crushing the particles are irregular in shape. 

The details of actual processes, and the results of 
investigation of carbonization and activation are dis¬ 
cussed in detail in later sections of this chapter. Be¬ 
cause problems concerning the selection of raw ma¬ 
terials have been of serious moment during the his¬ 
tory of activated carbon, the next section is devoted 
to a discussion of the raw materials used in the manu¬ 
facture of gas mask carbon. 

3.3 RAW MATERIALS 

In the past, there has been an opinion that suitable 
gas mask carbon could only be manufactured from 
specialized and highly organized plant structures. 
Much attention was given to the morphological char¬ 
acteristics of the shells, pits, and like materials that 
were used in the early gas mask charcoal processes. 
During the last few years, however, a wide variety of 
raw materials has been used to prepare gas mask 
charcoals, and there seem to be no definite require¬ 
ments on raw materials save that they must be car- 



RAW MATERIALS 


25 


bonaceous and that they must not have been heated to 
such a high temperature that they have become inert. 

The main problem in manufacturing a suitable gas 
mask carbon is to obtain one that not only has satis¬ 
factory physical adsorption properties as measured 
by the PS life test, for example, but also to obtain a 
product that can be converted into an ASC whetler- 
ite that has a satisfactory canister performance and 
stability against CK under humid conditions. 

The raw materials now being used to manufacture 
charcoals are as follows. 

Bituminous coal of the Pittsburgh seam is the raw 
material for the largest single production. Coals from 
the Emerald and Black Diamond mines are used. 
Charcoal from these coals meets all present specifica¬ 
tions including those for the aging of ASC whetlerites 
under conditions of high humidity and high temper¬ 
ature. The charcoal is of unusually high retentivity. 
Its apparent density is also high and is in the range of 
0.48 to 0.52 g per ml before whetlerization. This char¬ 
coal is low in moisture pick-up and high in ash as 
compared with other charcoals. Its only deficiency is 
weight, which makes it unattractive for use in the 
lightweight canister. The process was developed and 
and is being operated by the Pittsburgh Coke and 
Chemical Company,Pittsburgh,Pennsylvania [PCC]. 

The standard low density charcoal is prepared 
from briquetted waste sawdust from Douglas fir. 
The briquettes or Prest-o-logs are carbonized under 
pressure and activated by steam. These charcoals 
have a lower density than those from bituminous 
coal, are somewhat less satisfactory with respect to 
retentivity and aging, but meet all present specifi¬ 
cations, and are more satisfactory than the PCC 
char in lightweight canisters. The charcoal is pro¬ 
duced by the Crown-Zellerbach Company of Seattle, 
Washington. 

Satisfactory charcoals are being made in smaller 
quantities from pecan shells, 25 English walnut shells, 23 
black walnut shells, 53,19 and peach pits. 53,19 The man¬ 
ufacture of charcoal from such materials is rather 
small because of the limited supply of raw materials. 
These chars are produced by the Barnebey-Cheney 
Engineering Company, Columbus, Ohio. 

Hardwood sawdust, activated chemically by zinc 
chloride using recently developed techniques, yields 
charcoals that meet present specifications. These ma¬ 
terials have the unusually low apparent density of 
about 0.3 before whetlerization. They have low re- 
tentivities and require expensive equipment and 
plants for their manufacture, and therefore they are 


not in procurement. Standby plants were available 
for operation, had the product been needed. 

The standard charcoals made in England are pre¬ 
pared from mixtures of British coals. The coals are 
blended in such a fashion that the carbonization 
process can be conducted without undue swelling 
and coking. 14 Because British practice does not in¬ 
clude whetlerization, it is not known whether the 
British coal mixture would give a satisfactory whet- 
lerite. 

Coconut charcoals prepared in relatively small 
quantities by laboratory methods yielded a charcoal 
that is satisfactory in initial ASC performance. These 
have not been commercialized and their character¬ 
istics in aging are unknown. 

Small experimental quantities of a relatively low 
density coal have been prepared by mixing Pitts¬ 
burgh seam coal with sawdust and processing the 
mixture in the PCC process. The materials had mod¬ 
erate density and satisfactory canister lives, but 
were deficient in hardness. 26 

Several other and unusual raw materials have been 
used to prepare charcoals of promising quality. In no 
case have the products been completely evaluated in 
canister lives and aging characteristics. They have 
been developed to a point, however, where it is quite 
probable that satisfactory materials could be pre¬ 
pared from them, but they are of interest only from a 
theoretical point of view as showing the wide variety 
of raw materials that can be used to make a satis¬ 
factory adsorbent. The Godfrey L. Cabot Company 
has prepared, from carbon black and a starch and tar 
binder, charcoals giving satisfactory ASC whetlerites 
as measured by tube tests. Charcoals made by car¬ 
bonizing Saran (a vinylidene hydrochloride polymer) 
have satisfactory characteristics as base charcoals. 
They whetlerize moderately well after steam activa¬ 
tion. Both of these products are of interest largely 
because they demonstrate that reasonably good ad¬ 
sorbents can be made from materials of synthetic 
origin rather than of plant structure. 

Considerable development work was done in the 
Kimberley-Clark Company, Neenah, Wisconsin, on 
a charcoal made by mixing 50 to 75% by weight of 
crude lignin precipitated from waste sulfite liquor 
with 25 to 50% of poplar wood flour. Char from this 
raw material was evaluated by tube tests and found 
to yield satisfactory ASC whetlerite. The lignin con¬ 
tributed substantially to the yield of carbon and did 
not function only as a binder. The aging character¬ 
istics of the material are not known. 



26 


MANUFACTURE OF ACTIVATED CHARCOAL 


A charcoal manufactured by the Colorado Fuel 
and Iron Company 56 from western bituminous coal 
gave satisfactory activated carbon (good PS life) but 
one that could not be whetlerized to a satisfactory 
product. The material was made by carbonizing and 
steam activating lump coal without previous briquet¬ 
ting. Its aging characteristics are not known. Newer 
information on the factors controlling whetlerizabil- 
ity suggest that this coal also might yield a satisfac¬ 
tory product if it were crushed and briquetted before 
carbonization. 

The older product obtained by the zinc chloride 
activation of hardwood was an excellent adsorbent 
and could be treated to form a superior Type A 
whetlerite. The material was deficient, however, as a 
raw material for ASC whetlerite, and plants manu¬ 
facturing the product were shut down when ASC 
whetlerite was adopted. During research and de¬ 
velopment, intermediate products, satisfactory in 
initial ASC lives but deficient in aging against 
CK under humid conditions, were made by this 
process. 

Several other raw materials yield satisfactory 
activated carbons which meet the specifications 
for unimpregnated charcoal but do not form 
satisfactory ASC whetlerites. Coquito nuts, 23 apri¬ 
cot pits, 24 - 17 Masonite, 46 high density carbonized 
hardwood, 50 Cliffs-Dow Char, 38 NRL-MPGO from 
Activated Carbon Incorporated, 35 and the pitch 
coke obtained from the low pressure carboniza¬ 
tion of coal 45 all yielded materials which could 
be activated to a satisfactory PS life and hard¬ 
ness, but either have yielded unsatisfactory ASC 
whetlerites or have not been evaluated as an ASC 
whetlerite. 

Several materials, which yielded activated carbons 
having PS lives between 20 and 40 min, have not 
been evaluated with respect to ASC lives because of 
their low quality as absorbents. The materials are: 
Morrell char, which is made of a mix of wood char, 
coke and tar binder; 46 carbons from lignocellulose; 29 
ordinary hardwood char; 27 low temperature coke 
freeze from bituminous coal; 45 anthracite coal; 32 
chlorinated anthracite coal; 3 Seabury carbon (Delco- 
Remy). 49 

A number of other carbonaceous materials yielded 
on activation products that have PS lives below 20. 
Some of these materials are: gas coke; 34 various 
woods treated with hydrofluoric acid: 48 scrub oak; 48 
semi-anthracite; 45 and a mixture of wood charcoal 
and pitch. 48 


Conclusions 

The raw materials listed above are typical of those 
that have been tried in the past and those used at 
present. The following conclusions can be drawn: 

1. Because charcoals of the highest grade as meas¬ 
ured by complete evaluation of all important proper¬ 
ties can be made from waste wood and bituminous 
coal, there is no necessity to consider the use of 
esoteric raw materials of special character, of limited 
availability, or of foreign origin. 

2. From a fundamental point of view, the fact 
that satisfactory adsorbents and reasonably satis¬ 
factory whetlerites have been obtained from mate¬ 
rials such as waste sulfite liquor, carbon black, and 
Saran, make it unnecessary to manufacture char¬ 
coals from naturally occurring raw materials. Mor¬ 
phological structure is not necessary. Even the de¬ 
graded type of vegetable structure left in bituminous 
coal is probably of little importance in the use of coal 
as a raw material. Indeed, the first step in the proc¬ 
essing of the coal is to grind it to 300-mesh size and 
thus largely destroy any structure that it might have. 

3. Many of the materials that were found to yield 
mediocre or poor charcoals were evaluated before 
present knowledge of the fundamentals of charcoal 
processing was available. A number of the above 
materials could probably be used by proper briquet¬ 
ting, carbonizing, and activating techniques if there 
were any reason for using them. 

4. A complete and final answer concerning the 
applicability of a given raw material for the manu¬ 
facture of gas mask carbon can only be given by pre¬ 
paring several large batches of the carbon and testing 
each batch thoroughly in canisters against the known 
agents, by preparing ASC whetlerites and determin¬ 
ing the aging characteristics and retentivities of the 
whetlerites, and by obtaining hardness and rough¬ 
handling data on the finished whetlerite. No single 
test is definitive in the evaluation of a gas mask 
charcoal. 

5. Unless future emergencies show that some very 
unusual characteristic, not at present identified, is 
necessary for a satisfactory gas mask carbon, there 
appears to be no reason to use raw materials other 
than waste wood or bituminous coal. 

3.4 BRIEF DESCRIPTION OF COMMER¬ 
CIAL MANUFACTURING PROCESSES 
FOR GAS ACTIVATED CARBONS 

Complete descriptions of the processes being used 
to manufacture gas mask charcoal are given in a 








COMMERCIAL MANUFACTURING PROCESSES FOR CARBONS 


27 


Chemical Warfare Service [CWS] report. 16 The fol¬ 
lowing descriptions are for the purpose of making the 
present chapter complete. 

3 . 4.1 Process of Pittsburgh Coke and 
Chemical Company a 

This process was the major one used in World 
War II and produced more gas-mask carbon than all 
others combined. It is used in two large plants oper¬ 
ated by the PCC. The process is of interest, first, be¬ 
cause the production of a gas-mask charcoal from a 
very large supply of common raw material has been 
reduced to its simplest terms through its use, and, 
second, the product obtained has unusual qualities 
not possessed by other charcoals. The material is 
especially noteworthy for the stability of ASC whet- 
lerite prepared from it. 

The raw material is Pittsburgh seam bituminous 
coal. The two coals that have been used in practice 
are Emerald seam coal and Black Diamond seam 
coal. Other analogous coals can be used. These two 
coals are very much alike and contain 35 to 38% 
volatile matter and 6 to 8% ash. The raw material is 
broken to a size between four and ten mesh U. S. 
standard screen, and is stored in an elevated bin 
holding some 70 tons of coal. From the bin, it is fed 
by gravity to impact mill pulverizers in which the 
size is reduced until at least 65% of the material 
passes through a 300-mesh screen. During early oper¬ 
ations, the coal was mixed with a coal tar pitch to 
aid in briquetting. Present practice omits the pitch 
and uses a small amount of steam intermixed with 
the pulverized coal to moisten it and to heat it suffi¬ 
ciently for briquetting. The ground coal is charged 
into large Kraft paper bags. Each bag contains sev¬ 
eral pounds of coal. The bag is placed in the dies of 
the briquetting press where it is briquetted at a pres¬ 
sure of 10,000 to 15,000 psi. The cylindrical bri¬ 
quettes, after being discharged from the hydraulic 
press, are passed through a series of crushers in which 
the material is broken to the proper size mesh distri¬ 
bution. The size of the final product is controlled 
during this screening operation. The fines, amount¬ 
ing to about 25% of the total material to the screens, 
are returned to the impact mill to be rebriquetted. 
The oversize material of the screens is recycled in 


a The information in this section was obtained through 
various visits of NDRC and CWS personnel to the PCC 
plants. 


closed circuit to the grinder. The intermediate ma¬ 
terial has a size range between 10 and 22 mesh U. S. 
standard. The size reduction obtained during the 
further processing steps reduces the material to a 
12- to 30-mesh size which passes standard CWS speci¬ 
fications. 

The sized material is elevated to a feed bin and 
weighed into the carbonizers or bakers. Each carbon- 
izer or baker consists of two parallel tubes mounted 
together in a gas-fired furnace. The tubes are %-in. 
plate steel. They are each about 60 ft long and 3 ft in 
diameter. The crushed charge passes in series through 
two bakers and emerges from the second baker at a 
temperature of about 1000 F. The temperatures are 
not measured in the bakers themselves, but in the 
gas space external to the tubes. These temperatures 
increase from 600 F at the feed end to about 1050 F 
at the discharge end. The time of baking is about 
434 hours. 

In both bakers, a small current of steam is passed 
to sweep out volatile matter. A certain amount of 
fortuitous air leakage also occurs and this leakage is 
probably important for the carbonization step. 

The baked material, which still contains some 12% 
volatile matter, is discharged into wheelbarrows and 
charged by hand into the activators. 

The activators are operated in batch. There are 
approximately 30 activators in each of the two 
plants. Each activator is a cast chrome-steel tube 
15 ft 6 in. long by 14% in. in diameter. The charge is 
heated externally by coke-oven gas. The activators 
are mounted in pairs. The activators are charged 
from the front by blowing the charge from hopper 
carts with compressed air. A lid with a 4-in. central 
hole makes a loose rolling fit with the wall end of the 
activator and is held in place by a flange which fits 
over the lip of the activator cylinder. Steam, in an 
unknown amount, is superheated by passing it 
through a chrome-steel pipe positioned in the furnace 
and is admitted to the back of the activators. Both 
the gas formed by activation and the excess steam 
issue from the 4-in. opening in the lid in the front of 
the activator. The combustible gases burn in the at¬ 
mosphere. The temperature in the furnace is 1760 F 
and the charcoal temperature is 1740 F. Tempera¬ 
ture control is manual. 

The charge to an activator is 225 lb; approxi¬ 
mately 113 lb of activated product is obtained after 
an activation time of 285 min. The activators are 
emptied by removing the lid in the front and raking 
the charge out over the lip into wheelbarrows. 








28 


MANUFACTURE OF ACTIVATED CHARCOAL 


Neither steam nor combustion gases are cut off dur¬ 
ing the discharge or charge operations. 

One feature of the activation process is the size 
separation that occurs in the activators. The large 
particles tend to rise to the top of the bed and are 
usually more thoroughly activated than those which 
remain submerged. 

The activated product cools in air and is given a 
final screening to insure proper size. The fines ac¬ 
cumulated during this screening are very small in 
amount. 

The yields are as follows: From 100 lb of coal 80 lb 
of primary char after baking and 37 lb of activated 
char are obtained. The block density of the briquettes 
is 1.2. The apparent density of the crushed bri¬ 
quetted material is about 0.60. The apparent density 
of the baked material is about 0.58 and the density 
of the activated product is about 0.50. 

The process is practiced in two plants; one at 
Neville Island, Pittsburgh, Pennsylvania, and the 
other at Carnegie, Pennsylvania. The processes in 
the two plants differ in minor respects but both oper¬ 
ations are essentially as described. 


3.4.2 The Prest-o-log Process 30 

This process successfully manufactures a satisfac¬ 
tory grade of gas-mask charcoal from waste wood. 
It is essentially the same as a process that was being 
developed at the end of World War I. Many practi¬ 
cal difficulties were overcome before satisfactory 
operation. Considerable effort was necessary both in 
plant and pilot plant before a satisfactory product 
was obtained. The process produces a carbon of rela¬ 
tively low apparent density which makes it attractive 
for use in lightweight canisters. It is not as satisfac¬ 
tory from the point of view of initial gas life, retentiv- 
ity, nor stability as the product from the PCC 
process. 

The problem of attaining a high density briquette 
from waste sawdust has been solved in a novel fash¬ 
ion by the development of a mechanical means for 
compacting sawdust to a briquette. The product of 
the briquetting operation is known as Prest-o-logs. 
The Prest-o-logs used in the Seattle plant are made 
by the Weyerhaeuser Company, and the logs are de¬ 
livered to the pilot plant ready for processing. The 
Prest-o-logs are about 13 in. long, and are 4^ in* in 
diameter. Each log is sawed into six 2-in. briquettes 
by means of gangsaws. The briquettes are charged 


into two carbonizing furnaces which consist essen¬ 
tially of tubes 60 feet long mounted in furnaces. Each 
furnace contains four vertical banks of seven tubes 
each. Holes are provided for gas escape at 4-in. inter¬ 
vals along the entire length of each tube. The essen¬ 
tial feature of the carbonization process is the use of 
pressure constantly applied to the briquettes during 
carbonization. Extensive and detailed pilot plant 
work done on the process 29> 31 shows that the pres¬ 
sure is essential during the period of the exothermic 
reaction in order to maintain proper density in the 
carbonized product. Between each briquette is placed 
a cast iron spacer ]/% in. thick. Pilot plant work 
demonstrated that these spacers are necessary to 
transfer heat to the center of the briquette dnd thus 
eliminate soft centers. 

The pressure is applied by a hydraulically oper¬ 
ated plunger. The total net pressure over the entire 
tube is 160 psi. Discharge of the carbonized bri¬ 
quettes at the end of the tube is accomplished by 
means of a hydraulically operated gate. An ingenious 
control system allows the operator at the end of the 
tube to charge fresh briquettes periodically at the 
entrance and discharge carbonized briquettes at the 
exit. The iron spacers are separated from the dis¬ 
charged briquettes, returned by a conveyor, and 
reused. The gases formed by the carbonization issue 
through the holes drilled in the carbonizing 

tubes and burn in the space surrounding the tubes. 
The heat requirement for the carbonization is more 
than met by the heat of combustion of the gases 
formed, and city gas is required only during the 
starting-up period. 

The primary charge is crushed in two steps. The 
first stage is accomplished in a Robinson sawtoothed 
crusher and gives a discharge consisting of particles 
approximately 3^ to 34s in. in diameter. The second 
stage is a Robinson gyratory crusher. The product is 
screened over Rotex screens to give three fractions. 
The first fraction is larger than 6 mesh and is re¬ 
turned to the feed of the second press; the second 
fraction is 6-20 mesh and is used for further process¬ 
ing; the third fraction is fine material which is wasted. 
The percentage of fines is about 22 %. Because there 
is no possible way of recycling fines, they are com¬ 
pletely lost from further processing. 

After size separation the char is calcined. The cal- 
ciner is a rotary kiln like those used in cement manu¬ 
facture. It is 77 ft long and 8 ft 9 in. inside diameter. 
It is lined with 12 in. of refractory and insulation. 
The calciner is divided into three sections. The first 







COMMERCIAL MANUFACTURING PROCESSES FOR CARBONS 


29 


section, or preheater, is 39 ft long and is separated by 
a bridge wall from a second, or calcination, section 
which is 26 ft long. The third division is a cooling 
section 13 ft long. The calciner rotates at about 
3^ rpm. The temperature of the charcoal at the feed 
end is about 800 F, and at the bridge wall about 
1400 F. Air inlet pipes supply air to burn the com¬ 
bustible gases formed by the calcinators in the kiln. 
In the calcining section, the charcoal temperature is 
about 1700 F at the entrance and 1900 to 2100 F as 
the end where the material passes to the cooling 
section. Electrical heating is used in the calciner sec¬ 
tion. The current is applied in two circuits through 
commutator rings and the charcoal itself acts as an 
electric conductor. The heat required to bring the 
carbon to 2000 F is obtained in part from the electric 
energy supplied through the electrodes and in part 
from the heat of combustion of gases formed by the 
continued devolatilization of the charcoal. 

The purpose of the calcination step is to develop 
strength and density in the particle and to complete 
the devolatilization. Pilot plant work showed that a 
satisfactory product can be prepared by this process 
without the calcination step but that very careful 
carbonization is necessary if this step is omitted. Also, 
the maximum PS life cannot be obtained without 
calcination. 30 ’ 32 The carbonization step is consider¬ 
ably easier to operate if followed by calcination and 
to some extent deficiencies in carbonization can be 
eliminated in calcination. 

The activator-is a continuous rotary kiln. It is 
60 ft long, 8 ft 8 in. inside diameter, and has a 12-in. 
refractory and installation lining. It rotates at 
% rpm. The activating section is 48 ft long and the 
unlined cooling section is 9 ft long. Both measure¬ 
ments are taken on the inside. The heat required for 
the activation process is obtained first, by burning 
the combustible gases generated during activation, 
and second, by electrical heat supplied through elec¬ 
trodes in the furnace walls. Steam is blown through 
nozzles placed in the wall of the activator. The steam 
pipes are connected to manifolds outside the wall of 
the activator and the manifolds brought to the auto¬ 
matic valve which emits steam to the activator bed. 
The steam in each set of inlet tubes is on during one- 
fourth of each revolution. The flow of steam is auto¬ 
matically shut off when the steam ports are not cov¬ 
ered by the charcoal bed. Air pipes connected to an 
air manifold pass through the activator wall into the 
center of the activator to provide air for the com¬ 
bustion and volatile matter. The product of the 


activator is given a final screening. Fines amounting 
to 14% are wasted. 

The overall yield of the process is between 6 and 
8%. The losses are distributed approximately as 
follows: in the saws, 14p£%; in the charring furnace, 
about 71%; grinding loss 22 %; calcination loss 24%; 
activation loss 36%; and loss in the final grinding, 
16%. Loss in each step is based on the weight of 
material charged to that step. 

The material is in the calcinating tubes about 
130 min, in the calciner about 36 hr, and in the acti¬ 
vator about 24 hr. Pilot plant work shows 29,31 that 
these long times of carbonization, calcination, and 
activation are unnecessary. 

3.4.3 Miscellaneous Processes for Manu¬ 
facture of Gas-Activated Charcoal 

Several charcoal processes have been developed 
through the laboratory or pilot plant stage but have 
not been used commercially. There is but little likeli¬ 
hood that any of these processes will ever be used to 
make gas mask carbon, but they will be described 
briefly because of the information they provide on 
the general problem of charcoal manufacture. 

Manufactured Charcoal from Carbon Black 22 

This process was carried through the pilot plant 
scale by the Godfrey L. Cabot Company, Boston, 
Massachusetts. 

Channel black, made by burning natural gas with 
a deficiency of air under steel channels, is the main 
raw material for the process. The size of the particles 
is 50 to 100 A. The carbon black is mixed with ap¬ 
proximately an equal weight of Barrett coal tar pitch 
and wet with 20% casein solution, which acts as a 
mixing agent. The mixture has a consistency about 
equal to that of axle grease. The mix is pelleted at a 
pressure of 50,000 to 100,000 psi. The pellets are 
% in. diameter by % in. long. 

The pellets are broken to 8-10 mesh before carbon¬ 
ization. About 45% of the material is fines, which 
are reprocessed. 

The broken pellets are carbonized by being passed 
through a gas fired furnace. The charge is heated to 
1400 F and cooled to room temperature. The charge 
is at or near 1400 F for about 45 min. The material 
shrinks during carbonization and has an apparent 
density of 0.80 after the process. 

The carbonized raw char is steam activated in a 
continuous horizontal tube, 7 ft long. The temper- 




30 


MANUFACTURE OF ACTIVATED CHARCOAL 


ature of activation is 1600 F maximum, and the time 
is 8 hr. The feed rate is 2 lb per hr and the steam rate 
was 4 to 12 lb per hr. The overall yield of the process 
is approximately 35% of the weight of the pellets. 
The product contains practically no ash. 

The product of this process was found to be con¬ 
vertible to ASC whetlerite that gave reasonably well 
balanced protection against SA, CK, and AC. 6 The 
PS life of the unwhetlerized char was in the range 
50 to 60 min. The evaluation was largely by tube 
tests and no aging data are available. The estimated 
cost of charcoal from this process, including an eight¬ 
een month write-off, was 30 cents per pound. 

The process did not go into commercial use be¬ 
cause by the time the pilot plant work was done, the 
PCC process, which gives a cheaper and better 
product, was in operation. 

Manufacture of Charcoal from Waste Sulfite 
Liquor and Wood Flour 

The Kimberley-Clark Company of Neenah, Wis¬ 
consin, completed a pilot plant investigation and 
preliminary plant design for a process to make gas¬ 
mask carbon from a mixture of wood flour and liquor 
precipitated from waste sulfite. Again, a satisfactory 
product was obtained (with a possible exception of 
aging characteristics) but the cost-quality relation¬ 
ship was inferior to that shown by the PCC process, 
so the plant was not constructed. 

The essential steps in the process 1 are: waste sul¬ 
fite liquor, which has a pH of 2.5 to 3.0, is neutralized 
with caustic soda, and the pH raised to 11.5 to 12.0. 
The alkaline material is cooked in a digester at 75 psi 
and 320 F for 2 hr. The cooked liquor is pumped into 
a wood precipitating tank and concentrated sulfuric 
acid added until the pH is 3.5 to 4.0. Lignin is pre¬ 
cipitated from the solution. On addition of cold 
water the lignin hardens and can be broken into 
pieces approximately 346 x 34 in* The lumps are 
washed twice with water and dried to a moisture 
content of 5%. 

The crude mix for carbon manufacture consists of 
lignin, oak or birch wood flour of 60-80 mesh size, 
and recycled fines. The lignin and fines are ground 
to — 200 mesh. The minimum proportion of lignin to 
produce a carbon of satisfactory density and hard¬ 
ness is 50 to 66 % of the total of lignin and wood flour. 
Sodium qarbonate, an activation catalyst, is added 
in amount equal to 0.5% of the weight of the mixture 
to the material in the blender. 

The final mix is pelleted at sufficient pressure to 


produce a density of 1.16 to 1.22. The pellets are of 
%-in. diameter, and are made in a commercial 10-ton 
pelleting machine. A pelleting lubricant, such as 
Sterotex, is used. 

A typical mix has the following raw materials: 


Material Per cent 

Lignin (200 mesh) 66 

Oak or birch flour ( — 60 mesh) 22 

Recycled fines ( — 200 mesh) 12 


100 

Sterotex, 1 % of above 

Na 2 C0 3 , 0.5% of above 

The pellets are carbonized in batch, without pre¬ 
liminary crushing, in a rotary retort. The temper¬ 
ature is increased at a uniform rate to a maximum 
of 1030 F. Two exothermic reactions, one at 510 F 
and one at 800 F, are encountered during the heat¬ 
ing. The carbonizing time is 5 hr. The hot carbonized 
material is discharged into air-tight containers and 
cooled. The primary carbon pellets are strong, hard, 
and retain their original cylindrical shape. They are 
considerably smaller than the uncarbonized pellets. 

The carbonized pellets are crushed and screened 
to 10 to 18 mesh. The fines, which are approximately 
25% by weight of the pellets, are recycled. The ap¬ 
parent density of the carbonized material is 0.5. 

Activation is conducted in a rotary batch retort 
heated by producer gas. The material activates rap¬ 
idly with steam and activation requires only 60 min. 
A total of 1 lb of steam per pound of primary carbon 
is used. 

The yield of carbonized material from the pellets 
is 56% and the yield from the activation step is 
43 to 45%. The overall yield is 21 to 22% based on 
starting material. 

Considerable performance data on the product 
from the process are available, including tube and 
M10 canister tests on ASC whetlerite made from 
the charcoal. 36 The PS service life of the base carbon 
was 50 to 55 min, and the apparent density was 0.41. 
ASC whetlerite characteristics were excellent in com¬ 
parison with other charcoals available at the date the 
tests were made. Aging data and M10A1 canister 
data are not available as the process was eliminated 
from consideration before the determination of such 
data was customary. 

The cost of the process is excessive in comparison 
with that of the PCC process. For example, 25 lb of 
caustic soda and 25 lb of sulfuric acid are required 
for 17.5 lb of lignin, and the total cost of the lignin 


.FT 



COMMERCIAL MANUFACTURING PROCESSES FOR CARBONS 


31 


alone is 7 K cents per lb on a basis of a two-year de¬ 
preciation period. The pelleting process is expensive 
in comparison with the briquetting of coal. Costs of 
carbonizing and activating are comparable in the 
two processes, but costs of raw material alone in the 
Kimberley-Clark process are 20 cents per lb of carbon 
and the total cost, including an 18-month write-off, 
was estimated to be about 50 cents per lb. The actual 
price of PCC carbon is approximately 20 cents per lb. 

Saran 

The preparation of activated carbon from Saran 
has been achieved in the laboratory. The cost of the 
raw material precludes its ever being used and no 
work has been done beyond the laboratory stage. The 
results obtained on the material are of some interest 
theoretically, because they demonstrate that acti¬ 
vated carbon can be made from a completely syn¬ 
thetic raw material which has no morphological 
structure. 

The Saran charcoals were prepared from a co¬ 
polymer of 15% vinyl chloride and 85% vinylidene 
chloride. 18 A controlled carbonization, in which HC1 
is driven off and nearly pure carbon left behind, 
yields a product that has PS lives of 40 min or more, 
without steam activation. During carbonization 
from 20 to 40% of the HC1 is removed between 125 
and 150 C, and the remainder by heating to 400 C. 
Some carbon is also driven off. Saran charcoals ob¬ 
tained by carbonization only are not satisfactory 
bases for ASC whetlerite. Steam activation increases 
the PS life of the charcoal to a 65 min level, and the 
steam activated material can be used to prepare 
reasonably satisfactory but not outstanding ASC 
whetlerites. 37 

No practical use for Saran charcoals has appeared, 
and because of the limited supply of raw material 
and the high cost of the product their further de¬ 
velopment and commercial manufacture cannot be 
justified. 

Coconut Charcoal 

The older types of coconut char, which were made 
by carbonizing the shells in lump form and steam 
activating the carbonized char, do not form satis¬ 
factory ASC whetlerites. Pore distribution analyses 
(see Chapter 6) show that such materials are defi¬ 
cient in macro pores. Preliminary laboratory results 42 
have been obtained showing that coconut chars can 
be much improved by either of the following proc¬ 
esses. 


The first process consists in sizing pit-carbonized 
coconut shells, slow carbonization of the sized ma¬ 
terial to 1500 F, and activation at 1700 F. The acti¬ 
vated product, when whetlerized with an ASC solu¬ 
tion containing 4.25% Cr0 3 produced a whetlerite 
comparing favorably with a U. S. Grade I, Seattle 
wood whetlerite. 

The second process consisted in pulverizing the 
shells, briquetting hot with 20% by weight of pitch 
binder, sizing, carbonizing one hour at 1000 F, and 
activating at 1700 F. When whetlerized with the 
same solution, the product compared favorably with 
U. S. Grade I coal char made in the PCC process. 

Coconut chars of the above type will probably not 
compete with the better products manufactured from 
domestic materials, and there is no reason for de¬ 
veloping the above process further. 

3.4.4 The Manufacture of Gas Mask 
Charcoal — Conclusion 

Consideration of the various processes used to pre¬ 
pare gas-activated charcoals that were or could be 
used leads to the following conclusions. 

1. Just as scarce unusual raw materials are un¬ 
necessary, so are tricky, complicated processes un¬ 
essential for manufacturing a high-grade modern 
absorbent. Essentially the most successful processes 
consist in building a briquette of finely ground parti¬ 
cles and of a particle density of about 1.2, carboniz¬ 
ing the briquetted material under such conditions 
that the strength and density of the material are not 
destroyed, and steam-activating the carbonized 
materials. 

2. Although the above method is quite generally 
applicable, the optimum conditions for each raw 
material must be found by laborious trial-and-error 
experiments. Also, different raw materials, although 
yielding satisfactory products when treated in the 
optimum manner, yield products of varying char¬ 
acteristics and quality. 

3. The success of any process in producing uni¬ 
form charcoal of good quality depends upon careful 
selection and standardization of the raw material and 
careful operation and control of all process steps. 

4. The manufacture of charcoal is inherently a 
high-temperature process from the point of view of 
metallic construction materials. Steam activation re¬ 
quires a temperature of 900 C to 1000 C, if a reason¬ 
able plant capacity is desired, and only the better 
high-chromium alloys withstand such temperatures. 
This problem is discussed in Section 3.5. 


. SECRET ! 





32 


MANUFACTURE OF ACTIVATED CHARCOAL 


5. The mechanical characteristics of the char are 
important and must be determined by experiment. 
The strength of the final particle seems to be deter¬ 
mined in the original briquetting operation, but even 
a strong briquette can be weakened to disintegration 
during carbonization and activation. 

6. Expensive processing of raw material before 
briquetting is unnecessary, because ground bitumi¬ 
nous coal and waste woodj sawdust provide excellent 
raw materials without such processing. 

3.5 FUNDAMENTALS OF MANUFACTURE 
OF CHARCOAL BY STEAM 
ACTIVATION PROCESSES 

From the foregoing review of present and potential 
processes for the manufacture of steam-activated 
charcoal, it is apparent that there are three key steps: 
(1) crushing and briquetting; (2) carbonization; and 
(3) activation. It is the purpose of this section to pre¬ 
sent the current knowledge of each of the steps gen¬ 
erally taken. The method to be followed is to present 
the scientific and fundamental background of these 
operations and to correlate such knowledge with 
practice. 

3 . 5.1 Crushing and Briquetting 

A method for evaluating fundamentally the effects 
of process variables in charcoal making is to follow 
changes in the pore structures during the various 
steps in the manufacturing process. The methods 
used to determine pore structures and the definitions 
of sub-micro, micro, and macro pores 21 are discussed 
in Chapter 6. It is pointed out there that a charcoal 
that will give balanced protection has a balanced 
pore structure, and the relative proportions of micro 
and various sizes of macro pores is important in 
establishing the characteristics of the final whetlerite 
prepared from the material. If a final char is deficient 
in macro pores of the proper sizes, it will not yield a 
satisfactory whetlerite, especially if the product is 
evaluated in terms of its wet CK life in thin-bed 
canisters. If the charcoal is deficient in micro pores 
it will not be satisfactory as a physical adsorbent. 
The sub-micro pores seem to have no value. 

Large macro pores are built into the charcoal parti¬ 
cle before carbonization and activation. 20 - 21 Certain 
materials such as walnut shells and peach pits possess 
a morphological structure that insures an adequate 
system of macro pores. In general, however, to rely 
upon a natural structure for such pores is to limit 


seriously the raw materials that can be used for char¬ 
coal manufacture. The performance of charcoals de¬ 
scribed in Section 3.4, in which the morphological 
structure of the raw material either never existed or 
was destroyed before carbonization, shows that the 
equivalent of the proper morphological structure 
can be obtained artificially by grinding the raw ma¬ 
terial and briquetting the fine powder so obtained. 

Pore distribution studies of PCC coal charcoal 
show that the crushing and briquetting operation 
creates large spaces between the primary particles 
and that these spaces fall in the large macro pore 
range. The macro pores formed by briquetting are in 
the range of about 50 to 700 microns. 20 It is doubtful 
that they function in a manner to yield a good ASC 
whetlerite, but they are available as feeder pores 
from which smaller macro pores can be developed 
during carbonization and activation. They also facili¬ 
tate the escape of volatile matter during carboniza¬ 
tion and provide channels throughout the charcoal 
particle during activation. Too large a volume of such 
large pores is disadvantageous because they represent 
a waste of charcoal volume if they are present in 
excess. 

It is well known that monolithic graphitic carbon 
cannot be satisfactorily activated. It is also probable 
that if such material has been too thoroughly graphi- 
tized by excessive heating, an active carbon cannot 
be made from it even after crushing and briquetting. 

An important problem in forming a briquette from 
a finely ground raw material is that of obtaining 
strength and rigidity in the briquette. To meet this 
requirement, various binders are usually used. The 
most important material used for this is ordinary 
petroleum pitch. Other materials are starch and 
lignin. Most binders do not contribute an appre¬ 
ciable part of the final product. Lignin, however, as 
shown by the Kimberley-Clark process, does break 
down and add activated carbon to the final product. 
Experience with the PCC process has shown that by 
heating the carbon with steam it is possible to bri¬ 
quette the material without binder and the use of 
pitch for this purpose in the PCC process has been 
discontinued. 

The obtaining of a suitable briquette and the 
choice of binder and the proportion of binder to char 
can only be worked out by empirical experiment. 
No method of predicting the answer to such -prob¬ 
lems has been found. Attempts to obtain a satisfac¬ 
tory carbon from uncrushed Emerald mine bitumi¬ 
nous coal failed. 10 



MANUFACTURE BY STEAM ACTIVATION PROCESSES 


33 


An increase in briquetting pressure over the range 
10,000 to 80,000 psi was accompanied by an increase 
in particle density from 1.02 to 1.16, and a decrease 
in macro pore volume of 0.23 to 0.11 cc per cc 
granule. 20,21 

Increased briquetting pressures are in the main 
beneficial, but on a diminishing return basis. Pres¬ 
sures up to 20,000 psi tend to improve hardness and 
strength, and the gas lives are somewhat improved. 
Pressures in excess of 20,000 psi have but little effect. 

Experiments on the use of very small primary coal 
particles (1 to 2 microns mean diameter) yielded 
products having slightly better 80-80 CK canister 
lives than those made from the usual size of crushed 
coal particles (1 to 159 microns). The charcoal from 
the micronized coal (1 to 2 microns) yields a superior 
secondary whetlerite after a leaching of the primary 
whetlerite and a second whetlerization. 43 

3.5.2 Carbonization 

The function of carbonization is primarily that of 
removing the bulk of the volatile matter present in 
most raw materials without destroying the density 
and strength of the particle. During carbonization 
certain changes are brought about in the pore dis¬ 
tribution. All the volumes of sub-micro, micro, and 
macro pores increase. 20 The increase in micro pore 
volume does not, however, bring about an increase 
in the adsorbing qualities of the char. 

The most difficult problem in carbonization is usu¬ 
ally the prevention of coking, which results in a 
porous, puffed-out particle full of large voids. Many 
materials on carbonization pass through a soft or 
plastic stage and, if the volatile matter is evolved 
during such a stage, coking can readily result. 

Two techniques useful in preventing coking have 
been developed. In the carbonization of wood the 
application of pressure to the wood briquette, as 
practiced in the Seattle process and as studied on the 
pilot plant basis by National Defense Research 
Committee [NDRC], allows the retention of the 
density of the briquette by applying direct pressure 
while it is in the plastic stage. It has been found by 
experiment that the pressure is unnecessary except 
at a temperature of about 400 F. If pressure is main¬ 
tained during that stage, the resultant crude char 
can be further processed to obtain a satisfactory 
product. In the usual distillation of wood, coking 
occurs and the primary char obtained possesses too 
low a density to yield a satisfactory product. 


The second technique of carbonization is appli¬ 
cable to coal. It is difficult to carbonize crushed coal 
briquettes in the absence of oxygen. 10 When carbon¬ 
ization is attempted in a stream of nitrogen, for ex¬ 
ample, a long carefully conducted carbonization is 
necessary to obtain material suitable for activation. 
If, however, air is present 'during the carbonization, 
the process can be conducted with considerable 
rapidity and a satisfactory carbonized char obtained 
in a total time less than one hour. 41 

A small amount of air can reduce the coking tend¬ 
ency of a coal significantly even if the oxygen ab¬ 
sorbed by the coal is negligible. 9 The manufacturing 
process normally conducted allows a certain amount 
of air to be fortuitously drawn into the bakers. Also 
the partially carbonized char is exposed to the air 
during transfer from one baker to the next. 

A deliberate supply of controlled air reduces the 
coking tendency and allows an easier and shorter 
carbonization. 41 The critical time at which air is re¬ 
quired is during the softening and coking period 
which occurs at about 600 F. If air is present during 
this temperature interval an exothermic reaction 
occurs, which reduces the fuel consumption and 
which accelerates the carbonization process. 

Certain definite indications were obtained showing 
that the yield versus quality relationship of the final 
carbon can be improved by air carbonization. 41 An 
increase of approximately 15% in the CK life of the 
product was found in some cases. Since this increase 
is near the limit of precision of the canister test and 
can also be obtained by variations in whetlerization, 
this result is not too clearcut. 

Carbonization in the presence of air at a maximum 
temperature of about 1000 F often yields a carbon¬ 
ized product that has considerable PS life, sometimes 
as much as twenty minutes. b A carbonization carried 
to a higher temperature, 1800 F, for example, gives 
a product which shows no PS life. There is evidence 
that shrinkage occurring between the temperatures 
of 1000 and 1800 F may account for this difference. 20 

Not all raw materials are equally difficult to car¬ 
bonize. Peach pits, 40 walnut shells, and coconut 
shells 2 can be carbonized with relative ease without 
coking. It is doubtful that air has any beneficial 
effect in such cases. The carbonization of sawdust- 
lignin mixtures was quite easy. Bituminous coal 
represents material which is most difficult to carbon¬ 
ize, but the use of air, as described in the preceding 


b A good charcoal has a PS life of 45-60 min. 


SECRET \ 






34 


MANUFACTURE OF ACTIVATED CHARCOAL 


paragraph, simplifies the problem of obtaining satis¬ 
factory materials for activation by carbonizing 
briquetted coal. 

3.5.3 Activation 

The final definitive step in preparing a charcoal by 
non-chemical means is that of activation. The activa¬ 
tion process cannot produce a satisfactory material 
if the earlier steps are not conducted properly. With 
the exception of materials such as Saran, however, 
carbonized chars have little or no activity, and gas 
activation is required to develop their inherent 
properties. 

As far as the process is concerned, activation is 
simple. It consists essentially in bringing carbonized 
char into intimate contact with hot activating gases. 
Although oxidizing gases such as carbon dioxide, 
chlorine, and sulfur, can be used for activation, only 
one active agent (superheated steam) is used in prac¬ 
tice. The purpose of the activation process is to cre¬ 
ate the final desired pore structure in the granule, 
and also to develop the proper kind of surface in the 
pores. During activation the particle loses weight, 
both from the inside and the outside, and both the 
size and density of the particle decrease significantly. 

3.5.4 Process Variables— Steam 

Activation 

The important requirements for a satisfactory 
commercial activator are: (1) the energy require¬ 
ment must be provided; (2) uniformity of contact 
between gas and particles must be obtained; and 
(3) the proper time of treatment must be provided. 

The reaction of carbon and steam is highly endo¬ 
thermic. Approximately 4000 Btu must be supplied 
for each pound of each carbon gasified. Heat require¬ 
ments in a small experimental unit can be easily sup¬ 
plied by means of the hot walls of an externally 
heated container. In a large unit, however, the sup¬ 
plying of heat to the charge is a serious problem. Un¬ 
less regenerators are used, the supply of heat by 
means of the hot gases themselves is not practicable. 
The radiation from the hot gas to the particle is not 
rapid enough to supply the heat at an appropriate 
rate unless the gases are at a temperature well above 
the activation temperature to be used. For example, 
if the active temperature to be used is 1700 to 1800 F, 
the hot gases, even when supplied in large quantity 
as in the Jiggler process (see Section 3.6.1), must be 


at temperatures above 2500 F. In retort activation, 
in which the flow of gases is very much less than in 
Jiggler activation, it is not practicable to supply all 
of the heat requirement by means of the gases them¬ 
selves. In general, heat must be transferred through 
the retort wall. Furthermore, in order that all parti¬ 
cles in the activating bed can be reached by heat, the 
thickness of the bed is limited. Other methods of 
supplying heat to the charge are the use of electrical 
heat such as used in the Seattle process, and the sup¬ 
ply of heat by burning, in direct contact with the 
charcoal particles, the gases formed by activation 
supplemented by external fuel. 

Uniformity of activation is important. The uni¬ 
formity problem has two aspects: (1) activating con¬ 
ditions must be the same throughout the activator; 
and (2) the individual particles must be activated 
under uniform conditions. Activators are usually hori¬ 
zontal rotary furnaces in which the particles are 
brought into contact with the activating gas by con¬ 
tinually circulating in the activator. Such activators 
do not give perfect uniformity; 37 larger particles 
tend to activate more quickly than the smaller. Sat¬ 
isfactory uniformity of activation can also be ob¬ 
tained by using long continued low-temperature 
activation processes in which the partially activated 
material is continually withdrawn in the bottom of 
the activator and returned to the top. 16 The Jiggler 
method of activation provides maximum uniformity 
of contact between gas and char. 

In practice, fortunately, a reasonable lack of uni¬ 
formity in the activated char can be tolerated, but 
at the expense of a somewhat lowered yield. The de¬ 
velopment of the activity of the char, both as an ad¬ 
sorbent and as a catalyst base, occurs rapidly during 
the early stages, but the extent of development of the 
desired properties becomes constant during the later 
stages and the characteristics of the final carbon are 
relatively independent of the amount gasified over a 
range of 10 to 15% of final yield. Therefore, if certain 
particles activate somewhat more slowly than others, 
they tend to reach approximately the same peak if 
the process is continued long enough, but the yield 
is lower by 5 to 10% than that obtainable under 
uniform conditions. 12 

Although steam is the activating agent used in 
most industrial processes, carbon dioxide can also be 
used, and is usually present in activators in which 
steam is used because some C0 2 and much CO is 
formed during the activating process. In some cases, 
for example in the Prest-o-log process, the carbon 




MANUFACTURE BY STEAM ACTIVATION PROCESSES 


35 


monoxide is allowed to bum in the activator to sup¬ 
ply a portion of the heat of activation. Also, if steam- 
enriched flue gases are used, C0 2 will be present. The 
activation of carbon by C0 2 alone is slower than with 
steam under corresponding conditions. In addition, 
the quality of the product as measured by its ca¬ 
pacity for physical adsorption tends to be somewhat 
less. 28 The presence of 10% or more of C0 2 in the 
activating gas does no harm and can be tolerated 
without difficulty. 

3 . 5.5 Temperature Control 

The temperature of the char in the activator should 
be measured and, for best results, maintained under 
reasonably close control. The accurate measurement 
of char temperature is not a simple matter because 
of the effects of rotation and non-uniformity of the 
char bed both in depth and in length. Also the parti¬ 
cles absorb heat rapidly. There is doubt that the 
activating temperature in one plant can be correlated 
with that in a different plant. For best results, the 
temperature measuring device (usually a thermo¬ 
couple) should be immersed well into a dense bed of 
carbon. 

The effect on product quality of variation in acti¬ 
vation temperature over a range of 100 to 150 F is 
not great. The main effect of temperature is upon 
rate of gasification, and the control of temperature 
is essentially a control of rate. The optimum temper¬ 
ature of activation depends upon the char, and usu¬ 
ally lies in the range of 1500 to 1800 F. The temper¬ 
ature of activation should not be more than 75 F 
above or below the optimum. As a rule, if uniformity 
of contact between gas and char is obtained, the re¬ 
lationship between yield and quality is relatively 
insensitive to temperature, total gas flow, gas com¬ 
position, and gas velocity. 27 Large variations in these 
factors do, however, influence quality. 55 

Close temperature control in itself is of no avail if 
the time of treatment varies among the particles, or 
if some particles are in a different gas environment 
from others. To obtain controlled uniformity of acti¬ 
vation all particles must be activated at the same 
temperature, for the same time, and in contact with 
gas of the same velocity and analysis. 

Activating temperatures are at just about the 
metallurgical limit, and high-chromium alloys are 
the best material of construction for externally 
heated activators. Internally heated activators can 
be constructed of refractory-lined steel shells. 


3 . 5.6 Changes During Activation 

The activation process modifies the crude char in 
a number of ways. Formerly, the process of activa¬ 
tion was considered essentially as a selective oxida¬ 
tion of hydrocarbonlike materials which were re¬ 
tained by adsorption in the'pores of the char after 
carbonization. In this simple explanation, activation 
was considered to be a cleaning or purging process by 
which existing pores were purged of high molecular 
weight materials that were occupying the active cen¬ 
ters of the char, and therefore when these materials 
had been oxidized the existing activating centers 
were uncovered and made useful. 

There is an element of truth in this assumption, 
but there is reason to believe that it is not the main 
part of the activating process. It is true that there is 
a widespread existing pore structure in char after 
carbonization and before activation. Pores of the 
sub-micro, micro, and macro size range are present. 21 
It is also reasonable to assume that the surface of 
these pores is contaminated with debris resulting 
from the cracking of hydrocarbons and analogous 
processes. During the early part of the activating 
process, such debris is removed and the existing pore 
structure uncovered. Charcoal at this stage, how¬ 
ever, is not well activated, and has but little more 
adsorptive capacity than before activation. In fact, 
in some cases, chars obtained by long continued car¬ 
bonization have fair PS lives which are destroyed 
during the initial stages of steam activation. The 
essential purpose of steam activation is now con¬ 
sidered to be a development of a proper pore system 
in the micro and macro range. The development of 
the required system is a continuation of the pore 
development originally set up in the briquetting 
step. 21 

The final activated char, when studied by X-ray 
methods, 17 seems to consist of a number of small 
packets. The sizes of the packets are of the order of 
10 to 20 A. 55 ’ 18 The packets themselves are con¬ 
structed of layers of carbon laid down in a crystal 
structure essentially graphite, except that the dis¬ 
tance from corner to corner of the hexagon rings and 
the interplanar ends are larger than those of a true 
graphite. The adsorptive characteristics of the pack¬ 
ets may result from the fact that the departure of 
the crystal parameters from those of graphite distort 
the force fields in such a way that residual forces are 
available for attracting foreign molecules. 

When carbons are given a prolonged heating at a 







36 


MANUFACTURE OF ACTIVATED CHARCOAL 


temperature of 1000 C or more, the lattice dimen¬ 
sions tend to approach those of graphite and the 
carbon has little or no adsorptive power. 17 

The sequence of events during activation has been 
followed by determining, as a function of extent of 
activation, such properties of the char as apparent 
densities, 5 - 8 heats of wetting, 44 ’ 5> 8 particle densities, 5 
ultimate analysis, 44 ’ 5 tube 5 and canister lives 39> 8 
of the whetlerites against various toxic agents, water 
absorption, 8 and development of pore structure as 
shown by pore analyses 20 and surface areas as shown 
by nitrogen adsorption. 13 

If the char that has been carbonized at a lower 
temperature than that of activation is placed in a 
hot activator, the first stage of the process is 
thermodevolatilization, which is accompanied by a 
shrinkage of the particle and an increase in particle 
density. Generally, the devolatilization is completed 
before appreciable activation is accomplished. 44 

The percentages of hydrogen and oxygen in the 
carbonized material depend primarily on the tem¬ 
perature at which the char is heated, and these per¬ 
centages are higher as this temperature is lowered. 
Accordingly, when the char is placed in the hot acti¬ 
vator, the percentages of hydrogen- and oxygen-drop 
parallel rapidly with the devolatilization and reach 
concentrations characteristic of the activator tem¬ 
perature. 44 The important observation was made in 
the activation of coal charcoal that once the devola¬ 
tilization is completed the only change in the ulti¬ 
mate analysis of the char during the activation 
proper is the increase in ash content. 44 The hydrogen 
content remains surprisingly constant. This obser¬ 
vation strongly indicates that the essential process 
of activation is not one of a selective oxidation of 
hydrocarbonlike materials, otherwise it could be ex¬ 
pected that the percentage of hydrogen would stead¬ 
ily decrease during the activation proper. 

Tube and canister lives of the char and the whet¬ 
lerites made from it increase rapidly during the first 
stages of the activation, but level off later. The vari¬ 
ous lives do not reach their peaks at the same time. 
If the activation is carried well beyond the normal 
yield, most gas lives tend to fall off because of the 
loss of carbon and the enlargement of pores to such 
a size that they are no longer useful. The final result 
is the production of ash. Sometimes, subsequent to 
this, the particle disintegrates. There is, therefore, an 
optimum yield or extent of activation. If the material 
is underactivated, the yield is high but the gas lives 
are well below their peaks. If the material is activated 


too far, gas lives are at a maximum, but the yield is 
lower than necessary. 

3 . 5.7 Internal versus External 

Weight Loss 

During activation, a very substantial weight loss 
occurs. For most charcoals a loss of approximately 
40 to 60% of the original weight is necessary before 
the material is completely activated. The loss in 
weight occurs in two ways. First, the outside of the 
particle can be burned completely and a smaller 
granule obtained. Such external weight loss is en¬ 
tirely deleterious and represents nothing but a loss 
in yield. Second, the interior of the particle loses 
mass and it is this loss that accompanies the activa¬ 
tion process itself. 55 The internal loss is useful and 
the ratio of the internal loss to the total loss is one 
measure of the efficiency of an activation process. In 
general, the ratio of internal loss to total loss varies 
from about 0.2 to approximately 0.5. 

There is no apparent difference between extent of 
activation of the interior of a granule and that at the 
surface, provided the granules are in the usual gas 
mask absorbent size. 44 English work showed that, in 
the activation of very large particles several inches 
in diameter, the outside surface is more quickly acti¬ 
vated than the inside, assuming, however, that all 
particles are subject to precisely the same environ¬ 
ment. If conditions in the activator are such that 
particles of one size are hotter or are more thoroughly 
in contact with steam, these particles will be acti¬ 
vated before the remaining particles. In penetrating 
to the center of the particles, the gas utilizes the 
macro pores existing in the primary char. After pene¬ 
tration, the activating gas enlarges existing pores, 
removes by gasification any inactive pore lining ma¬ 
terial, uncovers active centers, and develops small 
pores that may or may not be present in the original 
char. There is considerable evidence to support the 
hypothesis that many of the small, final pores exist 
in the carbonized char as small voids hidden among 
the crystallites, and that many of these pores are 
rendered accessible by the attack of the activating 
gas during the process. 55 The fact that the block 
density, as measured by helium, of the char increases 
during activation supports such an hypothesis. The 
development of such hidden voids probably occurs 
during carbonization, although in naturally occurring 
materials it is possible that such voids are in the 
original raw material. 



ACTIVATION METHODS 


37 


* 3 . 5.8 Rate of Activation 

The rate of activation is most easily determined 
by measuring the weight rate of loss during activa¬ 
tion. Many such data are available. It has been 
shown, first, that the rate has a high temperature 
coefficient and shows an Arrhenius constant of 
47,500 cal per mole. 55 This implies a rapid increase 
in rate with increase in temperature and demon¬ 
strates that the rate of the activation is not con¬ 
trolled by diffusion of activating gas either to the 
outside surface of the granule or through the pores. 
The rate of activation under constant conditions of 
temperature, steam supply, and steam velocity is 
constant with time. This indicates that the effective 
area taking part in the oxidation is constant, and 
implies that the basic pore structure of the particle 
has been largely established before pore activation 
occurs. 

The rate is influenced by the composition of the 
gas in contact with the particle. Actual activation 
processes in practice may require 6 hours or many 
days, depending upon the temperature, the rate of 
supply of activating gas, and steam content. In the 
Jiggler process, in which large quantities of activat¬ 
ing gas are in intimate contact with the char, activa¬ 
tions can be conducted in a few minutes. 

The gases formed by the activation contain CO, 
C0 2 , and undecomposed steam. The fraction of the 
steam decomposed varies from 10 to 50% depending 
upon the temperature and the rate of steam supply. 
The ratio of CO to C0 2 is approximately that ex¬ 
pected from the water-gas equilibrium, provided the 
reaction is not catalyzed by the ash. 55 In the activa¬ 
tion of coal char by the PCC process, the percentage 
of CO was considerably higher than that called for 
by the water-gas reaction, probably because of the 
influence of the high ash content of this charcoal. 52 

Effect of Rate of Activation on Quality 

Certain chars, such as bituminous coal chars, can 
be activated very rapidly, and still yield very satis¬ 
factory products. Other chars, such as the Prest-o-log 
char, must be activated more slowly if optimum re¬ 
sults are to be obtained. The effective rate of activa¬ 
tion in a given case can only be found experimentally. 

3.6 ACTIVATION METHODS 

In present commercial plants, charcoal is activated 
either in horizontal, rotary retorts or in large, vertical 
shelf furnaces. The retorts may be supplied either in 


batch or continuously. The PCC process utilizes 
batch retorts as described above. The Carlisle process 
utilizes continuous retorts as does a process operated 
by the Atlas Company of Los Angeles, California. 19 
The Barnebey-Cheney Company utilizes large shelf 
activators through which the charcoal is repeatedly 
passed for many days until the required activity is 
developed. 

3 . 6.1 The Jiggler Process 

Considerable pilot plant and laboratory work was 
done on a method of activation that utilizes an up¬ 
ward stream of gas sufficient to agitate or suspend 
the particles being activated. 47 ’ 51> 54> 33 This method 
has been known as either the Jiggler method or the 
boiling bed method depending upon whether the parti¬ 
cles were suspended or merely agitated. The process 
was not used industrially because satisfactory results 
were being obtained in existing industrial activators 
and ample activation capacity was available when 
the pilot plant work on the Jiggler was completed. 

The Jiggler method gives an extremely rapid acti¬ 
vation and can be used in preparing very large quan¬ 
tities of char in a small unit, provided the char is of 
a type that can take a high rate without destroying 
quality. The process yields the most uniform activa¬ 
tion obtainable by any activation process and repre¬ 
sents a standard of comparison on this factor. Tenta¬ 
tive commercial designs of this equipment are avail¬ 
able in case its use is ever desired. 

The boiling bed variant of this type of activator 
utilizes a lower flow rate of steam and causes an agi¬ 
tated bed type of process. The action of the carbon 
particles in the boiling bed method as compared with 
that in the Jiggler is analogous to the relationship of 
a liquid to a gas. 

The heat requirement for the Jiggler process can 
be supplied from the activator walls by utilizing the 
walls as heat storage between activations. The heat 
supply required by the boiling bed furnace is obtain¬ 
able by using a reverberatory roof to radiate heat 
directly to the rather shallow high density bed of 
particles characteristic of this method. 

3.6.2 Air Treatment of Activated Charcoal 

Air is an unsatisfactory agent for the primary acti¬ 
vation of charcoal. The reaction between carbon and 
air is the usual exothermic combustion reaction, and 
the effect is to burn the outside of the particle to ash 
rather than to develop the internal pore structure. 



38 


MANUFACTURE OF ACTIVATED CHARCOAL 


Air or air-steam mixtures can be used, however, to 
improve charcoal already activated. 4 Air-steam 
treatment at temperatures of 750 to 1060 F, followed 
by steam devolatilization at 1800 F brought about 
a 50% increase in the CK (80-80) M10A1 canister 
life of the whetlerite. The loss in volume caused by 
the process was 17%. The method has not been eval¬ 
uated for industrial use. 

3 . 6.3 Chemical Activation of Charcoal 

The second main method of preparing activated 
carbon is by utilizing chemicals as activating agents. 
Ordinarily, the raw material for the chemical activa¬ 
tion is cellulose, ligno-cellulose, or for practical man¬ 
ufacture, waste wood. The essentials of the chemical 
method are as follows: 

The waste wood, usually finely ground, is brought 
into intimate contact with the activating chemical 
at a moderate temperature. During the mixing proc¬ 
ess, the raw material darkens and becomes semi- 
plastic. The reacted mix is then heat-treated to fix 
the carbon and to bring about the activation proper. 
Next, the activating chemical is leached out of the 
carbon. Crushing and sizing can be done at any stage 
in which the material has the appropriate hardness. 
Further heat treatment after leaching of the chemi¬ 
cal may or may not be practiced. 

Of the many chemicals that have been used in the 
past as activating agents, phosphoric acid and zinc 
chloride are the two to be preferred. All commercial 
carbon made by the chemical activation method 
utilizes zinc chloride. The remainder of this discus¬ 
sion is concerned with the zinc chloride process. 

Zinc chloride activated carbons were introduced 
by the Germans during World War I, and continued 
development of the process was conducted in the 
United States in the period between wars. At the 
time of the national emergency of 1940, zinc chloride 
activated carbons were considered the highest grade 
activated carbons obtainable for gas mask purposes. 
This supposed high quality was a result of the tests 
used at that time in evaluating gas mask charcoal. 
The 1940 tests emphasized physical adsorption and 
the tube lives of Type A whetlerite under dry con¬ 
ditions against AC, CG, and SA. Heat of wetting was 
also considered of considerable importance. Against 
such tests the zinc chloride carbons obtained at that 
time were superior to any other charcoal available. 
Coal char had not appeared, as yet, upon the scene. 

When emphasis was placed on the canister testing 


of ASC whetlerite against CK, especially under wet 
conditions, it was found that the old style zinc chlo¬ 
ride carbons were definitely defective. These carbons 
did not take well to ASC whetlerization and ASC 
whetlerites made from them did not possess satis¬ 
factory initial gas lives. Furthermore, when the initial 
canister lives were corrected by improvements in the 
processing, it was then found that these carbons were 
highly unstable as ASC whetlerites and deteriorated 
rapidly in storage as absorbents for CK under high 
humidity conditions. Intensive work was done to 
modify the processing of zinc chloride char to meet 
these deficiencies. In the main, results were satisfac¬ 
tory and the objective of the work was reached. How¬ 
ever, because of the large production and low cost of 
the coal chars, zinc chloride carbons have not been 
put into procurement during the last few years. 
Their main interest under present conditions is be¬ 
cause of the fact that the newer products have an 
unusually low density of 0.30. Large plants con¬ 
structed when zinc chloride chars were the standard 
of performance are in stand-by condition, and if 
necessary large quantities of this char can be made. 

Manufacture of Zinc Chloride Chars by the 
National Carbon Company Process 15 

The present method of manufacturing zinc chlo¬ 
ride chars of suitable quality is as follows. Virginia 
hardwood, milled through 12 mesh, is used as the 
raw material. The activating solution consists of 65% 
zinc chloride in water, with 0.25% excess hydro¬ 
chloric acid to prevent hydrolysis of the zinc. The 
mix is made from 110 parts of zinc chloride solution, 
100 parts of sawdust, and 86 parts of recycled fines. 
The mix is processed by batches in an agitated, 
steam-heated mixer. The maximum steam pressure 
in the mixer jacket is 900 psi gauge. It is important 
that the reaction be conducted over a definite time- 
temperature schedule. The maximum temperature 
of the mix should not rise above 131 C. The temper¬ 
ature at the end of the mix period should be 129 C. 
The mixing time is 60 min to the maximum temper¬ 
ature and 67 min total to discharge. The mixers are 
dough-mixers that can be tilted and discharged by 
dumping. The mix, after reaction, is dumped di¬ 
rectly to the feed of an extrusion machine and im¬ 
mediately extruded through a 7-in. auger. The ex¬ 
truded plug is sliced longitudinally into 1-in. thick 
slabs. 

The extruded slabs are dried in open trays at a 
temperature of 200 C ± 25 C. The time is 8 hr. Dur- 







ACTIVATION METHODS 


39 


ing this operation, the charge loses 26% of its weight, 
and becomes hard enough for crushing. 

The dried plugs are crushed in closed circuit and 
screened to obtain a product through a 9-mesh screen 
and on 20-mesh screens. The oversized particles from 
the screens are returned to the crushers and the un¬ 
dersized particles are returned as fines to subsequent 
mixes. The granules are of proper size to give the 
desired size distribution in the final product at the 
end of the process. 

A more essential step, namely primary calcination, 
is conducted next. The char is heated in the absence 
of air in a rotary calciner at a temperature of 700 C 
for 45 min. At this stage of the process, the charcoal 
is completely activated. It still contains, however, 
most of the zinc chloride added in the mixer. To re¬ 
move the zinc chloride, the char is thoroughly washed 
by dilute hydrochloric acid and water. About 80 to 
85% of the zinc chloride is recovered in the washing 
and used again in the mixers. 

The final step is a secondary calcination at a tem¬ 
perature of 1050 C in a rotary calciner. The time of 
passage is 60 min. 

Notes on the Zinc Chloride Process 15 

The reaction of the mixer appears to be the critical 
step in the process and a number of the deficiencies 
of the earlier chars were eventually traced to inade¬ 
quate control during the mixing operation. It is im¬ 
portant that the reaction be carried to a point where 
the temperature in the mixer drops from its peak. 
This drop in temperature is probably associated with 
a drop in the boiling point elevation of the zinc chlo¬ 
ride in the mix. 55 The mix obtained by proper control 
of the mix reaction is called a “reactive mix.” Such 
chars have lower kindling temperatures and consid¬ 
erably higher canister lives than chars obtained from 
so-called non-reactive mixes, which result from im¬ 
proper mixing technique. The maximum temperature 
of 130 ± 2 C also appears to be very critical. 

The drying operation is necessary to solidify the 
extruded mass and to develop enough hardness to 
allow crushing and sizing. The temperature of this 
step does not appear to be critical. 

The primary calcination at 700 C is conducted at 
this temperature rather than at lower temperatures. 
The recalcination at 1050 C allows increased initial 
CK lives and also improves the stability of the char 
when made into an ASC whetlerite. If the secondary 


calcination is less than 1050 C, the resulting char 
will be unstable. 

Mechanism of Chemical Activation 55> 15 

Considerable work was done in the study of the 
chemical mechanism of activation of carbon by zinc 
chloride. The opinion of investigators in this field is 
that at the end of the mixing operation the reaction 
between the zinc chloride and wood produced a sus¬ 
pension of chemically modified but relatively carbo¬ 
hydrate-free lignin particles in a peptized colloidal 
solution of carbohydrates derived from cellulose. 55 
The zinc chloride attacks the cellulose portion of the 
ligno-cellulose preferentially to the lignin. During 
later processing, especially in the 700 C calcination, 
the peptized carbohydrates and lignin both degener¬ 
ate to carbon. The zinc chloride decomposes to zinc 
oxide and HC1. The products from the decomposition 
of the peptized cellulose are highly aromatic and un¬ 
der the heat treatment the lignin residues, together 
with the carbon precipitated from the decomposed 
cellulose, form the final carbon particle and yield a 
structure that exhibits a desirable macro and micro 
pore structure. The character of the surface depends 
on the final calcining temperature. 

The zinc chloride process is the most effective proc¬ 
ess with respect to the utilization of the carbon con¬ 
tent of the raw material. The total yield of char from 
this process is approximately 35%. This represents 
approximately 60 to 70% of the carbon in the original 
char. This carbon recovery is higher than that ob¬ 
tained in the Carlisle process (approximately 10 to 
15%); (1) because of the recycling of fines which is 
not practicable in the Carlisle process, and (2) be¬ 
cause of the absence of carbonization and gas activa¬ 
tion steps. It is larger than the corresponding recov¬ 
ery obtainable in the PCC process (approximately 
45%) because in the latter process carbonization and 
gas activation destroy much of the original carbon 
content of the coal. 

Counterbalancing the excellent yield of the zinc 
chloride process is the fact that the process is com¬ 
plex and requires acid resisting equipment because 
of the acidity of the solutions used, and high temper¬ 
ature calciners to obtain satisfactory stability. The 
process is, therefore, inherently expensive. 

The activation obtained in the zinc chloride proc¬ 
ess is internal rather than external, whereas gas acti¬ 
vation is the reverse. 


;cre; 



Chapter 4 

IMPREGNATION OF CHARCOAL 

By R. J. G^ahenstetter and F. E. Blacet 


4.1 GENERAL CONSIDERATIONS 

4 . 1.1 Introduction 

T he impregnation of gas mask charcoals to in¬ 
crease their capacity to absorb toxic gases has 
been practiced since the inception of gas warfare in 
World War I. The charcoal used in early German gas 
masks was found to be impregnated with either alkali 
or hexamethylene tetramine. 96 This use of charcoal 
impregnants by the Germans stimulated Allied in¬ 
vestigation of the subject. 

It was discovered early that ammonia greatly in¬ 
creased the SA absorptive powers of activated char¬ 
coal. The name Larsonite was given to ammonia im¬ 
pregnated charcoal. It was prepared either by soaking 
charcoal in aqueous ammonium hydroxide or by 
passing gaseous ammonia through the charcoal, fol¬ 
lowed by heating to 100 C under a 28-in. vacuum 
for 4 to 5 hr. 

Perhaps the most important development in the 
field of charcoal impregnation made during World 
War I was the use of copper as an impregnant. As 
compared with an unimpregnated charcoal, copper- 
impregnated materials, when tested dry, had at least 
double the protection against CG and similar gases; 
triple the protection against AC; and more than ten 
times the protection against SA. The copper-impreg¬ 
nated charcoal produced at the close of World War I 
was called whetlerite, after J. C. Whetzel and E. W. 
Fuller who were instrumental in its development. 
The impregnated gas mask charcoal in production 
in 1940 was designated Type A whetlerite, although 
produced by an entirely different process, and con¬ 
tained the copper in a different form from any of the 
materials earlier called whetlerites. 

In the sections of this chapter which follow, a gen¬ 
eral survey of the field of impregnation of activated 
charcoals up to May 1945 is presented. The various 
aspects of charcoal impregnation appear in the fol¬ 
lowing order: 


1. Copper and copper-silver impregnations of 
charcoals. Types A and AS whetlerites, and others. 

2. Hexamine- and thiocyanate-impregnation of 
whetlerites. 

3. General studies of charcoal impregnation. 

4. Development of copper-silver-chromium im¬ 
pregnation of charcoals. Types ASC whetlerite. 

5. Development of copper-silver-molybdenum and 
copper-silver*vanadium impregnations. Types ASM 
and ASV whetlerites. 

6. Organic base impregnations of charcoal. 

7. Absorbent resins as substitutes for activated 
charcoal. 

4.1.2 Copper and Copper-Silver 

Impregnations of Charcoals — Types A 
and AS Whetlerites, and Others 

Impregnated Charcoals Developed During 
World War I 

Five types of copper-impregnated charcoals were 
developed during World War I. 96 These were whet¬ 
lerites A and B, Rankinite, Rankinite A, and Copper 
Carbonite. 

Whetlerites A and B. Whetlerite A was prepared 
by precipitating hydrated copper oxide on charcoal 
by the action of hot caustic on a slurry of copper sul¬ 
fate solution and charcoal. Whetlerite B was pre¬ 
pared by treating the charcoal first with a copper 
sulfate solution, and then with finely divided metallic 
iron or zinc, resulting in the deposition of metallic 
copper on the charcoal. After impregnation, the ma¬ 
terials were dried at 350 C in either trays or rotating 
driers. Rotating driers with a limited air flow (3^ lb 
of air per lb of charcoal per hour) gave the best re¬ 
sults. Whetlerite A has a distinct brown color, 
whereas the best grades of whetlerite B are a dark, 
rich red, indicating that both cuprous copper and 
metallic copper are present, a larger proportion of 
metallic copper occurring in the latter. Whetlerites A 
and B were considered equally effective. 

The development of these materials began in Feb- 



GENERAL CONSIDERATIONS 


41 


ruary 1918. An experimental plant was built in the 
latter part of May of that year, and by July the 
process had reached the stage where plans were made 
for the manufacture of 70,000 lb per day. Semi plant- 
scale production was started in September, and at 
the time of the Armistice, impregnated charcoal was 
going into some canisters. 

Whetlerites A and B are quite different from the 
adsorbent now designated as Type A whetlerite. The 
treatment given whetlerites A and B results in re¬ 
duction of copper compounds to cuprous oxide and 
copper, either through heat treatment at elevated 
temperatures (in the case of whetlerite A) or by re¬ 
duction with metallic iron or zinc at the time of im¬ 
pregnation (in the case of whetlerite B). On the other 
hand, Type A whetlerite is made by depositing cop¬ 
per ammine carbonate in the pores of the charcoal, 
and decomposing it to CuO by heat treatment at 
150 C. Reduction of the CuO does not occur under 
these conditions. 

Rankinite and Rankinite A. Rankinite is acti¬ 
vated charcoal impregnated with copper salts and a 
small amount of silver nitrate. It is similar to Type 
AS whetlerite only in the metallic elements used in 
its preparation. Rankinite was prepared by impreg¬ 
nating charcoal with copper sulfate or nitrate and 
a small amount of silver nitrate, and drying at 250 C. 
Rankinite A differed from Rankinite in being sub¬ 
jected to an additional calcination at 400 C or higher, 
which resulted in reduction of the copper compounds 
to cuprous oxide and copper. The silver nitrate in¬ 
creased the SA protection appreciably, although 
Rankinite and Rankinite A were still not good SA 
absorbents under 80-80 conditions. It is now be¬ 
lieved that this deficiency was due to the pore struc¬ 
ture of the charcoal. 

Copper Carbonite. Copper Carbonite is the name 
applied to a carbon absorbent made by briquetting 
carbon fines, copper oxide, and a binder. The bri¬ 
quetted material was roasted, screened, and acti¬ 
vated. It had good PS and CG activities. 

There was some investigation of the application of 
copper compounds to charcoal by spraying, followed 
by heat treatment. Tests indicated that these ma¬ 
terials were as good as the other copperized charcoals 
and whetlerites being produced at the time. 

Impregnated Charcoals Developed Since World 
War I 

The copper impregnating technique was developed 
further in the period 1919-1940. 102 - 103 At the begin¬ 


ning of World War II, Type A whetlerite was the 
standard copper-impregnated charcoal in use for 
canister fillings. It was chiefly used in the Type D 
mixture which contained 20% soda lime and 80% 
Type A whetlerite. 

Preparation 

Type A whetlerite was made by impregnating 
activated charcoal with a solution containing 8 to 
10% copper, 12 to 15% ammonia, and 8 to 10% 
carbon dioxide. The impregnated material was 
drained and dried at 150 to 175 C for about 3 hr, or 
long enough to reduce the moisture and ammonia 
contents to specified limits. In large-scale production, 
the whetlerizing solution was made by dissolving 
copper scrap in an aqueous solution of ammonium 
carbonate containing excess ammonia. An air stream 
was used to agitate the solution and to provide oxy¬ 
gen for the oxidation of the copper. Gaseous carbon 
dioxide and ammonia were introduced into the solu¬ 
tion until the proper concentrations were attained. 
The solution was removed from contact with the 
copper when the desired concentration was reached. 
Air agitation was continued until all the cuprous 
copper in solution was oxidized. 

Small laboratory batches of whetlerizing solution 
are prepared from basic copper carbonate, ammo¬ 
nium carbonate or bicarbonate, and ammonium 
hydroxide. 

Performance in Canisters 

Typical canister service lives for Type A whetlerite 
and other types of adsorbents are shown in Table 1. 
The material known as Type D mixture, containing 
20% soda lime granules and 80% Type A whetlerite, 
was the specified canister filling prior to the middle 
of 1942. Service lives of this material also can be 
found in Table 1. It is evident that the addition of 
soda lime to Type A whetlerite is not justified by the 
performance of the mixture. 

Nature of the Impregnant 

In an effort to determine the nature of the copper 
compound left in the charcoal after heat treatment, 
portions of the whetlerizing solution were evaporated 
to dryness in evaporating dishes at various rates and 
under various conditions. 2 The results indicated that 
the nature of the copper compounds was profoundly 
affected by the conditions of evaporation and de¬ 
hydration-decomposition. 

Circumstances which allow ammonia to escape 
faster than carbon dioxide or water (such as rapid 




Table 1. Service times of standard canisters with different fillings. 
(Lives in minutes.)* 


42 


IMPREGNATION OF CHARCOAL 


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GENERAL CONSIDERATIONS 


43 


heating, or heating in an atmosphere saturated with 
water vapor) result in the formation of basic copper 
carbonate, which decomposes to copper oxide only at 
temperatures above the 150 C generally applied to 
Type A whetlerite. The presence of appreciable 
amounts of basic copper carbonate in the whetlerite 
results in reduced SA and AC absorption. Relatively 
slow drying at 150 C in a moderate air stream results 
in the formation first of a complex copper ammine 
carbonate which subsequently decomposes into finely 
divided copper oxide with evolution of ammonia and 
carbon dioxide. 

Copper ammine carbonate can be reduced to a 
mixture of cuprous oxide and copper by treatment 
at high temperatures. 

The best samples of Type A whetlerite produced 
in the laboratory were made bj r drying the drained 
impregnated charcoal in thin layers in trays at room 
temperature for several hours before oven-drying at 
150 C. Convection ovens which allowed a plentiful 
air flow, and other ovens which were equipped to 
permit a plentiful flow of preheated air through the 
sample, produced the best whetlerites. The good 
samples showed no evidence of reduction of cupric 
oxide to cuprous oxide and copper. 

Copper is not selectively adsorbed by activated 
charcoal during impregnation. Whetlerizing solution 
is sorbed into the pores of the charcoal and held 
mechanically until the water evaporates from the 
solution. Copper ammine carbonate is deposited in 
the pores and by proper heat treatment copper oxide 
is formed. 

Type AS Whetlerite 

In the search for a charcoal impregnant capable of 
producing an adsorbent with high SA effectiveness 
under 80-80 conditions, the effect of using silver 
nitrate with Type A whetlerizing solution was again 
investigated 3 ’ 4 in 1941. The adsorbent developed 
(Type AS whetlerite), containing copper and silver, 
bears some resemblance to the Rankiniteof World War 
I. However, it showed a good SA protection under 
80-80 conditions, in contrast to Rankinite. It must 
be remembered that great advances had been made 
in activated charcoal production in the period be¬ 
tween 1919 and 1940, and it appears that the lack of 
SA 80-80 protection exhibited by Rankinite might be 
caused in some measure by the properties of the 
charcoal itself. 

Preparation of Type AS Whetlerite. The condi¬ 
tions for preparing Type AS whetlerite are identical 


with those of Type A whetlerite. The addition of 
from 0.1% to 0.5% of silver (as nitrate) to a Type A 
whetlerizing solution results in a good Type AS so¬ 
lution. Some types of the early zinc-chloride acti¬ 
vated, extruded charcoals did not produce an ad¬ 
sorbent with satisfactory SA 80-80 protection when 
impregnated with Type AS whetlerizing solution. 
The reason for this is not certain, but seems to have 
been the result of pore size distribution and the 
nature of the surface of the extruded rods. This fault 
was corrected by changing the manufacturing proc¬ 
ess. At present, all samples of activated charcoal 
otherwise acceptable for use as gas mask charcoal 
can be converted to a Type AS whetlerite without 
trouble. In impregnations effected by stirring char¬ 
coal and impregnant until saturation is achieved, it 
was found that the charcoal remote from the point 
of entry of the solution did not acquire enough silver 
to achieve a good SA 80-80 protection. Rapid mixing 
corrected this condition. Experiments showed that 
silver could be introduced as satisfactorily by spray¬ 
ing a finished Type A whetlerite as by incorporation 
with the original whetlerizing solution. 8 ’ 104 

Plant Production 

A study of the whetlerizing techniques used at the 
various plants producing Type A whetlerite showed 
that the equipment could be used without change for 
the manufacture of Type AS whetlerite. 9 Since silver 
requirements are different for different charcoals, the 
following table of requirements for Type AS solution 
was compiled: 

0.2% AgNCb in Type AS solution for Barnebey- 
Cheney nut charcoals 

0.1% AgNCb in Type AS solution for PCI coal 
charcoals 

0.5% AgN0 3 in Type AS solution for National, 
zinc-chloride activated wood charcoals 

The National charcoals adsorbed silver from solu¬ 
tion so rapidly that the larger concentrations were 
necessary to get some silver on all particles. Rapid 
mixing also helped and was recommended in plants 
using these charcoals. 

In view of the possible formation of explosive silver 
azides in whetlerizing solutions, an investigation was 
undertaken to determine the conditions under which 
such compounds might be produced. It was found 
that a solution containing copper, silver, and am¬ 
monia could not be made to yield explosive com¬ 
pounds, although ammoniacal silver solutions con¬ 
taining no copper form an explosive residue when 



44 


IMPREGNATION OF CHARCOAL 


treated with sodium hydroxide. 10 It was concluded 
that Type AS whetlerizing solution constitutes no 
explosion hazard in plants using it. 

4.1.3 Summary of Preparative Con¬ 
ditions for Types A and AS Whetlerites 

Numerous studies in Types A and AS whetlerites 
have brought forth the following conclusions. 4-6 ’ 103 

1. Type AS whetlerizing solution should contain 
8 to 10% Cu, 12 to 15% NH 3 , 8 to 10% C0 2 , and 
0.1 to 0.5% Ag. 

2. Solution-charcoal contact time should be at 
least 5 min. 

3. Method of drainage is not important. 

4. Temperature of impregnation may vary be¬ 
tween 25 C and 70 C. Above 70 C large amounts of 
basic copper carbonate are found in the whetlerite. 

5. Air drying before heating is not essential. 

6. Oven-heating in trays at 150 C for 3 hr pro¬ 
duces a good product. A moderate flow of air through 
the oven is desirable to sweep away NH 3 , C0 2 and 
H 2 0 vapor. Rotating kiln-type driers provided with 
a preheated air flow can be used to prepare excellent 
Type A whetlerites. This type of drier is desirable 
but not essential. 

7. In Type AS solution 0.1% is usually sufficient 
for good SA protection. Up to 0.5% Ag may be neces¬ 
sary for some types of charcoal. 

8. Rapid mixing of solution and charcoal is de¬ 
sirable since silver is removed rapidly from the solu¬ 
tion by adsorption on the charcoal. 

4 .1.4 Studies of Whetlerizing Solutions 

Adsorption of Constituents from Whetlerizing 
Solutions 

The adsorption of constituents from a whetlerizing 
solution was studied as a function of concentration. 6 
The concentration ranges covered were 0.5% to 
10% copper; 0.7% to 15% ammonia; and 0.7% to 
13% carbon dioxide. At low concentrations the ad¬ 
sorption of copper is positive but becomes negative 
at higher concentrations. (Negative adsorption indi¬ 
cates that the solvent is adsorbed to a greater extent 
than the solute, resulting in an increase in the con¬ 
centration of the solute in solution.) The adsorption 
of ammonia is positive and of carbon dioxide nega¬ 
tive over the entire range studied. 

A continuous impregnation was run in which the 
type of charcoal and the concentration of whetleriz¬ 


ing solution were kept constant. The procedure in¬ 
volved the saving of the solution and drainings after 
impregnation, and adding fresh solution to restore 
the original volume. Successive equal volumes of 
charcoal were impregnated by recovered and replen¬ 
ished solution until analyses showed the concentra¬ 
tion of the constituents of the solution to be essen¬ 
tially invariant from batch to batch. This procedure 
corresponded to continuous impregnation wherein 
the amount of impregnated charcoal being with¬ 
drawn from the impregnation is balanced by a flow 
of fresh solution and charcoal into the tank. The 
solution in the tank some time after the start of the 
process attains an equilibrium concentration slightly 
different from the original solution. This concentra¬ 
tion remains constant for any particular set of con¬ 
ditions, and will change if the type of charcoal or the 
concentration of feed solution is changed. For the 
particular experiments mentioned above, equal vol¬ 
umes of charcoal and replenished solution were used 
at each step. The original and equilibrium concen¬ 
trations are as follows: 

Solution Density %Cu %NH 3 %C0 2 

Original Type A 1.211 9.67 14.90 12.66 

Equilibrium 1.277 10.04 14.44 13.06 

When a Type AS solution is used for continuous 
impregnation, the silver concentration of the original 
solution must be increased slightly over the concen¬ 
tration found adequate for a one-step impregnation. 
The required concentration is determined by the 
nature of the charcoal being impregnated. The con¬ 
centration used in industrial production is usually 
between 0.2 and 0.5% silver. 9 

Silver adsorption was studied by a radioactive 
tracer technique. 7 A solution containing 0.01% silver 
was used. The adsorption was found to take place at 
a measurable rate, and was a function of the silver 
concentration. Over a 1,000-fold concentration range 
the data fitted a Freundlich isotherm of the form 



where X = weight of material adsorbed, 

M = weight of adsorbent, 
c = equilibrium concentration, 
n and k = constants to be determined in each 
case. 

In the experiments performed, using CWSN-44 
and CWSC-11 charcoals, from 73% to 90% of the 


- . ■ 





GENERAL CONSIDERATIONS 


45 



Figure 1. Removal of silver from solution by charcoal. 

silver was removed from the solution in 30 min. The 
data are shown in Figures 1 and 2. 

In general, the extruded charcoals activated by 
the zinc chloride process, like CWSN-44 and CWSN- 
P5, required more silver to give good SA performance 
than did gas activated charcoals such as the PCI 
briquetted coals, Seattle pressure carbonized wood 
charcoals, and nut shell charcoals. 

Results of X-Ray Studies of Types A and AS 
Whetlerites 

X-ray studies on Types A and AS whetlerites in¬ 
dicate that the copper is present as copper oxide 
spreads uniformly throughout the grain. 11 There is 
a direct correlation between the activity of the whet- 
lerite toward AC, and the absence of crystallinity of 
the impregnants, indicating that the more finely di¬ 
vided or amorphous the copper oxide, the greater the 
tendency to react with AC. The presence of silver or 
ammonium nitrate seems to assist in the formation 
of finely divided copper oxide. The silver appears to 
be present as finely divided metal. 

In the case of some coconut charcoals the solids 
deposited by impregnation are found in concentric 
shells in the charcoal granule. These rings appear to 
be analogous to growth rings in coconut shells. In 
coconut shell charcoals, about half of the silver de¬ 
posited by impregnation is on the outside of the 
granules. Spraying results in the depositing of all 
the silver on the outer surfaces of the charcoal 
granules. 

Whetlerites dried at low temperatures (25 to 


105 C), incompletely dried at higher temperatures, 
or prepared from whetlerizing solutions having a low 
ammonia to copper ratio, are likely to contain com¬ 
plex copper ammine carbonate or basic copper car¬ 
bonate. Neither material reacts with AC when moist. 

Heat treatment at 200 to 500 C converts cupric 
oxide to cuprous oxide and copper. The AC lives of 
adsorbents thus treated are low, but the SA lives are 
not appreciably affected. In fact, the presence of 
some cuprous oxide seems to accompany higher SA 
protection in Type A whetlerites. Upon equilibration 
at 80% RH cuprous oxide in whetlerite is converted 
to cupric oxide. After finely divided cupric oxide is 
formed in the charcoal, it is quite stable and is not 
appreciably affected by long heating at 150 C, or 
wetting by water and redrying in the standard way. 


Vapor Pressure of Whetlerizing Solutions 


The vapor pressures of the volatile constituents in 
whetlerizing solutions have been measured. 13 - 14 The 
data indicate that the complex ion present in pre¬ 
ponderance is Cu(NH 3 )t + , although other complex 
ions may be present to a much smaller extent. For 
solutions of high ionic strength the reaction 

NH 3 + HCOJ “ NH| + C0 3 “ 
was found to have an equilibrium constant of 2.1 


(NH+) (CQ7 ~) 
(NH 3 ) (HC07 -) 


= k = 2.1 


( Concentration in 
moles per 1,000 g 
of water 



0.0 0.4 0.8 1.2 1.6 


log t 

Figure 2. Removal of silver from solution by charcoal. 






46 


IMPREGNATION OF CHARCOAL 


The ammonia pressure may be calculated from 
Henry’s law: p = k( NH 3 ); k = 16.8 when pressure 
is expressed in mm of Hg at 25 C. 

The pressures of C0 2 are low and only a rough 
correspondence between calculated and observed 
values was found. 

Variations in the vapor pressure of water were in 
agreement with Raoult’s law. Vapor pressure curves 
for the components of Type A solution over all pos¬ 
sible concentration ranges, and curves showing the 
variation in vapor pressure of the constituents with 
temperature in the range 15 to 70 C (calculated from 
the Clausius-Clapeyron equation) are given in the 
original report. 13, 14 Similar curves for Type ASC 
solution appear in a later section of this chapter. 

Heats of Solution of Volatile Constituents 

The average heats of solution of the volatile con¬ 
stituents in Type A solution are: 

Heat of solution, kg-cal per mole 
NH 3 CO., H 2 0 

9.1 15.9 11.0 

The values for Type AS solution were not meas¬ 
ured but should not vary appreciably from the above. 

Gases Evolved During Drying of Type A Whet- 

LERITES 

A study was made of the composition of the gases 
evolved from whetlerites during drying. 12 For this 
study, a 5-g sample of charcoal was whetlerized in 



Figure 3. Temperature-time relation in the drying of 
impregnated charcoal. 


temperature 

25 50 75 100 125 150 



TIME (MIN) 

Figure 4. Gas evolution during the drying of charcoal. 

the usual way and dried in an oven at 150 C with an 
air stream of 110 ml per min passing through the 
sample. The gases were collected and analyzed. Am¬ 
monia was driven off most rapidly, followed by car¬ 
bon dioxide and water. The evolution of water lagged 
predominantly in the early stages, and that of carbon 
dioxide in the latter stages of drying. Gas evolution 
was most rapid during the period of drying corre¬ 
sponding to a temperature increase in the charcoal 
bed from 72 to 85 C. The data are presented in Fig¬ 
ures 3 and 4. Figure 3 shows the time versus temper¬ 
ature curves for the charcoal and for the effluent air. 
Figure 4 shows the percentage evolved of each gas as 
a function of time and of temperature. Additional 
data are given in Table 2. 

4.1.5 Reactions of Types A and AS 
Whetlerites with Absorbed Gases 

Performance data of Types A and AS whetlerites 
are given in Table 1. It can be seen that the SA 80-80 
protection afforded by Type A in the M10A1 can¬ 
ister is negligible, while that afforded by Type AS is 
entirely adequate. 

Adsorption of SA 

SA removal is apparently a catalytic oxidation of 
SA by atmospheric oxygen to As 2 0 3 and perhaps to 
As 2 0 5 . The product of adsorption of SA is deposited 
in a shell around the outside of the charcoal granule. 
It can be extracted with alcohol as As 2 0 3 from both 
Type A and AS whetlerites. Sixty-five per cent of the 
total As 2 0 3 can be extracted easily; the remainder 










GENERAL CONSIDERATIONS 


47 


slowly and with difficulty. The action of cupric oxide 
is apparently catalytic when the whetlerite is dry. 
Silver alone acts as a catalyst, but is not so effective 
as when mixed with cupric oxide. Exhaustion of the 
adsorbent occurs through deposition of As 2 0 3 or 
As 2 0 5 on the active surface, effectively screening it 
from further contact with SA. Hence SA is an effec¬ 
tive poison for AC adsorption, since it also depends 
on contact with cupric oxide for removal (see below). 


Table 2. The drying of Type A whetlerite. 


Period 

I 

II 

III 

IV 

V 

Total time of drying, min 

16 

24 

48 

70 

100 

Length of period, min 
Temperature range within 

16 

8 

24 

22 

30 

period, degrees C 

22-72 

72-85 

85-100 

100-150 150 

Per cent of total amount of 






each constituent during 
period 






nh 3 

26 

53 

16 

6 

1 

C0 2 

23 

45 

17 

11 

4 

h 2 o 

9 

38 

37 

15 

1 

Cumulative per cent of each 






constituent evolved 






nh 3 

26 

79 

93 

99 

100 

C0 2 

23 

68 

85 

96 

100 

h 2 o 

9 

47 

84 

99 

100 

Average pressure of each 






constituent during pe¬ 
riod, mm Hg 






nh 3 

64 

56 


12 


C0 2 

18 

17 


7 


H 2 0 

118 

342 


152 


Air 

540 

325 


569 



Adsorption of AC 

Types A and AS whetlerites have practically the 
same protection against AC, when used as a canister 
filling. The mechanisms of removal appear to be 
identical. The reactions postulated are: 16-18 

2HCN + CuO —^ Cu(CN) 2 + H 2 0, 
and Cu(CN) 2 —> CuCN + K(CN) 2 . 

Cyanogen is present in the effluent air stream near 
the break point. 

A more complete discussion of the mechanism of 
gas removal can be found in Chapter 7. 

Adsorption of Basic Vapors 
Copper-impregnated charcoals such as Types A 
and AS whetlerites have greater ethylene imine pro¬ 
tection than do unimpregnated charcoals. 36-39 How¬ 
ever, impregnated charcoals allow a much more 
rapid penetration after the break point. A compari¬ 


son of several basic gases tested against CWSE-1- 
TE1, a coconut charcoal converted to Type A whet¬ 
lerite at Edgewood Arsenal, is given in Table 3. 


Table 3. Protection afforded by Type A whetlerite 
against basic gases. 5-cm tube test, flow rate 500 
ml/cm 2 /min. 


Gas 

Qonc. mg/1 

Per cent 
RH 

Breaktime, 

min 

EN* 

3.17 

50 

110 

Diethylene amine 

3 

50 

180 

Piperidine 

3 

50 

171 

Trimethylene imine 

3 

50 

161 


* Ethylene imine. 


With the exception of ammonia, basic gases are 
well adsorbed. As the number of carbon atoms in the 
methylene imine series increases, the whetlerite pro¬ 
tection for the compounds increases, corresponding 
to the decrease in vapor pressure of the materials. 

CWSE1TE1 can be poisoned toward EN by 
H 2 0, AC, and C0 2 . Also, the protection decreases 
with increasing temperature, indicating a straight 
adsorption mechanism as the principal one. At 25 C 
the protection is adequate below 70% RH, but is in¬ 
adequate at higher humidities. 

Type A whetlerite, broken by EN, is not regener¬ 
ated on standing. It is possible that some of the EN 
is held by formation of a copper coordination com¬ 
plex, but it appears likely that some is held also by 
adsorption (capillary condensation) since it can be 
desorbed to some extent by passing air through the 
charcoal. EN is adsorbed by whetlerite from air-free 
systems as well as in the presence of air, showing that 
atmospheric oxygen is not involved in the adsorption 
mechanism. 

Adsorption of Other Vapors 

Adsorbed organic vapors and certain reactive gases 
such as H 2 S, Cl 2 , and CK reduce the AC and SA 
lives of Types A and AS whetlerites. This effect is re¬ 
ferred to as 'poisoning. In some cases, it is due to 
simply plugging the pores or covering the reactants 
or catalysts with an inactive layer or film, rendering 
the active part of the charcoal unavailable to the 
toxic gas. This effect may be observed with hydro¬ 
carbons and water. Active gases such as H 2 S and 
Cl 2 react with CuO, thus rendering it inactive toward 
SA or poisoning it as an SA catalyst: 

CuO + H 2 S —> CuS + H 2 0; 

2CuO + 2C1 2 + (H 2 0) CuCl 2 + Cu(C10) 2 . 












48 


IMPREGNATION OF CHARCOAL 


Silver is similarly affected by some active gases and 
particularly by AC. 

Protection of Types A and AS whetlerites against 
CG is adequate either wet or dry. Apparently CG is 
hydrolyzed very rapidly even by the small amount 
of residual water on dry whetlerites. Copper oxide 
serves to retain the hydrochloric acid formed by hy¬ 
drolysis. Wet, unimpregnated charcoals also have 
very high CG capacity, the large amounts of mois¬ 
ture apparently retaining IiCl effectively. 

Many gases are restrained by simple adsorption, 
particularly those with high boiling points and low 
vapor pressures at normal temperatures. PS and H 
are examples of this type. Long protection is afforded, 
but eventual desorption may occur in canisters ex¬ 
posed to larger dosages. 

Tests have been carried out using a large number 
of different types of gases. The results are shown in 
Table 4. 19 - 20 It will be noticed that NH 3 and CO 

Table 4. Absorption of various gases by Type A 
whetlerite. Test conditions: 5-cm layer equilibrated 
at RH given in column 2, flow rate 500 cm 3 /cm 2 /min 
at concentration indicated. 


Gas 

Percentage Gas concen- 
relative tration, Breaktime, 

humidity mg/1 min 

S0 2 

95 

5.2 

38 

so 2 

50 

5.2 

65 

so 2 

0 

5.2 

36 

Nickel carbonyl 

50 

5.2 

120* 

CO 

50 


1 

Methyl isocyanide 

50 

2.8 

114 


95 

2.8 

11 

Methyl sulfonyl chloride 

50 

3-5 

140 


95 


120 

Ammonia 

95 

3-5 

5 


95 

3-5 f 

3 

Ethylene imine 

0 

3.17 

80 


52 

3.17 

100 


100 

3.17 

59 

Trimethylene imine 

52 

3.22 

160 

Pentamethylene 

52 

3.28 

181 


* Showed a CO break in 1 min. 
f On E-l broken with N-hexane. 


penetrate almost instantaneously. All the other gases 
tested were well retained by the whetlerite. Only 
methyl isocyanide showed a rapid, wet penetration, 
and it was not instantaneous. 

4.1.6 Type D Mixture 

It was found during World War I that dry acti¬ 
vated charcoal did not retain CG well, particularly 
when the charcoal had a low capacity for pure ad¬ 
sorption. Exposure of a canister to high concentra¬ 


tions of CG followed by a long wearing of the gas 
mask resulted in redistribution and desorption of CG 
and the production of uncomfortable or dangerous 
concentrations of gas in the effluent. Humidifying 
the charcoal resulted in the hydrolysis of CG and the 
production of uncomfortable, although not danger¬ 
ous, concentrations of hydrogen chloride in the 
effluent. 

By using a layer of soda lime on the effluent side 
of the charcoal bed, or dry mixing about 20% by 
weight of granular soda lime with the charcoal, the 
retentivity of the canister for CG and HC1 was in¬ 
creased, thus producing a satisfactory absorbent 
for CG. 

The use of soda lime was carried over from World 
War I and was included in the specification for can¬ 
isters filled with copper-impregnated charcoal. The 
results in Table 1 indicated that soda lime admixed 
with Type A or AS whetlerite served no useful pur¬ 
pose. A complete study of the use of soda lime was 
made in 1942. 21 The results were as follows: 

1. Type D mixture (20% soda lime, 80% Type A 
whetlerite) gives greater CG protection when the 
whetlerite is of poor quality. High quality whetlerite 
gives protection as good as, or better than, the mix¬ 
ture. 

2. Soda lime mixtures give somewhat better pro¬ 
tection than Type A whetlerite against gases which 
liberate H 2 F 2 on adsorption. However, the protection 
given by Type A whetlerite is very large. 

3. Type D mixture is inferior to Type A whetlerite 
for protection against CK, SA, PS and all other gases 
with which soda lime does not react. The decrease in 
protection caused by the addition of 20% of soda 
lime to Type A whetlerite may be more than 20% 
in cases where the bed depth of the canister is close 
to the critical bed depth of the gas being adsorbed. 

4. Use of soda lime in the MIXA1 canister is not 
objectionable since the canister over-protects for all 
gases except CK at high humidity; in the M10 or Ml 
canister soda lime is a disadvantage. 

Since the development of Type ASC whetlerite, 
the use of soda lime is no longer a consideration and 
has been dropped from the specifications. 

4.2 HEXAMINE AND THIOCYANATE 
IMPREGNATIONS OF WHETLERITES 

4.2.1 Introduction 

As indicated in Table 1, the protection afforded by 
Type A and Type AS whetlerites against CK and 







HEXAMINE AND THIOCYANATE IMPREGNATIONS OF WHETLERITES 


49 


AC is considerably below the desired level. The best 
gas mask adsorbents for these agents prepared prior 
to 1940 were made by a secondary impregnation of 
Type A whetlerite with a basic solution of sodium 
thiocyanate or hexamethylenetetramine (hexamine). 
These materials when used in canisters, that were 
standard before 1940, absorbed 43 to 176% 94 more 
CK and 11 to 71 % more AC than the Type A whet¬ 
lerite and Type D mixtures in use previously. The 
protection toward PS, CG, and SA was equivalent 
to that of Type A whetlerite and Type D mixture 
and in each case SA life was practically zero for the 
humidified canister. 

Hexamine and thiocyanate impregnated materials 
possessed the following disadvantages: 

1. Deterioration on storage. 

2. Evolution of uncomfortable concentrations of 
ammonia during use. 

,3. Necessity for a secondary impregnation for ap¬ 
plication of the hexamine or thiocyanate. Both of 
these impregnants are destroyed at the temperature 
necessary to prepare a good quality Type A whet¬ 
lerite. 

One of the problems under consideration in the 
period 1941 to 1945 was the improvement of this 
type of adsorbent with respect to (1) the CK pro¬ 
tection after storage, (2) humid SA protection, and 
(3) the diminution of evolved ammonia. 

4.2.2 Hexamethylenetetramine (Hexamine) 
Impregnations 

Hexamethylenetetramine [(CH 2 )6N 4 ] was used as 
a charcoal impregnant in German gas masks during 
World War I. It was believed that it was added to 
improve CG protection. It was found later that CK 
protection also was improved by the use of this com¬ 
pound. In 1927, a procedure 97 for the plant impreg¬ 
nation of hexamine charcoals was published by work¬ 
ers at Edgewood Arsenal. Later publications 98-100 
summarized the work on this particular type of im¬ 
pregnation. Inasmuch as sodium thiocyanate was 
considered superior to hexamine, little work was 
done on hexamine between 1936 and 1942. The work 
done in this period was concerned mainly with thio¬ 
cyanate impregnated materials. 

Methods of Application of Hexamine 

In 1942, the investigation of hexamine was re¬ 
opened and further experiments were performed. 22 ’ 23 
These indicated that hexamine could be added to 


Type A or AS whetlerite as a secondary impregnant. 
This procedure is troublesome but is to be preferred 
to addition to the original solution since the heat 
treatment necessary to produce a Type A whetlerite 
of high quality causes extensive decomposition of the 
hexamine. It was found that sodium hydroxide 
should be added with the hexamine to reduce the 
rate of deterioration of the adsorbent. Absence of 
sodium hydroxide favors higher initial lives but re¬ 
sults in a rapid decrease of CK protection during 
storage (see Table 5). More than 2% of hexamine in 
the secondary impregnating solution results in evo¬ 
lution of intolerable concentrations of ammonia in 
use. Optimum concentrations of the secondary im¬ 
pregnating solution were found to be 2% hexamine 
and 5% sodium hydroxide. 

Impregnation is performed by soaking dry char¬ 
coal or whetlerite in an aqueous solution of hexamine 
(containing other desired constituents). In labora¬ 
tory preparations, the material is soaked for 30 min, 
drained for 30 min, and oven-dried in a %-in. layer 
on a wire screen tray at about 45 to 50 C for 12 to 
20 hr. An air stream at a linear velocity of 25 cm 
per min is passed through the layer of drying whet- 
lerites. 

Effect of pH on Hexamine Impregnants 

Addition of acid to a hexamine impregnating solu¬ 
tion decreases the initial CK and AC lives of the 
adsorbent, as is shown in Table 5. 

Table 5. Effect of pH on hexamine impregnation of 
CWSC-11 Type A whetlerite. Test conditions: 5-cm 
bed depth; 500 cm 3 per cm 2 per min flow rate; gas 
concentration: CK = 2.5 mg per 1; SA = 4 mg per 1; 
AC = 3 mg per 1. 


Composition of 
impregnating solution 

Tube test service lives, min 
80-80 conditions 

2 % hexamine 

SA 

CK 

AC 

+5% NaOH 


48 


+0.5 NaOH 

13 

67 

34 

+0.005 NaOH 

35 

67 

35 

+0.0 

29 

67 

31 

+0.001 nh 2 so 4 

36 

71 

31 

+0.1 nh 2 so 4 

60 

57 

13 

+3.0 NH 2 S0 4 

10 

0 

2 

+0.1 nch 3 cooh 

58 

62 

21 


Effect of Added Salts on Hexamine Impreg¬ 
nation 

Salts of the ammine-forming metals Cu, Cd, Co, 
Ni, and Zn, were added to the whetlerite with the 
hexamine in an effort to decrease the evolution of 









50 


IMPREGNATION OF CHARCOAL 


ammonia from hexamine-impregnated whetlerite. 
When enough metal was added to decrease the am¬ 
monia evolution appreciably, the odor of formal¬ 
dehyde 15 became noticeable and in most cases was 
more objectionable than the odor of ammonia. In 
every case where such metals were added, the CK 
life was reduced, the degree of reduction depending 
upon the amount of metal added. Cadmium and zinc 
diminish CK life to a smaller extent than do cobalt, 
nickel, and copper. However, cadmium seriously de¬ 
creases AC protection. 

A sample of hexamine whetlerite containing cad¬ 
mium and emitting a strong odor of formaldehyde 
was sprayed with sodium hydroxide until the odor 
was no longer that of formaldehyde but became that 
of ammonia. It is possible to liberate either of the 
hydrolytic products of hexamine from the absorbent 
by controlling the conditions in this way. Probably 
it would require a very delicate balance of pH and 
metal ion concentration to produce an absorbent 
having satisfactory canister performance. 

X-ray Studies of Hexamine Impregnations 

X-ray studies of these materials have revealed 
that hexamine is precipitated on the charcoal in a 
different crystalline form from that obtained by the 
evaporation of a water solution. When standard 
Type A whetlerite is treated with hexamine in a so¬ 
lution containing cobalt or nickel nitrate, an X-ray 
pattern characteristic of the copper nitrate hexamine 
complex appears. The standard pattern for this ma¬ 
terial was made from a precipitate formed by the 
addition of copper nitrate to a water solution of 
hexamine. When hexamine is added in the presence 
of cadmium nitrate, an altogether different reaction 
occurs, the products of which have not yet been 
identified. Some of the copper of the whetlerite ap¬ 
parently is reduced, but it is not dissolved and repre¬ 
cipitated as a hexamine complex, as is the case when 
hexamine is applied to Type A whetlerite in the pres¬ 
ence of cobalt and nickel nitrates. y 

CK Surveillance of Hexamine Impregnated 
Adsorbents 

The CK protection of a base charcoal impregnated 
with hexamine was better than that of a Type A 
whetlerite similarly treated. After aging in sealed 
containers at 80% RH and 45 C for 243 days, the 
CK life of the hexamine impregnated charcoal was 

b Formaldehyde is formed in decomposition of the hexa¬ 
mine. 


better than that of the hexamine impregnated whet¬ 
lerite. Typical results are shown in Table 6. 

Table 6 . CK surveillance of hexamine impregnated ad¬ 
sorbents. Tube test conditions: 5-cm bed depth, 500 
cm 3 per cm 2 per min flow rate, cone, of CK = 2.5 
mg per 1. 


CK 80-80 tube lives, min 
Adsorbent Initial after 243 days 

CWSC-11 charcoal + 2% hexamine + 
5% NaOH 

49 

41 

CWSC-11 Type A whetlerite + 2% 
hexamine + 5% NaOH 

33 

22 

CWSC-11 Type A whetlerite + 1% 
hexamine + 5% NaOH 

28 

11 

CWSC-11 charcoal + 4% hexamine 

70 

8 

CWSC-11 Type A whetlerite + 4% 
hexamine 

90 

3 


Hexamine impregnation of charcoal or Type A 
whetlerite produces an adsorbent with fairly good 
CK protection but the difficulties encountered in 
overcoming ammonia evolution and deterioration on 
aging render it of little value. In case of extreme 
emergency it might prove to be useful. 

4.2.3 Thiocyanate Impregnations 

Sodium thiocyanate impregnated whetlerite (or 
Type E 6 impregnated charcoal as it is officially desig¬ 
nated) was developed in an effort to produce an ad¬ 
sorbent superior to hexamine impregnated whetlerite. 

In 1926, during a search for new impregnants, it 
was discovered that the CK protection of charcoal 
could be improved markedly by impregnating the 
charcoal with ammonium thiocyanate, alone or in 
combination with sodium carbonate." In 1933 and 
1934 this impregnation was further improved 99 by 
using a solution of sodium thiocyanate together with 
sodium hydroxide to impregnate Type A whetlerite. 
The adsorbent had improved protection for both CK 
and AC. Designated as Type E 6 impregnated char¬ 
coal, it was also found to be more stable than Type A 
Avhetlerite impregnated with hexamine and sodium 
hydroxide. 

Application of Thiocyanate to Type A Whet¬ 
lerite 

The material as originally specified was produced 
by soaking Type A whetlerite in a solution contain¬ 
ing 5% sodium hydroxide and 0.5% sodium thio¬ 
cyanate, draining, and drying to less than 5% mois¬ 
ture in any convenient type of drier at any temper¬ 
ature up to 150 C. 








HEXAMINE AND THIOCYANATE IMPREGNATIONS OF WHETLERITES 


51 


Adsorbents prepared by the above method and 
used as canister fillings evolved an odor of ammonia 
strong enough to be objectionable to sensitive ob¬ 
servers. During storage, these canisters continued to 
evolve ammonia, and a decrease in CK and AC life 
was noted. This decrease was much greater during 
tropical storage than during normal storage at Edge- 
wood Arsenal. 

A program was initiated 93 to provide a process of 
manufacture which would yield a product substan¬ 
tially free from the odor of ammonia. The work 
proved that insufficient drying was mainly respon¬ 
sible for the ammonia odor of the whetlerite. An ad¬ 
sorbent free from this odor was produced by oven¬ 
drying the impregnated material in trays at 80 to 
100 C for 20 hr with free circulation of air around the 
trays. This drying procedure was sufficient to reduce 
the moisture content to 1.0% or less and to remove 
the excess ammonia present in the impregnated char¬ 
coal. For this study, the same type of secondary im¬ 
pregnating solution was used as had been used previ¬ 
ously and techniques of impregnation and drainage 
were similar. The moisture content had to be reduced 
to 1 % before drying was considered complete. 

A study of the preparation 26 of E 6 impregnated 
charcoal showed that the amount of sodium hydrox¬ 
ide used in the secondary impregnation could be re¬ 
duced from 5% to 1% and still yield a good product. 

Effect of Storage on Thiocyanate — Impreg¬ 
nated Type A Whetlerite 

The E 6 impregnated charcoal showed a tendency 
to adsorb a slightly larger quantity of moisture than 
Type D fillings under conditions of tropical storage. 
In tropical storage E 6 impregnated charcoal slowly 
lost adsorptive capacity for AC and CK. However, 
the decrease is not appreciably different from that of 
the Type D filling then in use. These effects are com¬ 
pared in Table 7. 


Table 7. Changes in absorptive capacity after two 
years storage in Panama and storage in simulated trop¬ 
ical conditions at Edge wood Arsenal. 


Test 

gas 

E 6 impregnated 
charcoal 

Type D 
filling 

PS 

47% decrease 

36% decrease 

CG 

79% increase 

29% increase 

SA 

19% decrease 

2 % decrease 

CK 

75% decrease 

69% decrease 

AC 

22 % increase 

17% increase 

Moisture content after 2 years 
surveillance 

15.0 to 17.6% 

11.0 to 14.1% 

Water content before surveil¬ 
lance 

1-5% 

3.4% 


The development of E 6 impregnated charcoal was 
at this stage in 1940, when further work during the 
period 1940 to 1945 was done in an attempt to pre¬ 
pare samples in which deterioration of the AC and 
CK protection in tropical storage would be small. 

Decrease in the CK life of an E 6 impregnated 
charcoal is accompanied by a decrease in the thio¬ 
cyanate content and an equivalent increase of the 
sulfate content of the adsorbent. Investigation 
showed that the thiocyanate of the impregnated 
charcoal is present in two forms, one of which was 
easily extractable with hot water and the other not. 24 
The extractable form is apparently the part of the 
thiocyanate that is oxidized during storage. Samples 
stored at elevated temperatures in a vacuum also 
show this effect. It appears that atmospheric oxygen 
is not essential for this reaction. Adsorbed or chemi¬ 
sorbed oxygen is probably responsible for that oxida¬ 
tion of thiocyanate which occurs in vacuo. 

The CK life falls off as the extractable thiocyanate 
is oxidized to sulfate, until the life reaches a constant 
level about twice as great as the CK life of untreated 
Type A whetlerite. This residual life has been at¬ 
tributed to the unextractable thiocyanate. The data 
in Table 8 show this effect. 

Table 8 . Correlation of CK life with extractable 
thiocyanate content of E 6 impregnated charcoal heated 
at 100 to 110 C in air. Tube test conditions: 5-cm layer, 

500 cm 3 per cm 2 per min flow rate, 50% RH, 25 C. 
Adsorbent dry when tested. 


Heating 
time, hr 

CK life 
min 

Extractable 

S as SO;": 
extractable 

S as SCN- 

% Unex- 
tractable SCN - 

0 

71 


— 

2 

69 

0.089 

32 

4^ 

56 

0.46 

34 

8 

52 

0.93 

34 

24 

48 

3.74 

32 

67 

46 

>20 


Type A 
whetlerite 

27 




The CK life approaches a constant value as the 
extractable thiocyanate approaches complete oxi¬ 
dation. 

Application of Thiocyanate to Type A Whet¬ 
lerite 

Type AS whetlerite was impregnated with thio¬ 
cyanate. Optimum drying conditions appeared to be 
6 hr at 100 C, oven-drying. The initial SA and AC 
lives were slightly lower than those of Types A or 










52 


IMPREGNATION OF CHARCOAL 


AS whetlerites but not seriously so. The use of 
sodium hydroxide was found to decrease the amount 
of unextractable thiocyanate. The rate of oxidation 
of extractable thiocyanate to sulfate was not affected 
by the presence of sodium hydroxide. In addition, it 
was found that the 80-80 CK protection was superior 
both initially and after aging for those samples with 
the lower sodium hydroxide contents. 

E 6 impregnated charcoals produced by the above 
method have approximately as good canister pro¬ 
tection for SA, AC, and CG as the Type A whetler- 
ite. CK protection is satisfactory but not outstand¬ 
ing under 80-80 conditions. Silver nitrate sprayed on 
E 6 impregnated charcoal increases SA protection 
but decreases CK protection. 

Using a radioactive tracer technique, 25 some re¬ 
search was done to determine the solubility of silver 
thiocyanate in whetlerizing solutions and to deter¬ 
mine the adsorption of Ag+ and SCN - from whetler¬ 
izing solution. No precipitation of AgSCN takes 
place in a whetlerizing solution containing 0.1% of 
AgSCN. The Ag + and SCN - are adsorbed com¬ 
pletely and fairly rapidly by charcoal. 

Since the development of the ASC process the 
study of both hexamine and thiocyanate impregna¬ 
tions has ceased. Thiocyanate appears to be more 
useful than the hexamine in whetlerite impregnation. 
Full manufacturing directives can be quickly com¬ 
piled from data available. 

4.3 GENERAL STUDIES OF CHARCOAL 
IMPREGNATION 

4.3.1 Introduction 

It has been known for many years that the ad¬ 
sorptive and catalytic properties of charcoals are de¬ 
pendent upon the nature of the pores in the charcoal 
and upon the chemical materials other than carbon 
which are present in the charcoal. Each operation 
used in the preparation of activated charcoal (for 
example, carbonization and activation) has an effect 
on the nature of the pores. The raw material used 
determines the materials other than carbon which 
may be found in activated charcoal. The impurities 
may be altered by impregnation, thus increasing the 
kind and amounts of chemical materials present, or 
by leaching, to reduce the kinds and amounts. Or¬ 
dinarily impregnation is used to add to the charcoal 
a material which it does not contain initially and 
which promotes the adsorption of a specific toxic 
agent. 


4.3.2 Catalytic Reactions and Types of 
Catalysts 

Impregnants either react directly with the gas be¬ 
ing absorbed or act as catalysts for reactions of the 
gas with oxygen, water, and so forth. 

Although not all of the mechanisms for the absorp¬ 
tion of toxic gases by gas mask charcoals have been 
proved, the reactions that are most likely to occur 
after physical adsorption are oxidation, decompo¬ 
sition, hydration, hydrolysis, and perhaps reduction. 
In many cases, more than one reaction may occur. 
Various catalytic reactions and the catalysts best 
suited to them are listed in Table 9. 28 This is a gen¬ 
eralized table and has been built up from data on 
many different catalyst carriers under various con¬ 
ditions of use. The elements listed are used in many 
different forms, for example, pure metal, alloy, oxide, 
halide, molybdates, and phosphate. 


Table 9. Catalysts frequently used (in order of ef¬ 
ficiency). 


Periodic group 

Oxidation catalysts 


VIII 

Pt, Rb, Ir, Ni, Fe, Co 


V 

V, Nb, Ta, Bi 


VI 

W, Cr, Mo, U 


VII 

Mn 


I 

Cu, Li, D, Na, Ag 


IV 

Si, Th, Ph, Sn 


II 

Zn, Hg, Cd 


Decomposition catalysts 

VIII 

Fe, Ni, Pt, Pd, Os, Rh, Ir 


I 

Cu, Au, Ag, Na 


II 

Zn, Ca, Mg 


III 

A1 


IV 

Ti, Th, Sn, Zr 


VI 

Mo, Cr, W, U 


Hydration catalysts 

III 

A1 


IV 

Th, Ti, Ce, Si 


II 

Zn, Cd, Hg, Ca, Mg 


I 

Ag, Au, Cu 


VI 

Mo, W, Cr 


VIII 

Fe, Co, Ni 


Reduction catalysts 

VIII 

Ni, Fe, Co, Pd, Pt 


II 

Mg, Zn, Hg, Cd 


I 

Cu, Ag, Au 


VI 

Mo, Cr, W 


VII 

Mn 



4.3.3 Charcoal as a Catalyst Carrier 

Charcoal has been used as a carrier for many types 
of catalysts and in many types of reactions. A few of 
these are listed below: 













GENERAL STUDIES OF CHARCOAL IMPREGNATION 


53 


1. Synthetic reactions. Example: 

ch 3 ch 2 oh + ch 2 = ch 2 ^Sc 4 h 9 oh. 

Catalyst = bone charcoal containing Fe 2 0 3 + 
A1 2 0 3 promoted by Yb, La, or Zr. 

CO + 3H 2 £^S CH 4 + H 2 0 

Catalyst = charcoal + Ni, Mn, and A1 catalysts. 

2. Decomposition reactions. Example: 

H 2 Q 2 cataly > t H 2 Q + ±0 2 

Catalyst = Mn0 2 on charcoal. 

3. Oxidation reactions. Example: 

0 2 + As 2 0 3 cat . aly >As 2 05 

Catalyst = CuO on activated charcoal. This re¬ 
action may have prompted the first use of copper 
oxide as an SA catalyst. 

4. Reduction reactions. Example: Reduction of 
oxygen-containing organic compounds by H 2 over 
activated charcoal impregnated with Fe, Cr, or Ni. 

5. Hydration and dehydration. Example: Hydra¬ 
tion of ethylenic hydrocarbons to alcohols at 150 C 
over CuO + W0 3 on activated charcoal. 

6. Hydrogenation and dehydrogenation. Example: 
Hydrogenation of fats over Ni on activated charcoal. 

7. Desulfurization. Example: Desulfurization of 
crude oil by the use of colloidal molybdenum and 
copper chromite on activated charcoal. 

8. Chlorination, et cetera. Example: 

CO + C1 2 ^^C0C1 2 

Catalyst = SbCl 5 on activated charcoal. 

Thus a large variety of reactions are catalyzed by 
the use of the proper impregnant on activated char¬ 
coal. 

In addition to being a good catalyst carrier, char¬ 
coal has the ability to adsorb gases which have rela¬ 
tively low vapor pressures at room temperature and 
which do not undergo catalytic reaction on impreg¬ 
nated charcoal. Therefore, protection can be ex¬ 
pected for the large bulk of toxic materials not specif¬ 
ically considered in selecting the impregnant. 

4.3.4 Possible Reactions in the Adsorp¬ 
tion of Gases on Gas Mask Charcoal 

Since activated charcoal contains a certain amount 
of adsorbed oxygen, probably present as chemisorbed 
oxygen, the following reduction reaction is a possi¬ 
bility in some cases: 

(carbon + chemisorbed oxygen) + reducible sub¬ 
stance + catalyst- > C0 2 + reduced substance. 

Carbon + chemisorbed oxygen may be considered 


as incipient carbon monoxide and should function 
as a good reducing agent in the presence of reducible 
material. 

Copper oxide when dry, and a mixture of metallic 
silver and copper oxide when moist have proved to 
be good catalysts for SA absorption. The reaction in¬ 
volves oxidation of the SA and possibly decomposi¬ 
tion prior to the oxidation. Both copper and silver 
act as oxidation and decomposition catalysts (see 
Table 9). 

Hydration and hydrolysis are possible steps in the 
absorption of gases like CG and CK. 

The impregnants that have proved to be most ac¬ 
tive toward CK and AC are copper combined with 
chromate, molybdate, or vanadate. The state of the 
impregnant after heat treatment is not known defi¬ 
nitely, except that chromium must be present with 
copper in the hexavalent state to form an active 
catalyst for the destruction of CK. The copper 
molybdate and copper vanadate impregnants require 
a drastic heat treatment in preparation. The catalyst 
may be present as a compound of copper with molyb¬ 
denum or vanadium, or as a mixture of copper oxide 
with molybdenum or vanadium oxide. X-ray analy¬ 
sis has not been helpful because the catalyst is either 
amorphous or, if crystalline, is too finely divided to 
produce a characteristic X-ray scattering pattern. 

Since catalysts have such manifold functions, it is 
difficult to determine from the nature or kind of cata¬ 
lyst what reaction or reactions are occurring in the 
presence of the catalyst. Hence, it is difficult also to 
select a material that will catalyze the removal of a 
certain toxic gas. In the case of certain acid-base and 
similar reactions, catalysis is probably not involved 
and an impregnant can be selected on the basis of the 
properties of the toxic gas involved and the reaction 
desired. 

As a consequence of the factors enumerated in the 
foregoing discussion, a large number of compounds 
were tried as charcoal impregnants and promoters 
for whetlerites, alone and in various combinations. 
In Table 10, all the materials tested as impregnants 
for charcoal and Type A whetlerite are listed with a 
comment indicating the quality of the absorbent 
compared to Type A whetlerite. No comment indi¬ 
cates negligible or nonexistent activity toward SA, 
AC, and CK when tested under conditions stated 
in the table. Tube tests were employed to evaluate 
all exploratory impregnations. Whenever promising 
activity was indicated, further work was carried out 
to test the value of the impregnant. 








54 


IMPREGNATION OF CHARCOAL 


Table 10. Summary of exploratory impregnations. 

Compound 

Reference Comment f 

Compound Reference Comment! 

Part A.* 

Compounds! and mixtures used as impregnants for activated charcoal. 


Acetamide; CH 3 CONH 2 

109 


CoC0 3 + MnS0 4 + (NH 4 ) 2 C0 3 

108 


AICI 3 

33 


Co(NH 3 ) 4 C0 3 + Cd(NH 3 ) 4 C0 3 

108 


Ammonia catalyst 

108 


CoC0 3 + nh 4 oh + nh 4 no 3 

108 


Aniline; C 6 H 5 NH 2 

107 


CoC0 3 + H 2 0 2 77, 

108 

CO odixation 

Na 3 As0 3 

109 




catalyst 

BaBr 2 

109 

Slight CK activity, 

CoC0 3 + ZnC0 3 

108 




AR-80 

Co-Ni-Cd (ammine carbonates) 

108 


Beeswax in CeH 6 

108 


Co-Ni-Cd-Zn (ammine carbonates) 108 


Beeswax in CCI 4 

108 


KCNO 107, 109 


Bi(N0 3 ) 3 

109 


Formamide 

109 


Na B0 3 

109 


AuCL 

108 

SA activity, 0-50 

NH 4 Br 

33 




and 80-80 

NaBr0 3 

33 


Hydrazine sulfate 

109 


HBr 

33 


Hydroxylamine hydrochloride 

109 


CdC0 3 

108 


H 2 S + ZnCl 2 

109 


CdC0 3 + H 2 0 2 

108 


HI0 3 33, 107, 108 

SA activity, 0-50 

Cd(N0 3 ) 2 

109 




and 80-80 

Cd(N0 3 ) 2 + Zn(N0 3 ) 2 

108 


NaI0 3 

33 


CdCl 2 , CdBr 2 , Cdl 2 

33 


KI0 3 33, 

108 


(NH 4 ) 2 C0 3 

109 


KI (Aq) 

108 

SA activity, 0-50, 

nh 4 ci 

33 




80-80 

KC1 

108 


KI + I 2 (Aq) 

108 


KC10 3 

33, 108 


NH 4 I + NaOH + NaSCN 

108 


Chloramine T 

33 


Pb(C 2 H 3 0 2 ) 2 108, 

109 


K 2 Cr 2 0 7 

48, 50 


LiN0 3 

108 


K 2 Cr 2 0 7 ~b AgN0 3 

109 

SA activity, 0-50 

LiCl 

108 




and 80-80 

Mg(C 2 H 3 0 2 ) 2 + Cu(NH 3 ) 4 . 



[Ag(NH 3 ) 2 ] 2 Cr0 4 

109 

SA activity, 0-50 

(C 2 H 3 0 2 ) 2 + nh 4 c 2 h 3 o 2 

107 




and 80-80 

MnS0 4 + CoC0 3 + (NH 4 ) 2 C0 3 

108 


CuCr 2 0 7 (acid solution) 

109 

SA, 0-50; CK 0-50 

KMn0 4 

108 


Cr0 3 in Type A solution 

48 

SA, 0-50; AC and 

Hgl 2 in C 2 H 5 OH 

108 

SA activity, 0-50 



CK 0-50; 80-80 



and 80-80 

Cr0 3 + AgN0 3 in NH 4 OH 

48 

SA, 0-50 and 80-80 

Hgl 2 + KI 33, 108 

SA activity, 0-50 

Cu-Cr-Ni-Ag in NH 4 OH and 

48 

Like ASC; good SA, 



and 80-80 

(NH 4 ) 2 C0 3 


AC, and CK 0-50, 

HgCl 2 

33 

SA activity, 0-50 



and 80-80 



and 80-80 

(NH 4 ) 2 Cr 2 0 7 

108 


HgBr 2 + NH 4 Br 

33 

SA activity, 0-50 

Cr(N0 3 ) 3 

108 




and 80-80 

Cr(NH 3 ) 6 (C 2 H 3 0 2 ) 3 

107 


Ni(NH 3 ) 4 C0 3 

107 

Like Type A 

Cu-Cr-Ag-Mo-W-V 

40, 41 

Like ASC 



whetlerite 

CuCl 2 

33 


NiC0 3 , saturated 

108 


CuCl 2 + 2KC1(K 2 CuC1 4 ) 

33 


NiN0 3 -b H 2 0 2 

108 


Cu(C10 4 ) 2 

33 


Ni-Cu-Ag-Cr 

48 

Like ASC whetlerite 

Cu(OH) 2 

107 


kno 2 

109 

CK activity, 0-50 

Cu(NH 3 ) 4 (OH) 2 

107 


NaN0 2 

109 

CK activity, 0-50 

Cu(N0 3 ) 2 

107, 108 


Ag(NH 3 ) 2 N0 2 

109 

SA activity, 0-50 and 

Cu(N 0 3 ) 2 + Mn(N0 3 ) 2 

109, 107 




80-80 

Cu(N0 3 ) 2 + NH 4 OH + KI 

108 


HN0 3 + (NH 4 ) 2 HP0 4 

109 


CuCN in Cu _ (excess) 

109 


K 2 0sBr 6 + Type A solution 

3 


CuS0 4 + Fe 2 (S0 4 ) 3 + (NH 4 ) 2 S0 4 108 


Os0 4 + Type A solution 

3 


Cu( C 2 H 3 0 2 ) 2 

107 


Os0 2 + Type A solution 

3 


Cu(NH 3 ) 4 S0 4 

107 


(NH 4 ) 2 S 2 0 8 

109 


Cu(ethylene diamine) 4 C0 3 

107 


(NH 4 ) 2 S 2 0 8 + Type AS solution 

109 


Cu(C 2 H 3 0 2 ) 2 + Mn(C 2 H 3 0 2 ) 2 + 


h 3 po 4 

109 


nh 4 c 2 h 3 o 2 

107 


H 3 P0 4 + FeCl 3 

109 


Cu-Ag-Fe 

109 

SA and AC activity, 

Na 2 HP0 4 +.AgN0 3 

109 

SA activity, 0-50, 



0-50 and 80-80 



80-80, CK, 0-50 

Cu-Ni-Zn whetlerite (carbonates) 109 

Like Type A whet¬ 

(NH 4 ) 2 HP0 4 + hno 3 

109 




lerite 

[Ag(NH 3 ) 2 ] 2 HP0 4 

109 

SA activity, 0-50 and 

Fehling’s solution + dextrose 

107 




80-80 

CoCl 2 

33 


AgN0 3 3, 104, 108, 109 

SA activity, 0-50, 

Co(N0 3 ) 2 

77, 107 

CO oxidation 



80-80* 



catalyst 

' Tannic acid 

108 















GENERAL STUDIES OF CHARCOAL IMPREGNATION 


55 


Compound 


Reference 


Table 10 ( continued) 


Commentf 


Compound 


Reference 


Comment§ 


Part A. ( continued) 


Thioacetamide 

109 


Thiosemicarbazide 

109 

CK activity, 0-50 

Na 2 S 2 0 3 ; AgN0 3 Double 

109 

S A activity, 0-50 and 

impregnation 


80-80 

NaSCN + NH 4 I + NaOH 

108 


NaSCN + I 2 + KI + NaOH 

108 


Ag(NH 3 ) 2 SCN 

109 

SA activity, 0-50 and 
80-80 

SnCl 2 

108 


SnCl 4 

33 


[Ag(NH 3 ) 2 ] 2 W0 4 

109 

SA activity, 0-50 and 
80-80 

NH 4 V0 3 + Type AS solution 

40, 109 

Slight SA, AC, and 
CK activity, 0-50 
and 80-80 


Ag(NH 3 ) 2 V0 3 109 SA activity, 0-50 

and 80-80 

Zn(NH 3 ) 4 C 03 41, 108, 109 AC activity, 0-50 

ZnC0 3 + CoC0 3 in excess NH 4 OH 108 


Zn halides 

33 


ZnCl 2 + H 2 S (two step) 

109 


Zn(N0 3 ) 2 

109 


Zn(N0 3 ) 2 + AgN0 3 (acid) 

109 

SA activity, 0-50 and 
80-80 

Zn(NH 3 ) 4 S0 4 

109 


ZnS0 4 -)- MnSOi 

108 


Zn(NH 3 ) 4 C0 3 -T AgN0 3 -(- Mo0 3 

109 

SA and AC activity, 

in excess NH 4 OH and 


0-50 and 80-80, 

(NH 4 ) 2 C0 3 


CK activity, 0-50 

Zn-Cd-Ni (ammoniacal carbonate 

108 


solution) 


Part B. Compounds used in secondary impregnation of Type A whetlerites 


A1(N0 3 ) 3 

3 


Mg(N0 3 ) 2 + NaOH 

3 


A1(N0 3 ) 3 + NaOH 

3 


MnC0 3 

3 


K 2 H 2 Sb 2 0 7 

3 


Mn(N0 3 ) 2 

3 


K 2 H 2 AsOi + NaOH 

3 


Hg(N0 3 ) 2 

3, 32 


Ba(N0 3 ) 2 

3 


Mo0 3 

3, 40, 41 


Ba(N0 3 ) 2 + NaOH 

3 


Mo 0 3 + NaOH 

3 


Bi(N0 3 ) 3 + NH 4 N0 3 

3 


KMn0 4 

3 


Bi(N0 3 ) 3 + 5% HN0 3 

3 


Ni C0 3 • 2Ni(OH) 2 

3 


k 2 b 4 o 7 

3 


Ni(N0 3 ) 2 

3 


CdC0 3 

3 


nh 4 no 3 

3 

Improves SA 0-50 

Cd(N0 3 ) 2 

3 


Os0 4 

3 


Ca(N0 3 ) 2 + NH 4 N0 3 

3 


AgN0 3 

3, 107 

SA activity, 0-50 and 

Ca(N0 3 ) 2 + NaOH 

3 




80-80 

Ce(N0 3 ) 3 

3, 107 


Sr(N0 3 ) 2 

3 


Ce(N0 3 ) 2 + NH 4 N0 3 

3 


Sr(N0 3 ) 2 + NaOH 

3 


Cr 2 0 3 

3 


NaSCN 

3 

SA-dry 

Cr0 3 

107 




AC, CK 0-50, and 

K 2 Cr 2 0 7 + NaOH 

3 




80-80 

CoC0 3 

3 


NaSn0 3 

3 


Co(N0 3 ) 2 

3 


Th(N0 3 ) 4 

3 


Cu(C 2 H 3 0 2 ) 2 

3 


Na 2 W0 4 

3 


AuC1 3 

3 

SA activity, 0-50 and 

[Ag(NH 3 ) 2 ] 2 W0 4 

109 

SA 0-50, 80-80 CK 



80-80 



0-50 

Fe(N0 3 ) 3 

3 


U0 2 (N0 3 ) 2 

3 


Pb(N0 3 ) 2 

3 


U0 2 (N0 3 ) 2 + nh 4 no 3 

3 


Pb(N0 3 ) 2 + NH 4 N0 3 

3 


nh 4 vo 3 

3 


LiN0 3 

3 


nh 4 vo 3 + nh 4 no 3 

3 


Mg(N0 3 ) 2 

3 






* Compounds are listed alphabetically with respect to element being investigated. 

t No comment indicates poorer performance than is given by Type A whetlerite for SA, AC, and CK. 

+ Silver, in the form of any soluble salt or complex, produces an absorbent having SA activity 0-50 and 80-80. 

§ No comment indicates poorer performance than is given by Type A whetlerite for SA. Not tested against AC or CK. 


4.3.5 Charcoal Impregnants for the 
Absorption of CK 

Clues to new CK absorbents resulted from an ex¬ 
amination of the properties and reactions of CK. 
The work showed that: 29> 30 

1. CK has an oxidation potential similar to that 
of oxygen. 

2. CK reacts with water and ammonia thus: 


2CNC1 + H 2 0-> 2CNO- + 2H+ + 2C1~ 

CNC1 + NH 3 ->• NCNH 2 + H+ + ci- 

3. CK reacts readily with aniline, hexamethylene¬ 
tetramine, and other amines. 

4. Many substances containing sulfur are either 
oxidized by or form addition compounds with CK. 

5. Polymerization of CK is catalyzed by many 
substances, such as Cl 2 and acids. 

6. Phenol-formaldehyde resins impregnated with 


SECBB 




















56 


IMPREGNATION OF CHARCOAL 


tetraethylenepentamine had better CK lives than 
whetlerite. 

7. CK reacts most readily with compounds con¬ 
taining nitrogen or sulfur with free electron pairs. 

8. Hopcalite oxidizes CK at temperatures above 
40 C. 

9. The CK life of Type A whetlerite increases with 
increase in temperatures. 

10. The CK life of unimpregnated activated char¬ 
coal decreases with increase in temperatures. This fact, 
together with item No. 9, shows that Type A whet¬ 
lerite either reacts with or catalyzes a reaction of CK. 
The CK activity of Type A whetlerite is very low at 
room temperature. 

11. CK containing radioactive carbon exhibited 
radioactivity in the effluent gases after absorption by 
Type A whetlerite. 

12. Approximate free energy calculations show 
that for the reaction, 

CNC1 + 2H 2 0 = Cl- + 4H+ + C0 2 + ^N 2 

+ 36, E° = -0.7 v. 

Therefore, oxidizing agents should be capable of 
oxidizing CK. 

13. Mixtures of the oxides of Cu, Mn, Ni, V, and 
Mo in various combinations promoted the destruc¬ 
tion of CK by activated charcoal. 

The work on the use of metallic oxides led to the 
development of Types ASM, ASV, and ASC whet- 
lerites. In early experiments, charcoal impregnated 
simultaneously with Cu, Mn, Ni, and V and heat- 
treated in a manner that was designed to convert the 
impregnants to oxides produced a good CK absorb¬ 
ent. Later work 31 showed that a Type A or AS solu¬ 
tion in which vanadate, molybdate, tungstate, or 
chromate is dissolved, produces an excellent impreg- 
nant. Molybdenum, vanadium, or tungsten in com¬ 
bination with Type A solution as an impregnant re¬ 
quires a high-temperature heat treatment, (300 to 
350 C) either in a vacuum or in the absence of at¬ 
mospheric oxygen, to produce a satisfactory absorb¬ 
ent. On the contrary, chromium requires a low- 
temperature heat treatment (150 to 180 C) in a 
system that is swept out continuously by an air 
stream. The early experiments with molybdenum 
and vanadium did not produce an absorbent with 
satisfactory activity under humid conditions. This 
is now attributed to the type of activated charcoal 
employed, since present charcoals can be impreg¬ 
nated with these metals to produce an absorbent 
satisfactory both dry and humidified. 


4.3.6 Charcoal Impregnants for the 
Absorption of SA 

As indicated by research performed during World 
War I, silver has proved to be the best SA catalyst 
investigated. 4 ’ 7 ~ 9 ' 104 American work has favored 
copper-silver combinations, while British practice 
has been to use a straight silver impregnant applied 
either by impregnation or spraying, keeping the 
charcoal humidified to maintain a satisfactory CG 
protection. Silver is easily incorporated with charcoal 
or whetlerite, is not subject to deterioration in stor¬ 
age, and only a small amount is required for optimum 
protection. In addition it does not interfere appre¬ 
ciably with the original desirable properties of the 
charcoal or whetlerite to which it is added. 

The other effective SA reactants found were gold 
chloride, mercuric halides, potassium iodide or iodine 
in potassium iodide, ammonium iodide, and iodic 
acid. None of these had all the desirable properties 
exhibited by silver. 

Impregnation by Mercury 

A study was made of mercury, 32 halogen, and 
halogen salt impregnation. Mercury, as the bromide 
or chloride, can be added easily to whetlerites as a 
secondary impregnant and absorbents with good 
SA 80-80 protection are produced. However, the 
hazard of mercury poisoning from mercury vapor 
contained in the effluent air stream is too great to 
permit its use. The concentration of mercury in the 
effluent varied from 2.3 to 18.0 X 10“ 4 mg per 1 
when air was passed through a 5-cm bed of the ma¬ 
terial contained in a tube with a 3 sq cm cross section 
at a rate of one 1 per min. In industry, the incidence 
of chronic mercury poisoning increases rapidly as the 
mercury content of the air rises above 2 X 10 -4 mg 
per l. 35 

X-ray evidence indicates that the mercury is pres¬ 
ent in the charcoal entirely as metallic mercury. 

Iodic Acid Impregnation 

Iodic acid impregnated charcoal also exhibited 
good SA 80-80 activity. However, this material aged 
badly and had a very low SA 80-80 life after standing 
30 days at room temperature. Iodic acid gave best 
results in a whetlerite containing copper and nickel 
in the mole ratio 9/1. NHJ also showed some SA 
activity but was not tested after aging. 





MOLYBDENUM AND VANADIUM IMPREGNATION 


57 


4.3.7 Impregnations from Solvents other 

than Water 

Results of the use of nonaqueous solvents in im¬ 
pregnation 3 were uniformly unpromising. The sam¬ 
ples were no better than Type A whetlerite (regard¬ 
ing SA protection) and usually were poorer. With 
liquid ammonia as a solvent, Cu(N0 3 ) 2 , Mg(N0 3 ) 2 , 
Cu(CH 3 CoO) 2 , Pb(N0 3 ) 2 , Zn(N0 3 ) 2 , Hg(N0 3 ) 2 , 
Co(N 0 3 ) 2 , Ni(N0 3 ) 2 and AgN0 3 were used as im- 
pregnants. Only AgN0 3 yielded absorbents with 
good SA 80-80 lives. 

Impregnations with copper nitrate in acetic acid 
and copper acetyl acetonate in chloroform gave fair 
SA 80-80 lives. Nickel carbonyl in benzene gave poor 
SA lives. 

4.3.8 Impregnations from the Vapor Phase 

Impregnations from the vapor phase were also un¬ 
successful. The following substances were added to 
charcoal in the presence of a hydrogen stream at 
1 to 2 mm pressure: Te, Zn, Cd, As, Sb, Pb, Mg, Se, 
and FeCl 3 and these were put on in vacuo : BiCl 3 , 
Ni(CO)4, 106 nickel dimethylglyoxime, SnCh, 0s0 4 , 
Zn, Se, HgCl 2 , copper acetyl acetonate, Te0 2 , and 
TiCU. Only HgCl 2 and Te0 2 showed any SA activity. 
Both were much less effective than Type A whet¬ 
lerite. 

4.4 MOLYBDENUM AND VANADIUM 
IMPREGNATION 

4.4.1 Introduction 

The development of copper-silver-molybdenum 
[ASM] and copper-silver-vanadium [ASV] impreg¬ 
nations for activated charcoal was initiated by the 
discovery that the CK activity of charcoal could be 
increased by the use of certain metallic oxides as im- 
pregnants. 30 The first of this type of absorbent was 
prepared by impregnation of charcoal with solutions 
of the nitrates of metals such as Cu, Ni, and Mn, or 
Co, Ni, and Mn, together with small amounts of V, 
Cr, Hg, or Fe. The impregnated charcoal was heated 
at 400 C in a vacuum or in the absence of oxygen to 
decompose the nitrates to oxides. 

Thus prepared, many metal oxides increase the 
absorption of CK by charcoal at elevated tempera¬ 
tures, but only those mentioned in the preceding 
paragraph are effective at 25 C. Further experiments 


showed that combinations of copper and molyb¬ 
denum or copper and vanadium were the best im- 
pregnants (excepting ASC) and that the other metals 
were of questionable value for the removal of CK. 
The combination of copper and tungsten also has 
some CK activity when used as an impregnant, but 
has not been developed bleeause it is decidedly in¬ 
ferior to copper and molybdenum or vanadium. 

The use of nitrates as impregnants was avoided by 
the addition of molybdenum, vanadium, or tungsten 
to a Type AS solution as molybdate, vanadate, or 
tungsten, respectively. These materials are readily 
soluble in Type AS solution. The resulting impreg¬ 
nated charcoal retains its SA and CK protection as 
in the Type AS whetlerite but has in addition much 
superior CK and AC protection. 

The original samples prepared by impregnation 
with nitrate solution of Cu, Ni, Mn, and V, or with 
Type AS solution containing molybdate had poor 
CK 80-80 protection. This has been since attributed 
to the type of charcoal used in the preparation of the 
samples. In certain zinc chloride activated, extruded 
charcoals of the type used in early experiments, the 
pore size distribution was unfavorable to CK pro¬ 
tection. Any charcoal now available, which is other¬ 
wise acceptable as gas mask charcoal, can be made 
into a satisfactory Type ASM whetlerite (as the 
copper-silver-molybdenum impregnated charcoal is 
designated). 

4.4.2 Effect of Temperature of Heat 
Treatment 

The effect of variation in heat treatment temper¬ 
ature on tube test lives of Type ASM whetlerite is 
shown in Table 11A. This table brings out clearly 
the variations caused by the differences in the base 
charcoals used. 

Vanadium impregnations resulted in poor absorb¬ 
ents under similar conditions of heat treatment. SA 
and AC lives were equivalent to those of the molyb¬ 
denum-impregnated absorbents but the CK 80-80 
lives were poorer. Tungsten absorbents were still less 
satisfactory than vanadium absorbents in this re¬ 
spect. 

Zinc can be used in place of copper in the ASM im¬ 
pregnation. The CK lives of such absorbents are con¬ 
siderably lower, however, than those of the copper 
containing materials. Some typical results are shown 
in Table 11. 

The use of zinc in place of copper results in rather 








58 


IMPREGNATION OF CHARCOAL 


Table 11 A. Performance of Cu-Ag-Mo* impregnated charcoals. 


jj ea t, Tube test lives, t min 

treatment SA AC CK 


Charcoal 

temp C 

AR-50 

80-80 

AR-50 

80-80 

AR-50 

80-80 

PCI-1 

150 

93 

103 

62 

40 

51 

30 

PCI-1 

200 

134 

125 

83 

56 

no 

36 

PCI-1 

250 

148 

151 

31 

36 

80 

45 

PCI-1 

300 

156 

158 

32 

46 

99 

66 

PCI-1 

350 

143 

165 

35 

38 

99 

77 

PCI-1 

400 

132 

155 

26 


66 

53 

C-ll 

200 

128 

109 

15 

59 

55 

20 

C-ll 

350 

135 

141 

25 

28 

67 

32 

N-44 

200 

162 

136 

95 

97 

29 

8 

N-44 

350 

138 

192 

26 

50 

68 

25 

N-P5 

200 

134 

85 

34 

34 

68 

8 

N-P5 

350 

112 

101 

34 

68 

125 

5 


* Made from a solution containing 10% Cu, 15% NH 3 , 10% CO 2 , 1% AgNC>3, and 2.5% M 0 O 3 . 

t Layer depth = 5 cm; flow rate 500 cm 3 per cm 2 per min. Concentration: SA = 4 mg per 1; AC 3 mg per 1; CK = 2.5 mg per l. 


Table 11B. Zinc-silver-molybdenum impregnated charcoals. 


Charcoal 

Heat 

treatment 
temp C 



Tube test lives,* min 


SA 

AR-50 80-80 

AC 

AR-50 80-80 

CK 

AR-50 80-80 

PCI-P58 

150 

67 

108 

33 

37 

30 

11 

PCI-P58 

250 

85 

105 


43 

30 

5 

PCI-P58 

350 


118 

26 

50 

34 

12 

PCI-P58 

450 

77 

125 


45 

29 

5 


* Tube Tests: 5 cm layer; Flow rate, 500 cm 3 per cm 2 per min. Concentration SA = 4 mg per 1, AC = 3 mg per 1, CK = 2.5 mg per I. 
Impregnating solution contained 5% Zn, 8% NH 3 , 5% CO 2 , 1.7% Mo. 0.6% Ag. 


Table 12. Impregnation with mixed Cu, Ag, Mo, Cr, V, and W. (Tube test conditions as in Table 8.) 


Heat Tube test lives, min 

treatment 

temp C SA AC CK 


Charcoal 


AR-50 

80-80 

AR-50 

80-80 

AR-50 

80-80 

PCI-P58 

150 

163 

154 

89 

93 

88 

19 

PCI-P58 

400 

187 

219 

50 

60 

135 

8 


poor performance on all tests, although the SA and 
AC lives are high enough to be useful. The CK life, 
however, is very short. 

A mixed impregnation of activated charcoal was 
made with a solution containing 8 % copper, 1 % silver 
nitrate, and 0.6% each of molybdenum, chromium, 
vanadium, and tungsten in the form of molybdate, 
chromate, vanadate, and tungstate, respectively. 
The resulting absorbent when heated at 150 C had 
approximately the absorptive properties to be ex¬ 
pected of a sample containing only chromium, silver 
nitrate, and copper. The CK 80-80 protection after 
heating at 400 C in a manner designed to activate 
the molybdenum, vanadium, and tungsten was 
negligible. The results are shown in Table 12. 

It is evident that the SA 80-80 and CK AR-50 


lives of the high-temperature sample are quite long. 
The mixture of oxides of Mo, Cr, V, and Ni acts as 
a good SA catalyst in the presence of silver and cop¬ 
per. However, this mixture is not so efficient a cata¬ 
lyst for CK as is an equivalent amount of molyb¬ 
denum in the presence of copper. Vanadium and 
tungsten are very easily poisoned by moisture under 
some conditions of preparation. 

4.4.3 Effect of Organic Acids 

An investigation of the variables involved in the 
preparation of Type ASM whetlerite 42 showed that 
the addition of some organic acids to the impregnat¬ 
ing solution resulted in a superior whetlerite. The 
series of organic acids used is shown in Table 13. 


















MOLYBDENUM AND VANADIUM IMPREGNATION 


59 


Table 13. Effect of the addition of organic acids to 
ASM impregnating solutions.* 


Acid added 

Tube test life, CK 80-80, min 

None 

44 

Adipic 

51 

Fumaric 

62 

Maleic 

70 

Z-Malic 

51 

Succinic 

59 

Tartaric 

81 

Citric 

59 

Formic 

47 

Glycolic 

68 

Phenylacetic 

29 

Salicylic 

50 

Sebacic 

32 


* Solution composition: 10% Cu, 15.8% NH3, 10% CO 2 , 2 % Mo, and 
5% organic acid. Heat treatment: 130 C for 45 min followed by 315 C 
for 3H hours. No air present during high temperature treatment. 


Almost every organic acid used resulted in an in¬ 
creased CK life. Tartaric acid was definitely superior 
to the others since it had approximately double the 
CK protection of ASM whetlerite without added 
acid. The solution containing tartaric acid is desig¬ 
nated as ASMT impregnating solution and hereafter 
is referred to as such. 

4.4.4 Optimum Concentrations of Com¬ 
ponents of ASMT Impregnating Solution 

A study of ASMT impregnation revealed the fol¬ 
lowing information: 

1. CK life is practically independent of the copper 
concentration in the impregnating solution above 
7.5 g of copper per 100 ml of solution. The data are 
inconclusive at lower copper concentrations. The 
optimum concentration is approximately 10% copper 
(12.5 g of copper per 100 ml of solution). 

2. A concentration of approximately 5 g of molyb¬ 
denum per 100 cc of solution (3.9%) is the optimum. 
Satisfactory CK results have been obtained between 
3 and 6 g per 100 cc. 

3. The optimum tartaric acid concentration is 
approximately 6.2% (8 g per 100 ml of solution) for 
a solution containing 3.9% of molybdenum. For 
lower molybdenum contents a lowered tartaric acid 
content is advisable. Increase in tartaric acid con¬ 
centration is accompanied by a decrease in AC life. 

4. The optimum ammonia content is approxi¬ 
mately 10% (13.3 g of NH 3 per 100 ml of solution). 
A large excess of ammonia tends to decrease CK life. 

5. The optimum carbon dioxide content is ap¬ 


proximately 9%. For maximum CK and AC lives, 
the CO 2 content should be kept at a low level. 

6. The optimum silver content is 0.18% (0.35 g 
of AgN0 3 per 100 ml of solution). Apparently quanti¬ 
ties of this magnitude show no effect on CK or AC 
lives. 

The optimum concentrations are summarized in 
Table 14. 


Table 14. Optimum concentrations of constituents in 
ASMT impregnating solution. 



g 

of constituent 

% by 



per 100 ml of 

weight of 

Constituent 

Added as 

solution 

constituent 

Mo 

(NH 4 ) 2 Mo0 4 

5.0 

3.9 Mo 

Cu 

CuC0 3 -Cu(0H) 2 

12.5 

9.7 Cu 

Tartaric acid Tartaric acid 

8.0 

6.2 T.A. 

Ag 

AgN0 3 

0.35 

0.2 Ag 

C0 2 

(NH 4 ) 2 C0 3 -H 2 0 

CuC0 3 -Cu(0H) 2 

jg total C0 2 9.2 C0 2 

nh 3 

nh 4 oh 

8.0 

10.3 NH 3 


(NH 4 ) 2 C0 3 -H 2 0 

4.1 



(NH 4 ) 2 Mo0 4 

1.2 



Specific gravity = 1.29 g per ml at 25 C. 


One liter of solution is prepared as follows*. 


(NH 4 ) 2 M 0 O 4 (54% Mo) 93 g 

(NH 4 ) 2 C0 3 -H 2 0 136 g 

NH 4 OH, 28% solution 320 ml 

CuC0 3 -Cu(0H) 2 (55% Cu) 255 g 

Tartaric acid 80 g 

AgN0 3 3.5 g 


Half the molybdate is dissolved in water, half 
in NH 4 OH. Powdered (NH 4 ) 2 C0 3 -H 2 0 is added to 
the aqueous molybdate solution and stirred until 
completely dissolved. The ammoniacal molybdate 
solution is then added and if any undissolved ma¬ 
terials are present the stirring is continued until solu¬ 
tion is complete. Then the basic copper carbonate is 
added and dissolved. This is followed by the tartaric 
acid and finally 35 ml of a 10% AgN0 3 solution. The 
resulting solution is diluted to 1 liter. 

4.4.5 Laboratory Preparation of ASMT 
Whetlerite 42 

Impregnation and draining in the usual manner 
are satisfactory for ASMT. If oven-drying is em¬ 
ployed, a two-step process is best. This consists of a 
preliminary tray-drying at 135 C for 6 hours, fol¬ 
lowed by a final drying in loosely stoppered Erlen- 
meyer flasks for a short time at 300 to 305 C. The 















60 


IMPREGNATION OF CHARCOAL 


second drying can be discontinued as soon as the 
charcoal reaches 300 to 305 C. The materials should 
be removed from the oven and allowed to cool in the 
flasks without free exposure to air. 

Wetting the charcoal between preliminary and 
final drying lowered the AC and CK lives appre¬ 
ciably. Passage of ammonia through the sample at 
this stage had no effect on the CK and AC lives. This 


Table 15. Comparison of ASMT samples prepared in 
rotary and static oven driers. 


Method of drying 

Maximum 
temp C 

Tube test lives, min 

CK 80-80 AC 0-50 

Oven dried, 2 step 

303 

105 

59 

a u « 

303 

107 

56 

it a it 

303 

90 

42 

Rotary drier, 1 step 

320 

126 

48 

it a a 

320 

119 

59 

a it it 

332 

118 

47 


indicates that the removal of excess water is desirable 
before high temperatures are reached, and removal of 
ammonia is not important for development of CK 
and AC protection. A study previously mentioned 
has shown that as a whetlerite dries at 150 degrees, 
ammonia, carbon dioxide, and water are removed in 
that order. 

The procedure for drying ASMT whetlerites in 
rotary driers 43 differs in that the impregnated char¬ 
coal is heated as rapidly as possible to the maximum 
temperature and allowed to cool in the oven to a 
temperature low enough to preclude combustion 
when the sample is exposed to air. This procedure 


produces samples as good as and in some cases better 
than multistep procedures. Representative results 
of this type of drying procedure compared to oven¬ 
drying are shown in Table 15. 

Rotary driers, when available, are to be preferred 
since samples can be produced faster and more con¬ 
veniently, and also are of higher quality with respect 
to CK life. 

The flow of various gases through the rotary drier 
while drying ASMT whetlerites had measurable 
effects. Results of the experiments are shown in 
Table 16. 

Use of gas flow through the drier in general pro¬ 
duced a sample with lower CK protection than sam¬ 
ples dried with no gas flow. Water vapor was the only 
gas passed through the drier which produced a sam¬ 
ple with approximately the same CK protection as 
no-flow samples. The type of gas used in the pro¬ 
duction of the whetlerite may be classified with re¬ 
spect to decreasing CK protection of the product as 
no flow, water vapor, nitrogen, carbon dioxide, car¬ 
bon monoxide, and air. This order, after water vapor, 
is not conclusive. Absence of gas flow is clearly su¬ 
perior, with regard to the CK protection of the sam¬ 
ple produced, to flow of any gas with the possible 
exception of steam. 

On the other hand, AC protection is depressed to 
the greatest extent by materials such as CO and 
water vapor and is least affected by air flow. There 
may be a correlation between oxidizing power of the 
gas used in drying and the AC protection of the whet¬ 
lerite. Water vapor and hot carbon would produce 


Table 16. Effect of gas flow during drying on the quality of ASMT whetlerite. 


Gas used 

Linear 
flow rate 
cm/min 

Max temp of 
whetlerite 

C 

Time to 
reach 300 C 
min 

Temp at which 
flow was 
stopped, C 

Tube test ] 

CK 

80-80 

lives, min 

AC 

0-50 

Air 

16 

310 

155 

127 

107 

65 

Air 

16 

309 

33 

130 

89 

57 

Air 

55 

319 

30 

143 

98 

55 

Air 

3 

300 

38 

Continuous 

86 

48 

Air 

3 

334 

34 

Continuous 

93 

44 

n 2 

32 

303 

90 

154 

88 

51 

n 2 

32 

301 

35 

158 

89 

44 

n 2 

32 

304 

35 

Continuous 

95 

36 

co 2 

48 

307 

98 

Continuous 

83 

36 

co 2 

48 

327 

33 

Continuous 

95 


CO* 

16 

310 

45 

310 

80 

35 

CO* 

16 

321 

98 

Continuous 

106 

24 

None 


320 

95 

Continuous 

126 

48 

None 


320 

50 

Continuous 

119 

59 

None 

•• 

332 

33 

Continuous 

118 

47 


* Preheated to 350 C. 






















MOLYBDENUM AND VANADIUM IMPREGNATION 


61 


Table 17. Aging of ASC, ASM and ASMT, whetlerites, 
sealed and equilibrated. 


Base 

charcoal 

Type 

Aging conditions 

Tube test 
lives, min 
CK 80-80 

Temp C 

Time 

PCI 1042 

ASC 

Freshly e 

equilibrated 

73 

PCI 1042 

ASC 

85 

13 hr 

9 

PCI 1042 

ASC 

60 

2 days 

11 

PCI 1042 

ASC 

60 

8 days 

8 

PCI 1042 

ASC 

25 

16 days 

40 

PCI 1042 

ASC 

25 

26 days 

14 

PCI 343 

ASC 

Freshly equilibrated 

122 

PCI 343 

ASC 

85 

6 hr 

11 

PCI 343 

ASC 

60 

1 day 

70 

PCI 343 

ASC 

60 

2 days 

38 

PCI 343 

ASC 

60 

4 days 

14 

PCI 343 

ASC 

60 

8 days 


PCI 343 

ASM 

Freshly equilibrated 

71 

PCI 343 

ASM 

80 

1 day 

39 

PCI 343 

ASM 

60 

2 days 

55 

PCI 343 

ASM 

60 

4 days 

58 

PCI 343 

ASM 

60 

12 days 

39 

PCI 343 

ASMT 

Freshly equilibrated 

91 

PCI 343 

Tartaric 





acid added 

85 

2 days 

78 

PCI 343 

ASMT 

85 

9 days 

81 

PCI 343 

ASMT 

60 

7 days 

84 


carbon monoxide, thus explaining why carbon mon¬ 
oxide and water vapor have the same effect on AC 
protection. It appears that reducing conditions favor 
high CK protection and low AC protection, and oxi¬ 
dizing conditions favor the reverse. High tempera¬ 
tures favor high CK lives and low AC lives. The 
optimum temperature is 310 to 320 C. A compromise 
had to be made between CK life and AC life and a 
temperature was chosen to give satisfactory pro¬ 
tection for both toxic agents. 

4.4.6 Aging Characteristics of ASMT 
and ASC Whetlerites 

ASMT whetlerite has excellent aging qualities 
when stored equilibrated in sealed containers. Under 
these conditions ASC whetlerite deteriorates very 
rapidly. On the other hand, ASMT whetlerites de¬ 
teriorate in open containers as much as do ASC whet¬ 
lerites. Both retain a satisfactory protection under 
these conditions for a relatively long time. 

Comparisons of the aging rates of ASC and ASMT 
are found in Tables 17 and 18. From these data it is 
evident that ASMT is superior when stored moist in 
closed containers. The use of tartaric acid with ASM 
solution enhanced the aging properties of ASM whet¬ 
lerite. This difference disappears, however, when the 


absorbents are stored in open trays at high relative 
humidity and high temperature. 

Under the conditions of aging shown in Table 18, 
the CK lives of the materials are almost identical 
after 24 days of aging, although a higher initial life 
was characteristic of the ASMT materials. One 
ASMT material, prepared in an atmosphere of water 
vapor, retained its life at a high level all through the 
aging period. This effect may be worthy of more in¬ 
vestigation. 

It is probable that aging in contact with an excess 
of air more nearly approaches field conditions than 
sealed aging since diurnal temperature variation, 
body movement, and occasional wearing of the mask 
cause some fresh air to enter the canister periodically. 

AC lives of ASMT are usually improved by equi¬ 
libration at 80% RH. Cyanogen is never observed in 
the effluent gases when AC is absorbed by ASMT as 
it is when a Type A or AS whetlerite is used. Both 
AC and CK are irreversibly absorbed by ASMT 
whetlerite indicating a chemical change following 
adsorption rather than physical absorption as the 
major factor in the functioning of the whetlerite. 


Table 18. Comparison of ASC and ASMT aged in 
open trays in air at 110 F and 80 per cent RH. 


Base 

Type of 

Original 

CK 80-80 Tube test lives 

charcoal 

whetlerite 

life 

Aged 19 days 

Aged 24 days 

PCI 1042 

ASC 

101 

55 

42 

BC 3 

ASC 

36 

28 

29 

PCI 1042 

ASC 

70 

68 

64 

PCI 1042 

ASC 

88 

69 

69 

PCI 343 

ASMT 

93 

44 

64 

PCI 343 

ASMT 

101 

54 

68 

PCI 343 

ASMT 

114 

96 

62 

PCI 343 

ASMT 

131 

143 

125 


4.4.7 Pilot Plant Experiments 

A pilot scale preparation of ASMT whetlerite was 
attempted in the pilot plant at Northwestern Uni¬ 
versity, 44 which had been used in the development of 
the plant scale production of ASC whetlerite. 

The purpose of the investigation was to determine 
whether existing plant equipment could be used in 
the production of ASMT whetlerite without major 
changes in design. The rotary drier had been designed 
for the preparation of material requiring high air 
flow and relatively low temperature (150 C). ASMT 
production required rapid heating to relatively high 
temperatures and no air flow. In fact a leak-tight 
system is desirable. The ASMT produced was in- 





























62 


IMPREGNATION OF CHARCOAL 


ferior by far to laboratory produced samples. A com¬ 
parison of the ASMT and ASC whetlerites produced 
in the pilot plant is shown in Table 19. 


Table 19. A comparison of ASC and ASMT whetlerites 
produced in the Northwestern University whetleriza- 
tion pilot plant. 


Base charcoal 

M10 canister lives,* CK 80-80 

ASMT 

ASC 

PCI-Drum Q 

11 

30-35 

PCI-Drum Q 

20 

30-35 

PCI-Drum NB 

11 

30-35 

PCI-Drum NM 

23 

30-35 

PCI-Drum NN 

17 

22 

National Drum NI 

3 

0-3 

National Drum X 

0 

0-3 


* Canister tests in M10 iMi-inch canister: CK concentration, 4 mg per 1, 
SIP indicator. Flow rate 50 1pm, breather machine. 


In general, the ASMT whetlerites produced had 
an initial CK life about two-thirds as great as those 
obtained by ASC impregnation of the same base 
charcoal. Dry AC tube lives of the ASMT whetler¬ 
ites were about three-quarters as great as the corre¬ 
sponding ASC materials, and seemed to be relatively 
independent of drying conditions. There seemed to 
be no correlation between CK and AC lives. 

The quality of the ASMT was markedly affected 
by the retention time in the drier. Best results were 
obtained by a very rapid passage through the drier. 
The optimum charge temperature was approximately 
500 F (260 C), although this was not a critical factor. 

In order to obtain a satisfactory product and to 
facilitate temperature control, it was necessary to 
exclude rigorously all air from the drier. Leakage 
occurred in some runs causing a sudden rapid rise in 
temperature. This was attributed to ignition of the 
charge although there was little evidence of burning. 

Unless predrying or backfeeding was employed, 
the wet feed stock caused caking near the inlet and 
made cleaning necessary after about 40 hours of op¬ 
eration. This situation was not encountered fre¬ 
quently in the processing of ASC whetlerite. Mixing 
previously dried product with the feed stock (re¬ 
ferred to as backfeeding) was a satisfactory method 
for the prevention of caking. It is not clear whether 
such practice is harmful to the quality of the product. 
Backfeeding is practiced in some ASC whetlerization 
plants and apparently has no harmful effect if a 
fairly high quality material is used as backfeed. As 
far as is known the result is equivalent to a mechan¬ 
ical mixing of the backfeed and product after proc¬ 
essing. 


For reasons not clearly defined at present, some 
National Carbon Company zinc chloride activated 
charcoals which were suitable for ASC production 
proved to be unsuited for conversion to ASMT whet¬ 
lerites. A very inferior product resulted from all such 
attempts in the pilot drier. 

It was concluded that the adaptation of existing 
plants to ASMT production would involve a major 
change in equipment in order to exclude air and allow 
very rapid heating and short retention time. These 
changes were considered not expedient. 

4.4.8 Simultaneous Impregnation with 

Molybdenum and Chromium 

In an effort to combine the advantages of ASC and 
ASM whetlerites in one absorbent, a study of ASCM 
impregnation was made. 45 It was found to offer no 
advantages over ASC or ASMT, since preparation 
at high temperature resulted in a material having the 
properties of ASMT whetlerite, and preparation at 
low temperatures resulted in an absorbent similar to 
ASC whetlerite. A secondary impregnation of ASMT 
whetlerite with (NH^CrCh and heat treating at 
150 C produced a material with very large initial 
CK 80-80 protection, but it had the same aging prop¬ 
erties as ASC. Since the preparative procedure was 
more complicated than that of ASC, it was not con¬ 
sidered worthy of further investigation. The study 
was abandoned when it became clear that the mixed 
impregnation had no outstanding advantages. 

4.4.9 Impregnations with Vanadium 

The development of ASV and ASVT whetlerites 
was similar to that of ASMT whetlerite. The efficacy 
of vanadium in combination with copper as a char¬ 
coal impregnant capable of enhancing the CK ab¬ 
sorption of the charcoal was discovered at the same 
time that the properties of molybdenum as an im¬ 
pregnant were discovered. The preparation of the 
vanadium absorbent 46 closely resembles that of the 
molybdenum absorbent. 

4.4.10 Impregnating Solution 

The initial CK 80-80 protection of copper-silver- 
vanadium impregnated charcoal (or Type ASV whet¬ 
lerite, as it is designated) is greatly increased by addi¬ 
tion of tartaric acid to the impregnating solution, 
just as in the case of the ASM whetlerite. The opti¬ 
mum concentrations of the components of the im¬ 
pregnating solution are found in Table 20. 














MOLYBDENUM AND VANADIUM IMPREGNATION 


63 


Table 20. Optimum concentrations of components of the impregnating solution. 


Compound 

Amount of compound 
for 1 liter 

Grams of constituent 
per 100 ml of solution 

% of constituent 
by weight 

NH 4 VO 3 

82 g 

3.6 V 

2.9 V 

CuC0 3 Cu(0H) 2 

225 g 

12.5 Cu 

10.0 Cu 

NH 4 OH (28% aqueous solution) 

320 ml 

13.3 NH 3 

10.6 NH 3 

(NH 4 ) 2 C0 3 -H,0 

136 g 

11.0 CO, 

8.8 C0 2 

Tartaric acid 

80 g 

8.0 T.A. 

6.4 T.A. 

AgN0 3 

3.5 g 

2.2 Ag 

0.18 Ag 


The solution is prepared by mixing the vanadate 
and basic copper carbonate to a paste with a small 
amount of water. Ammonium hydroxide is then 
added to dissolve the paste. To this is added am¬ 
monium carbonate, 35 ml of a 10% solution of silver 
nitrate, and finally the tartaric acid (slowly, to avoid 
loss of C0 2 ). The solution is diluted to 1 liter with 
water. 

4.4.11 Preparation of ASVT Whetlerite 

Impregnation and draining are carried out in the 
usual manner. The drying procedure requires a labo¬ 
ratory rotary drier 43 which can be efficiently sealed to 
prevent air leakage into the drum. A small exit port 
is necessary to allow water vapor, ammonia, and 
carbon dioxide to escape during drying without allow¬ 
ing appreciable back diffusion of air. 

The optimum drying temperature is 300 to 350 C, 
although a satisfactory product can be made at a tem¬ 
perature as low as 225 C. The rate of heating is not a 
critical factor. Good products can be obtained by 
either slow or rapid heating rates. Exposure of the 
whetlerite to small amounts of air during drying 
seriously decreases CK protection. The sample also 
must be cooled in the absence of air. Use of a stream 
of N 2 during cooling produces excellent results. 

Both CK and AC protection pass through a maxi¬ 
mum as tartaric acid content of the ASVT impreg¬ 
nating solution increases. The optimum concentra¬ 
tion is approximately 6% tartaric acid. In contrast 
to ASMT whetlerite, this is independent of vanadium 
content. 

A few representative tube test results are given in 
Table 21. 

AC protection is considerably increased by mois¬ 
ture equilibration. Cyanogen never occurs in the 
effluent gas stream from this type of absorbent when 
AC is absorbed. Both CK and AC are adsorbed irre¬ 
versibly and cannot be desorbed. 

The lives shown above are initial lives and are 
rather high compared to ASMT results. The material 


Table 21. Performance of ASVT whetlerites. 


Treatment of sample 

Tube test lives* 

CK 80-80 

AC 0-50 

Rotary drier heated to 250 C 

138 

68 

Rotary drier heated 1 hr at 250 C 

145 

58 

Rotary drier heated to 300 C 

148 

54 

Rotary drier heated 1 hr at 300 C 

157 

47 

Rotary drier heated rapidly to 300 C 

152 

52 

Rotary drier heated to 300 C 

159 

40 

Oven dried 3 hr in flask at 300 C 

100 

42 


* 5-cm bed depth; Flow rate 500 cm per min; 2.5 mg CK per liter. 


is approximately as stable as ASMT when stored 
equilibrated in sealed containers. It is less stable, 
however, when stored in open or semi-open contain¬ 
ers such as might be encountered in a canister under 
field conditions. Some aging results are shown in 
Table 22. 


Table 22. Aging of equilibrated Type ASVT whetlerite 
under Various conditions. 


Aging conditions 

Tube test life 

Temp C 

Time, days 

Container 

CK 80-80 


none 


139 

85 

2 

Stoppered bottle 

68 

60 

10 

Stoppered bottle 

56 

60 

30 

Stoppered bottle 

53 

50 

10 

Stoppered bottle 

62 

50 

30 

Stoppered bottle 

60 

50 

10 

Open basket 

31 

50 

30 

Open basket 

8 

50 

10 

Open bottle 

38 

50 

30 

Open bottle 

11 

25 

80 

Stoppered bottle 

100 


This material is definitely less stable than Type 
ASMT or Type ASC whetlerites under conditions of 
open storage. 

In general it has been observed that when Type 
ASVT whetlerite is stored in tightly stoppered bot¬ 
tles the aging is slow or virtually ceases after the first 
rapid decrease in CK life. The amount of initial de¬ 
crease is practically independent of the temperature 
of storage. This can be explained, if the aging is the 




























64 


IMPREGNATION OF CHARCOAL 


result of oxidation, by the removal of all oxygen from 
the container. The increased aging in open containers 
is in agreement with this hypothesis. 46 With open 
containers, and with bottles fitted with Bunsen 
valves (to allow the internal pressure to remain at at¬ 
mospheric pressure) ASVT whetlerites aged to a CK 
protection equivalent to that of base charcoal in 
from 10 to 30 days at 50 C. 

Two mechanisms have been suggested for this 
aging: (1) oxidation of V+ 4 to V+ 5 ; (2) oxidation of 
Cu 2 0 to CuO. No definite analytical data to support 
these mechanisms is available. 

AC protection of Type ASVT whetlerite is satis¬ 
factory when the material is equilibrated but is poor 
when dry. The AC tube life when tested under 80-80 
conditions is 80 to 95 min. No cyanogen can be de¬ 
tected in the effluent. Samples exposed to air at high 
temperatures (thereby almost completely destroying 
CK protection) gave AC tube test lives of 140 min 
when tested at 0-50 conditions. This suggests an oxi¬ 
dation mechanism operative in both equilibration 
and high-temperature air treatment which results in 
improved AC protection. A life of 140 min is longer 
than can be accounted for by any known chemical 
reaction with the impregnant and is probably due to 
a catalyzed reaction. Perhaps a copper-vanadium 
compound in the oxidized state is an efficient catalyst 
for the oxidation of AC. In this connection it is inter¬ 
esting to note that a sample prepared with both 
molybdenum and vanadium in the impregnating 
solution (Type ASMV whetlerite) ran 250 min be¬ 
fore a trace of AC was transmitted. Cyanogen was 
detected after 160 min. However, the sample was not 
an outstanding CK absorbent. 

Because of the rapid deterioration of Type ASVT 
whetlerite when stored in unsealed containers, it was 
considered an unsuitable filling for present canisters. 

In the foregoing discussion no comment has been 
made concerning the general absorption character¬ 
istics of ASMT and ASVT for toxic agents other than 
CK and AC. In general, the materials absorb CG, 
SA, PS, H, and other typical toxic agents satisfac¬ 
torily. CO is not absorbed. 

4.5 DEVELOPMENT OF COPPER-SILVER- 
CHROMIUM IMPREGNANTS 

4.5.1 Introduction 

The superior properties of mixtures of copper, sil¬ 
ver, and chromium as charcoal impregnants for the 
absorption of CK and AC were first recognized in 


1942. 48 Impregnation of charcoal with chromium, 
and in one case with copper and chromium, had been 
attempted earlier, but through improper preparation 
or lack of testing facilities for CK and AC the advan¬ 
tages of this impregnant were not appreciated. 

Activated charcoal impregnated with copper and 
either molybdenum or vanadium, when properly 
heat-treated, has the ability to adsorb from an air 
stream, and destroy, rather large quantities of CK 
and AC. In turn, molybdenum acts more efficiently 
than tungsten in the removal of CK and AC. From a 
comparison of the relative positions in the periodic 
table of tungsten, molybdenum, and chromium with 
the abilities of these impregnants to affect the ab¬ 
sorption of CK, it is indicated that chromium would 
be more useful than either molybdenum or tungsten. 
Broadly speaking, such was found to be the case. Al¬ 
though heat treatment conditions required for the 
preparation of copper-chromium impregnated char¬ 
coals are quite different from those used in preparing 
copper-molybdenum or copper-tungsten impregnated 
charcoals, the CK-destroying properties are equal to 
or better than the best molybdenum-containing ab¬ 
sorbents. 

The first samples of ASC whetlerite were prepared 
in the laboratory by impregnating activated charcoal 
with a Type AS solution to which had been added 
1.5% chromium in the form of (NH 4 )2Cr 2 0 7 . These 
products were dried in the same manner as Type AS 
whetlerites (in wire screen trays in a convection-type 
oven at 150 C for three hr). The resulting absorbents 
had good AC and CK lives, superior to those of any 
previous samples, but inferior to the present Type 
ASC whetlerites. Later work showed that practically 
any chromate salt could be used. The material chosen 
as most convenient for both laboratory and plant 
operations was chromic anhydride, Cr0 3 . The ma¬ 
terial is very easily soluble in the impregnating solu¬ 
tions used, readily available, and relatively cheap. 

4.5.2 Optimum Concentrations of Constituents 
of Type ASC Whetlerizing Solution. 

Copper and Chromium Concentrations 

Experimental results on the variation of AC and 
CK lives with variation in the copper and chromium 
concentrations of the whetlerizing solution are given 
in Figures 5 through 9. The work was evaluated at 
different times by different kinds of tube and canister 
tests. Early work was evaluated entirely by means of 
tube tests which cannot be correlated quantitatively 






COPPER-SILVER-CHROMIUM IMPREGNANTS 


65 


with canister tests. However, the results of both 
kinds of tests indicate approximately the same opti¬ 
mum concentrations. The best method of expressing 
test results, which was perfected at a later date, is by 
means of layer depth studies leading to an evaluation 
of A T 0 and X c . Knowing these values permits the esti¬ 
mate of the service life of the absorbent in any par¬ 
ticular canister (see Chapter 8). 



Figure 5. Effect of variation in Cr concentration (of 
whetlerizing solutions) on the AC and CK lives of can¬ 
isters. 

Figure 5 shows the variation of CK 80-80 life with 
the chromium content of the whetlerizing solution 
for three different charcoals, using a constant copper 
and silver content (10% and 0.1% respectively). 
These charcoals represent approximately the range 
available, from poorest to best. The three charcoals 
show an increase in CK life with chromium content, 
the rate of increase depending upon the charcoal. 
Curves might flatten out at high chromium content, 
but they were plotted as straight lines over the entire 
range studied since the experimental error is great 
enough to hide any leveling off at the higher concen¬ 
trations. The reason for this great difference among 
charcoals is not fully understood, although recent 
work indicates that pore size distribution in the char¬ 
coal is the controlling factor. 49 Figure 6 shows some 
M10A1 canister results concerning the dependence 
of CK and AC lives upon hexavalent chromium con¬ 
tent of the whetlerite at two different copper con¬ 
tents. The canister results in Figure 6 indicate the 
same general trend for CK as the tube test results in 
Figure 5. The AC life also is dependent upon the 
chromium content of the whetlerite. 50 In the 5-cm 
tube test (thick beds), the effect is very small or non¬ 


existent, whereas in canister tests (thin beds) the 
effect is important, as is clearly shown in Figure 6. 
This indicates that the activity toward AC is being 
affected by change in chromium content to a greater 
extent than the capacity for AC absorption. 


1.0 1.2 1.4 1.6 1.0 1.2 1.4 1.6 

PER CENT Cr vl ON WHETLERITE 

Figure 6 . Effect of hexavalent Cr and copper content 
of whetlerite on CK and AC lives. Gas lives are for 
M10A1 canisters, loaded PCC whetlerite. 

The variation of CK life with the copper content 
of the ASC solution at constant chromium content is 
shown in Figure 7. The data indicate a leveling off of 
the curve at about 8% copper. The effect of copper 



Figure 7. Effect on CK life of ASC solution with con¬ 
stant Cr and varying Cu content. 


is also shown in Figure 6. There, in the case of AC, 
the curve representing a copper concentration of 8% 
has a much smaller slope than that representing 5% 
copper, thus showing a much greater dependence of 
AC protection on chromium content at low copper 
concentration than at high. The CK curves, on the 
other hand, show the same slope at both copper 





















66 


IMPREGNATION OF CHARCOAL 


levels. However, for both cases, at a given chromium 
concentration, protection is at a higher level for the 
higher copper concentration. 

Figures 8 and 9 present similar data 51 for the vari¬ 
ation of No and A c for CK 80-80 with chromium and 
copper concentrations. Here the data lead to much 
the same conclusions as the tube and canister tests, 
except that here the question of thick and thin beds 
does not enter into the interpretation of the data and 
choice of optimum conditions. 



PER CENT Cr v ‘ 


Figure 8. Effect of Cr VI content upon critical depth, 
X c , and capacity, No, of impregnated charcoal, Type ASC. 



Figure 9. Effect of Cu content upon critical depth, X c , 
and capacity, No, of impregnated charcoal, Type ASC. 


The solution composition chosen as optimum con¬ 
tains 8% copper, 2% hexavalent chromium, and 
0.2% silver. (The silver concentration had no effect 
on the CK and AC lives in this low range and was 
retained on the basis of the data on Type AS whet- 
lerite. Two per cent silver was sufficient in every case 
with the charcoals in general use.) The 8% copper 
concentration, which was chosen to provide AC 
protection at the desired level, limited the chromium 
concentration to 2%, because with this amount of 
copper present at higher chromium concentrations, 
a heavy crystalline precipitate of CuCNH^CrCh 


forms at laboratory temperatures (25 C). The heats 
of solution and reaction warm the solution during 
preparation resulting in considerably higher solu¬ 
bility of the chromate. The precipitate forms when 
the concentrated solution is allowed to cool to room 
temperature. Use of 5% copper allows the inclusion 
of more chromium, but results in a lower level of 
protection at any given chromium concentration for 
both CK and AC, as shown in Figure 6. It is feasible 
to use higher chromium concentrations at 8% copper 
if the solution is heated. Similarly the normal ASC 
solution containing 8% copper and 2% chromium 
will produce a precipitate if allowed to cool much be¬ 
low room temperature. From a practical point of 
view the advantage (in increased AC and CK lives) 
of using more than 2% chromium is more than offset 
by the trouble encountered due to deposition of solids 
in the equipment. 

Ammonia and Carbon Dioxide Concentration 

The ammonia and carbon dioxide concentrations 
are fixed at that level which keeps the copper in 
stable solution as Cu(NH 4 )4C0 3 and CufNH^CrCh. 
Variations in the carbon dioxide and ammonia con¬ 
centrations do not affect the properties of the final 
whetlerite as long as they do not fall low enough to 
permit formation of solid basic copper carbonate, 
chromate (or possibly hydroxide). The solutions have 
been found to be satisfactory when the concentra¬ 
tions of copper, ammonia, and carbon dioxide are 
approximately in the ratios of 1:1.5:1. Slight vari¬ 
ations in this ratio have no apparent effect. 

The commonly used ASC solutions are listed be¬ 
low. 

Solution Symbol %Cu %NH 3 %C0 2 %Cr %Ag 

Edgewood ASC ASC 8.0 12.0 8.0 2.0 0.2 

Modified ASC ASC-1 5.0 8.0 5.0 2.0 0.2 

ASC-1 solution is now seldom used, but was used 
extensively during the period of development. 

Functions of the Metallic Constituents 

The function of each metallic constituent is 
brought out in Table 23. 

It is apparent that both copper and chromium 
must be present to produce CK activity. Copper 
alone, as in Type A whetlerite, produces a whetlerite 
having dry SA protection, dry AC protection and 
some wet AC protection, and CK protection equiva¬ 
lent to that of the base charcoal or less. The CG pro¬ 
tection of coppered charcoals is usually quite good, 
wet or dry. Silver alone produces a whetlerite having 









COPPER-SILVER - CHROMIUM IMPREGNANTS 


67 


Table 23. Function of the metallic constituents in ASC solution on charcoal CWS PCI-P58. 


Solution composition 

Service lives* 

SA 

AC 

CK 

nh 3 

CG 

%Cu 

% Cr 

%Ag 

0-50 

80-80 

0-50 

80-80 

0-50 

80-80 

AR-50f 

AR-50 

10 

1.37 

0 . 

126 

4 

90 

124 

140 

141 

30 

54 

0 

1.37 

0 . 

33 

0 

16 

15 

38 

8 

12 

46 

0 

1.37 

0.5 

70 

123 

17 

15 

37 

8 

14 

42 

10 

1.37 

0.1 

128 

105 

87 

118 

137 

111 

19 

54 

10 

0 . 

0 . 

120 

4 

80 


23 

0 




* 5-cm tube tests, t AR = moisture content as received. 


Table 24. Materials for a 1-kilo batch of ASC solution. 


Compound 

Assumed formula 

Purity (by analysis) 

Amount used 

Basic copper carbonate 

CuC0 3 Cu(0H) 2 

55.6% Cu, 2.0% C0 2 

114 g 

Aqueous ammonia 

NH 4 OH 

28% (25.2% by vol.) NH 3 

284 cc 

Ammonium carbonate 

(NH 4 ) 2 C0 3 

34.2% NH 3 , 54.3% C0 2 

142 g 

Chromic anhydride 

Cr0 3 

52% Cr 

34.6 g 

Silver nitrate 

AgN0 3 

63.5% Ag 

3.2 g 

Water 



390 cc 


Total 

Sp gr 

1,000 g 

1.12 


SA protection, when wet, but having no protection 
for any other test gas not absorbed by activated 
charcoal. Use of both silver and copper in the whet- 
lerite results in good SA protection wet or dry; the 
properties of this absorbent for other gases are sim¬ 
ilar to those of Type A whetlerite. To produce an 
absorbent with good CK activity wet or dry requires 
both copper and hexavalent chromium on the char¬ 
coal. The necessity for the presence of hexavalent 
chromium as such has been illustrated by numerous 
experiments in which the change in the hexavalent 
chromium content of the whetlerite during aging has 
been related to the CK life of the aged material. 52 
Magnetic susceptibility measurements on aging 
whetlerites 53 also indicate that the CK life is de¬ 
pendent on the presence of hexavalent chromium. 
Direct impregnations with trivalent chromium 
(which never exhibits any CK activity) also point 
toward the same conclusion. However, hexavalent 
chromium in the absence of copper seems to have no 
effect on CK protection. 

Preparation of ASC Solutions 

The solution used in the laboratory usually con¬ 
tains chromic anhydride and silver nitrate. Plant 
practice is to prepare a copper ammine carbonate 
solution by dissolving copper scrap in an aqueous 
solution of ammonia and carbon dioxide agitated by 


an air stream which also serves to oxidize the copper. 
As the copper goes into solution, gaseous ammonia 
and carbon dioxide are added to bring the compo¬ 
sition up to the desired level. When the copper, am¬ 
monia, and carbon dioxide reach the proper concen¬ 
tration, the solution is removed from contact with 
the copper, air is bubbled in until all the cuprous 
copper in the solution is oxidized, and the required 
quantities of chromic anhydride and silver nitrate 
are added. 

All calculations for the amounts of material to be 
added to the solutions should be based upon actual 
analyses of the compounds used, since the basic cop¬ 
per carbonate and ammonium carbonate are rarely 
of formula composition. An example of the purity 
and composition of the materials used in making up 
an ASC solution is given in Table 24. 

A small amount of ammonium hydroxide is re¬ 
served for dissolving the silver nitrate. The remainder 
is mixed with the water and chromic anhydride is 
added. The resulting solution of ammonium chro¬ 
mate in excess ammonia is used to dissolve the basic 
copper carbonate and ammonium carbonate. The 
solution is stirred until all materials are in solution. 
The solution of silver nitrate in ammonium hydroxide 
is added last. This order of solution avoids the liber¬ 
ation of carbon dioxide which occurs if the acid 
chromic anhydride is added to either of the carbon¬ 
ates before being neutralized. 
































68 


IMPREGNATION OF CHARCOAL 


Impregnation with ASC Solution 

Laboratory impregnation is carried out as follows: 
The charcoal, prepared by sieving to the proper mesh 
distribution, is placed in a beaker and an approxi¬ 
mately equal volume of solution is poured over it 
with stirring. The stirring is continued for a minute 
or two until the foaming has ceased and the charcoal 
is completely wet. The charcoal is then allowed to re¬ 
main in the solution for about 30 min. Although 
there is some evidence that the charcoal is completely 
impregnated after about 7 min, the 30-min period is 
used to allow a safety factor for any unknown vari¬ 
ations in the charcoal. After impregnation the 
“slurry” of solution and charcoal is poured into a 
cylindrical wire screen basket with a conical bottom, 
and allowed to drain. The basket is shaken vertically 
until only a few drops of solution are removed each 
time the basket is raised. By this method it is pos¬ 
sible to obtain reproducible solution-charcoal ratios 
of between 1.0 and 1.2 g of solution per g of charcoal, 
which is an optimum for good whetlerite perform¬ 
ance. The ratio should lie in this range for repro¬ 
ducible performance of the whetlerite. The drained 
material is then dried in a rotating drum drier. 54 

The laboratory rotating drum drier consists of a 
metal drum, 15 in. long and 8 in. in diameter, fitted 
with interior lifts to keep the charcoal moving while 
drying. The drum is mounted inside a well-insulated 
electric oven, and is rotated at a rate of 3 rpm by a 
small electric motor mounted outside the oven. The 
charcoal is heated by heaters installed within the 
oven, and by a stream of heated air which is blown 
through the rotating drum. Adequately baffled exit 
ports are provided to carry off the air and gases 
evolved during drying. The optimum operating con¬ 
ditions for this drier are as follows: 


Volume of charge 
Air flow 


Maximum charge temp 
Time at maximum temp 
Influent air temp 


1,200 ml (wet im¬ 
pregnated charcoal) 
75 1pm (linear 
flow of approxi¬ 
mately 94 in. 
per min through 
drum) 

180 C (±10C) 

30 min 
185-195 C 


The charge volume 1,200 ml corresponds to a load¬ 
ing of about 10% of the volume of the drum. Larger 
loading ratios require greater air flow through the 
drum to produce a high quality material. However, 


use of air flows greater than 75 1pm in drums of this 
design results in loss of product through the air vents. 

The drier is provided with two temperature con¬ 
trolling devices. A Fen well Thermoswitch controls 
one 500-watt heater and is activated by the air tem¬ 
perature outside the rotating drum. It is adjusted to 
turn the heater off at a temperature approximately 
30 degrees below the maximum charge temperature. 
The other device, a Capacitrol, is connected to a 
thermocouple in the charcoal bed, indicating the 
charge temperature and controlling another 500- 
watt heater. The lag at 180 C is approximately ± 5 C. 
Hence at maximum temperature the charge temper¬ 
ature variation is from 175 to 185 C. Having two 
heaters allows a rapid heating of the charge; by con¬ 
trolling one heater at a temperature 30 degrees be¬ 
low the maximum, slower final approach to the maxi¬ 
mum temperature and smaller variation at the maxi¬ 
mum temperature are obtained. The maximum tem¬ 
perature is not critical in the range between 150 and 
200 C. However, at 150 C a long heating period is 
required to reduce the ammonia content of the whet¬ 
lerite to the specification value, while at 200 C and 
higher there is danger of ignition of the whetlerite. 
The compromise maximum of 180 C for 30 min seems 
to be optimum. The total time of a run is about two 
hours, since it takes the 1,200-ml charge about 90 min 
to come to maximum temperature. 

Vapor Pressure of the ASC Solution 55 

The vapor pressures of NH 3 , C0 2 , and H 2 0 over 
Types A and ASC solutions were measured at 25 and 
50 C. The data for ASC are presented in Figures 10 
through 18. Because the data are valuable from the 
point of view of plant design, the complete set of 
curves is presented. Variations of the vapor pres¬ 
sures of all components when any one is varied are 
shown. 

Assuming that the Clausius-Clapeyron equation 
holds within the range of temperatures studied and 
for an additional 10 degrees below and 20 degrees 
above, the effect of temperature on the partial pres¬ 
sures of ammonia and carbon dioxide has been cal¬ 
culated. The effect of temperature on the partial 
pressure of ammonia in Type ASC solution is shown 
in Figures 19 through 22. Similar data for the carbon 
dioxide pressures are shown in Figures 23 through 26. 

The effect of adding chromium to Type AS solu¬ 
tion (producing Type ASC) is to lower the ammonia 
pressure and to raise the carbon dioxide pressure, as 






PRESSURE MM Hg 


COPPER—SILVER-CHROMIUM IMPREGNANTS 


69 



Figure 10. Effect of concentration of ASC-1 solution 
(at 25 C) on vapor pressure (partial pressure) of H 2 0, 
NH 3 , and C0 2 . (ASC-1 solution is diluted with water to 
the indicated concentrations; the 100% values are for 
undiluted solution.) 



Figure 11. Effect of varying ammonia content (10 
to 17%) ASC solutions at 25 C on partial pressure of 
H 2 0, NH 3 , and C0 2 . 



Figure 12. Effect of varying ammonia content (8 to 
16%) of ASC solutions at 25 C on partial pressure of 
H 2 0, NH 3 , and C0 2 . 



Figure 13. Effect of varying copper content (0 to 10%) 
of ASC solutions at 25 C on partial pressure of H 2 0, 
NH 3 , and C0 2 . 















PRESSURE MM Hg 


70 


IMPREGNATION OF CHARCOAL 



Figure 14. Effect of the concentration of ASC-1 solu¬ 
tion (at 50 C) on the partial pressures of H 2 0, NH 3 , and 
C0 2 . (ASC-1 solution diluted with water; the 100% 
values are for undiluted solution.) 



Figure 15. Effect of varying ammonia content (11 to 
17%) of ASC solutions at 50 C on partial pressure of 
H 2 0, NH 3 , and C0 2 . 



Figure 16. Effect of varying ammonia content (8 to 
16%) of ASC solutions at 50 C on partial pressure of 
NH 3 , H 2 0, and C0 2 . 



Figure 17. Effect of varying copper content (0 to 10%) 
of ASC solutions at 50 C on partial pressure of NH 3 , 
H 2 0, and C0 2 . 

















COPPER-SILVER-CHROMIUM IMPREGNANTS 


71 



Figure 18. Effect of temperature (C) on ammonia 
pressure of Type A solution and 55% Type A solution 
(diluted with water). 



Figure 19. Effect of temperature (C) on ammonia 
pressure of Type ASC solution and 55% Type ASC solu¬ 
tion (diluted with water). 


would be expected from the addition of any acidic 
component. 



Figure 20. Effect of temperature on ammonia pressure 
of three dilutions of Type ASC solutions (NH 3 variable). 



Figure 21 . Effect of temperature on ammonia pressure 
of Type ASC solution with different solutions (NH 3 
variable). 


Heats of Solution 

The integrated form of the Clausius-Clapeyron 
equation is 


where C is the constant of integration, and AH is the 
heat of solution of the vapor. Assuming that plots of 
In p versus 1/T are straight lines, and determining 
the vapor pressures of ammonia and carbon dioxide 


for the solution at 25 and 50 C, values of AH were 
obtained. The average values are given in Table 25. 

Table 25. Average heat of solution of the volatile 
constituents of whetlerizing solutions. 


Solution 

nh 3 

o 

o 

H 2 0 

Type A 

9.1 

15.9 

11.0 

Type ASC 

10.2 

15.6 

10.7 

As might have been predicted 

from 

the vapor 



















PRESSURE MM Hg PRESSURE MM Hg PRESSURE MM Hg 


72 


IMPREGNATION OF CHARCOAL 



22. Effect of temperature on ammonia pressure 
of Type ASC solutions (Cu variable). 



Figure 23. Effect of temperature on C0 2 pressure of 
Type ASC solution and of 55% Type ASC solution di¬ 
luted with water. 



Figure 25. Effect of temperature on C0 2 pressure of 
three dilutions of Type ASC solutions (NH 3 variable). 



Figure 26. Effect of temperature on C0 2 pressure of 
three dilutions of Type ASC solutions (Cu variable). 



Figure 24. Effect of temperature on C0 2 pressure of 
three dilutions of Type ASC solutions (NH 3 variable). 


pressure data or from a consideration of the types of 
solutions involved, the heat of solution of ammonia 
increased while that of carbon dioxide and water de¬ 
creased as a result of the addition of chromic an¬ 
hydride to Type A whetlerizing solution. 

These vapor pressure data should be useful in the 
calculation of the composition of the gases leaving 
the make-up tanks during the air-blowing procedure 
now used in the industrial whetlerizing plants. In 
addition, the composition of the gas leaving the re¬ 
covery tower can be calculated or approximated for 
known concentrations of recovery tower solution. 
The efficiency of such recovery processes might be 
improved or new systems designed on the basis of 
such data. 


























COPPER—SILVER-CHROMIUM IMPREGNANTS 


73 


Mechanism of Sorption of Chromium from ASC 
Solution by Charcoal 

The impregnation of charcoal with whetlerizing 
solution apparently involves only a sorption of the 
solution into the pores of the charcoal. Little or no 
reaction occurs during the relatively short time that 
the charcoal is in contact with the solution. 56 The 
data indicate that most of the chromium present in 
ASC whetlerite is not taken up by selective adsorp¬ 
tion from solution during impregnation, but remains 
after evaporation of the water from the solution con¬ 
tained in the pores of the charcoal. The adsorption 
of chromium from ASC solution is a very slow process 
which is accompanied by some reduction to the 
trivalent state. The trivalent chromium returns to 
the solution, and after a few days standing, is pre¬ 
cipitated as a complex basic carbonate, a gelatinous 
mixed precipitate of the following composition: 
Cr 2 0 3 , 32.8%; CuO, 6.8%; C0 2 , 20.8%; Si0 2 , 6.8%; 
NH 3 , 8.8%; H 2 0, 22.4%. The silica found in the pre¬ 
cipitate was apparently leached from the charcoal by 
the action of the impregnating solution over a period 
of several days. Coal base charcoals in particular 
have a large silica content. 

The mechanism for the formation of the precipi¬ 
tate may be postulated as follows: 

1. Charcoal + ASC solution —> hexavalent chro¬ 
mium adsorbed on charcoal 

2. Cr +6 adsorbed on charcoal —> Cr +3 adsorbed 
on charcoal 

3. Cr +3 adsorbed on charcoal —> Cr+ 3 in solu¬ 
tion + charcoal 

4. Cr+ 3 in solution —> Cr+ 3 precipitated. 

Data showing the rate of adsorption of chromium on 
CWS PCI-P58, 12 to 20 mesh, is shown in Table 26. 


Table 26. Adsorption of chromium from ASC solutions 
by charcoal CWS PCI-P58. 


Time, min 

%Cr +6 in solution 

0.0 

1.06 

9.0 

1.05 

14.0 

1.03 

31.5 

0.983 

67.5 

0.937 

120. 

0.917 

748. 

0.690 

3027. (2 days) 

0.467 


The time intervals involved in the experiment show 
that very little chromium is adsorbed from the solu¬ 
tion in the normal impregnation process since the 


time of contact is only thirty min. During this period 
only about 0.08% of chromium is adsorbed from the 
solution. It is evident that mechanical holding of the 
solution in the pores and voids accounts for practi¬ 
cally all of the chromium found on a whetlerite. 

When an aqueous solution of ammonium chromate 
is allowed to remain in contact with charcoal for sev¬ 
eral days, the chromium is adsorbed and partially 
reduced to trivalent chromium which remains on 
the charcoal. No trivalent chromium appears in 
the solution, as in the case of ASC solution. On char¬ 
coal the chromium is believed to be reactive with, or 
catalytic toward, the decomposition of CK when in 
the hexavalent state. Little direct evidence is avail¬ 
able to prove this point, because the state of the im- 
pregnant on charcoal frequently is so different from 
the ordinary state of the material that the usual 
X-ray diffraction experiments give little but the 
halos or fogs which indicate a very finely divided or 
amorphous condition. Analytical results, correlated 
with the change in CK life of ASC whetlerite on 
aging, indicate clearly that hexavalent chromium is 
involved in the removal of CK. In an effort to study 
the state of the impregnant without the drastic 
treatment involved in analytical procedures, mag¬ 
netic susceptibility measurements were made on a 
Gouy balance. 53 The large differences between the 
magnetic susceptibilities of compounds of copper and 
compounds of chromium suggested that the valence 
state of the impregnant might be determined by this 
means. The results indicated that: 

1. CuO on charcoal in a Type A whetlerite has a 
much higher susceptibility than it has normally. 
This may be caused by the fact that it is very finely 
divided, or that it is adsorbed molecularly and the 
carbon-copper oxide forces act as a diluting effect, 
increasing the susceptibility of the copper oxide. 
Large changes in the susceptibility of iron, cobalt, 
nickel, and manganese salts have been observed 
when they are adsorbed on charcoal, and these 
changes seem to be due to surface complex formation 
with the charcoal. 

2. The chromium on Type ASC charcoal changes 
to the trivalent form upon aging or absorption of CK. 
Previous work using analytical methods had pointed 
toward this conclusion. Furthermore, the magnetic 
measurements strongly indicated that after reduc¬ 
tion the chromium is present as Cr 2 0 3 -4H 2 0. The 
magnetic susceptibility of Cr0 3 is small while that 
of Cr 2 0 3 is very large. The change observed on ex¬ 
posing ASC whetlerite to CK was greater than 











74 


IMPREGNATION OF CHARCOAL 


could be accounted for by the formation of anhy¬ 
drous Cr 2 0 3 . Because there is more than enough 
water present to allow the formation of the hydrate, 
and since it forms readily, its presence is a reasonable 
explanation of the high linal susceptibility. 

Hexavalent chromium may be present on the char¬ 
coal as basic copper chromate (CuCr0 4 • 2CuO) or 
copper dichromate (CuCr 2 0 7 ). Both of these com¬ 
pounds exist as the dihydrate at room temperature. 
The basic chromate is the most probable compound 
under the conditions of deposition of the materials 
on the charcoal. The hydrates are: 

CuCr0 4 • 2CuO • 2H 2 0 (loses water at 260 C), basic 
copper chromate dihydrate. 

CuCr 2 07 • 2H 2 0 (loses water at 100 C), copper 
dichromate dihydrate. 

Although these materials, when on charcoal, may be 
sufficiently altered in their properties so that they 
lose water at a lower temperature than normal, it is 
possible that hydrates may exist even after being 
heated to 180 C, as is done in whetlerite preparation. 

There is some semi-quantitative data available 
that can be interpreted as favoring the existence of 
the basic copper chromate as the material active in 
the removal of CK. As shown in Figure 7, when an 
impregnating solution contains about 2% chromium, 
the CK life increases as the copper concentration of 
the solution is increased up to approximately 8% of 
copper, with no further increase at higher copper con¬ 
centrations. Thus, when the copper-to-chromium 
ratio reaches a value of about 4 to 1 there is no fur¬ 
ther increase in CK life. This implies that the copper- 
chromium compound or complex responsible for the 
CK activity of the whetlerite might contain copper 
and chromium in that ratio. In basic copper chromate 
(CuCr0 4 • 2CuO) the ratio is 3Cu/Cr = 194/52 or 
3.7 grams of copper per gram of chromium. 

If basic copper chromate is the material in ASC 
whetlerite which is active in the removal of CK, then 
any hexavalent chromium above that necessary for 
the formation of basic copper chromate would not be 
expected to increase the CK life. Therefore, it is in¬ 
dicated that the total amount of chromium on a 
whetlerite is no measure of the CK reactivity that 
can be expected of the whetlerite. For example, an 
ASC whetlerite treated with hexavalent chromium 
in secondary impregnations was found by analysis to 
contain a very large amount of hexavalent chromium. 
This material was found to have an unsatisfactory 
CK life. Although both copper and chromium were 


present, the copper-chromium complex apparently 
was rendered inactive by the layer of hexavalent 
chromium put on by the secondary impregnation. 

4.5.3 Mechanism of Removal of SA, AC, 
and CK by Type ASC Whetlerite 

A brief description of the mechanism of removal of 
the common test gases is given in the following para¬ 
graphs. A more detailed discussion of removal mech¬ 
anisms is to be found in Chapter 7. 

SA 

SA is removed by catalytic oxidation of SA to 
As 2 0 3 . The catalyst is predominantly silver, the 
action of which is apparently enhanced by the pres¬ 
ence of copper and chromium. 

CK 

The following reactions have been postulated for 
the removal of CK. 78 

1. 5CNC1 + 5H 2 0—>- 5HOCN + 5HC1 

2. 2HC1 + CuO—> CuCl 2 + H 2 0 

3. 3HC1 + Cr+ 6 —>■ %C1 2 + Cr+* + 3H+ 

Hexavalent chromium in combination with copper 
apparently functions as a hydrolysis catalyst. The 
HC1 produced by hydrolysis reacts with CuO until 
all the available CuO is used. Then the HC1 reacts 
with the chromates present resulting in the destruc¬ 
tion of the catalyst. Five moles of CK react with 
1 mole of hexavalent chromium as indicated above. 

AC 

The following mechanism is postulated: 

1. 2HCN + CuO —> Cu(CN) 2 + H 2 0 

2. 2Cu(CN) 2 —>Cu 2 (CN) 2 + (CN) 2 

3. (CN) 2 + Cr+ 6 ^ Cr +6 - (CN) 2 Complex 

The first two steps are identical with the mecha¬ 
nism postulated for the reaction of Type A impreg- 
nant with AC. The third reaction accounts for the 
absence of (CN) 2 in the effluent from the absorption 
of AC by Type ASC whetlerite. Apparently no re¬ 
duction of Cr+ 6 is directly involved. 

Variation of ASC Whetlerite Quality with 
Charcoal 

The reactivity of ASC whetlerites toward CK at 
80-80 conditions varies with the base charcoal. Indi¬ 
cations are that this variation is a function of the 
pore size distribution in the charcoal, 49 but the exact 


secki:i\ 





COPPER—SILVER-CHROMIUM IMPREGNANTS 


75 


relationship between the pore size distribution and 
the CK activity has not been developed. Apparently 
the manner in which water is absorbed by the char¬ 
coal and in which the pores are filled is an important 
factor. 57 Using CWS PCI-1042 and CWSN-S5 char¬ 
coals (12 to 16 mesh), a study was made of the effect 
of water content on the SA, AC, and CK lives of the 
corresponding whetlerites. The PCI whetlerite was 
found to give ample protection for all three test gases 
up to and including equilibration at 97 to 100% RH. 
The SA and AC lives were almost independent of the 
moisture content of the whetlerite, while the CK 
lives decreased approximately linearly from 130 min 
at zero water content to 46 min at the maximum 
(33.3% water). 

The N-S5 whetlerite gave adequate AC protection 
over the entire range. The SA lives dropped steadily 
above 35% RH, and became zero at 85% RH. The 
CK lives dropped rapidly above 30% RH, and be¬ 
came zero at 60% (35.2% water absorbed). Five-cen¬ 
timeter tube test conditions were used in both cases. 

Thus when the two whetlerites have absorbed 
about the same amount of water (although at differ¬ 
ent humidities), one has an adequate CK and SA 
life and the other does not. The fact that the N-S5 
has absorbed enough water to bring the reactivity to 
zero at 60% RH while the PCI-1042 never absorbs 
enough to do this even at 97 to 100% RH seems to 
indicate that the pore structure involved is the de¬ 
termining factor (see Chapter 6). 

Deterioration of ASC Whetlerites 

The greatest disadvantage of ASC whetlerite is its 
tendency to lose CK reactivity on standing equi¬ 
librated in a tightly closed container. Under these 
conditions a reduction of the hexavalent chromium 
takes place 58> 52 which results in poor CK perform¬ 
ance. There is also some loss of AC life under the 
same conditions, but this effect is not as serious, par¬ 
ticularly under field conditions. ASC whetlerite 
stored dry in a sealed system shows negligible aging. 
Equilibrated and stored in air, C0 2 , NH 3 , 0 2 , or N 2 , 
it shows deterioration in every case. The deteriora¬ 
tion was greatest in C0 2 , least in NH 3 , and inter¬ 
mediate in air, 0 2 and N 2 . 

It is believed that the variation in the rate of aging 
in the presence of NH 3 and C0 2 is attributable to 
their effect on the pH, since in reactions involving 
chromate ion the concentration of hydrogen ion is 
important. If true, the reduction of the hydrogen ion 
concentration effected by the NH 3 atmosphere would 


be expected to reduce the rate of aging. Because the 
data show that such reduction in rate does occur, 
this possibility should be borne in mind when con¬ 
sidering aging reactions. However, the rate of aging 
even in ammonia was not negligible. Attempts to use 
the control of pH as a means of eliminating aging 
have not been successful. Spraying the whetlerite 
with sodium hydroxide, or inclusion of sodium hy¬ 
droxide in the impregnating solution were not ef¬ 
fective enough to be useful. 

ASC whetlerite, AS whetlerite, and base charcoal 
when equilibrated and stored in closed containers for 
two to four days at 50 C completely removed all of 
the oxygen from an approximately equal volume of 
air. The rate of adsorption of the oxygen decreased 
as the amount of water on a particular sample of 
whetlerite or charcoal decreased. It was also noticed 
that unimpregnated charcoals, if stored equilibrated 
in sealed containers at about 50 C for three weeks, 
became unsuitable for conversion to ASC whetler¬ 
ites. 59 Some base charcoals, after aging, produced 
whetlerites with CK 80-80 tube lives 50% as large as 
those of the un-aged charcoal, while others gave lives 
of less than 10% of the un-aged material. The effect 
was evident whether the aged material was dried by 
evacuation before whetlerization, or whetlerized in 
the equilibrated condition. The fresh material pro¬ 
duced whetlerite of the same CK life whether the 
material was equilibrated before impregnation or 
not. Heating the aged, wet charcoal at 100 C for 
three hours, or soaking the material for six hours in 
ASC solution, produced in most cases a whetlerite 
that had a CK life approximately equal to that pro¬ 
duced from the original material. Only certain zinc 
chloride activated charcoals, which ordinarily showed 
excessive aging when converted to ASC whetlerite, 
failed to respond to these treatments. Tube tests of 
the whetlerites prepared from aged charcoals fre¬ 
quently showed a large number of breaks before the 
true breakpoint was reached, in some cases running 
to as many as 12 breaks. This indicates that the 
activity of the whetlerite is low, resulting in a slow 
removal of CK and, with the particular bed depth 
used (5 cm), resulted in a slow leakage of CK through 
the tube prior to the true breakpoint (when the con¬ 
centration of CK in the effluent increases rapidly). 

On the basis of the foregoing data, certain specu¬ 
lations as to the nature of the aging process may be 
made. For both base charcoal and whetlerite, the 
first step in aging is the same, that is, formation of a 
layer of adsorbed water. The character of this layer 







76 


IMPREGNATION OF CHARCOAL 


is dependent on the nature of the charcoal surface 
prior to water adsorption, which in turn is dependent 
upon the source of the material and the process used 
in the activation of the charcoal. 

In view of the fact that some oxygen is probably 
present on the charcoal surface before the water is 
adsorbed, there are at least two processes by which 
the chromium compound in ASC whetlerite can be 
rendered inactive as a catalyst or a reactant: 

1. Reaction of the carbon-oxygen-water surface 
complex with hexavalent chromium, destroying the 
catalyst or reactant by reduction. 

2. Destruction of the active copper-chromium 
compound or mixture by a reaction (with water or 
carbon dioxide) not involving the reduction of 
chromium. 

The first postulate seems to be the most likely. It 
has been observed that ASC whetlerites which con¬ 
tain water do not deteriorate as rapidly when stored 
in containers which do not seal them from contact 
with the atmosphere (canisters, for example), as they 
do when stored in tightly sealed containers. If it be 
assumed that the carbon-water-oxygen surface com¬ 
plex is more easily oxidized by atmospheric oxygen 
than by the hexavalent chromium present, then the 
above observation and the absorption of oxygen 
from the air in storage containers are explained 
readily. 

The aging of base charcoals appears to proceed 
also by formation of a surface complex. When base 
charcoals are allowed to age in a sealed container, 
they remove oxygen from the air. The adsorbed oxy¬ 
gen may form an extensive layer or layers of surface 
complex. (The charcoal must be equilibrated before 
the rapid oxygen adsorption takes place.) The com¬ 
plex thus formed may react with ASC impregnant 
put on the charcoal to form a layer of trivalent chro¬ 
mium on the charcoal surface, thus rendering the 
surface inactive. 

Another possibility is that the surface becomes 
strongly hydrophobic when the carbon-oxygen- 
water surface complex forms. It is known that the 
carbon-oxygen surface complex formed on charcoals 
at about 400 C is more hydrophilic than the oxygen 
complexes formed at lower temperatures. 60 It is pos¬ 
sible that the complex formed under the conditions 
of aging may cause the surface to be hydrophobic 
enough to prevent the whetlerizing solution from 
entering the fine pores of the charcoal. 

Extensive studies of the aging of ASC whetlerites 
under field conditions and simulated field conditions 


have been carried out 61 (see Chapter 5). The results 
show that for field service under fairly rigorous con¬ 
ditions of temperature and humidity (85 F and 
above, 70 to 90% RH), an ASC whetlerite prepared 
from a PCI or a Seattle-wood charcoal and used in 
an M10A1 canister and carrier is satisfactory from 
the standpoint of CK protection. With respect to 
SA, AC, or CG, some deterioration of the whetlerite 
has been found in laboratory tests (sealed and equi¬ 
librated), but under field conditions in the M10A1 
canister this has been negligible. 

ASC whetlerites, when aged, lose activity more 
rapidly than capacity. Hence canisters with high 
flow rates or thin beds show more pronounced aging 
effects than do canisters with low flow rates or thick 
bed depths. The M-ll assault canister presents a 
problem from this point of view because of its short 
bed depth, and because it is carried in an air-tight 
carrier which, in hot humid climates, provides ex¬ 
cellent conditions for the deterioration of ASC whet¬ 
lerite, particularly after having been partially hu¬ 
midified by being worn for some time. 

Pilot Plant Production of ASC Whetlerite 65 

The best operating conditions for plant production 
of ASC whetlerite were determined in pilot plant 
studies. The product was evaluated on the basis of 
CK 80-80 lives, and the ammonia content of the fin¬ 
ished whetlerite. It was found that when these prop¬ 
erties were satisfactory, other properties were also 
satisfactory. 

The most critical step in the production of ASC 
whetlerite is drying. The impregnation step can be 
varied over wide ranges without having an appre¬ 
ciable effect on the quality of the product. 

A complete description of the pilot plant equip¬ 
ment can be found in an OSRD report. 66 The plant 
consisted essentially of two parts, the impregnator 
and the drier. The impregnator consisted of a sheet 
iron tank with a 4-ft screw (23^ in. in diam and 2-in. 
pitch) leading from the bottom at an angle from the 
horizontal that could be varied between 20 and 40 
degrees. The liquid level in the lower trough could be 
adjusted to cover up to one-half of the screw length 
by means of a variable overflow pipe. Screw speed 
was adjustable to four values (5.8, 4.5, 3.5, and 
2.8 rpm). Charcoal was introduced from a tank stor¬ 
age hopper by means of calibrated orifices. With 
PCI activated, charcoal orifices from 1 %4 to 
1 %4 in- i n diameter permitted a flow of charcoal of 
0.15 to 0.30 lb per min. Impregnating solution flow 





COPPER-SILVER-CHROMIUM IMPREGNANTS 


77 


was maintained constant by gravity through an over¬ 
flow Weir meter. Both solution and charcoal entered 
the tank at the same point where they were thor¬ 
oughly mixed by an electric stirrer to assure uni¬ 
formity of impregnation. The impregnator could be 
adjusted to deliver a wet fe*ed stock containing from 
0.75 to 1.1 lb of solution per lb of dry charcoal. The 
screw delivered the wet feed stock either to a storage 
crock from which it was transferred to the drier by 
hand, or to the drier storage hopper from which it 
was introduced into the drier by means of a screw 
mechanism, at a controlled rate. 

The drier was constructed from three sections of 
standard 8-in. steel pipe. It was 10 ft long, externally 
heated by four 60-ft sections of straight 14-gauge 
Chromel A resistance wire wound directly over two 
insulating layers of asbestos tape. A coil was wound 
on each end-section, and the remaining two 60-ft 
lengths wound on the middle section of the drier. 
Electric contact was furnished by five commutator 
rings. The exterior surface of the drum was lagged 
with 1 in. of 85%, magnesia pipe covering. Temper¬ 
atures of the walls and charge were taken from 
built-in thermocouples. The heaters were separately 
controlled to provide a definite heating schedule for 
the charge as it passed through the drum. The com¬ 
plete drier was mounted on a supporting framework, 
fabricated from standard steel forms. It was rotated 
by a pair of idling and a pair of motor-driven grooved 
pipe-rolls. The slope of the drum was varied by 
means of a hinge-and-jack system. The drum was 
constructed to receive a blower at either the feed or 
discharge end, so that the air flow could be either 
countercurrent or parallel, and an electric heater was 
provided to heat the air when desired. The discharge 
was arranged so that the product could be collected 
in the absence of air, although in normal operation 
the product was discharged directly into cans in free 
contact with the air. 

Using the pilot plant, the optimum operating con¬ 
ditions discussed in following paragraphs were de¬ 
termined with respect to CK protection. 

Charge Temperature. With plentiful air flow, a 
maximum charge temperature up to 400 F (205 C) 
has no deleterious effect on CK life. Above 400 F, 
and up to ignition temperature, the evidence is in¬ 
conclusive, but indications are that some reduction 
of CK life takes place. 

Ignition temperature varies for each charcoal, as 
is shown in Table 27. 81 

With a limited air flow, the CK life reaches a maxi¬ 


mum at a temperature well below ignition tempera¬ 
ture, although the life is lower than the maximum 
life reached with plentiful air flow. Ammonia con¬ 
tent also is dependent on maximum temperature at 
any given flow rate. For standard conditions (air 
flow rate of about 1.5 linear fps), the ammonia con¬ 
tent of the whetlerite was about 0.2% at 370 to 390 F. 


Table 27. Ignition temperature of whetlerites made 
from various charcoals. 



Ignition 

Material 

temperature 


F 

C 

PCI activated charcoal B1196 

>542 

>283 

National Carbon charcoal CWSN196B1X 

>542 

>283 

PCI-ASC containing 1% NaOH, run WR-7811 440 

227 

PCI-ASC BD1063 

438 

226 

Barnebey-Cheney nutshell ASC, drum A116 

435 

224 

PCI-ASC, run WR-52 

428 

220 

Seattle ASC, drum B-825 

420 

216 

National Carbon ASC CWSN196B1X ASC 

385 

196 

PCI E-ll 1.5% pyridine, run WR-40 

375 

190 

Seattle E-ll, 0.8% pyridine, drum B837 

375 

190 

Seattle E-ll, 2.0% pyridine, drum B846 

343 

173 


Temperature Schedule. Extremely rapid increase 
in temperature during heating is detrimental to CK 
life. A moderate heating rate is desirable so that the 
whetlerite reaches maximum temperature in 40 to 
60 min. The retention time (time in the drier) has no 
visible effect as long as the whetlerite is not heated 
too rapidly. A total time of about 30 min at maximum 
temperature is desirable, which in turn results in a 
retention of from 70 to 90 min. Proper control of the 
feed-end heater, speed of rotation, and pitch of the 
drum results in the desired rate of heating and re¬ 
tention time. 

Air Flow. Air flows less than 0.8 linear fps coun¬ 
tercurrent through the drier, or 3 fps parallel-flow, 
resulted in inferior CK life. The effect is caused by 
the influence of the vapors in contact with the drying 
whetlerite. The air acts as a diluent, reducing the 
rate of whatever deleterious reactions take place in 
the presence of high concentrations of vapors of H 2 0, 
C0 2 , and NH 3 . Parallel flow is the most objectionable 
because the dried whetlerite is in contact with the 
moist saturated air, whereas in countercurrent flow 
the dried whetlerite comes in contact only with fresh, 
dry air. The most convenient flow rate was found to 
be approximately 1.5 linear fps (80 F basis), or 
90 fpm, in good agreement with laboratory driers 
which operate at a flow of 94 linear fpm. 

All data point toward the conclusion that during 







78 


IMPREGNATION OF CHARCOAL 


the drying operation (especially at the higher tem¬ 
peratures), the whetlerite must not be exposed to 
high concentrations of H 2 0, C0 2 , or NH 3 vapors. It 
is not known which gas is the most harmful. 

Flue Gas Atmosphere. A large proportion of ex¬ 
cess air is necessary if flue gas is used in the drier. 
Low C0 2 and H 2 0 vapor concentrations cannot be 
maintained in the drier if undiluted flue gas is used 
as a drying agent, and lowered CK life results. 

Back Feeding. In order to obtain a free-flowing 
feed stock, dried product is sometimes mixed with 
the wet feed stock. No material effect on the product 
was observed when up to 50% of the dried product 
was used as feedback. Other experiments using a dif¬ 
ferent material as feedback resulted in a product ap¬ 
proximately equivalent to that obtained by mechan¬ 
ically mixing the feedback material with the product 
obtained without using any feedback in the drier 
feed stock. This indicates that the whetlerite is not 
improved by a second passage through the drier in 
company with some wet material . 67 Therefore, in¬ 
ferior feedback stock is not desirable. 

It was found that 30% or more of dry feedback 
gave a dry, free-flowing feed material, whereas 20 % 
feedback resulted in a rather cohesive material. With 
the drier used in pilot plant productions, 20 % was 
sufficient to prevent caking. Other driers of different 
heating characteristics may have different require¬ 
ments. 

Variation of the feed rate, liquid content of the 
feed stock, or drier loading had no effect on the qual¬ 
ity of the product. 

4.5.4 Evolution of Ammonia by Type 
ASC Whetlerites 

Type ASC whetlerites require careful temperature 
control during drying to avoid de-activation of the 
catalyst by overheating. Type A whetlerites can be 
heated to much higher temperatures without dele¬ 
terious effects. Consequently, when the plant pro¬ 
duction of Type ASC whetlerite using Type A plant 
equipment was started in 1943, some trouble was en¬ 
countered in temperature control and frequent over¬ 
heating resulted. When it became definitely estab¬ 
lished that good quality Type ASC whetlerite could 
be produced at lower temperatures, many lots of in¬ 
sufficiently heated whetlerite were produced. These 
materials had a relatively high ammonia content, and 
evolved ammonia vapor when moist. Use of such 
whetlerite in canister fillings in the tropics (where 


the whetlerite soon absorbed appreciable amounts of 
water from atmosphere) resulted in the evolution of 
large amounts of ammonia with consequent discom¬ 
fort to the person using the canister. 

As soon as the situation was realized, measures 
were taken to prevent the production of such whet¬ 
lerites, and a specification test was devised to detect 
samples which evolve obnoxious amounts of am¬ 
monia when equilibrated at 80% RH. Samples which 
cannot meet this specification are rejected. 

The preparation of whetlerites containing large 
quantities of ammonia is prevented by careful con¬ 
trol of the drying temperature (at about 380 F, ± 
10 degrees), and use of an adequate air flow through 
the drier. Such treatment results in a whetlerite 
which contains approximately 0.15% total ammonia, 
and which when equilibrated and used in a canister 
will evolve less than 10 to 20 7 per 1 a of ammonia at 
normal breathing rates. 

The intensity of the odor of ammonia, and its ef¬ 
fect on an observer varies with the sensitivity of the 
observer and with his conditioning. If the observer 
expects to find the odor of ammonia, he may be able 
to detect it at concentrations less than 10 7 per 1 , but 
will not find concentrations as high as 25 to 30 7 per 1 
unendurable. On the other hand, unprepared ob¬ 
servers have a higher threshold for the odor, but will 
usually find the odor intolerable at a lower concen¬ 
tration than the prepared observers. Therefore, in 
tropical field tests of Type ASC whetlerite which 
contained rather high concentrations of ammonia, 
troops who were prepared for the odor of ammonia 
while wearing their gas masks rarely found a canister 
which evolved intolerable concentrations. 

Extensive tests of recently produced Tj^pe ASC 
whetlerite which meets ammonia evolution specifica¬ 
tions have shown that in tropical regions an odor of 
ammonia will usualty develop in a canister that has 
been worn long enough to moisten the whetlerite 
appreciably, but the odor is slight and does not be¬ 
come completely intolerable. 

Leaching and Rewhetlerization 

In an effort to determine the cause of the variation 
observed in plant whetlerites made from apparently 
uniform, high quality charcoals, a study was made of 
variations in whetlerizing techniques. In some cases 
the primary whetlerite was leached with hydro- 


a Normally the odor of ammonia cannot be detected at 
concentrations less than 10 to 12 7 per 1 (1 7 = 0.001 mg). 








COPPER-SILVER-CHROMIUM IMPREGNANTS 


79 


Table 28. The effect of rewhetlerization on the performance of whetlerites. 


% Cu in rewhetlerizing 
solution* 

% Cu 

%Cr 

% Cr 4-6 

Cr 4 * 

Cr 

Service life 
CK 80-80 
M10A1 min 

%h 2 o 

equilibrium 

80% RH 

Original lot AD3-749 

5.94 

1.52 

0.78 

0.51 

56, 50, 50 

24.7 

2.5 

7.57 

2.63 

1.86 

0.71 

91, 82 

24.7 

2.5 

6.32 

2.80 

1.73 

0.62 

69, 66 

25.5 

5.0 

6.48 

2.89 

1.87 

0.65 

111, 90 

23.0 

5.0 

7.78 

2.63 

1.75 

0.87 

107, 96 

23.4 

8.0 

9.33 

2.18 

1.70 

0.78 

98, 81 

22.6 

8.0 

9.76 

2.22 

1.70 

0.77 

98, 77 

22.9 


*1.8 per cent Cr present in all rewhetlerizing solutions. 


Table 29. The effect of multiple whetlerization on CG life. 




M10A1 canister lives, min 

% h 2 o 

Sample 

Description 

\ 

CG 

PS 

equilibrium 

80% RH 



80-80 


0-50 

80-50 (tube life) 

PC 518 

PCI charcoal not whetlerized 

44, 46 


9, 10 

31, 35 

29.2 

6727 

PC 518 whetlerite 

53, 52 


55, 55 

28, 22 
(45, 43)* 

26.2 

6728 

6727 rewhetlerite 

38, 45 


51, 44 

21.4 

6739 

6728 rewhetlerite 

30 


38 

.. .. 

24.3 


* Unlikely result. 


chloric acid, ammonia, and water, then rewhetler- 
ized. With other samples of whetlerite, a simple re¬ 
whetlerization with ASC-1 solution without any 
previous leaching treatment resulted in phenomenal 
increases in the CK M10A1 canister lives. 69 A series 
of experiments was made in which the solution used 
for rewhetlerization contained from 2.5 to 8% copper, 
and 1.8% chromium. The results are given in Table 
28. 

It can be seen that the CK canister life has been 
approximately doubled by the use of ASC-1 solu¬ 
tion (5% Cu), resulting from a combination of in¬ 
creased hexavalent chromium and increased copper 
on the whetlerite. It will be noticed that using an 8% 
copper solution resulted in a slightly lower CK life, 
although the lives are not low enough to be signifi¬ 
cant. 

Life-thickness curves for the original and rewhet- 
lerized product show that rewhetlerization resulted 
in an increase in capacity without changing the criti¬ 
cal layer depth appreciably. 

A study was made of the rewhetlerization of vari¬ 
ous grades of whetlerite from various sources. In 
many cases Grade II whetlerite (CK M10A1 can¬ 
ister life of less than 35 min) produced a Grade I 
whetlerite having at least twice the life of the original 
material. Grade II PCI whetlerites are usually more 
responsive to this treatment than a material like a 
Barnebey-Cheney whetlerite because the base char¬ 


coals are capable of producing a better whetlerite. 
The second whetlerization simply realizes the full 
possibilities of the charcoal. 

It was noticed that CG protection seemed to drop 
on rewhetlerization although not seriously. A second 
rewhetlerization lowered the CG life even more. 
These results are shown in Table 29. 

These tests were made at 50-lpm intermittent flow. 
At 32-lpm steady flow, there is an increase in the 
CG AR-50 lives on rewhetlerization; (40, 42 before 
rewhetlerization; 60, 64 after). This indicates that an 
increase in capacity and a decrease in activity for 
CG has occurred. The PS data are too scanty to 
allow any conclusions. 

Leaching of whetlerite is carried out as follows: 
The whetlerite is boiled with an equal volume of 
1/1 HC1 (approximately 6 N) for 10 min, then 
washed free of acid with water, treated again with 
acid, washed with water, and the process repeated 
with 6 N NH 4 OH. After being washed until neutral, 
the material is drained and dried at 150 C in the 
laboratory rotary drier. 

After leaching, the charcoals are whetlerized as 
usual. The results of leaching on a Grade II and a 
mediocre Grade I are shown in Table 30. The results 
of various studies on the treatment of activated 
charcoal with different solutions prior to whetler¬ 
ization are shown in Table 31. Various types of oxi¬ 
dizing agents were used. It appears that leaching and 




























80 


IMPREGNATION OF CHARCOAL 


Table 30. Effect of leaching on the performance of rewhetlerized charcoal. 


Sample 

Description 

CK 

80-80 

CG 

AC 

on QA 

% h 2 o 

equilib¬ 

Whetlerite analysis 


80-50 

0-50 

oU—oU 

rium 

%Cr 

% Cr 6 

Cu 

% Ag 

BD 1518 

Grade II PCI 

27, 27 

44 

. # 

54 


1.50 

0.70 

9.48 

0.28 

6731 

Above rewhetlerized 
ASC-1 solution 

64, 63 



68 , 71 

24.4 

1.97 

1.81 

5.07 

0.25 

BD 1518L 

BD 1518 leached 

. . . 



. . 


0.06 

0.02 

0.50 

0.14 

6730 

Above rewhetlerized 

EASC solution 

68 , 78 

51, 45 


69, 70 

24.5 

1.67 

1.36 

7.80 

0.38 

AD3 1549 

Grade I PCI 

39, 30 

52, 50 

49, 45 

57, 57 

26.1 

1.56 

0.89 

5.70 

0.20 

6737 

Above rewhetlerized 
ASC-1 solution 

75, 65 

49, 49 

36, 31 

103, 74 

25.4 

2.17 

1.73 

6.74 

0.16 

Above leached 



.. 



.. 

0.03 

0.00 

0.00 

0.15 

6732 

Above rewhetlerized 

EASC solution 

66 , 70 



68 , 70 

25.6 

1.69 

1.48 

7.15 

0.14 


« 


Table 31. Studies of the leaching process. 




%h 2 o 

Pickup 



Cr 6 



M10A1 
canister lives 

Sample 

Treatment 

Cr 

Cr 6 

Cr 

Cu 

Ag 

CK 

80-80 

CG 

80-50 

TNW 6741R-A 

PC518 whetlerized EASC solution 

24.8 

1.74 

1.06 

0.61 

7.27 

0.43 

58, 60, 61 


TNW 6741R-B 

Product A leached 


0.14 

0.001 


0.00 

0.23 



TNW 6741R-C 

Product B whetlerized with ASC solution 

25.2 

1.61 

1.40 

0.869 

7.19 

0.57 

76, 78, 78 


TNW 6741R-D 

PC518 (Activated charcoal) leached and 
dried as Product B, then whetlerized 
with ASC solution 

26.4 

1.54 

1.21 

0.786 

6.08 

0.29 

66 , 69, 71 


TNW 6751R 

PC518 boiled with 1/1 HC1 and 2 % Cr0 3 
(char basis), washed, dried, and whet¬ 
lerized with ASC 

24.7 

1.51 

1.18 

0.782 

9.04 

0.24 

61, 55, 59 

56 

TNW 6752R 

PC518 boiled with 2 N H 2 SO 4 and 2% 
Cr0 3 ; washed, dried and whetlerized 
ASC 

25.1 

1.58 

1.10 

0.692 

6.79 


56, 57 

52 

TNW 6758R 

PC518 soaked in 1/1 HN0 3 for 15 min¬ 
utes, washed, dried and whetlerized 
with ASC 

25.2 

1.48 

1.25 

0.845 

6.07 

0.16 

74, 55, 66 

41 

TNW 6762R 

TNW 6758R repeated 

24.0 

1.51 

1.14 

0.755 

7.21 


54, 71, 60 

45 

TNW 6763R 

PC518 soaked 30 min in ASC solution, 
washed, boiled with- 1/1 HC 1 , washed, 
boiled with 1 /I NH 4 OH, washed, dried 
and whetlerized with ASC 

23.2 

1.65 

1.16 

0.703 

8.79 


53, 56, 53 

54 


rewhetlerization are slightly more effective than 
whetlerization alone, but not sufficiently so to justify 
the additional treatment. 

The results on the use of oxidizing agents prior to 
whetlerization are not conclusive. Better results were 
obtained by double whetlerizations than by a whet¬ 
lerization preceded by any other treatment. 

In every case where production PCI whetlerites 
were leached and rewhetlerized, a very striking in¬ 
crease in CK 80-80 M10A1 canister life occurred. 
However, laboratory-prepared samples given the 
same treatment did not show as great an improve¬ 
ment, apparently because they were prepared under 


controlled conditions which initially came closer to 
realizing the full possibilities of the charcoal. It 
would appear that faulty plant operation was the 
cause of many mediocre or poor whetlerites. Ad¬ 
mittedly the leaching and rewhetlerization process in 
itself does result in improvement, but the amount of 
improvement caused by this treatment does not ac¬ 
count for the remarkable difference in CK 80-80 pro¬ 
tection between some plant whetlerites and the 
leached and rewhetlerized materials prepared from 
them. Present plant practice usually produces excel¬ 
lent products, ordinarily as good as those prepared 
by laboratory procedures. 
























































COPPER-SILVER-CHROMIUM IMPREGNANTS 


81 


Table 32. Results of spraying or soaking Types A or AS whetlerites in chromium solutions. 


Charcoal 

Treatment 

SA 

80-80 

AC 

80-80 

CK 

80-80 

%h 2 o 

equilibrium 

PCI-P58 

Type AS sprayed with 3.4% aqueous Cr0 3 

45 

123 

82 

23.1 

PCI-P58 

Type AS soaked with 3.4% aqueous Cr0 3 

32 

139 

116 

25.0 

PCI-P58 

Type AS soaked in (NH 4 ) 2 Cr0 4 , aqueous 


139 

204 


PCI-P58 

Type AS soaked in (NH 4 ) 2 Cr0 4 aqueous in excess NH 3 

83 

99 

138 


PCI-P58 

Type AS soaked in ASC solution 

161 

136 

172 



Conversion of Types A and AS Whetlerites to 
Type ASC 

In the early work on ASC whetlerite, it was found 
that a Type A whetlerite prepared from PCI char¬ 
coal could be converted to an ASC whetlerite having 
the good qualities of one prepared directly from the 
base charcoal in one step. 50 Spraying or soaking the 
Type A whetlerite with an aqueous solution of Cr0 3 
or with a solution of (NH 4 ) 2 CrCh in excess ammonia 
resulted in a product with CK activity. Best results 
were obtained by soaking in an ammoniacal solution. 
Later results 82 indicate that even better results are 
achieved by the use of a solution containing carbon¬ 
ate. This behavior suggests again that the chromium 
and copper must be in chemical combination in order 
to be active, since both an ammoniacal and a carbonic 
solution favor the solution of copper from the Type A 
whetlerite, allowing it to combine with the chromate 
present in the solution before being redeposited upon 
the surface of the charcoal. In Table 32 are shown 
some tube test results obtained in experiments of 
this kind. 50 

It will be noticed that the best results on the basis 
of tube tests were obtained by use of an ASC solu¬ 
tion. Later work on the solution used for conversions 
has shown that a solution containing 8% NH 3 , 5% 
C0 2 , 3.5% Cr0 3 , and 0.4% AgN0 3 produces the 
best results. 82 Presence of soluble copper, in addition 
to hexavalent chromium, is essential to the develop¬ 
ment of CK life; the solution described dissolves 
enough from the Type A whetlerite to produce a 
good product. An excess of copper tends to reduce 
PS life. 

Not all Types A and AS whetlerites which are avail¬ 
able in quantity can be converted to a satisfactory 
ASC whetlerite. These materials were produced from 
base charcoals made before the effects of pore struc¬ 
ture of charcoal on its suitability for an ASC whetler¬ 
ite were known. It is not possible to produce a Grade 
I whetlerite from base charcoal of some types, and it 
is equally impossible to convert Types A and AS whet¬ 
lerites made from such base material into Grade I 


ASC. Various studies on this problem 68 - 79 - 80> 82 
have shown that few of the converted whetlerites 
are Grade I because of: (1) failure in PS protection 
by PCI-converted whetlerites; (2) failure in SA pro¬ 
tection by Atlas and Barnebey-Cheney Type A whet¬ 
lerites (converted); (3) failure in CK protection by 
Barnebey-Cheney Type AS whetlerites (converted). 

Type ASC whetlerites of borderline quality may 
be obtained by reimpregnation of existing stocks of 
Type A and AS whetlerites, with the probability of 
getting very little Grade I whetlerite, especially from 
Barnebey-Cheney charcoals. 

It was thought that an additional activation treat¬ 
ment might possibly improve the qualities of certain 
Type A and AS whetlerites which could not be con¬ 
verted to ASC whetlerite. Experiments on reactiva¬ 
tion have shown that such procedure is not fruitful. 
Reactivation seems to injure PCI and Atlas Type A 
whetlerites, and to have no effect on Barnebey- 
Cheney Type AS whetlerites. 

At this time it does not appear that reworking 
charcoals is a useful process. Grade II whetlerites 
that can be improved by reimpregnation are used as 
backfeed to an extent governed by the quality of the 
product obtained. The materials that cannot be im¬ 
proved by any treatment are too poor to be used as 
backfeed. Because the only materials that can be 
treated by the reimpregnation process find a use 
elsewhere, there seen;s to be little advantage in de¬ 
veloping the process further. 

4.6 ORGANIC BASE IMPREGNATIONS 
OF CHARCOAL 

4.6.1 Reactions of Certain Organic Bases 
with CK 

The general reaction of CK with primal and 
secondary amines is as follows: 62 

RNH 2 + CNC1—> HC1 + RNH-CN /substituted\ 
R 2 NH + CNC1 —^ HC1 + R 2 N-CN Vcyanamidesy 
















82 IMPREGNATION OF CHARCOAL 


Table 33. Organic bases used as specific charcoal impregnants for CK. 

Diethylene triamine 

N-ethyl morpholine 


Triethylene tetramine 

N-aminoethyl morpholine 


Tetraethylene pentamine 

N-hydroxyethyl morpholine 


Ethylene diamine 

Piperidine 


Diethanol diamine 

Piperazine hexahydrate 


Monoethanol amine 

Ammonium nicotinate 


Diethanol amine 

Nicotine 


Triethanol amine 

Pyridine 


Ethyl monoethanol amine 

0-picoline 


Ethyl diethanol amine 

Y-picoline 


Dipropyl amine 

0-7 picoline, commercial mixture 


Diisopropanol amine 

Aniline 


Dibenzyl amine 

Imidazole 


Benzyl ethyl amine 

N-ethyl acetamide 


Diisoamyl amine 

Amino guanidine 


Morpholine 

Isoquinoline 



The HC1 formed reacts with excess amine to form the 
amine hydrochloride. 

The reaction takes place readily and was the basis 
for the use of amines as specific charcoal impreg- 
nants for the absorption of CK. Extensive research 
has been carried out on a large number of organic 
bases in exploratory impregnations. Many of them 
have proven to be capable of yielding an absorbent 
with a rather large capacity for CK. A list of the or¬ 
ganic impregnants which removed CK is shown in 
Table 33. 62 - 63 - 89 No attempt has been made to show 
the test lives of these materials because test condi¬ 
tions varied with the source of the experimental 
work. All materials shown produced an absorbent 
much better than the original unimpregnated char¬ 
coal. 

Of these materials, the most useful appeared to be 
pyridine, the picolines, and N-ethyl morpholine. The 
reaction of CK with pyridine, and 0- and y-picoline 
is analogous to the reaction with a primary or second¬ 
ary amine, except that it is the hydrogen atom on the 
carbon atom adjacent to the nuclear nitrogen which 
reacts thus: 


HC 

HC 


N 


\ 

CH 

I 

CH 



+ CNC1 


HC 

HC 


N 


\ 


C-CN + HC1 


CH 


✓ 


a-picoline (a-methyl pyridine) is not active as a 
charcoal impregnant for CK because there is no re¬ 
active hydrogen on one of the carbon atoms adjacent 
to the nitrogen. Replacement of one a hydrogen by a 
methyl group apparently renders the other hydrogen 
inactive. 


A number of the materials which produce good 
CK absorbent are unsatisfactory for use in a gas 
mask absorbent, due to desorption or decomposition, 
both of which result in an objectionable odor in the 
effluent air stream. Pyridine and the picolines when 
used in small quantities do not have these disadvan¬ 
tages and produce a useful absorbent. 

4.6.2 Quality of Pyridine or Picoline 
Impregnated Charcoals 

Pyridine or picoline impregnated charcoals are 
extremely active, having a critical layer depth of ap¬ 
proximately one cm but they have a fairly low ab¬ 
sorptive capacity. The absorptive capacity N 0 for a 
pyridine impregnated charcoal is of the order of 
30 mg of CK per ml of absorbent. PCI-ASC whet- 
lerite has an N 0 of from 80 to 190 mg of CK per ml 
of absorbent, depending on the base charcoal and the 
quality of the impregnation. 101 M10A1 canister CK 
lives are of the order of 25 min for the pyridine im¬ 
pregnated charcoals compared to a life of 60 to 
70 min for a good ASC. A comparison of the proper¬ 
ties of these materials is shown in Table 34. 

Pyridine and picoline impregnated charcoals show 
very little, if any, aging effects. 

Either pyridine or picoline can be used as an addi¬ 
tional impregnant for T}^pe A, AS, ASC, or ASM 
whetlerite. The properties of the original absorbent 
are usually retained practically unchanged, with the 
added advantage of a greater resistance to aging. 
Type A and AS, in addition, gain from the treatment 
some measure of CK protection although it is smaller 
than that of ASM or ASC. (The pyridine or picoline 
containing materials are designated by adding P or 
Pi, respectively, to the usual designation for the par¬ 
ticular type of whetlerite in question.) 






ORGANIC BASE IMPREGNATIONS OF CHARCOAL 83 


Table 34. Comparison of various types of whetlerites with pyridine and picoline containing absorbent PCI charcoal. 

Impregnation 

Comment 

Xc 

No 

g/ml abs. 

CK 80-80 life 

2.5-cm tube 

None 

initial life 

2.91 

9.7 

4 

3% pyridine, aqueous solution 

initial life 

2.15 

23.4 

11 

AS solution 

initial life 

3.57 

11.1 

4 

AS + 3% pyridine 

initial life 

3.48 

30.5 

6 

ASC 

initial life 

1.90 

83.7 

32 

ASC 

aged 281 hr 

2.93 

63.2 

8* 

ASC 

aged 480 hr 

3.65 

54.0 

5 

ASC 

aged 954 hr 

4.48 

34.5 

3 

ASC + 1% pyridine 

initial life 

1.69 

68.5 

33 

ASC + 1% pyridine 

aged 280 hr 

1.73 

48.5 

21 

ASC + 1% pyridine 

aged 480 hr 

2.15 

55.4 

22 

ASC + 3% pyridine 

initial life 

1.58 

38.5 

18 

ASC + 3% pyridine 

aged 290 hr 

1.97 

36.5 

18 

ASC 4- 3% pyridine 

aged 479 hr 

2.03 

23.3 

14 

ASC + 3% pyridine 

aged 1440 hr 

2.18 

33.1 

12 

ASC + 3% pyridine 

aged 1922 hr 

2.36 

31.4 

9 

ASC + 3% pyridine 

aged 2401 hr 

2.39 

27.4 

10 

ASC +3% picoline 

initial life 

2.13 

69.0 

23 

ASC 4- 3% picoline 

aged 247 hr 

2.45 

63.9 

18 

ASC 4- 3% picoline 

aged 440 hr 

2.67 

61.9 

17 


The ability to confer great resistance to aging upon 
ASC whetlerites is the principal reason for the inter¬ 
est in these organic bases. The initial life of an ASCP 
whetlerite is very slightly different from those of an 
ASC, and in the M10A1 canister tests is usually 
slightly lower than that of the corresponding ASC. 

The organic bases can be added directly to the 
original impregnating solution, and the impregnated 
charcoal is processed in approximately the same way 
as the usual ASC whetlerite, except that a lower 
maximum temperature is recommended. 

The following conclusions are the results of numer¬ 
ous studies 47> 64 on these impregnants: 

1. The method of introducing pyridine or picoline 
into the whetlerite does not affect the degree to which 
aging is retarded. The material may be added directly 
to the impregnating solution or adsorbed by the char¬ 
coal or whetlerite from a vapor-laden air stream. 

2. The addition of pyridine to ASC whetlerite by 
vapor treatment does not result in an appreciable 
reduction of hexavalent chromium. There is some in¬ 
dication that addition of pyridine to the whetlerizing 
solution results in a lower hexavalent chromium con¬ 
tent in the finished whetlerite than is found in a 
normal ASC. 

3. Mixing pyridine-saturated whetlerite with un¬ 
treated whetlerite is a convenient method of prepar¬ 
ing vapor-treated whetlerite. Standing three days in 
a sealed container at room temperature resulted in 
practically complete redistribution of the pyridine. 

4. The upper permissible pyridine concentration 


on PCI ASC whetlerite is 2%. Above this concentra¬ 
tion the odor of pyridine becomes detectable. The 
upper limit for picoline is 3 g per 100 ml of solution. 
Both pyridine and picoline are selectively adsorbed 
from the impregnating solution. 

5. Equilibration to 80% RH results in the evolu¬ 
tion of considerable ammonia from some batches of 
ASCP whetlerite, but the amount of pyridine de¬ 
sorbed is not detectable by present analytical 
methods. 

6. The introduction of a uniform, small concen¬ 
tration of pyridine or picoline into whetlerite in 
loaded canisters does not appear feasible by the 
aeration method since a tremendous volume of air 
would be required to distribute the pyridine. 

7. A somewhat lower temperature than that used 
for ASC should be used to dry ASCP and ASCPi ab¬ 
sorbents in which the pyridine or picoline is incor¬ 
porated in the impregnating solution. At the normal 
temperature used for the laboratory preparation of 
ASC (180 C), frequent ignition of the pyridine or 
picoline-treated materials occurs. Because the pres¬ 
ence of the organic base accelerates the release of 
volatile ammonia, a temperature of 150 to 160 C for 
2 hr will produce a material which meets the am¬ 
monia specification. 

Actual plant production of ASCP whetlerite has 
been carried out in the CWS impregnating plant at 
Zanesville, Ohio. The material (officially designated 
as Type E 11 impregnated charcoal) was produced 
with existing equipment without difficulty. The only 








84 


IMPREGNATION OF CHARCOAL 


condition changed was the maximum drying temper¬ 
ature, which was lowered slightly. Type Ell impreg¬ 
nated charcoal showed a slightly greater tendency to 
ignite than A$C whetlerite at the temperature or¬ 
dinarily used for ASC plant production (400 F). At 
370 to 390 F, no ignition occurred. The following 
observations were made at the time this particular 
plant production*was carried out. 88 

1. Type Ell impregnated charcoal gives slightly 
less protection in canisters against all gases than does 
ASC impregnated charcoal made from the same base 
charcoal. The extent of the loss in protection is ap¬ 
proximately proportional to the amount of pyridine 
present. 

2. The CK protection of Type Ell impregnated 
charcoal decreases more slowly during moist closed 
storage at elevated temperatures in canisters than 
does Type ASC impregnated charcoal made from the 
same base charcoal. The use of pyridine, therefore, 
considerably lengthens the period during which a 
canister gives adequate protection against CK. 

3. Type Ell impregnated charcoal can be made 
in existing charcoal impregnating plants without 
difficulty. 

4. Type Ell impregnated charcoal can be dried 
at a lower temperature than Type ASC impregnated 
charcoal because pyridine appears to accelerate the 
release of volatile ammonia. 

5. Seattle and PCI Type Ell impregnated char¬ 
coals containing as much as 2% of pyridine showed 
no significant desorption of pyridine and possessed 
no odor of pyridine. 

The inclusion of pyridine, picoline, or other or¬ 
ganic bases in ASC whetlerite appears to be a useful 
method of improving the aging properties of this type 
of absorbent. If such an improvement proves to be 
necessary, practically no changes in existing plants, 
or plant procedures are required to convert to the 
new process. 

It has been observed that aging toward CK of 
Type ASC whetlerite in canisters in the field is not 
as serious as first supposed. Hence the advantages of 
the use of pyridine or picoline are not as significant 
as laboratory tests indicated. 

4,7 ABSORBENT RESINS AS SUBSTI¬ 
TUTES FOR ACTIVATED CHARCOAL 

4.7.1 Introduction 

Simultaneously with the developments in charcoal 
impregnation was the investigation of possible non¬ 


charcoal materials which might be used as gas mask 
absorbents. Two distinct types were investigated: 
(1) reactive materials such as granular magnesia, 
Hopcalite, and aminated Xerogels; (2) inert catalyst 
carriers such as silica gel, activated alumina, and 
kieselguhr which have no chemical reaction with ad¬ 
sorbates and act chiefly as catalyst carriers. 

The first class of materials have a definite capacity 
for specific agents depending upon the amount of 
chemical reaction which occurs with the agent. The 
second group are able to adsorb vapors to some ex¬ 
tent quite similarly to charcoal, and rarely have any 
chemical reactivity with the material adsorbed. They 
must be impregnated, just as charcoal, in order to 
gain a satisfactory capacity for specific materials. 
Class I materials have a definite disadvantage in that 
they have a negligible capacity for materials with 
which they do not react chemically. 

Among inert absorbents, charcoal is far better 
than any other similar material in having a much 
larger surface area, a more diversified pore structure, 
and a greater absorptive capacity for capillary con¬ 
densible gases. Silica gel, activated alumina, etc., 
are not suitable for impregnation with ASC solution. 
No results were obtained in the impregnation of ma¬ 
terials of this type which compared favorably with 
the results of the charcoal impregnation. 

In the search for a good CK absorbent many 
Class I (chemically reactive) materials mentioned 
above were tried. Granular magnesia and Hopcalite 
showed some ability to destroy CK at elevated tem¬ 
peratures, but none at room temperature. Attempts 
at impregnation of granular magnesia were uniformly 
unsuccessful. 

4.7.2 Aminated Phenol-Formaldehyde 
Xerogels 70 

Resins of this type were originally developed to 
purify water by removal of acidic ions. In conjunc¬ 
tion with a hydrogen-ion exchange resin, they are 
capable of completely removing ions from aqueous 
solutions. In the preparation of such ion-exchange 
materials the phenol-formaldehyde resins were im¬ 
pregnated with a polyamine such as tetraethylene 
pentamine. The amine reacts to form a part of the 
resin structure, and yet retains part of its ability to 
act as an amine. For this reason the aminated resins 
react readily with CK and certain acid bases. By the 
addition of metallic constituents the resin can be 



RESINS AS SUBSTITUTES FOR CHARCOAL 


85 


modified to absorb SA and AC. AC is apparently too 
weakly acidic to be removed by a neutralization re¬ 
action with the aminated resins. 


4.7.3 


Preparation 


Aminated resins are prepared from porous phenol- 
formaldehyde resins. The porous resin is granulated, 
dried, and made to react with a polyamine, as follows: 


OH CH 2 OH 


—CH< 



CH S 


-CH 2 —l 


Resin 


—CHs-n 



+ 2NH 2 (CH 2 -CH 2 -NH) 3 
,0H -CH 2 -CH 2 -NH 2 —> 

(tetraethylene pentamine) 

ch 2 oh 

ch 2 nh (CH 2 - ch 2 - NH) 3 - ch 2 
-ch 2 -nh. 


CH 2 (aminated resin) 2H 2 0 

OH 


-CHo—l 


CH 2 - NH (CH 2 - CH 2 - NH) 3 - CH 2 
-CH 2 -NH 2 


The polyamine may react with one or more re¬ 
active -CH 2 -OH groups, but experiments indicate 
that a considerable portion of the polyamine mole¬ 
cules is attached to the resin by one bond only. The 
aminated resin may be pictured as a large porous 
granule, the exposed surfaces of which are covered 
with molecular flagellae. The length of the flagellae 
is determined by the kind of polyamine used in the 
amination process. 

During amination the resins swell to an extent 
depending upon the amount of condensation which 
has taken place in the original resin. If over-con¬ 
densed (few -OH groups remaining), the resin will 
not react with enough amine to produce a good prod¬ 
uct. Under-condensation results in too much amine 
entering the molecule. The result is that the resin 
swells uncontrollably and the mechanical strength 
of the product is poor. The resin finally chosen for 
amination was intermediate, and when aminated at 


120 to 150 C it swelled about 100%. Upon removal 
of the excess amine and drying, a shrinkage of ap¬ 
proximately 25% occurred. The resulting product 
had good mechanical strength and good absorptive 
capacity for CK. 

The gas absorbing capacity of aminated resins is 
dependent almost entirely upon a chemical reaction 
of the gas in question with the aliphatic amine groups 
in the resin or with metallic impregnants introduced 
during preparation. Resin absorbents have very 
small surface areas compared to a good physical ad¬ 
sorbent like charcoal (see Chapter 6). Comparative 
values are shown in Table 35. 71 


Table 35. Surface areas of resins. 


Adsorbent 

Surface area 
from nitrogen 
adsorption 
sq m/g 

Surface area 
from water 
adsorption 
sq m/g 

Aminated resin TR-2 

63.0 

139 

Aminated resin TR-4 

62.5 

188 

Aminated resin TR-4A 

59.5 

148 

Non-aminated resin HCR 5/25 164 


Non-aminated resin HCR 3/9 

108 


Type A whetlerite 

1400-1800 



Because the surface area of aminated resins are 
approximately one-twentieth of those of whetlerites, 
it is apparent that their absorptive capacities must 
be dependent on chemical reaction rather than physi¬ 
cal adsorption. In order to be useful for gas masks, 
such absorbent should be capable of a specific re¬ 
action with every possible type of toxic agent. Ab¬ 
sorbents of the aminated resin type are at a distinct 
disadvantage, compared to charcoal, because their 
absorptive capacity for toxic agents which did not 
react probably would be small or nonexistent. The 
property of physical adsorption possessed by char¬ 
coal is a tremendous advantage. 

Aminated resins exhibit an objectionable volume 
change with variation in the relative humidity of the 
air with which they are in contact. Swelling of from 
15% to 25% occurs as the relative humidity varies 
from 0% to 100%. Between 21% and 71% relative 
humidity the corresponding resin volume changes are 
8% to 12%. This is decidedly undesirable in an ab¬ 
sorbent to be used in a gas mask canister. Impreg¬ 
nation with metals which form amine-complexes re¬ 
duces somewhat the tendency of the resin to shrink 
as the relative humidity decreases. The effect of such 
impregnants is apparently to reduce the hydrophylic 
nature of the amine groups on the resin surface. This 







86 


IMPREGNATION OF CHARCOAL 


results in an increased contact angle between the 
meniscus of the liquid in the pore and the wall of the 
pore. This, in turn, results in a less effective exertion 
of the constricting effect of the surface tension of the 
liquid. Therefore, the mechanical strength of the 
resin is better able to resist constriction. The overall 
effect is the lowered shrinkage of the resin. On this 
hypothesis resins with high mechanical strength 
should show negligible shrinkage, and indeed some 
resins do show these properties. 

When amine resins, metal-impregnated or non- 
impregnated, are tested against CK at 0% RH, after 
having been dried at 50 C and 0% RH, they show a 
greatly reduced capacity. This loss of activity does 
not extend to such gases as AC, SA, and HC1. When 
the resins, dried as above, are tested against a gas 
stream of CK at 80% RH, a normal life is obtained, 
indicating that enough moisture is taken up from the 
gas stream to restore its activity. A possible explana¬ 
tion is that the molecular flagellae, with which the 
CK reacts, may be coiled up against the surface when 
dry, and hence are not available for reaction. The 
presence of moisture makes the flagellae again avail¬ 
able for reaction. If this is true, then the use of a ma¬ 
terial such as glycerine to keep moisture on the sur¬ 
face, or the complete replacement of the moisture by 
a high molecular weight hydrocarbon (the replace¬ 
ment of the water film by an oil film to keep the 
flagellae in an extended position) should result in re¬ 
sistance to deterioration upon drying. Accordingly, 
glycerine and clear mineral oil were applied to ami- 
nated resin to test this hypothesis. Both failed to 
alter the properties as desired. The treated materials 
had fair CK protection at 0-80 conditions, but had 
very slight protection at 0-0 conditions. 

Shrinkage can be reduced to about 9.6% for the 
aminated resin, and to 6.6% for the Ag 2 0 impreg¬ 
nated resin in a change of RH from 0% to 100%, by 
careful control of preparative conditions and the ad¬ 
dition of a small amount of an aliphatic long chain 
amine in isopropyl alcohol to the animation solu¬ 
tion. 72 

4.7.4 Impregnation of Aminated Resins 

Aminated resins are impregnated with metallic 
constituents capable of forming stable complexes 
with amines. Impregnation is accomplished by ad¬ 
sorption from aqueous solution. Copper, silver, 
nickel, chromium, and zinc have been used. Silver 
must be present to effect the removal of SA, but 


presence of other metals with silver seems to improve 
the action. SA removal is presumably catalytic oxi¬ 
dation as in the case of whetlerites. AC appears to be 
removed by complex formation with the metal im- 
pregnants. Apparently the metals combine with the 
resin by formation of the normal ammonia-type com¬ 
plex. Aminated resin capable of absorbing two moles 
of hydrochloric acid can absorb one-half mole of cop¬ 
per, indicating that each mole of copper combines 
with four moles of amine, probably in the usual 
amine-complex form [Cu(RNH 2 )t + ]- It is possible, 
of course, that part of the copper or other complex¬ 
forming metal may be absorbed as the mixed aquo- 
ammino complex. 

4.7.5 Effect of Impregnants 

The general effect of the impregnants on each gas 
considered may be summarized as follows: 

CK 

With the exception of Ag 2 0, all metallic impreg¬ 
nants tend to reduce CK protection. The effect is 
greater when the impregnant is in the form of a salt 
than when in the form of an oxide. 

SA 

Silver must be present to effect removal of this gas, 
which is removed by catalytic oxidation. Silver may 
be present as metal, compound, or oxide. Other me¬ 
tallic constituents present as oxides promote the 
catalytic effect of silver, although they have no effect 
in the absence of silver. 

AC 

AC is too weakly acidic to be removed by amine- 
cyanide salt formation. Oxides of metals capable of 
forming stable cyanides remove AC in proportion to 
the amount of metal present. Metals capable of form¬ 
ing cyanide complexes are particularly efficient. Cu¬ 
pric copper is avoided because of the possible forma¬ 
tion of cyanogen. Impregnation has little effect on 
the capacity of aminated resins for HC1. Metal oxides 
may improve the HC1 capacity slightly. The effect is 
similar to that for other active acid gases. 

CO 

Sodium nitroprusside reacts with both carbon 
monoxide and amines. Hence, by reaction with ami¬ 
nated resin, sodium nitroprusside is incorporated 
into the resin, thereby conferring an absorptive ca- 



RESINS AS SUBSTITUTES FOR CHARCOAL 


87 


pacity for CO on the resin. The reactions proposed 
are: 

RNH 2 + Na 3 [Fe(CN) 5 NO] — 

Resin 

R[-NH 2 Fe(CN) 5 ]Na 3 + NO 

nitroprusside impregnated resin 
and 

R[-NH 2 Fe(CN) 5 ]Na 3 + CO —> 

Na 3 [Fe(CN) 5 CO] + RNH 2 

The reaction with carbon monoxide is not very 
rapid. Resins prepared in this way showed a 90% 
penetration by a 0.1% CO test mixture after 5 min. 
The resin is not effective enough to be useful in a 
canister, but may be developed into a satisfactory 
material for other purposes. 

Silver nitrate-nickel nitrate impregnated aminated 
resins and ruthenium chloride impregnated aminated 
resins also show some carbon monoxide capacity. 

4.7.6 Evolution of Ammonia from Ami¬ 
nated Resins 

A distinct disadvantage of aminated resins as gas 
mask absorbents is the evolution of ammonia when 
used. Intolerable concentrations are found in the 
effluent stream from certain resins at normal breath¬ 
ing rates. Oxygen, moisture, and free alkali are active 


in promoting ammonia evolution. The ammonia is 
attributed to (a) action of water and oxygen upon 
the resin amine groups, with the formation of alco¬ 
holic groups and ammonia, and (b) the action of 
ammonia present in the commercial tetraethylene 
pentamine on the resin, producing an aminated resin 
which is split hydrolytically by moisture to form an 
alcohol and ammonia. 

Use of an anti-oxidant to reduce reaction (a) re¬ 
sulted in decreased SA protection without appre¬ 
ciable decrease in ammonia evolution. The best 
resins from the point of view of low ammonia evolu¬ 
tion were produced by washing the aminated resin 
with water prior to impregnation with silver oxide. 
The resulting impregnated aminated resin had only 
a slight odor of ammonia. 

4.7.7 Other Types of Absorptive Resins 

The very reactive -CH 2 -OH groups in phenol- 
formaldehyde resins are capable of reacting with sub¬ 
stances such as Na 2 HS0 3 , H 2 S, PH 3 , etc. The result¬ 
ing resin contains the groups -CH 2 , -S0 3 H, -CH 2 
-SH 3 , -CH 2 -PH 2 , et cetera. These reactive groups in 
turn are capable of a variety of reactions and there¬ 
fore offer the possibility of the development of a spe¬ 
cific absorbent for any particular material of known 
chemical properties. 




Chapter 5 

SURVEILLANCE OF IMPREGNATED CHARCOAL 

By W. Conway Pierce and Thurston Skei 


5.1 INTRODUCTION 

ext to initial protection the most important 
requirements for a gas mask canister are that 
the adsorbent shall not deteriorate with age and that 
the canister shall have mechanical strength to remain 
effective after rough usage. While it would be possible 
to provide for frequent and periodic replacement of 
gas mask canisters, this would entail a tremendous 
additional burden on supply organizations. It is 
highly desirable to provide canisters whose lives un¬ 
der normal conditions of use are in excess of 6 to 12 
months. Throughout the gas mask development pro¬ 
gram much emphasis has been placed upon surveil¬ 
lance and rough-handling characteristics. 

Prior to the development of ASC whetlerite, the 
only surveillance problem concerning the gas ad¬ 
sorbent was the effect of moisture on performance. 
It is now well established that canisters issued to 
field troops pick up moisture to an amount depend¬ 
ing upon the prevailing relative humidity. This hap¬ 
pens whether the canisters are used or not, but the 
rate of water pickup is much faster if the canisters 
are being worn. A canister worn for 10 to 15 hours in 
rainy weather may be completely equilibrated with 
water vapor. In the tropics, the equilibrium amount 
of water adsorbed by charcoal is about that which 
corresponds to equilibration at 80% RH. 

The Type A whetlerite used in U. S. canisters prior 
to 1943 was fairly stable indefinitely as long as it re¬ 
mained dry. In the period before the war, gas masks 
were packaged in tin cans to insure dryness of the 
charcoal until the mask was issued. After a mask was 
issued, the protection against some gases fell off 
rapidly as water was picked up by the charcoal. The 
protection against CG was not affected, but the PS 
and AC protection was lowered somewhat, the latter 
because of the C 2 N 2 penetration which occurred 
when a humidified canister was exposed to AC: 

2HCN + CuO ^ Cu(CN) 2 + H 2 0 
2 Cu(CN ) 2 —*■ 2CuCN + C 2 N 2 . 


The CK and SA protections fell to nearly zero as the 
moisture content approached the saturation value. 

Because of the effect of moisture on protection and 
the knowledge that moisture is absorbed when can¬ 
isters are used, the British have (and still do) “wet 
up” the charcoal in manufacturing. They use a cop¬ 
pered charcoal which is sprayed with dilute silver 
nitrate a solution to a water content about two-thirds 
the moisture saturation value [MSV]. By addition of 
water, CG protection is gained without use of the 
heavy CuO impregnation which is necessary to im¬ 
part dry CG protection. After humidification, the gas 
protection of the British canister is about the same as 
that of corresponding U. S. canisters with Type A 
whetlerite; both are weak in CK and AC protection. 

The recognized weakness in 80-80 CK protection 
led to attempts at improvement. 17 - 21 The most prom¬ 
ising of these, prior to the ASC development, was the 
thiocyanate treatment (see Chapter 4). This was 
never put into production because Type E 6 whet¬ 
lerite was not stable in storage. 

The problem of CK protection at high humidity, as 
well as improved AC protection, was solved by the 
development of the ASC process which went into 
production in 1943. Shortly after this process was de¬ 
veloped it was discovered that it, too, had surveil¬ 
lance problems. When an ASC whetlerite has become 
humidified and is then stored in absence of air, par¬ 
ticularly at elevated temperatures, its effectiveness 
toward CK and AC decreases and, in the limiting 
case, the protection becomes equivalent to that of 
humidified Type A whetlerite. In normal times, adop¬ 
tion of the ASC process would doubtless have been 
postponed for perhaps a year or two, pending a thor¬ 
ough surveillance study. However, because of the 
emergency and the knowledge that ASC at its worst 


a Silver nitrate is added to impart SA protection. This is 
perhaps unnecessary, since no good method has yet been found 
to disperse SA; but since it adds little to the cost, the use of 
silver is continued as a precaution. The same is true of silver 
in U. S. ASC whetlerite. 



88 



SURVEILLANCE METHODS 


89 


would never be inferior to Type A whetlerite, it was 
decided to initiate production and, if necessary, pro¬ 
vide for frequent canister replacements. Concur¬ 
rently, very extensive surveillance tests were made. 1 
Current opinion is that the aging of ASC whetlerite 
under field conditions is not a serious problem, but it 
is recognized that some loss in protection does occur 
with use and that a canister cannot be continued in 
service indefinitely. The experimental programs and 
the data on which these conclusions are based are 
reviewed in the following sections. 

5.2 SURVEILLANCE METHODS 

5.2.1 Early ASC Surveillance 

The first studies of the stability of ASC whetler- 
ites were made under conditions which were known 
to give accelerated aging. Equilibrated samples were 
stored in sealed bottles 2) 3 at elevated temperatures, 
up to 85 C. Control was by CK life tests, since it had 
been found that the first and most important effect 
in aging was a loss in CK protection. At this stage 
tube tests were used, since the available sample was 
usually small. From these early tests the following 
facts became apparent: 1 

1. Tube tests are not reliable indices of the pro¬ 
tection given by a sample in the thin-bed canister 
such as the M10, which was in use at the time of the 
tests. A sample which appeared to have undergone a 
slight decrease in effectiveness, as judged by the tube 
test life, might give zero life in an M10 canister. 
Later, it was recognized that the first step in aging 
is an increase in the critical depth while the capacity 
remains about constant. Because of this, the tube 
life did not drop greatly until the sample was badly 
aged. This is shown in the tube and canister data of 
Table 3 in Chapter 2. 

2. The accelerated aging was too severe. All sam¬ 
ples soon lost CK protection and became equivalent 
to Type A whetlerite. This extreme aging did not 
permit any conclusions regarding the stability which 
an ASC-filled canister might have in field usage where 
conditions are not so drastic. 

3. The rates of aging were found, even by tube 
tests, to vary from one type of charcoal to another. 
This is discussed later. 

4. The presence or absence of air and the moisture 
content of the charcoal played important roles in the 
rates of aging. 


5.2.2 Canister Aging Programs 

When it was recognized that absence of air and 
elevated temperatures drastically accelerate aging, 
and that canister tests are necessary for control of 
aging programs, the attempts to conduct accelerated 
aging programs with tube* tests were discontinued. 
Instead, efforts were made to set up conditions sim¬ 
ilar to those found in the field. With these changes, 
it was realized that accelerated aging procedures may 
produce misleading results because of effects which 
may not be present in normal use of a canister. 

A variety of conditions has been employed in 
the aging studies of the Chemical Warfare Service 
[CWS] and National Defense Research Committee 
[NDRC] laboratories. 

Edgewood Arsenal Chambers 15 

To simulate various climatic conditions the fol¬ 
lowing canister storage chambers are used at Edge- 
wood Arsenal: 

1. Arctic: operated at — 40 F and saturated RH. 

2. Desert: operated at 150 F and 10% RH. 

3. Tropical: operated at 113 F and 87% RH. 

Canisters are either placed open in these chambers 

and allowed to take up moisture or, in some tests, 
particularly in the tropical chamber, pre-equilibrated 
canisters may be used. 

NDRC Cyclic Chamber l ’ 7 

This chamber was designed to operate with cyclic- 
temperature changes to simulate day and night vari¬ 
ations, on the assumption that the “breathing” of 
canisters might have a different effect on aging than 
constant temperature conditions. Daily operation 
was for eight hours at 130 F and 60% RH, and six¬ 
teen hours at 90 F and 90% RH. There was some 
lag in the transition period from one condition to the 
other. A continuous automatic record was kept of 
both temperature and humidity. 

Storage Methods. A variety of storage methods 
was tried in the NDRC cyclic chamber as questions 
arose about the correlation of laboratory and field 
results. The following were used for bulk charcoal: 

1. Closed-dry: samples were sealed in pint fruit 
jars, with as received moisture contents. This repre¬ 
sented unused canisters in storage. 

2. Open-dry: samples were originally dry but 
were stored in open containers which permitted ac¬ 
cess to humid air. These represented canisters after 
issue, originally dry, but exposed to atmospheric 
humidity. 



90 


SURVEILLANCE OF IMPREGNATED CHARCOAL 


3. Open-wet: equilibrated samples (80% RH) 
were stored in open containers. 

4. Closed-wet: equilibrated samples were stored 
in tightly sealed jars. This condition represented 
canisters which had been used, then tightly stop¬ 
pered by plugging the inlet and outlet. 

Since storage of bulk charcoal was always open to 
the objection that reloading into test canisters would 
mix the outer and inner portions (which might have 
different moisture contents) the more important 
surveillance programs were carried out with four 
types of preloaded canisters stored in a variety of 
conditions. 

The Types of Canisters. The four types of canisters 
used included the following: 

1. M10, old style, J^-in. baffle. b 

2. M10, new style, in. baffle. 

3. M10A1. 

4. Mil. 

Storage Conditions. The more important storage 
conditions were: 

1. Sealed-dry: canisters were sealed, as in normal 
depot storage. This simulated depot storage in a 
tropical climate. 

2. Open-dry: canisters were stored with the inlet 
valve in place but with the nozzle open so that there 
was free access to moist air. This represented the 
condition of canisters issued to troops, that were not 
used but stored in carriers permitting free access 
to air. 

3. Sealed-partially equilibrated: this represented 
canisters which had picked up some moisture in the 
assembly plant and had then been sealed and put in 
depot storage. 

4. Open-wet: canisters were equilibrated at 80% 
RH, then stored open. This condition partially sim¬ 
ulated canisters which had been worn a few hours 
in a humid climate and were then stored where they 
might have access to fresh air. 

5. Open-wet carrier: limited numbers of canisters 
were stored wet, completely assembled in the carrier 
with which the canister is normally used. This con¬ 
dition was the most realistic approach to actual field 
use since the assembled mask in its carrier does not 
have completely free air interchange with the sur- 

b The baffle in radial-flow canisters covers the end sections 
of the central tube. Its function is to prevent a gas channel 
at the top or bottom of the adsorbent bed if the packing 
should become loosened by rough handling. The first M10 
canisters had a baffle % in. in length, but later this was 
changed to in. to gain the added protection of an addi¬ 
tional length of charcoal at each end. 


rounding atmosphere. Of particular interest were the 
tests with Mil canisters in M7 carriers, which are 
practically airtight. 

Field Tests 

From the beginning, it was realized that labora¬ 
tory aging tests were useful to indicate the relative 
stability of samples, but that there was not a direct 
correlation between the useful lives in laboratory 
surveillance and in the field. It was very difficult, 
however, to obtain canisters of known history which 
had been in field use in tropical climates, and it was 
not until February 1945, that reliable data were ob¬ 
tained for canisters of known history. The available 
field test data are the following: 

1. Wearing tests (I) at Camp Sibert, Alabama. 4 5 
In the summer of 1943, canisters with various types 
of absorbents were issued to troops at Camp Sibert. 
These were used in normal training activities for 
three months, then withdrawn for gas testing. 

2. Wearing tests (II) at Camp Sibert. Following 
a wearing period from September 1943 to May 1944, 6 
canisters were tested against gas. 

3. Canisters from Finschafen. 20 In September 
1944, wearing trials were conducted at Finschafen, 
New Guinea, for the purpose of obtaining data on the 
magnitude of ammonia evolution under tropical con¬ 
ditions. At the conclusion of these tests, selected Ml, 
M10, and M10A1 canisters were sent to the United 
States for gas tests. The canisters did not arrive until 
early in 1945, almost a year after some of them had 
been issued. 

4. Miscellaneous canisters returned to Edgewood 
Arsenal for testing. Numbers of canisters have now 
been gas-tested at Edgewood Arsenal, after return 
from the field. Unfortunately, in most cases, there 
were not any data regarding the date of issue, the 
amount of wear, the amount of water picked up in 
the field, and the amount of time spent in the tropics. 

5. San Jose canisters. 1 Selected canisters were 
equilibrated at 80% RH, assembled with the mask, 
and stored for three months in the open at San Jose 
Island near Panama. They were then returned to the 
laboratory for gas tests. Both M10A1 and Mil can¬ 
isters were used, each stored in the carrier normally 
used. 

5.2.3 Results of Aging Studies of ASC 
Whetlerites 

This section presents a resume of the present 
knowledge regarding the aging of ASC whetlerites 








SURVEILLANCE METHODS 


91 


and the factors which contribute to, or accelerate, 
the rate of deterioration. From the thousands of tests 
which have been made, quite definite conclusions can 
now be drawn. These are based chiefly upon data 
from NDRC reports, but are confirmed by extensive 
data from the CWS laboratories. 11-14 

Moist Storage 

When an ASC whetlerite is stored moist, the fol¬ 
lowing changes occur: 

1. The 80-80 CK protection drops to that of the 
base charcoal; that is, the effect of the impregnant 
disappears. 

2. Hexavalent chromium is reduced to the triva¬ 
lent state. There appears to be, for a given sample, a 
correlation between the rate of loss in CK protection 
and the rate of reduction of chromium. 

3. The AC protection at high humidity decreases, 
but at a slower rate than the CK protection. Eventu¬ 
ally, the AC protection becomes that of Type A 
whetlerites. 

4. There is some decrease in CG protection. 7 ’ 8 
This appears to be due to a decrease in activity of the 
adsorbent and not to a change in capacity. It is not 
of practical importance. 

5. The protection for SA and PS is not affected by 
aging but is dependent upon the water content of the 
charcoal. 

Rate of Aging 

The rate of aging is affected by the following 
factors: 

1. Presence or absence of air. 2 - 3 Moist samples in 
a sealed container age far more rapidly than if free 
access to air is permitted. Oxygen is consumed and 
carbon dioxide formed in the aging process. In a 
sealed container, all the oxygen may be used. 

2. Amount of moisture adsorbed. Partially equi¬ 
librated samples age more slowly than those which 
contain saturation amounts of water. The end result 
on prolonged storage is the same regardless of the 
water content. 

3. Temperature of storage. There is a large tem¬ 
perature coefficient for the reactions which occur on 
aging. Numerical values for this temperature coeffi¬ 
cient have not been determined, but all data indicate 
that as the temperature is elevated, aging is accel¬ 
erated. 

Dry Storage 

Samples which are stored dry and kept in a dry 
condition are quite stable. Canisters in depot storage 


probably remain usable for years if they are originally 
dry and are kept dry. At present replacement can¬ 
isters are sealed in tin cans at the time of manufac¬ 
ture. It is extremely important to take every possible 
precaution to insure that no moisture is picked up 
by the charcoal prior to sealing, since even slight 
amounts of moisture eventually cause aging, par¬ 
ticularly in the absence of air. In humid weather, any 
delay in the assembly line may easily permit adsorp¬ 
tion of enough water to cause aging. An M10A1 can¬ 
ister should not contain more than 5 to 10 g of water 
when put into storage and preferably the amount 
should be less than 5 g. 

Rate of Aging 

The rate of aging varies with the base charcoal 
used. This is illustrated in the accelerated aging data 
from Edgewood Arsenal shown in Table 1 for a vari¬ 
ety of base charcoals. Available data indicate that 
the rate of field aging is relatively in the same order 
for these samples as in the accelerated aging. 

Several points of interest may be noted in Table 1. 

1. The M10 canisters subjected to sealed-wet 
aging at 113 F had aged badly in three days. From 
other data, it is now known that this is due to a rapid 
increase in the critical bed depth for CK and that at 
slower flow-rate tests these canisters might still give 
good protection. 

2. From the open-wet data for M10A1 canisters 
it is seen that PCC, Seattle, and Atlas apricot char¬ 
coals give the best initial lives and stability and that 
most of the nut-shell charcoals deteriorate rapidly. 
It is because of this that most of the present produc¬ 
tion is of PCC and Seattle charcoal (see Chapter 3). 

3. When the canister is stored open-dry in a humid 
atmosphere, the rate of aging is far less than if the 
charcoal is equilibrated before storage. 

In view of the varying stability exhibited by dif¬ 
ferent base charcoals, present whetlerite specifica¬ 
tions (No. 197-52-123 C, December 20, 1944) con¬ 
tain a stability clause : 

Accelerated Aging. The Grade I impregnated charcoal aged 
for 7 days (168 hours) as described in C.W.S. Pamphlet 
No. 2, Part II, Section N, and tested as prescribed in Para¬ 
graph F-Sb shall have a minimum life of 20 minutes against 
CNC1 and the life after aging shall be at least 40.0 per cent 
of the initial life. 

CK Protection Effect 

The first effect noted for CK protection on aging is 
an increase in the critical bed depth. (See Table 7.) 
Later, as aging proceeds, there is a drop in capacity 





92 


SURVEILLANCE OF IMPREGNATED CHARCOAL 


Table 1. Summary of tropical storage surveillance data, ASC impregnated charcoal. 


Charcoal 

base 

Lot 

No. 

Approxi¬ 
mate 
date of 
mfg. 

Type 

canister 

Concn. 

CK 

mg/1 

CK gas lives 80-80, 50 1pm 

Type* 

stored 

Refer¬ 

ences 

Original 

min 

After simulated tropical storage 

3 days 
min 

7 days 
min 

14 days 
min 

Atlas W 

ID-239 

1943 

Mio {%") 

4 

14, 16 

3.3 

2 

2, 1.5 

A 

TCIR 35 

Atlas OW 

ID-244 

1943 

M10(^") 

4 

12, 14 

2.5, 2.5 

1,2 

2, 1 

A 

TCIR 35 

Atlas OA 

ID-251 

1943 

M10(^") 

4 

12, 14 

2,3 

1, 1.5 

1.5, 1.5 

A 

TCIR 35 

Seattle 

HD-140 

1943 

M10(^") 

4 

14, 16 

4, 3.5 

2.75, 2 

3 

A 

TCIR 35 

PCC 

AD-255 

Sept. 1943 

M10(*g") 

4 

21, 23 

6,7 

6, 5 

4, 4.5 

A 

TCIR 35 

PCC 

BD-1063 

Jan. 1944 

M10A1 

4 

57 

48 

40 

41 

C 

TCIR 153 

PCC 

AD-255 

1943 

M10A1 

4 

43 

31 

27 

15 

C 

TCIR 210 

Seattle 

HH-529 


M10A1 

4 

50 


30, 31 

. . 

C 

TCIR 210 

Seattle 

HH-531 


M10A1 

4 

43 


22, 27 


C 

TCIR 210 

BC pecan 

CC-1105 

1944 

M10A1 

4 

44 

14, 25 

16, 12 

18, 19 

C 

TCIR 189 

BC pecan 


1944 

M10A1 

4 

26 

12 

5 


C 

TCIR 210 

BC flash bake coal 


1944 

M10A1 

4 

35 

30, 30 

11, 21 

19, 20 

C 

TCIR 179 

BC std extruded coal 


1944 

M10A1 

4 

46 

31 

16, 28 

21 

C 

TCIR 179 

BC mixed nutshell 


1944 

M10A1 

4 

53 

36, 33 

15, 20 

26, 20 

C 

TCIR 179 

BC peach pit 

. . 

1944 

M10A1 

4 

29 

21, 25 

9, 11 

12, 16 

C 

TCIR 210 

Atlas apricot 

. . 

1944 

M10A1 

4 

82 


52, 56 

. . 

C 

TCIR 210 

Atlas walnut 


1944 

M10A1 

4 

56 


3,3 


C 

TCIR 210 







2 months 

4 months 

6 months 









min 

min 

min 



BC 

A-116 

1943 

M10(^") 

2.5 

21 

7 

3 

2 

B 

TCIR 110 

Seattle 

HD-140 

1943 

M10(^") 

2.5 

55 

26 

6 

5 

B 

TCIR 115 

Atlas 

ID-244 

1943 

M10 

4 

10 

4 

2 

1 

B 

TCIR 172 

Atlas 

ID-239 

1943 

M10 

4 

21 

5 

3 

1.5 

B 

TCIR 175 

PCC 

AD-255 

1943 

M10 

4 

26 

13 

5 

4 

B 

TCIR 158 

Atlas W 

ID-251 

1943 

M10 

4 

18 

5 

4 

1.5 

B 

TCIR 185 

National Carbon 

196B1X 

1943 

M10 

4 

35 

23 

6 

2 

B 

TCIR 188 

Seattle 

Composite of July 1944 










production 

Mil 

4 

32, 29 

18, 21, 15(D) 


. . 

B 


PCC 

same 

Mil 

4 

25, 27.5 

27, 27, 22 (D) 


. . 

B 

TCIR 188 

BC pecan 

same 

Mil 

4 

26, 21 

8, 8, 6.5, (D) 



B 

TCIR 188 


* A Canisters equilibrated to 80 per cent relative humidity and sealed airtight before storage. 
B Canisters stored with open nozzles, not equilibrated before storage. 

C Canisters equilibrated to 80 per cent relative humidity, then stored, with nozzles open. 


and a further increase in critical bed depth. Because 
of the bed-depth effect, aging occurs far more rapidly 
for a thin-bed canister, such as the M10, than for one 
of thicker bed depth, such as the M10A1 or M9A2. 
Another consequence is that a canister which is ap¬ 
parently badly aged, as tested at high flow rate, may 
still give excellent protection at a lower flow rate. 
This is shown in the data of Table 2. 


Table 2. CK lives at different flow rates M10A1 
canister. Life in minutes. 


Condition 

50 1pm 

16 1pm 

Original 

40 

280 

Aged 

5 

120 


Since a flow rate of 16 1pm is far more typical of 
breathing rates under normal exercise conditions 


than 50 1pm, which corresponds to very vigorous ex¬ 
ercise, a badly aged canister may still give very good 
protection against CK. Further data in substanti¬ 
ation of this are shown in the following section. 

Canisters Used in Field 

The overall picture for canisters which have been 
used in the field for various lengths of time is quite 
reassuring. 

New Guinea. Canisters from wearing trials in 
New Guinea were shipped to the United States in 
September 1944. These canisters had been worn for 
14 hr. Some were freshly issued from depot stock and 
others had been issued at the POE in May 1944. 
Data for the water contents and gas lives are shown 
in Table 3. Since the tests were made in February 
1945, the period of use may be taken as the total 
















































































SURVEILLANCE METHODS 


93 


Table 3. Data for used canisters from New Guinea. 


Date 

Can. 

Type 

Type 

Lot 

Grams 
H 2 0 at 
start of 
wearing 

Grams 
H 2 0 
end of 
wearing 

Grams 
H 2 0 as 
received 
at 

labora¬ 

Grams 
H 2 0 
at 80% 

AP 

mm H 2 0 

Life in min 

issued 

No. 

can. 

char. 

number 

test 

test 

tory 

RH 

85 1pm 

50 1pm 25 1pm 


CK AR-80 performance 
4 mg/1, SIP indicator 


5/44 

621 

M10 

AD 

JJ-3-4-6 

23 

31 

44 


60 

24 

173 

5/44 

622 

M10 

AD 

JJ-3-4-5 

23 

32 

44 


57 

18 

155 

8/31/44 

718 

M10A1 

HH 

SC-12-4-2 

4 

19 

36 


55 

84 

299 

8/31/44 

719 

M10A1 

CC 

EV-10-4-5 

7 

23 

40 


55 

52 

229 

1943 

894 

Ml A1 

AD 

EV-C941-6A 





58 

3 

42 


CK 80-80 performance 
4 mg/1, SIP indicator 


5/44 

623 

M10 

BD 

JJ-4-4-3 

33 

33 

45 

49 

58 

13 

135 

5/44 

626 

M10 

AD 

JJ-3-4-5 

24 

31 

44 

50 

58 

14 

151 

8/31/44 

726 

M10A1 

HH 

SC-10-4-12 

5 

14 

32 

53 

50 

48 

214 

8/31/44 

736 

M10A1 

CC 

EV-10-4-5 

6 

17 

34 

57 

59 

23 

210 

1943 

896 

M1A1 

AD 

EV-C941-6A 




2.4* 

61 

2 

36 


AC AR-80 performance 
4 mg/1, Agl indicator 


5/44 

629 

M10 

AD 

JJ-3-4-5 

20 

28 

42 


59 

49 

8/31/44 

832 

M10A1 

CC 

EV-10-4-5 

6 

34 

45 


57 

53 


AC 80-80 performance 
4 mg/1, Agl indicator 


5/44 

627 

M10 

AD 

JJ-4-4-2 

23 

29 

44 

52 

53 

43 

8/31/44 

722 

M10A1 

HH 

SC-15-4-2 

6 

22 

35 

57 

55 

58 

8/31/44 

7110 

M10A1 

CC 

EV-10-4-5 

5 

14 

38 

61 

54 

50 


CG AR-50 performance 
10 mg/1, Kl-acetone indicator 


8/31/44 

7iii 

M10A1 

CC 

EV-10-4-5 7 

19 

38 


55 

49 


CG 80-50 performance 
10 mg/1, Kl-acetone indicator 


5/44 

631 

M10 

AD 

JJ-3-4-5 

23 

30 

44 

51 

60 

19 

8/31/44 

721 

M10A1 

HH 

SC-15-4-2 

5 

17 

30 

56 

50 

56 


SA 80-80 performance 
4 mg/1, KMn0 4 -HgI 2 indicator 


5/44 

632 

M10 

AD 

JJ-3-4-5 

23 

26 

41 

52 

55 

57 

8/31/44 

7210 

M10A1 

HH 

SC-10-4-12 

4 

12 

32 

58 

52 

>75 


* M1A1 canister No. 896 was almost equilibrated when received. It adsorbed only 2.4 g more of water at 80% RH. 


elapsed time from the date of issue to February 1945. 
In shipment, the canisters were intentionally left un¬ 
stoppered, to permit at least a limited access to air. 
Weights were recorded before and after the wearing 
period, and after arrival in the U. S. some canisters 
were tested as received and some at 80-80. 

The data of Table 3 show that the CK protection 
was still good, particularly at a 25 1pm flow rate, and 
•protection for other gases was apparently unim¬ 
paired, as judged by comparisons with data for fresh 


canisters. The water content of the used canisters 
was almost up to the 80 % RH equilibrium value, but 
the M10A1 canisters which were issued from depot 
stocks at the start of the test had gained only about 
two-thirds the saturation value. 

These tests provide the most reliable information 
available at present for field aging, and they indicate 
that average M10 and M10A1 canisters in the field 
give good protection. 

CBI Theater. Tests at Edgewood Arsenal on M10 


















































































































94 


SURVEILLANCE OF IMPREGNATED CHARCOAL 


Table 4. Data for used canisters from CBI theater. 


No. 

Type 

Humidity 

Can Air 

Flow 

1pm 

Gas 

Concentration life 
mg/1 min 

4145B 

MIXA1 

AR 

80 

50 

CK 

4 

3 

4148B 

MIXA1 

AR 

80 

50 

CK 

4 

7.5 

4152B 

MIXA1 

AR 

80 

50 

CK 

4 

4.5 

4155B 

MIXA1 

AR 

80 

50 

CK 

4 

3.5 

4174D 

M10 

15 

80 

50 

CK 

4 

27 

4176D 

M10 

AR 

80 

50 

CK 

4 

19 

4177D 

M10 

AR 

80 

50 

CK 

4 

16 

4180D 

M10 

80 

80 

50 

CK 

4 

5 

4180D 

M10 

80 

80 

25 

CK 

4 

55 

4192D 

M10 

80 

80 

50 

CK 

4 

6 

4192D 

M10 

80 

80 

25 

CK 

4 

74 

4194D 

M10 

80 

80 

50 

CK 

4 

23 

4I95D 

M10 

80 

80 

50 

CK 

4 

14 

4195D 

M10 

80 

80 

25 

CK 

4 

84 

4146B 

MIXA1 

AR 

80 

50 

SA 

4 

17 

4150B 

MIXA1 

AR 

80 

50 

SA 

4 

27 

4154B 

MIXA1 

AR 

80 

50 

SA 

4 

3 

4156B 

MIXA1 

AR 

80 

50 

SA 

4 

13 

4178D 

M10 

80 

80 

50 

SA 

4 

40 

4179D 

M10 

80 

80 

50 

SA 

4 

52 

4181D 

M10 

80 

80 

50 

SA 

10 

7 

4182D 

M10 

80 

80 

50 

SA 

10 

6 

4158B 

MIXA1 

AR 

50 

32 

CG 

20 

70 

4183D 

M10 

AR 

50 

50 

CG 

10 

18 

4184D 

M10 

AR 

50 

50 

CG 

10 

20 

4189D 

M10 

AR 

50 

32 

CG 

20 

34 

4187D 

M10 

AR 

50 

32 

AC 

10 

23 

4188D 

M10 

AR 

50 

32 

AC 

10 

25 

4144B 

MIXA1 

AR 

50 

32 

PS 

50 

26 

4151B 

MIXA1 

AR 

50 

32 

PS 

50 

17 

4185D 

M10 

AR 

50 

32 

PS 

50 

10 

4196D 

M10 

15g H 2 0 

50 

32 

PS 

50 

19 


and MIXA1 canisters used by troops in the CBI 
theater gave the data of Table 4. The MIXA1 can¬ 
isters contained only about 9 to 17% moisture when 
received, indicating that they had been used very 
little and had been kept in a rather dry place. M10 
canisters contained about 30 g of water or three- 
fourths the MSV at 80% RH. MIXA1 canisters were 
tested as received; part of the M10 canisters were 
equilibrated before testing, some were dried, and 
some were tested as received. Breather tests were 
made at 50 and 25 1pm and constant flow tests at 
32 1pm, the choice depending upon the conditions in 
use for the various gases. 

The data of Table 4 show that the CBI theater 
canisters have aged in CK protection but that the 
life is still good at low flow rates. There is no obvious 
deterioration in the protection for other gases. Since 
the M10 canisters were from a lot manufactured in 
1943 and the tests were made in 1945, it would ap¬ 
pear that, in general, the canisters used in the field 
give adequate protection. The data for MIXA1 can¬ 
isters were included merely for a comparison as they 


are not currently used by combat troops. Obviously 
these canisters are weak in CK and SA protection. 

San Jose Island. Few data are yet available for 
field surveillance of the Mil canister. In view of the 
known fact that free access to air is beneficial in pre¬ 
serving CK protection of moist ASC whetlerite, it 
has been feared that the Mil canister stored in its 
airtight carrier will not stand up as well as M10 and 
M10A1 canisters. Laboratory findings confirm this 
view. Only one carefully controlled field experiment 
has been reported. Fresh canisters were equilibrated 
at 80% RH and stored, assembled with the mask, in 
the regular carriers from April to September 1944 at 
San Jose Island, a typical tropical location with pre¬ 
vailing high humidity and a mean temperature of 
80 to 90 F. CK test data for these canisters are shown 
in Table 5. It is seen from these data that the Mil 
canisters deteriorate much more rapidly than M10A1 
canisters but that after 5 to 6 months (elapsed time 
from equilibration to testing) there is still ample pro¬ 
tection at 25-lpm flow rate. These data do not indi¬ 
cate that Mil canisters in the field at present have 


















SURVEILLANCE METHODS 


95 


Table 5. Comparison of CK protection for M10A1 and Mil canisters aged in carriers for 5 to 6 months. 


No. 

Type 

Filling 

H 2 0 canister 
grams 

CK life (breather pump)* 

50 1pm 25 1pm 

Control 

M10A1 

PCI 

25 

43 

Control 

M10A1 

PCI 

25 

46 

1 

M10A1 

PCI 

26 

36 

2 

M10A1 

PCI 

27 

24 

3 

M10A1 

PCI 

26 

36 

Control 

Mil 

Seattle 

33 

21 

Control 

Mil 

Seattle 

33 

22 

Control 

Mil 

Seattle 

33 

25 

Control 

Mil 

Seattle 

33 

22 

4 

Mil 

Seattle 

33 

2 70 

5 

Mil 

Seattle 

34 

3 81 

6 

Mil 

Seattle 

32 

11 102 


* The 25-lpm tests were made following 50-lpm tests to a break and lives are computed as additional 25-lpm life plus 2 X 50 1pm life. 


deteriorated to this extent, for in a non-gas condition 
these canisters have not been worn much and, stored 
in the airtight M7 carrier, the majority of canisters 
have probably picked up very little water. If an 
emergency should develop it would be possible to 
screen out doubtful canisters very rapidly by weigh¬ 
ing, since all Mil canisters show the original weight 
at the time of manufacture. Those whose weight- 
gain was slight could be considered safe, and prob¬ 
ably even those with weight-gains of 20 to 30 g might 
give adequate protection. 

Camp Sibert. The field tests on MIXA1, M10, 
and M10A1 canisters at Camp Sibert agree with the 
previously cited data for canisters from tropical the¬ 
aters. As might be expected with a temperate cli¬ 
mate, the rate of aging at Camp Sibert is less than in 
the tropics and the rate of water pickup is less. There 
is a decrease in CK protection, but no marked effect 
for other gases other than the effect of humidifica¬ 
tion. It seems safe to conclude that ASC-filled can¬ 
isters used in this country have a useful life of well 
over a year, and perhaps much more. 

5.2.4 Surveillance of ASM and ASV 
Whetlerites 19 

Early in 1943 the surveillance results with ASC 
whetlerite that had aged sealed-wet (under acceler¬ 
ated conditions) caused considerable alarm and the 
search for other impregnants which would be more 
stable was intensified. The most promising of the 
other impregnants were made by replacing chro¬ 
mium with molybdenum [ASM] or vanadium [ASV]. 
The first results, based upon sealed-wet aging, looked 
as if these impregnants were much more stable than 
ASC (see Chapter 4); but later, when aging condi¬ 


tions were made less drastic, the ASM and ASV whet¬ 
lerites were found to be less satisfactory than ASC. 
When aged in presence of air, ASM is actually less 
stable than when aged in absence of air. In the final 
recapitulation, these processes were discarded for the 
following reasons: 


Table 6. Typical CK aging for ASC and ASM 
whetlerites. 


Conditions 

Days 

80-80 CK life M10A1 — PCI 

of storage 

aging 

ASC 

ASM 

None 

None 

63, 59 

40, 41 

Open initially dry 

14 

56 



28 

61 

32, 30 


42 

52 



56 

39 



66 


19, 21 


84 

44 

. 


99 


6, 8 


112 

39 



131 


8, 3 


340 


4, 3 


400 

17, 19 


Sealed-wet 

None 


40, 41 


10 


36 


18 


26 


28 

4 

27 

Sealed-dry 

14 

57 



28 

61 



56 

42 



112 

34 



1. It was found difficult to prepare them with 
present plant equipment. 

2. ASM was less stable than ASC when aged in 
presence of air. 

3. ASC stability was found to be more satisfac¬ 
tory than the early sealed-wet aging results had in¬ 
dicated. 


























96 


SURVEILLANCE OF IMPREGNATED CHARCOAL 


4. The properties of pyridine and picoline in in¬ 
hibiting ASC aging had been discovered and it was 
felt that if a more stable adsorbent were needed it 
could best be obtained by use of one of these in con¬ 
junction with the ASC process. 

The data of Table 6 are presented to show typical 
ASC and ASM performances for comparison. Aging 
was in the NDRC cyclic chamber. 

5.2.5 Pyridine and Picoline Im¬ 
pregnations 10 16 19 > 22 

The use of pyridine and similar organic bases as 
charcoal impregnants to increase CK protection was 
first discovered by the British. Preliminary studies 
made at Edgewood Arsenal in 1943 looked very 
promising so that further investigations were under¬ 
taken along these lines. Descriptions of the condi- 


Table 7. Critical layer depth and capacity for CK of 
aged charcoals (OSRD 4013); Charcoal PCI — Sample 
A. 


Impregnant 

Hours aging 
sealed-wet 

40 C 

Critical 

depth 

cm 

Capacity 
mg CK/ml 
char 

None 

None 

2.9 

9.7 

P (3%) 

None 

2.2 

23 

ASC 

None 

1.9 

84 


281 

2.9 

63 


480 

3.7 

54 


954 

4.5 

34 

ASC + 1% P 

0 

1.7 

68 


281 

1.7 

48 


480 

2.2 

55 

ASC + 3% P 

0 

1.6 

39 


290 

2.0 

37 


479 

2.0 

23 


1440 

2.2 

33 


1922 

2.4 

31 


2401 

2.4 

29 


tions used for addition of pyridine, picoline, and re¬ 
lated compounds and the performance given by these 
impregnants are found in Chapter 4. Early surveil¬ 
lance studies were made by layer depth-life studies 
with tube tests. 18 Data for samples aged sealed-wet 
at 40 C are shown in Table 7 to illustrate the effect 
of pyridine. Picoline and other organic bases behave 
similarly. 


Table 8. Effect of pyridine on CK protection of Mil 
canisters aged in M7 carriers; Charcoal PCI. 


Whetlerite 

CK life at 501pm and 251pm (in parentheses) 

Initial 

14 days 

28 days 

56 days 

ASC 

+ 0.84% P 
+ 1.6% P 
+ 2.4% P 

32, 35 
31, 33 
34, 36 
31, 33 

13, 12 
20, 20 
25, 26 
16, 23 

4, 5 

14, 17 

16, 17 

15, 18 

2 (50) 

9, 10 (59) 
13, 16 

17, 17 


From the data of Table 7, and from numerous 
other series for various charcoals, it is concluded that 
pyridine has the effect of enhancing the CK protec¬ 
tion of aged ASC whetlerite. The first effect of aging 
is to increase the critical depth. When pyridine is 
added, its effect is to hold the critical depth constant, 
regardless of the aging of the other components. That 
is, the effect of pyridine is superimposed upon the 
effects of other components. Since the CK capacity 
due to pyridine is small in comparison with that of 
unaged ASC, addition of pyridine has little effect on 
an unaged sample; in fact, the protection is lowered 
slightly because adsorption of pyridine covers some 
of the available active centers and decreases the ad¬ 
sorptive capacity. But as the aging destroys the ASC 
effectiveness toward CK, the influence of the pyridine 
becomes apparent and aging lowers protection only 
to that which pyridine alone gives. 

With the accumulation of aging data for canisters 
used in the field, it became more and more apparent 
that aging is not a serious problem for the M10A1 
canister and, consequently, interest in the addition 
of a pyridine impregnation decreased. At the time of 
writing, however, there is still some interest in the 
possibility of using pyridine in the Mil canister 
which is, as mentioned above, perhaps subject to 
more drastic aging conditions than the M10A1 be¬ 
cause of the airtight M7 carrier. In view of this pos¬ 
sibility, a*n extensive program has been carried out 
in the NDRC cyclic chamber to study the effect of 
pyridine on the aging of Mil canisters stored wet in 
M7 carriers. Typical data are reproduced in Table 8. 
The beneficial effect of the pyridine is obvious. 
Whether such a treatment will ever be put into pro¬ 
duction depends upon what is learned from further 
field data, the applicability of present plant processes 
to addition of another constituent in impregnation, 
and further studies of any deleterious effects which 
might follow the use of pyridine. 
































Chapter 6 

ADSORPTION AND PORE SIZE MEASUREMENTS ON CHARCOALS 

AND WHETLERITES 

By Paul H. Emmett 


6.1 INTRODUCTION 

A s part of a fundamental program designed to 
throw light on the surface area, pore size and 
structural characteristics of an “ideal” charcoal, a 
great many measurements have been made during 
the last five years, both in NDRC and in British and 
Canadian research laboratories. The present report 
is an attempt critically to discuss and summarize 
such work, taking due cognizance of the current con¬ 
cepts of area and pore size measurements of porous 
solids. Tables and figures incorporated have been se¬ 
lected to illustrate the nature of the work that has 


summarize accurately the experimental work and to 
give his own opinions as to its meaning. It is hoped 
that the present writeup will serve to bring up to date 
our thinking relative to the surface characteristics, 
the pore size and the pore size distribution that we 
should aim to incorporate into a charcoal which is to 
be used for gas mask work. 

6.2 MEASUREMENT OF SURFACE AREAS 

6.2.1 Theory of the Adsorption Method 
and General Application 



_p_ 

Figure 1 . Method for measuring surface areas of vari¬ 
ous solids by means of low temperature adsorption 
isotherms. 


been carried out and the conclusions that have been 
reached. For more detailed accounts of the work, the 
reader is referred to the original articles listed in the 
extensive bibliography. 

It must be realized at the start that it is not always 
possible to give a final, categorical interpretation to 
the experimental results. The writer will endeavor to 


During the last few years h 2 a method has been de¬ 
veloped for measuring the surface area of various 
porous and finely divided solids by means of low- 



Po 


Figure 2. Linear Brunauer, Emmett, and Teller plots from 
Figure 1. 

temperature adsorption isotherms (Figure 1). It has 
been shown 3 that the adsorption data can be plotted 
according to the equation: 

P/Po _ i AC - l) P 
7(1 - P/P,) V m C + V m C P 0 
and yields straight lines over the relative pressure 
range of 0.05 to 0.35 (Figure 2). From this 7 m , the 




97 































98 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


volume of gas required to form a monolayer on the 
adsorbent can be evaluated. A simple multiplication 
of the number of adsorbate molecules in a monolayer 
by the average cross-sectional area of each adsorbate 
molecule will then yield a value for the surface area 
of the solid. In equation (1), V represents the volume 
of gas adsorbed (expressed at standard temperature 
and pressure) at the pressure P. P 0 is the liquefaction 
pressure of the adsorbate. C is a constant related to 
the heat of adsorption, E h by the equation 

c = *h e (E '- E ‘- )/,tT (2) 

a^bi 

where cq, b 2 , a 2 , and bi are constants and E L is the 
heat of liquefaction of the adsorbate. 

The validity of surface area calculations by equa¬ 
tion (1) has been greatly strengthened recently by 
an independent approach to the problem by Harkins 
and Jura. 4 By pre-saturating a non-porous solid Ti0 2 
with several layers of adsorbed water vapor and then 
measuring the heat of immersion in water of the 
Ti0 2 covered with adsorbed water, they are able to 
calculate directly the surface area of the solid. The 
heat of immersion, expressed in ergs, divided by the 
surface energy equal to 118.5 ergs per sq cm of sur¬ 
face, yields an absolute value for the area of the finely 
divided Ti0 2 . By this direct method, Harkins and 
Jura obtained a surface area value of 13.8 sq m per g 
for the adsorbent compared to 13.9 sq m per g by use 
of equation (1). This latter value involved the as¬ 
sumption that the cross-sectional area of the nitro¬ 
gen molecule is 16.2 A 2 , as calculated from the density 
of liquid nitrogen. Harkins and Jura 5 also developed 
a new equation for plotting the adsorption data to 
yield directly a value for the surface area of finely 
divided and porous materials. Their equation in¬ 
volves a constant, the numerical value of which is 
fixed by calibration with Ti0 2 , using the surface area 
value obtained by the heat of immersion. These al¬ 
ternative methods of plotting the low temperature 
adsorption data need not be discussed in detail here. 6 
It will suffice to point out that, for a large number of 
porous and non-porous solids, there is good agree¬ 
ment between the plots of Harkins and Jura and 
those making use of equation (1). 

Equation (1) has been applied to hundreds of dif¬ 
ferent samples of adsorbents with apparent suc¬ 
cess. 7-9 S-shaped isotherms of the type 12 shown in 
Figure 1 are invariably obtained if nitrogen is used 
as adsorbate and the measurements are made at 
—195 C, provided the adsorbent does not have a 


large surface area located in small pores. Thus it has 
been applied in measuring surface areas of carbon 
black, 7 paint pigments, 7 zinc oxide particles, 7 metallic 
catalysts, 3 metallic oxides, 7 gel catalysts, 3 and many 
other materials. 8 ’ 9 Thermodynamic 10> 11 as well as 
kinetic derivations lead to results expressed in equa¬ 
tion (1) if one postulates that curves of the shape il¬ 
lustrated by Figure 1 represent the building up of 
multilayers of adsorbed molecules on the surface. 
The higher the relative pressure, P/Po, the greater 
the average statistical thickness of the adsorbed 
layer. In view of all of the experimental evidence 
thus far obtained, it may be concluded that by plot¬ 
ting low temperature nitrogen adsorption isotherms 
according to equation (1), one can obtain reliable 
relative surface areas that are accurate to at least 
5%, and absolute values that are entirely repro¬ 
ducible on a given solid but might be in error by as 
much as 20% due to uncertainties of molecular di¬ 
ameters and molecular packing. 

In the original paper by Brunauer, Emmett, and 
Teller, 3 it was pointed out that if, for any reason, the 
maximum thickness to which adsorbed layers could 
build up on a surface is n molecular diameters, then 
the equation that one obtains to represent adsorption 
as a function of relative pressure (here designated for 
convenience as x rather than as P/Pq) is 

_ VmCx[_ 1 — (n + l)x n + nx n+r \ 

““ (1 - x)[l + (C - l)x - Cx n +^ ' 1 } 


Here the symbols have the same meaning as in equa¬ 
tion (1). Attention was also called to the fact that if 
n=l, equation (3) reduces to the form 


P _ _Po_ P_ 

v~ cv m + v„ 


(4) 


which is identical with the Langmuir equation. 

For materials such as charcoal having a large num¬ 
ber of very fine pores, n is conveniently interpreted 
as one-half the diameter (expressed as number of 
molecular diameters) of the pores, cracks, or crevices 
in which the adsorption occurs. It has been shown by 
Deitz and Gleysteen, 13 and by Joyner, Weinberger, 
and Montgomery 14 that equation (3) can be applied 
successfully to the adsorption isotherms for a number 
of materials having too many fine pores to fall in the 
class represented by equation (1). Figure 3 contains 
a number of isotherms that follow equation (3) over 
the pressure range 0.1 to 0.4; the values of n, C, and 
V m that fit well into the equation are also indicated. 

Pickett 15 has recently questioned equation (3) on 




MEASUREMENT OF SURFACE AREAS 


99 


the grounds that at relative pressures of 1.0 it does 
not postulate the complete filling of a crevice with 
adsorbate but only a fractional filling equal to 
( n -f 1)/2(1 + 1 /Cri). He carried out the summation 
up to n layers in a different manner than that em¬ 
ployed by Brunauer, Emmett, and Teller 3 and ar¬ 
rived at an equation of the form 

_ VJCx{\ - s») 

(1 — x)(l — x + Cx) 

This equation has the advantage of representing the 
complete filling of the capillaries at a relative pres¬ 
sure of 1; however, the value of V m obtained by 
equation (5) is substantially the same as that ob¬ 
tained by equation (3). Hence, Pickett’s suggestion 



Po 


Figure 3. N 2 isotherms for three carbons. 


is much more pertinent to the question of pore vol¬ 
ume than to that of surface area. Furthermore, equa¬ 
tion (3) and not equation (5) is obtained by a sta¬ 
tistical mechanical 16 or thermodynamic derivation. 
It seems probable, therefore, that equation (3) may 
be relied upon for surface area measurements of ma¬ 
terials having small pores even though there may be 
some question as to the course followed by the ad¬ 
sorption isotherm near saturation. 

It should be made clear in passing, however, that 
the measurement of the surface area is much less 
exact for materials such as charcoal, chabazite and 
some gels, having pores which in size approach mo¬ 
lecular dimensions, than for non-porous substances or 


those having large pores. For example, equations (3) 
and (5) have both been derived on the assumption 
that the adsorption is taking place on cracks having- 
plane parallel walls. Without doubt, the actual pores 
and capillaries have no such simple structure. Indeed, 
it may be that the small pores might better be de¬ 
scribed as cjdinders or cones rather than cracks or 
crevices. A further cause of uncertainty arises from 
the lack of any good independent means of checking 
the area of substances having pores of molecular di¬ 
mensions. There is no way of solving these uncertain¬ 
ties at the present time; their existence, however, 
should always be kept in mind. 

6.2.2 Measurement of Surface Area of 
Charcoals and Whetlerites 

The detailed calculation of surface areas by equa¬ 
tion (3) has not been used in most of the work that 
has been done on charcoal during World War II be¬ 
cause the calculations involved are too time-consum¬ 
ing. For most samples, equation (4) has been em¬ 
ployed; in a few instances 17 even equation (1) has 



I 1.5 2.0 2.5 3.0 3.5 4.0 


TRUE n - 

Figure 4. Ratios between areas obtained by equations 
(4) and (3) as a function of the value of n. 

been used. However, as pointed out by Joyner and 
co-workers, 14 the use of equation (4) for adsorption 
isotherms for which n = 1.5, yields an area value 
about 15% higher than that obtained by using equa¬ 
tion (3), whereas employing equation (1) for plotting 
the adsorption data will yield a value 18% lower 
than obtained by equation (3). The exact ratios be¬ 
tween the area obtained by equations (4) and (3) as 













































100 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


a function of the value of n are shown in Figure 4, 
the figure having been taken from their paper. Ac¬ 
cordingly, even though equations (1) and (4) have 
been used extensively as approximations for measur¬ 
ing the surface areas of charcoal, nevertheless, in the 
writer’s opinion, the most reliable surface area values 
on nitrogen adsorption are obtained by fitting the 
adsorption isotherms to equation (3) and evaluating 
V m after determining the values of n and C that are 
needed to fit the data to the equation over the range 
0.1 to 0.4 relative pressures. The area values obtained 
for charcoals by equation (4) probably represent 
upper limits, and those obtained by equation (1) 
represent lower limits to the correct areas. 



Figure 5. N 2 isotherms at —195 C for three small pore 
charcoals. 


The numerical value of the surface area that one 
will obtain by the use of equations (1), (3), or (4) 
will, of course, depend markedly on the gas used as 
adsorbate. Even on non-porous or coarsely porous 
solids, there is some indication that surface areas ob¬ 
tained by the use of large molecules are a little 
smaller than those obtained by the use of smaller 
molecules, providing the molecular cross sections are 
calculated from the density of liquids in the usual 
way. 18 For materials with fine pores this effect of 
molecular size is much magnified. For example, it has 
been known for many years that chabazite when 
properly dehydrated will exhibit a screening action 
on molecules larger than ethane. 19 It has been shown 
that it is possible to make the pores so small in de¬ 
hydrated chabazite as to permit the adsorption of 
hydrogen molecules but not nitrogen; 20 nitrogen 
but not C 4 Hi 0 ; 20 and straight-chain hydrocarbons 
but not branched chain. 21 ’ 22 On charcoal, similar 


screening effects are very much in evidence. On a 
charcoal such as Saran 23 shown in Figure 5, the ad¬ 
sorption of isooctane is only one-twelfth as large as it 
should be if nitrogen and isooctane were being ad¬ 
sorbed on the same pore walls. 23 On charcoals with 
larger pores (Figures 5 and 6), such as are produced 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 


_p 

P 0 "~ 

Figure 6. N 2 isotherms at —195 C on two charcoals 
with large pores. 

by more extensive activation, the screening is still in 
evidence but much less pronounced. A plot of surface 
area [calculated by equation (4)] as a function of 
molecular size is shown in Figure 7. As indicated, a 
surface area value for charcoal will, in general, so 
decrease in size as the molecule employed for the 
adsorption measurements increases in size. 

For obvious reasons it seems likely that the surface 
area measured by gases will be more important in 
judging the properties of charcoal than the areas 













































































MEASUREMENT OF SURFACE AREAS 


101 


Table 1. Maximum millimols of acids adsorbed, and surface 
Report 1, III-1-1232, Sept. 20, 1943 by Lemieux and Morrison. 

areas in sq m, per g charcoal. Taken from C. E. 151, 

Measuring acid Measurement 

1 

2 

3 

Charcoal number 

4 5 

6 

7 

8 

Acetic acid 

Millimols t 

2.15 

2.55 

2.85 

3.22 

3.25 

3.70 

4.00 

* 


Sq mj 

338 

402 

449 

507 

512 

583 

630 


Propionic acid 

Millimols 

1.63 

2.04 

2.47 

2.91 

2.93 

3.46 

3.75 

3.96 


Sq m 

257 

321 

389 

458 

462 

545 

590 

624 

Butyric acid 

Millimols 

1.24 

1.66 

2.06 

2.63 

2.74 

3.43 

3.84 

4.25 


Sq m 

195 

262 

324 

415 

432 

540 

605 

670 

Valeric acid 

Millimols 

0.88 

1.31 

1.75 

2.40 

2.41 

3.18 

3.66 

4.01 


Sq m 

139 

203 

276 

378 

380 

501 

577 

632 

Benzoic acid 

Millimols 

0.89- 

1.26 

1.71 

2.25 

2.31 

2.91 

3.38 

3.70 


Sq m 

140 

198 

269 

354 

364 

458 

533 

583 


* Insufficient charcoal, 
t Areas measured in millimols per gram. 
X Area range in square meters per gram. 


measured by adsorbing molecules from a suitable 
liquid solvent. This is primarily due to the difficulty 
involved in causing a solute to diffuse through a 
solvent and cover the surface of capillaries when the 
latter are the order of a few molecular diameters in 
size. Nevertheless, some measurements of the surface 
area of charcoal by the adsorption of molecules from 
the solution have been made. In Figure 7 a compari¬ 
son is made between the area values obtained by 
phenol and methylene blue from solution and those 
obtained by adsorbing gas molecules of comparable 
size. The agreement on the crushed sample is fairly 
good; the areas on the uncrushed sample seem to be 
about 40% lower by adsorption from liquid than by 
adsorption from gas. It is interesting to note that the 
areas obtained by Lemieux and Morrison 25 using 
acetic, propionic, butyric, valeric, and benzoic acids, 
all lie in the range 583 to 670 sq m per g on a given 
sample of well activated charcoals (Table 1). As 
would be expected, the area measured by acetic acid 
was much larger for small degrees of activation than 
that measured by valeric acid, just as the area 
measured by PS or other large molecules is much 
smaller 17> 23 than that measured by nitrogen in the 
early stages of activation when, presumably, the 
smaller pores are predominant. No areas by nitrogen 
adsorption methods are available for their charcoals 
though the combined effect of molecular screening 
and incompleteness of equilibration probably cause 
all these solution results to be low by a least 50%. 


6.2 .3 Application of Area Measurement in 
Predicting the Performance of Charcoals 

The application of surface area measurements in 
charcoal research is much less extensive and signifi¬ 



2000 
1900 
1700 
1500 
1300 
1100 
900 
700 
90 0 
300 
0 




-1 1 

YOUNG’S f X * l 

JNCRUSHED 


HgO-' 


VALi 

UES 

CRUSHED 



J 

"XT 

PH 3 

_ r TOLUENE 






\ 






Lh 

HEPTANE 

iso-octane 




O 


Q 



PHEN 

X 

olA 


_ 





METHYLEf* 

BLUE 

IE- 






X 








4 5 6 

MOLECULAR DIAMETER IN A 


Figure 7. Charcoal CWSN-19. Liquid volume and 
surface area vs molecular size. 


cant than the application of pore size measurements. 
This arises from the fact that rate of adsorption as 
well as the sorption capacity enters into the actual 
process by which a poisonous gas is removed from a 
stream of air on passage through a sample of char¬ 
coal. Nevertheless, many hundreds of such measure¬ 
ments have been made. 25 *- 25b There have been a few 
uses for the area measurements, however, that are 
worth mentioning. 

1. Some limited conclusions as to the whetleriza- 
bility of a charcoal can be deduced from the nitrogen 
adsorption isotherm. For example, a charcoal giving 
















































102 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 



90 100 110 120 140 150 160 170 180 190 200 210 220 

Ng ADSORPTION CC PER CC (BULK) 


Figure 8. PS life vs N 2 adsorption at P/P 0 = 0. 4. 


an isotherm as flat as that of Saran (Figure 5) cannot 
be expected to be suitable as a support for the cata¬ 
lyst material that is added in whetlerization because 
apparently, as judged by a plot of the data by equa¬ 
tion (3), the pores are all very small. At one time it 
was suggested that a gently rising nitrogen adsorp¬ 
tion isotherm of the type shown in Figure 6 was a 
necessary prerequisite to a good charcoal. 26 It may 
still be said that such a rise usually exists for a char¬ 
coal capable of being effectively whetlerized for the 
removal of CK under 80-80 conditions. Actually, one 
must take into consideration the shape of adsorption 
isotherms not only up to relative pressures of 0.99 
but also to much higher ones. 27 This application, 
however, involves the question of pore size measure¬ 
ments and will be considered in a later section. 

2. For charcoals that are sufficiently well acti¬ 
vated to have a large supply of pores wide enough to 
accommodate PS molecules, it seemed likely that 
some correlation should exist between the nitrogen 
adsorption capacity and the PS life. Actually a plot 23 
of the PS life (Figure 8) as determined by standard 
tests against F 0 . 4 (volume of nitrogen gas adsorbed 
per cc of charcoal at a relative pressure of 0.4) seems 


to give an approximately straight line that fits the 
equation 

PS life (in minutes) = 0.53 (F 0 .4 — 48), (6) 

over the life range of 20 to 60 min with an accuracy 
of about 10 min. 

3. Surface area measurements on charcoals that 
have been partially saturated with water vapor are 
an essential part of the methods 17> 28> 29 used by 
Juhola in measuring pore size. They will be discussed 
in the following section. 

In this section only adsorption data for nitrogen 
have been discussed. Adsorption of water vapor, PS, 
and a variety of other gases will be considered in 
other sections of this chapter. 

6.3 ADSORPTION OF WATER VAPOR 

6.3.1 Adsorption Isotherms for Various 
Charcoals and Whetlerites 

For a number of reasons 17,23,24>27>30 hundreds of 
water adsorption isotherms have been determined in 
the course of the present work on a variety of char- 










GRAMS OF WATER PER GRAM OF CHARCOAL GRAMS OF WATER PER GRAM OF CHARCOAL 


ADSORPTION OF WATER VAPOR 


103 






Figure 9. Water adsorption on charcoals at room 
temperature. 


coals and whetlerites. To begin with, the 80-80 activ¬ 
ity of many whetlerites toward CK may be vanish¬ 
ingly small even though the 0-80 activity might be 
high. This raises the question as to the amount of the 
catalyst surface that is left uncovered when the 
whetlerite is equilibrated with water at 80% RH. 
Secondly, water is known 23 to be capable of inhibit¬ 
ing the adsorption of PS by charcoals and hence will 
influence the PS life of a canister. Finally, water ad¬ 
sorption isotherms have proved to be of great value 
in estimating the pore size and pore size distribution 
according to a method developed by Juhola. 17 ' 28> 29 

Figure 9 illustrates a number of various types of 
water isotherms 32 that have been found on charcoals 
by adsorbing and desorbing water vapor from a 
stream of air passing through the sample. Most of 
the adsorptions are characterized by hysteresis that 
extends clear back to zero pressure when the iso¬ 
therms are determined by a flow technique using air 
as a carrying gas. When the adsorption is measured 
by a static system after thorough evacuation of the 
sample, the shape of the hysteresis loop is somewhat 
altered and the desorption curve on some charcoals 
rejoins the adsorption curve at about 0.4 relative 
pressure 17 - 23 as illustrated in Figure 10. However, 
Juhola has found 17 a number of examples of par¬ 
tially activated charcoals for which even in a static 
system hysteresis persists down to approximately 
zero relative pressure. Any such hysteresis in physical 
adsorption extending to relative pressures below 
those corresponding to condensation on pores at least 
four molecular diameters in diameter, is to be ques¬ 
tioned seriously. Slow chemical adsorption and grad¬ 
ual evolution of CO or C0 2 from surface complexes 27 
in the presence of water vapor may both be factors in 
apparent low-pressure hysteresis in water adsorption. 

It has long been known that the shape of the ad¬ 
sorption isotherms for water vapor on a charcoal is 
radically influenced by the amount of oxygen present 
as a surface complex. For example, it was pointed out 
by Lawson 33 that the presence of an oxygen complex 
on the charcoal surface shifts the adsorption isotherm 
to lower pressures than in the absence of such a com¬ 
plex. The influence of oxygen-coating a sample is 
graphically illustrated by Figure 11 in which the 
water adsorption isotherm is shown for charcoal 
CWSN 19 both before and after exposing it to oxygen 
at 400 C. 24 ' 30 During this exposure the nitrogen 
isotherms remained practically unchanged. 

The amount of water adsorbed has proved to be 
substantially independent 39 of the temperature at a 


SKtT.rr 1 
















































































104 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 



Figure 10. Water on CWSN-19 in flow and static systems. All static runs desorb to zero. 



Figure 11. Water isotherms as a function of the 
amount of surface oxygen complex. 


given relative pressure for a number of 24 - 30 char¬ 
coals. One of these is illustrated 30 in Figure 12 for 
water isotherms determined by a flow system for two 
different temperatures. This is not surprising be¬ 
cause it is known that E x — E L in equation (2) is 
small for water. Consequently, the influence of tem¬ 
perature on the value of C, and hence the amount of 
adsorption according to equation (3), is negligible 
over short temperature ranges. 



_p 

>0 

Figure 12. Adsorption of water on Navy charcoal 

MSA Grade 40. 

Rate of Adsorption of H 2 0 

The rate of adsorption of water vapor has received 
considerable attention because of the importance of 
knowing the rate at which canisters might be con¬ 
taminated by picking up water vapor and the rate at 
which they could be dried out when necessary by 
sucking dry air through them. The following conclu¬ 
sions have been reached although no complete mathe- 


































































































ADSORPTION OF WATER VAPOR 


105 


matical analysis of the rates of adsorption and de¬ 
sorption have been reported. 

1. The rate of adsorption of water vapor by whet- 
lerites is a little faster and the rate of desorption 
somewhat slower than for the corresponding base 
chars. 30 This is probably due to the fact that the 
equilibrium water vapor curve is shifted toward 
lower relative pressures by whetlerization. Hence, for 
a gas stream of a given RH (relative humidity) the 
driving force for adsorption is greater than for the 
base char; similarly, the driving force for desorption 
into a dry gas stream is less for the whetlerites than 
for the base chars and hence the rate is slower. 

2. The rate of equilibration increases with the rate 
of gas passage 35-37 at a given RH in the entering gas 
stream. This is probably due to the increase in the 
average partial pressure of water vapor throughout 
the charcoal column, as a result of the higher gas 
velocity. 




0 0.1 0.2 0.3 0.4 0.5 0.6 Q7 0.8 0.9 1.0 


CURVE 1 

NO HYSTERESIS 

AFTER 

EXCEPTIONAL 

EVACUATION 


CURVE 2 

HYSTERESIS AFTER 
WATER AND CHARCOAL 
HAD INTERACTED 
FOR 15 MONTHS 


P_ 

p o 


Figure 13. Water adsorption on charcoal. McBain 
Porter & Sessions (J.A.C.S. 55, 2294, 1933). Tempera¬ 
ture of runs, 120 C. 


3. Apparently 35 the slow step in the equilibration 
of charcoal with water vapor is not the mass transfer 
of the water vapor from the stream of gas to the 
charcoal particles, but the resistance encountered by 
the passage of the water vapor from outside the par¬ 
ticle into the tiny capillaries. This has been pointed 
out by Colburn 35 who showed that the HTU (height 
of a transfer unit) for charcoal samples ranged from 
3 to 25 in. under his experimental conditions com¬ 
pared to values of 0.2 to 1 in. for silica gel particles of 
similar size. This observation is consistent with the 


idea that some of the penetration of gases into the 
smallest capillaries is due to surface migration on the 
adsorbent. If the adsorption of water vapor is low, it 
would naturally follow that the transport of water 
vapor into the pores of the capillaries by surface mi¬ 
gration, and hence the ra,te of equilibration, would 
be slow. 

4. At 30 C and a gas flow of 600 ml of air per min 
per g of charcoal' (a space velocity that is close to that 
of normal breathing rates through canisters) the 
time 30 for half-equilibration of several typical base 
chars ranged from 48 to 90 min; the time for half- 
desorption into a stream of dry air at this same flow 
rate was about 30 to 40% of the time of adsorption. 
The time required for equilibration (by adsorption) 
on the whetlerites was from 30 to 60% of the time 
required for equilibration of the base charcoals. 

6.3.2 Nature of Water Adsorption on 
Charcoal and Whetlerlites 

Much has been written 38-40 relative to the nature 
of water adsorbed on charcoal. This is understand¬ 
able since the interpretation of the water isotherms 
may be a key to the calculation of the pore size and 
pore size distribution of the adsorbent. If water is 
adsorbed in or desorbed from a state that may be 
called capillary condensation, then the adsorption or 
desorption curves may be used together with the 
Kelvin equation to estimate the pore size distribu¬ 
tion. In the next section we shall see how this method 
has actually been applied by Juhola and others. For 
the present we shall limit our discussion to a presenta¬ 
tion of the evidence that has accumulated as to the 
nature of water adsorption. In particular, the evi¬ 
dence will be presented on the question whether 
water pickup by charcoal is adsorption, capillary 
condensation, or a mixture of both. 

McBain 40 - 41 and his co-workers have contended 
that the sorption of water vapor by charcoal is an 
adsorption phenomenon rather than a capillary con¬ 
densation. In favor of this point of view are the fol¬ 
lowing experimental facts: 

1. When water vapor is taken up by charcoal the 
latter expands 40 rather than contracts. It seems 
agreed that pure capillary condensation would lead 
to a tension in the pores of the charcoal and hence to 
a slight contraction. 

2. McBain 40 succeeded in drying and evacuating 
a sugar charcoal sufficiently to eliminate all hysteresis 
in an isotherm at 120 C. The results of his measure- 





































106 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


ments are shown in Figure 13. The water sorption rises 
abruptly at a relative pressure of about 0.3 until 
about 80% of the sorption capacity of the charcoal is 
satisfied. It then levels off gradually to a constant 
saturation value. Desorption follows the same curve. 
On the other hand, after the charcoal stood in con¬ 
tact with the water vapor for a year with the develop¬ 
ment of detectable amounts of hydrogen, a repeat 
adsorption run showed the conventional type of ad¬ 
sorption curve (Figure 13) with hysteresis in de¬ 
sorption. 

3. The shape of the lower part of water isotherms 
such as shown in Figures 9 and 10 are not very dif¬ 
ferent from the shape of the water isotherms ob¬ 
tained by Emmett and Anderson 42 on samples of 
degassed carbon black (Figure 14). It will be noted 
that the nitrogen isotherm on the carbon black be¬ 
fore and after evacuation at 1000 C are practically 
identical. On the other hand, the water adsorption 
isotherms are greatly changed. The sample, after the 
high temperature evacuation, adsorbs no water at 
low relative pressures but increasing amounts as the 
relative pressure is increased. The isotherms appar¬ 
ently indicate a heat of adsorption that is smaller 
than the heat of liquefaction. The water isotherm 
before evacuation rises almost linearly with relative 
pressure in much the way one would expect if the 
heat of adsorption is substantially equal to the heat 
of liquefaction. It seems clear that on the degassed 
carbon black the water adsorption cannot be due to 
capillary condensation since there is no evidence of 
any capillaries being present. Certainly, the high 
temperature evacuation did not produce capillaries 
or the nitrogen adsorption isotherms would have been 
quite different before and after the evacuation. The 
similarity between the shapes of the two carbon 
black water adsorption isotherms and the shapes of 
the isotherms of water vapor on charcoals is striking; 
accordingly, one must certainly be cautious about 
interpreting the water adsorption isotherms on char¬ 
coal as due to capillary condensation. Both the capil¬ 
lary size measurements of Lowry, 38 and those of 
Fineman, Guest, and McIntosh, 43 based upon the 
assumption that the adsorption isotherms for water 
are due entirely to capillary condensation, are to be 
questioned. 

The evidence for interpreting the desorption part 
of the isotherms as capillary condensation may be 
also reviewed here. 

1. No satisfactory explanation of hysteresis in de¬ 
sorption has been advanced so far for any process 


other than capillary condensation. On the other 
hand, in the water isotherms on the degassed carbon 
black 42 in Figure 14, hysteresis appears to exist. If 
these observations are confirmed by further work 
they will tend to undermine the capillary condensa¬ 
tion interpretation of hysteresis since the particle 
size in the carbon black work is such that even capil¬ 
lary condensation between the particles seems to be 
ruled out. 

2. By assuming that the shape of the desorption 
isotherms of water vapor on charcoal is due to capil¬ 
lary condensation and that cos 0 in the Kelvin 
equation 


P 2aV cos 0 


(7) 


has a value of 0.5 to 0.6, Juhola has been able to cal¬ 
culate pore size distribution for charcoals that yield 
good values for the surface areas measured by nitro¬ 
gen adsorption. This is considered in detail in the 
next section. 



Figure 14. Adsorption on carbon black Grade 6. 


3. The most convincing evidence that even the 
adsorption curve is partly capillary condensation 
has been obtained by Juhola in his scanning runs. 17 
A typical set of these is shown in Figure 15. Unless 
some explanation for hysteresis based purely on ad¬ 
sorption is forthcoming, these scanning runs must be 
considered definite evidence that part of the adsorp¬ 
tion isotherms are due to capillary condensation. 

Perhaps the soundest interpretation of water 
isotherms at the present time is that they may be al¬ 
most any combination of adsorption and capillary 
condensation. In water isotherms such as shown in 
Figure 15, it seems reasonable to assume that on the 


























ADSORPTION OF WATER VAPOR 


107 


adsorption part of the curve, the adsorption increases 
with relative pressure, passes through a maximum, 
and then decreases as more and more of the surface 
is eliminated as a result of the capillaries filling with 
water vapor. At high relative pressure near satura¬ 
tion most of the water pickup is due to capillary 
condensation. It should be noted, however, that if 
this picture is adopted and if the same angle of wet¬ 
ting, density, and surface tension characterizes the 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 


P 



Figure 15. Water adsorption isotherms for CWSN 291 

AY1. 

condensed liquid during both adsorption and desorp¬ 
tion, then one must conclude that the capillary con¬ 
densation on the adsorption part of the curve does 
* not occur at the relative pressures indicated by the 
Kelvin equation. For some reason that is not yet cer¬ 
tain, it would appear that capillaries of a particular 
size fill with condensation only at relative pressures 
that are considerably higher on the adsorption side of 
the curve than on the desorption isotherm. Perhaps 
the bottleneck theory of Kraemer 44 or the open pore 
theory of Cohan 45 can supply the explanation for the 
hysteresis. 

Some idea as to the nature of water in capillaries 
might be expected to be obtainable from measure¬ 
ments of freezing points and measurement of the 
density of the water sorbed by the charcoal. Two sets 
of measurements of the density of the water in the 
charcoal have been made. They disagree sharply with 
each other. Morrison and McIntosh 46 obtained val¬ 
ues ranging from 1.02 to 1.166 when the charcoal was 
exposed to relative humidities below 100%. On the 
other hand, two runs with pure water at 100% RH 
resulted in the water picked up by the charcoal having 
an apparent density of aboutO.957. In contrast to this, 
Juhola 17a has found consistently that the apparent 
density of water is less than unity, values of approxi¬ 


mately 0.93 and 0.90 characterizing adsorption and 
desorption parts of a run. It is difficult to be sure of 
the cause of this discrepancy. The procedure used by 
the Canadian workers for getting relative humidity 
values smaller than 100% is subject to suspicion. The 
use of sulfuric acid to decrease partial pressure of 
water vapor in their experiments might have con¬ 
taminated the charcoals with small amounts of acid 
spray or S0 3 . Either of these would have a much 
higher density than water and would cause the ap¬ 
parent density values to be erroneously large. In 
agreement with this, it should be noted that the val¬ 
ues obtained by Morrison and McIntosh 46 using 
pure water for saturating the sample are in satisfac¬ 
tory agreement with Juhola’s results. Because of the 
fact that the blocking of submicropores by capillary 
condensation of water or the placing of water under 
tension in capillary condensation would both tend to 
make the density less than one, it seems likely that 
the values obtained by Juhola for the apparent den¬ 
sity of water are more nearly correct than the high 
density values obtained by McIntosh and Morrison. 

Freezing methods have also failed 23a to help much 
in revealing the nature of adsorbed water. Johnstone 
and Clark 47 found that charcoals such as CWSN 19, 
when equilibrated with water sufficient to cause a 
45% weight increase on dry basis (probably equi¬ 
librated at about 75% RH), failed to yield an ice 
pattern (X-ray diffraction) at — 30 C. On the other 
hand, a sample soaked in water initially and then air- 
dried to a damp powder showed ice crystals that were 
much smaller than those obtained by allowing mois¬ 
ture from the air to condense on the cold cassette. It 
seems likely that the water picked up during adsorp¬ 
tion at 75% RH is either held by adsorption as a 
monolayer or else is in the form of capillary condensa¬ 
tion in capillaries as small as 20 A in diameter. It 
is therefore understandable why the sample equili¬ 
brated at 75% RH failed to show an X-ray pattern. 
The pattern shown by the sample, initially exposed 
to liquid water vapor and retaining about 75% water 
by weight, could easily be due to a thin film of water 
located in the larger capillaries of the charcoal or ad¬ 
hering to the outer periphery of the particles. A 75% 
weight increase is considerably higher than one would 
expect from adsorbed water on CWSN 19 even at 
saturation. Accordingly, this observation does not 
reveal the nature of the water that is contained in the 
capillaries in normal water adsorption up to say 99 % 
RH. 

Another approach toward throwing some light on 




























108 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


the question of the nature of adsorbed water was 
made by comparing the nitrogen adsorption on dry 
charcoal with that on samples that had been par¬ 
tially equilibrated with water vapor. Such measure¬ 
ments 23 showed that on both PCI and CWSN 19 
charcoals there is no sudden expansion of water as 
the temperature is dropped until some point between 
— 78 and —195 C is reached. This seems to point to 
the conclusion 23a that the water held by the two 
above-mentioned charcoals at 83.5 and 96% RH, 
respectively, is not water having a normal freezing- 
point. However, much further work would be re¬ 
quired before one could be sure of the influence of the 
size of a capillary on the freezing point of liquid con¬ 
tained in it. Hence, even this observation is a bit in¬ 
definite as an indication of the nature of the water 
held in capillaries. 

6.4 PORE SIZE AND PORE SIZE 
DISTRIBUTION 

No entirely satisfactory method has been discov¬ 
ered for measuring pore size and pore size distribution 
in charcoal and other similar small pore materials. 
The difficulties encountered are many. Perhaps one 
of the principal complications has to do with the 
shape of the capillaries. Not only is it impossible to 
ascertain whether the capillaries are cylinders, cracks 
with parallel walls, crevices, cones, or other regular 
geometric shapes, but it is impossible to tell what 
combination of all of these and other irregular forms 
may be involved. Furthermore, it must be realized 
that in dealing with capillaries that are from one to 
ten molecular diameters in size, one has little infor¬ 
mation as to the way in which density, surface ten¬ 
sion, and other properties of the adsorbed molecules 
may differ from those of the adsorbate in bulk form. 
It would probably, therefore, be difficult to specify 
pore size even if we knew the exact shape of all capil¬ 
laries present of the adsorbate in bulk form. Accord¬ 
ingly, progress in estimating pore diameters of char¬ 
coal is possible only by virtue of making assumptions 
as to the shapes of the capillaries and the properties 
of the adsorbed molecule. It is gratifying that, in 
spite of the numerous assumptions and approxima¬ 
tions that had to be made, methods were worked out 
during the recent war that are certainly more satis¬ 
factory than any previously available and that give 
results that are useful in trying to approach the ideal 
type of adsorbent for gas mask work. 

Methods that have been employed for measuring 


pore size may be listed in the following five classi¬ 
fications : 

1. Study of adsorption as a function of the size of 
the adsorbate molecules. 23 

2. Application of the Kelvin equation to the ad¬ 
sorption and desorption of any gaseous adsorbate 
other than water vapor. 23 

3. Application of the Kelvin equation to the ad¬ 
sorption 38> 43 and desorption 17 isotherms of water 
vapor. 

4. Measurement of the change of surface area re¬ 
sulting from the pickup of water by the char¬ 
coal. 17 - 28 - 29 

5. Measurement of the pressure required to force 
mercury 17,27 - 50 - 65 into the charcoal capillaries. 

These five methods will now be considered in turn. 

6.4.1 Molecular Size as a Criterion of 
Pore Size 

In a general way it would seem to be possible to 
tell a great deal about the size of pores in charcoal 
by comparing the relative amounts of adsorption 
with the size of the adsorbate molecule. For example, 
experimental work on chabazite has shown rather 
clearly that it is possible to prepare the adsorb¬ 
ent 19_22 - 51 so as to make the pores capable of ad¬ 
sorbing molecules of a given adsorbate and yet screen 
out molecules of only a slightly larger size almost * 
completely. Thus, as a function of the temperature 
and time of dehydration, as pointed out in an earlier 
section, chabazite can be made to adsorb hydrogen, 
but not nitrogen; oxygen, but not nitrogen; nitrogen 
but not butane; and normal hydrocarbons but not 
branched-chain hydrocarbons. However, this appar¬ 
ently simple method becomes very complicated if the 
adsorbent is one in which only a partial screening 
out of the larger molecules occurs. One is then faced 
with the task of differentiating between screening 
effects and the influence of the tightness of packing 
of odd-shaped molecules in capillaries of unknown 
shape. For example, it is known that if one compares 
the surface area obtained by the adsorption of nitro¬ 
gen by CWSN 19 with that obtained by use of suc¬ 
cessively largpr molecules, the result (Figure 7) is a 
decrease of about 50% in going to isooctane. 23 It is 
not at all certain, however, that this means that one- 
half the area is located in pores intermediate in size 
between that of the nitrogen molecule (about 3.9 A) 
and that of the isooctane molecule (about 6.7 A). 
Much of the decrease may be attributed to the less 





PORE SIZE AND PORE SIZE DISTRIBUTION 


109 


efficient packing of large molecules onto a given area 
than the corresponding packing of smaller, more 
symmetrical molecules. Indeed, it is not even yet 
well established that, for non-porous adsorbents, the 
same areas can be obtained by using large molecules 
as measuring sticks, as by using smaller ones. 6 ’ 18 In 
spite of this, the use of adsorbates whose molecules 
are of different sizes has been used effectively for at 
least qualitative appraisal of the relative pore sizes 
of two different charcoals. For example, it is well 
known 33> 41 that large dye molecules are almost com¬ 
pletely excluded from the pores of many charcoals. 
In fact, decolorizing carbons used commercially to 
remove color from sugar solutions are known to have 
much larger pores than the charcoals or activated 
carbons intended to adsorb large quantities of gas. 
Furthermore, some unmistakable screening effects 
can be noticed for molecules differing as little in size 
as those of nitrogen and isooctane. For example, 
charcoals made from carbonization of certain plastics 
are known to have uniformly small pores. These 
Saran charcoals (Chapter 3) will adsorb as much as 
twelve times 23 as many molecules of nitrogen as of 
isooctane and will equilibrate very much faster with 
nitrogen than with isooctane. It seems likely that 
most of the pores of this material are in the size 
range 5 A to 10 A. Again, it is" well known that char¬ 
coals made by the activation of coal develop pores 
capable of adsorbing nitrogen much earlier than they 
develop pores capable of adsorbing molecules as 
large as PS or isooctane. Accordingly, in a qualitative 
sense, the relative amounts of adsorbate picked up 
as a function of the size of the adsorbate molecule 
can be used to obtain some idea as to the distribution 
of pore sizes in charcoal. 

Attention should, perhaps, be called to one other 
precaution in judging the size of capillaries by the 
size of the adsorbate molecules. If one compares the 
amount of adsorption in terms of the volume of ad¬ 
sorbate (calculated as normal liquid) picked up, 
some odd results are obtained. For example, on two 
samples of charcoals on which the pores had been 
partially plugged by the product from the oxidation 
of arsine, the volume of liquid isooctane adsorbed 
near saturation was greater 52 than the volume of 
nitrogen (as liquid) adsorbed near saturation. Spe¬ 
cifically, the ratios of the volumes of isooctane to 
nitrogen were 1: 3 and 1: 6 respectively, for the two 
samples. This can be understood if one remembers 
that if two plain, parallel walls were completely cov¬ 
ered with adsorbate molecules and were exactly 


12 A units apart, then the volume of liquid calcu¬ 
lated for an adsorbate that had molecules 6 A units 
in size would be nearly 50% greater than that of an 
adsorbate that had molecules 4.2 A in size. Such ex¬ 
treme cases are rarely encountered, though it is ob¬ 
served that the liquid volume of adsorbates of suc¬ 
cessively larger size picked up by a charcoal do not 
fall off (Figure 7) as rapidly as do the apparent sur¬ 
face areas as calculated from the molecular cross 
section. This may result from the effect of the thick¬ 
ness of the adsorbed molecule entering into a calcu¬ 
lation of the volume of liquid picked up when much 
of the adsorption is necessarily only a single layer in 
thickness. 

6.4.2 Pore Size from Isotherms of 
Adsorbates other than Water 

A general method for measuring the diameter D of 
pores that has often been suggested makes use of the 
Kelvin equation, 


RT 2.303 log P/P o 

where V is the molal volume, o- is the surface tension, 
T the temperature at which the adsorption is meas¬ 
ured, P/P 0 the relative pressure of the adsorption, 
and 0 is the angle of wetting of the walls of the capil¬ 
laries by the adsorbate. The equation in this form 
assumes that the capillaries are circular in cross 
section. 

Two serious complications arise from trying to use 
this method in practice. For substances having large 
enough pores to give smooth S-shaped curves of the 
type shown in Figure 1, it becomes very difficult to 
differentiate between an increase in adsorption due 
to capillary condensation and one due to multimolec- 
ular adsorption. Indeed, some 53 interpret the upper 
part of the adsorption isotherms of curves such as 
those shown in Figure 1 and also those shown in Fig¬ 
ure 16 for porous glass, some silica gels, and similar 
substances as due entirely to multilayer adsorption 
rather than to capillary condensation. Wheeler 54 is 
having some success in separating the multilayer ad¬ 
sorption effect from the capillary condensation effect 
and thereby is able to obtain fairly satisfactory pore 
distributions from nitrogen adsorption isotherms on 
gels at —195 C. For the most part, however, this 
confusion between multilayer adsorption and capil¬ 
lary condensation effects has not been satisfactorily 
resolved. 






110 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


A second difficulty encountered in attempting to 
calculate pore diameters by use of the Kelvin equa¬ 
tion has been pointed out in the literature 20> 55> 56 
on a number of occasions and is especially applicable 
to fine-pore solids such as charcoal. It is concerned 
with the question of whether the diameter mentioned 
in the Kelvin equation [equation (8)] is the diameter 
of the capillary after a monolayer has been adsorbed 
or before it has been adsorbed. If the capillaries are 



0 o.l 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 


Figure 16. Adsorption isotherms of porous glass. 

large enough to permit multilayer adsorption, the 
thickness of the layer left on the surface after a capil¬ 
lary empties at some given desorption pressure also 
comes into consideration, since, according to the 
multilayer theory 3 one may have several statistical 
layers left on the surface at sufficiently high relative 
pressures. This second difficulty can perhaps best be 
discussed in connection with Figure 17 showing the 
adsorption and desorption isotherms for nitrogen on 
several typical charcoals. It will be noted that the 
desorption isotherms show some hysteresis compared 
to the adsorption isotherms. The desorption curve, 
however, rejoins the adsorption curve at about 0.35 
to 0.4 relative pressure. 

It has been pointed out by Cohan 45 that for a large 
number of adsorbates, the desorption isotherms re¬ 
join the adsorption isotherms at a relative pressure 
which, according to the Kelvin equation, figures out 
to correspond to 4 molecular diameters. On such a 
basis the adsorption of nitrogen on the charcoals 
shown in Figure 5 would indicate only a compara¬ 
tively small pore volume in excess of about 20 A 
diameter and less than about 2000 A diameter (the 





Po 

Figure 17. Adsorption and desorption isotherms for 
nitrogen on several typical charcoals. 

upper limit fixed by the highest relative pressure 
0.99 to which the runs were carried). These curves 
also make it clear that for nitrogen, at least, empty¬ 
ing of a capillary by evaporation of the portion of the 
adsorbate held by capillary condensation, leaves at 
least a monolayer of adsorbate on the surface. For 
charcoals such as those shown in Figure 17, on the 
other hand, definite qualitative evidence is given by 
the nitrogen isotherms as to the presence of capil¬ 
laries in the range 20 A to 2000 A in diameter. 

The two complications discussed thus far are in- 

























PORE SIZE AND PORE SIZE DISTRIBUTION 


111 


volved even when the desorption curve shows marked 
hysteresis in comparison to the volume of gas picked 
up at a given relative pressure during adsorption. 
Matters are made even more complicated by the fact 
that, according to some interpretations of capillary 
condensation, one may not obtain any hysteresis 45 
even though capillary condensation is occurring. It 
is claimed for example that if capillaries are wedge 
shaped no hysteresis is to be expected. Also, if they 
are cylindrical but have some narrow portion less 
than four molecular diameters in diameter they will 
not, according to certain hypotheses, 45 give hyster¬ 
esis. For all these various reasons it may be concluded 
that deductions as to capillary size and distribution 
based on the adsorption of molecules other than 
water vapor are susceptible to only qualitative in¬ 
terpretations at best. Even if hysteresis (the usually 
accepted criterion for capillary condensation) occurs, 
the interpretation of the results on a quantitative 
basis is made very difficult if not impossible by the 
uncertainty as to the thickness of the adsorbed layer 
left after evaporation of the portion of the sorption 
that is due to capillary condensation. 

There is one adsorption region in which the Kelvin 
equation may be applied to nitrogen isotherms with 
a somewhat greater assurance than indicated above. 
It is the range near saturation extending up to the 
highest relative pressures that can be conveniently 
measured. By the use of the Pearson gauge 27 for 
measuring pressures very close to saturation, nitro¬ 
gen adsorption measurements have been made on 
several charcoals. Typical adsorption data 27 are 
plotted in Figures 18 and 19. The adsorption in the 
range 0.99 to 0.999 covers diameters between 1800 
and 18,000 A, if one assumes that the Kelvin equa¬ 
tion is valid for the calculation. The question may 
be asked whether the abrupt rise in some of the iso¬ 
therms in this relative pressure range may not be 
partially caused by the formation of multilayers on 
the surface of the large pores. It is difficult to give an 
exact answer in the absence of any certain knowledge 
as to the thickness of films that will be built up with¬ 
out capillary condensation. The BET equation, 3 if 
followed, would predict layers 1,000 molecular diam¬ 
eters in thickness at a relative pressure of 0.999 and 
a C value of 100. However, this is certainly much on 
the high side since the BET equation predicts ad¬ 
sorption that is too high at all pressures above 0.35. 
It seems more likely from the few measurements re¬ 
ported in the literature 4> 5 that no more than 50 lay¬ 
ers would be built up. This would mean that the 




p 



Figure 18. Typical adsorption data of various char¬ 
coals carried to high relative pressures. 
















CC OF N, (ST P) ADSORBED PER GRAM 


112 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 






Figure 19. Typical adsorption data of various char¬ 
coals carried to high relative pressures. 


multilayer built up would be no more than about 
10% of the total volume of liquid required to fill pores 
of this size and, hence, could be neglected. The exact 
utility of these measurements will be discussed in a 
later section though it may well be pointed out here 
that, as shown in Figure 19, both Saran and CFI 
“CC” charcoals show no adsorption increase between 
0.99 and 0.999 and are very poor bases for whetler- 
ization; on the other hand, the charcoals shown in 
Figure 18 can both be converted into whetlerites and 
have a considerable increase in adsorption in this 
range of relative pressure. 

It has been pointed out that by selecting proper 
adsorbates having large products of Va/T [see equa¬ 
tion (7)] it is possible to extend the pore measure¬ 
ments to larger diameters without working at higher 
relative pressures. CCI4, 57 pyridine, 58 and tributyrin 59 
have been employed in this way to extend the meas¬ 
urements to 4000, 5000, and 13500 A, respectively. 

6.4.3 Pore Size from Water Adsorption 
and Desorption Isotherms 

It was suggested many years ago 38 that adsorption 
isotherms for water vapor on charcoals could be used 
for calculating pore size distributions. However, as 
pointed out in an earlier section, there seems good 
reason to doubt that all of the water picked up by 
charcoal during adsorption is held by capillary con¬ 
densation. The similarity between the adsorption 
isotherms for water vapor on well degassed, non- 
porous carbon black 42 and those for charcoals such 
as shown in Figures 11, 12, and 15 suggests caution 
in making any pore size calculations from the adsorp¬ 
tion curves. On the other hand, the desorption iso¬ 
therms for some of the charcoals give every indica¬ 
tion of representing the emptying of capillaries with 
little or no residual adsorption. Calculations such as 
those made by Juhola, therefore, seem entirely war¬ 
ranted provided the charcoals used are those having 
negligible adsorption below about 0.4 relative pres¬ 
sure. 

If one applies the Kelvin equation to a desorption 
isotherm such as shown in Figure 15, and uses a value 
of unity for cos 0, one obtains pore diameters in the 
range 30 to 40 A for most of the sample. These are 
clearly too large for they would not afford a suffi¬ 
ciently large area to account for the surface area 
measured by nitrogen adsorption or by the adsorp¬ 
tion of other gases. There seem to be two alternatives 
in interpreting the desorption curves. The possibility 











PORE SIZE AND PORE SIZE DISTRIBUTION 


113 


exists that the angle of wetting is not zero degrees but 
an angle of such size as to yield a cos 0 between 0.5 
and 0.6. As will be seen in the next section, such a 
choice of cos 0 yields pore distribution curves that 
appear to be very reasonable. On the other hand, one 
might be inclined to interpret the result to mean that 
cos 0 is equal to 1, but that attached to each of the 
pores of the 30 to 40 A pores are a sufficient number 
of smaller pores in the range 10 to 20 A which adsorb 
water only when the larger pores are filled. An obvi¬ 
ous weakness with this latter interpretation is that it 
does not account for the absence of an appreciable 
number of pores in the range 20 to 30 A in which it 
is generally believed capillary condensation can 
occur. 

It must be kept in mind that it is entirely within 
the realm of probabilities that the value of cos 0 
changes as a function of the relative pressure. As a 
matter of fact, the heat of adsorption would be ex¬ 
pected to increase to a value corresponding to the 
heat of liquefaction of water vapor as soon as the 
surface is covered with a monolayer of adsorbed 
water vapor. From experiments on carbon black 42 
that has been stripped of its surface complex by high 
temperature evacuation, it appears that a monolayer 
of a sorbed water formed at about 0.85 relative pres¬ 
sure. It might not be surprising, therefore, by analogy 
to expect the cos 0 term to become substantially 
unity above 0.8 to 0.9 relative pressure. Furthermore, 
the shift 24 of the steep part of the desorption part of 
a water isotherm to lower relative pressures as one 
coats the surface with chemisorbed oxygen is an in¬ 
dication that cos 0 for a complex covered surface is 
greater than for one without a surface coating. 


6.4.4 Pore Size from Surface Area Changes 
Resulting from Water Take-up by 
Charcoals 


For cylinders, the diameter D, the volume V, and 
the area A , are related by the equation 



( 9 ) 


Similarly, if one pictures charcoal as a collection of 
cylindrical capillaries and imagines that a group of 
capillaries of a particular size are filled by capillary 
condensation, then the small change in available vol¬ 
ume in the charcoal will be related to the diameter of 


the capillary and the change in available area by the 
equation 



( 10 ) 


Juhola was the first to point out that by measuring 
the surface area of a charcoal [with nitrogen (at liquid 
nitrogen temperature) as a function of the amount of 
water present, one could obtain a curve from which 
the pore diameter distribution of the charcoal could 
be calculated. The H 2 0 desorption isotherms for the 
charcoals used are shown in Figure 20. The change in 



Figure 20. Water desorption isotherms. 


area vs volume curves are shown in Figure 21, and 
the resulting plots of pore diameters against relative 
pressure of condensation of water are shown in Fig¬ 
ure 22. It soon became apparent, however, that the 
technique of measuring pore diameters by this pro¬ 
cedure would be quite laborious. Juhola, therefore, 
suggested using the method merely as a means of 
evaluating the cos 0 term of equation (7) and there¬ 
after using this latter equation for pore size measure¬ 
ments in conjunction with water adsorption data. 
He has used this method extensively 17 for obtaining 
pore size distributions over the range up to about 
100 A. 

Juhola states 17 that the Kelvin equation, with 
cos 0 equal to about 0.53, agrees satisfactorily with 
the values obtained when equation (9) is applied to 
the surface area vs volume experiments at relative 
pressures up to about 0.9. Above this, he reports, the 

































114 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


260 


220 


180 


140 


100 


60 


20 

0 








- 





■ N 44 

A N 291 

AYYI 

— 

vD \\ 

KO 




X CFI 
□ PN112 

O PN 106 

A PN98 

— 

\ T V 

NP \\ 



® RA5: 
T RC7S 

5 

) 

— 







— 

— 

\ x t n 
\ \ 

vX^rv U X 

x\\ 



— 



W A ^ 






0.1 0.2 0.3 0.4 0.5 0.6 

VOLUME OF WATER + SUB-MICRO PORE VOLUME (CC PER CC OF GRANULE) 

Figure 21. Area vs volume curves. 


0.7 


Kelvin equation does not hold. Actually, there is less 
reason to expect the Kelvin equation to fail at rela¬ 
tive pressures above 0.9 than at lower relative pres¬ 
sures. From comparison with the water adsorption 
experiments on degassed carbon black, it seems prob¬ 
able that at a relative pressure of 0.9 the portion of 
the charcoal not covered by capillary condensation 
has at least a monolayer of adsorbed water vapor on 
it. Hence the angle of wetting is likely to be much 
more nearly zero than for lower relative pressures 
where no such film exists. Hence, one would expect 
that cos 0 above relative pressures of 0.9 might equal 
unity. Presumably, the objection to interpreting the 
water isotherms in this way has to do with the lack 
of smoothness with which the pore diameter vs pore 
volume curves (such as shown in Figures 23 to 25) 
extrapolate from the lower pore diameter range into 
the curves for the higher range determined by the 
mercury method discussed below. At any rate, 
Juhola has elected to leave the region between about 
100 A and 2000 A diameters as undetermined in 
most of the materials he has studied. 

In the application of the Kelvin equation to water 
desorption isotherms for pore diameter measure¬ 
ments, the cos 0 term has been considered as taking 


into account only the angle of wetting. Actually, it 
may be, perhaps, a constant that takes into consid¬ 
eration any variation in (1) the surface tensions, a; 
(2) the molal volume, V; and (3) the angle of wetting 
in the small pore regions where we have no direct in¬ 
formation as to the validity of the values for these 
terms as determined from bulk water. 

The choice of the value of 0.53 for cos 0 is, as 
pointed out by Juhola, 17 attended with considerable 
uncertainty. Depending upon the density selected 
for water and for the adsorbed nitrogen in the experi¬ 
mental work, this cos 0 term might vary from 0.44 to 
0.58. Nevertheless, for those charcoals in which there 
is negligible water adsorption at relative pressures 
below about 0.4, the method appears to give very 
reasonable values for pore diameters. Distribution 
curves for about 110 charcoals or charcoal-producing 
materials are given by Juhola in his final report. 17 

6.4.5 Measurement of Pore Size by High 
Pressure Mercury Method 

Washburn 50 was the first to suggest that one could 
measure the diameter of pores by measuring the 
pressure necessary to force mercury into them. It can 





























PORE SIZE AND PORE SIZE DISTRIBUTION 


115 



< 

1 

cr 

UJ 

b- 

UJ 

2 
< 
o 

111 

tr 

o 

Q. 


Figure 22. Variation of pore diameter with P/Po of water. 


be shown that the diameter of a cylindrical capillary 
is related to the density p, and surface tension a of 
mercury by the equation 


phg 

where 0 is the angle of wetting (taken as —180 de¬ 
grees), h is the pressure applied and g is the gravita¬ 
tional constant. This method was selected and ap¬ 
plied 32 to a number of charcoals using pressures up to 
100 atmospheres in some of the early war work at 
Johns Hopkins University; it has been much more 
extensively studied and applied by Juhola 17 on more 
than a hundred charcoals. Juhola 17 tested the 
method on a block of briquetted, carbonized coconut 
shell charcoal by boring a hole 0.015 in. (3.81 X 


10 6 A) in diameter and measuring the pressure re¬ 
quired to force mercury through it. Four runs gave 
results of 3.39, 3.96, 3.43, and 3.75 X 10 6 A, which 
agree well with the actual value, 3.81 X 10 6 A. 

Recently, Ritter and Drake 61 * 62 have published 
details of the method as applied to cracking catalysts 
and also to a number of commercially available char¬ 
coals. Their runs have extended up to 10,000 psi 
pressure and, therefore, include measurements to 
pore diameters as small as 200 A diameter. A number 
of their resulting curves are shown in Figures 26 
and 27. 

Several inherent characteristics of the mercury 
method should be noted. If bottleneck capillaries 
exist, it must be realized that the pore diameter meas¬ 
ured will be that of the narrow neck rather than the 






































116 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 

TOTAL PORE VOLUME-CC PER CC OF GRANULE 

Figure 23. Pore diameter vs pore volume curves. 



Figure 24. Pore diameter vs pore volume curves. 

larger bulk of the capillary. Accordingly, on an aver¬ 
age, one would expect that the pore diameters ob¬ 
tained by the mercury method will be somewhat too 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.6 

TOTAL PORE VOLUME-CC PER CC OF 6RANULE 

Figure 25. Pore diameter vs pore volume curves. 


1 DIATOMACEOUS EARTH 4 

2 DIATOMACEOUS EARTH 3 

3 DARCO CARBON 

4 COLUMBIA CARBON 



PRESSURE IN PS I 

85,360 1066 534 356 266 214 

PORE DIAMETER-A 

Figure 26. Pore diameter measurement curve by high- 
pressure mercury method. 

small. This would mean that all the curves in Fig¬ 
ures 23 to 25 should be shifted to somewhat larger 
pore sizes if some method were available for estimat¬ 
ing the difference on an average between the narrow 
necks and the larger main portion of the bottleneck- 
shaped capillaries. No method for making this cor- 












































































































EFFECT OF PORE SIZE AND DISTRIBUTION ON CHARCOAL 


117 


CURVE SILICA-ALUMINA GEL 

1 I3A 

2 I3B 

3 I3C 

4 130 



PRESSURE IN PSI 

85,360 1066 534 356 266 214 

PORE DIAMETER IN A 

Figure 27. Pore diameter measurement curve by high 
pressure mercury method. 

rection is now apparent. It is not surprising in this 
connection to note that the few measurements 27 on 
nitrogen adsorption in the pressure range 0.99 to 
0.999, corresponding to pore sizes from 1800 to 
18,000 A, show much smaller volumes for a given 
pore size than are shown by the mercury runs. A com¬ 
parison of seven charcoals is shown in Table 2. 


Table 2. Macropore volume in the 1800 to 18,000 A 
diameter range. 


Charcoal 

Pore volume 

By N 2 ads By Hg method 

CWSN 19 

0.04 

0.148 

CWSN 196 BIX 

0.042 

0.308 

CWSN 196 BIX TH 427 

0.039 

0.327 

CWSN 196 BIX TH 410 

0.050 

0.301 

NDRC SI 26 

0.006 

0.0044 

CFI“CC” 

0.0016 

0.019 

PCI P58 

0.062 

0.106 


The mercury pore measuring experiments are ac¬ 
companied 17 by a hysteresis which, for devolatilized 
or activated charcoals or charcoal materials, is usu¬ 
ally equal to 90 to 95% of the mercury in the pores. 
On the other hand, some of the baked charcoal stocks 
show prior to activation as little as 35% of the total 
mercury retained in the sample when the pressure is 
released. It is a curious fact that the samples showing 
the smaller mercury hysteresis are also those that 
show little or no water hysteresis. Juhola 17 has sug¬ 
gested that this may be interpreted as evidence for 


the formation of bottleneck pores during activation, 
the narrow constrictions in the small pores being re¬ 
sponsible for the water hysteresis and the narrow con¬ 
strictions in the larger pores, for the mercury hyster¬ 
esis. 

6.5 INFLUENCE OF F^ORE SIZE AND 
DISTRIBUTION ON CHARCOAL 
PERFORMANCE 

The object of all the pore distribution and size 
measurements described in the preceding sections has 
been the elucidation of the factors responsible for the 
activity of charcoals for gas mask work. Such activity 
is of two kinds. The charcoal, by virtue of its adsorp¬ 
tive properties, is able to remove some of the poison 
gases that are likely to be encountered. Other gases 
can be removed only by adding chemicals to the char¬ 
coal capable of catalyzing the oxidation of the poison 
gas or of chemically reacting with it. For this latter 
type of action, the charcoal acts as a catalyst support 
or a support for chemically active reagents. Accord¬ 
ingly, all correlations between pore distributions and 
activity are concerned with these two general meth¬ 
ods, adsorptive and chemical, by which the charcoal 
in the mask accomplishes its purpose. In this section, 
we shall summarize such conclusions as have been 
reached between the structure of the charcoal and its 
activity. 

6.5.1 Definition of Terms 

At the outset it will be convenient to define a few 
arbitrary terms that will be useful in the discussion 
of activity. The terms to be defined are free volume , 
submicropore volume, micropore volume, and macro¬ 
pore volume. 

Free volume is the term used 63 to designate the pore 
volume of a charcoal that is not filled with nitrogen 
at a relative pressure of 0.99. It is obtained by sub¬ 
tracting from the total pore volume, as measured by 
immersing charcoal in mercury at one atmosphere 
pressure, the volume equivalent to the amount of 
nitrogen taken up by the charcoal at a relative pres¬ 
sure of 0.99. A value of 0.808 was assumed for the 
density of nitrogen in this calculation. To a first ap¬ 
proximation, the value of the free volume should 
agree with the pore volume measured by mercury up 
to pressures of 100 atmospheres since the latter, as 
well as the 0.99 relative pressure measurement for 
nitrogen, corresponds (as calculated by the Kelvin 


' SECRET f 






















118 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


equation) to pore diameters of about 1800 A. In 
Table 3 are shown the values obtained 27 by the 
mercury method and by the free volume calculation 
on typical charcoals and whetlerites. The agreement 
•between the two methods is probably within the com¬ 
bined experimental errors. For example, the change 
in the calculation of the free volume for the charcoals 
and whetlerites listed that would result from assum¬ 
ing that the density of the liquid nitrogen in the cap¬ 
illaries is 1.0, rather than 0.808, would more than 
equal the largest differences between the mercury 
penetration and the free volume results in Table 3. 


Table 3. Free volume of charcoals compared to macro¬ 
pore volume to 100 atm by Hg method. 


Charcoal 

Free 

Volume* 

Volume by Hg 
method to 100 atm 

CWSN 19 

0.162 

0.199 

CWSN 196 BIX 

0.402 

0.475 

CWSN 196 BIX TH 427 

0.482 

0.491 

CWSN 196 BIX TH 410 

0.467 

0.461 

NDRC SI 26 

0.007 

0.026 

CFI“CC” 

0.009 

0.050 

PCI P58 

0.265 

0.304 


* Free volume is the difference between th& total pore volume and the 
nitrogen adsorption at 0.99 relative pressure (calculated as liquid). 


Zabor and Juhola 64 arbitrarily defined macropores 
as those that are too large to fill with water vapor by 
capillary condensation at 80% RH. The macropore 
volume is the difference between the pore volume as 
measured by mercury at one atmosphere pressure 
and the apparent volume occupied by the water 
picked up at 80% RH during adsorption as judged 
by helium displacement. Micropores are then defined 
as the pore volume filled with water at.80% RH. 
Submicropores were defined originally 64 as those too 
small to permit water to condense in them but large 
enough to admit helium atoms. The volume of the 
submicropores was determined by measuring by 
helium displacement the apparent volume occupied 
by the water picked up at 80% RH and subtracting 
from this volume the calculated volume for the water 
based on the assumption that the water condensed in 
the capillaries has a density of 1. 

6.5.2 Free Volume and Activity of 
Whetlerites Toward CK (80-80) 

Early in the work it was discovered that CK re¬ 
moval under 80-80 conditions by whetlerites made 
from some base charcoals was much less effective 


than by whetlerites made from other charcoals. As a 
first suggestion as to the possible cause of the differ¬ 
ences in base charcoals, it was pointed out 66 that the 
better base charcoals had nitrogen isotherms in which 
the adsorption between 0.4 and 0.99 relative pressure 
range increases 5% or more. This was construed as a 
qualitative indication that some pore volume in the 
range 20 to 1800 A diameter was essential to a base 
charcoal for a good whetlerite. It soon became evi¬ 
dent, however, that although this seemed to be 
necessary, it was not a sufficient property of a base 
charcoal to assure it being useful for making whetler¬ 
ites. For example, CFI charcoals yielded isotherms 
that increased 18%, over this relative pressure range, 
yet would not make good whetlerites. 

It was next suggested 63 that the free volume of the 
charcoal would be a more useful criterion by which to 
judge the effectiveness in making whetlerites. This 
suggestion was based on the belief that possibly pores 
larger than 1800 A were also important in determin¬ 
ing the quality of whetlerite. A comparison 23 of a 
number of charcoals showed that unless 10% or more 
of the pore volume was free volume the charcoal 
would not make a good whetlerite. Thus, Saran and 
CFI “CC” charcoals, with practically no free volume 
formed almost inactive whetlerites. However, there 
were clearly other factors entering into the picture, 
for a number of charcoals giving free volumes equal 
to 15% or more of their total pore volumes yielded 
poor whetlerites, whereas others gave good whet¬ 
lerites. 

All attempted correlations between the 80-80 CK 
activities of whetlerites and the free volume as 
judged by nitrogen adsorption were based on the 
belief that the nitrogen isotherms and free volumes 
might indicate the amount of pore space that would 
not be filled with water by capillary condensation at 
80% RH. Obviously, this correlation would be rather 
approximate since a Kelvin equation calculation for 
water vapor would indicate that a capillary retaining 
water at 80% RH would be 95 A or less in diameter 
if cos 6 is taken equal to 1, whereas nitrogen at 0.99 
relative pressure should be held in capillaries 1800 A 
or less in diameter. Use was, therefore, made of a 
corrected free volume 27 based on the volume not oc¬ 
cupied by nitrogen at a relative pressure of 0.745. 
This should agree with the volume not occupied by 
water at 80% RH if cos 6 for the water desorption is 
about 0.7. In Table 4, the activities of a series of 
whetlerites are shown together with values for free 
volume and corrected free volume. Also, values for 


SEC RE r \ 










EFFECT OF PORE SIZE AND DISTRIBUTION ON CHARCOAL 


119 


Table 4. Comparison of different pore measurements and 80-80 CK activities. 


Macropore 
Corrected* vol per 

Free vol free vol Zabor and 80-80 CK 


Charcoal 

Methods of preparing base charcoals 

cc per g 

cc per g 

Juhola 

Lives (min) 

CWSN 19 


0.13 

0.14 

0.22 

Of 

NDRC SI 26 (Saran) 


0.007 

~0.007 


Of 

CFI “CC” 


0.007 

~0.007 

0.02 

Of 

CWSN 196 BIX TH 423 

Impregnated 2% Cr 2 03 . Steamed to 22% weight loss 
at 950 C; heated in N 2 10 hr 1100 C. 

'0.25 


0.47 

13, 15 

CWSN 196 BIX TH 426 

Impregnated 5% Fe 2 0 3 ; steamed 9% weight loss, 
heated 10 hr in N 2 1100 C. 

0.26 

0.36 

0.46 

19 

CWSN 196 BIX TH 427 

Impregnated 5% Cr 2 0 3 , steamed 16% weight loss at 
950 C; heated 10 hr, N 2 1100 C. 

0.28 

0.38 

0.48 

14, 18 

CWSN 196 BIX TH 432 

Impregnated 1% Fe 2 0 3 , heated in N 2 10 hr at 1100 C 
to 60% weight loss. 

0.30 

0.34 

0.34 

24 

CWSN 196 BIX TH 433 

Impregnated 2% Cr 2 0 3 , heated in N 2 10 hr at 1100 C 
to 8.5% weight loss. 

0.26 

0.37 

0.46 

12, 12 

CWSN 196 BIX TH 434 

Impregnated 5% Cr 2 0 3 , steamed 20% weight loss at 
750 C; heated 10 hr at 1100 C. 

0.30 

0.42 

0.46 

16, 20 

CWSN 196 BIX TH 437 

Impregnated 0.2% Cr 2 0 3 , heated in N 2 10 hr at 1100 C 
to 5% weight loss. 

0.27 

0.30 

0.34 

22, 26 


* Calculated from N 2 adsorption for 0.745 relative pressure, 
t M10 canister test; others are 2.5-cm tube test. 

Table 5. Pore volume differences between base chars and whetlerites for samples prepared from CWSN 196 BIX. 


Vol difference between Vol difference between 


Sample 

Weight of 

whetlerite components 
g per cc granule 

Volume of 

whetlerite components 
cc per cc granule 

base and whetlerite 
(Hg penetration at 
100 atm) 
cc per cc granule 

base and whetlerite 
(N 2 adsorption at 
P/Po = 0.99) 
cc liquid per cc granule 

CWSN 196 BIX TH 432 

0.182 

0.036 

0.005 

0.0527 

CWSN 196 BIX TH 436 

0.127 

0.025 

0.001 

0.0681 

CWSN 196 BIX TH 429 

0.132 

0.026 

0.009 

0.0620 

CWSN 196 BIX TH 427 

0.157 

0.031 

0.003 

0.101 


the volume of macropores are shown as defined by 
Zabor and Juhola. 64 It will be noted, in general, that 
all the active whetlerites have macropore volumes 
and corrected free volumes that agree with each 
other and are large compared to those of the base 
charcoals that do not produce active whetlerites. 
These limited data afford no direct correlation be¬ 
tween the activity and the macropore or corrected 
free volumes, but they do seem to indicate the neces¬ 
sity of a macropore or corrected free volume larger 
than some minimum the exact value of which is not 
clearly defined. 

One other conclusion seems evident from measure¬ 
ment of the volume of pores greater than 1800 A by 
the mercury displacement method. 27 Of the whetler¬ 
ites made from the four charcoals listed in Table 5, 
the impregnated chemicals do not appear to be lo¬ 
cated in pores larger than 1800 A to any great ex¬ 
tent. Specifically, from 5 to 30% only of the whetler- 
izing materials are so located. This observation is 
checked by the fact that the decrease in volume of 


pores below 1800 A in size, as judged by the nitro¬ 
gen adsorption isotherms of impregnated and unim¬ 
pregnated charcoal, is more than enough to account 
for the entire volume of whetlerizing components. 
Presumably, the whetlerizing materials are not only 
located in pores smaller than 1800 A for the most 
part, but are in pores sufficiently small to cause some 
pore blocking. The data in this table point to the con¬ 
clusion that the necessity of a considerable macropore 
or corrected free volume in good charcoals may be to 
furnish a sufficient number of channels through 
which the gases can reach the whetlerite responsible 
for their removal. Nothing in these results throws 
any light on the question of the size pore in which 
most of the actual removal of the CK occurs. 

6.5.3 Macropore Volume and CK 80-80 
Activity 

Zabor and Juhola 64 and later Juhola 17 have made 
extended comparisons between the macropore vol- 



















120 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 



o O.l 0.2 0.3 0.4 0.3 


MACRO PORE VOLUME - CC PER CC OF GRANULE 

Figure 28. Break time for CK 80-80 M10A1 canister 

tests as a function of macropore volume. 

umes of charcoals and the CK 80-80 activities of 
their whetlerites. A plot of the break time in minutes 
for the CK 80-80 M10A1 canister tests 17 is shown in 
Figure 28 as a function of macropore volume. The re¬ 
sults for this large number of samples are less definite 
than indicated by the first paper of Zabor and 
Juhola, 64 in the fixing of a minimum macropore value 
below which a whetlerite will have practically zero 
activity. They indicate clearly, however, that the 
larger the macropore volume, the better the chance 
of the whetlerite having a high CK 80-80 life. Appar¬ 
ently macropore volumes below about 0.15 cc per cc 
granules are too small to yield active whetlerites. 

Juhola 17 has discussed in detail the various factors 
that could conceivably cause the scatter of the results 
in Figure 28. They are (1) location of impregnant, 
(2) macropore surface area, (3) pore size distribution 
in the macropores, (4) carbon surface properties, 
(5) state of the impregnant, and (6) pore size distri¬ 
bution in the larger micropores. Apparently all the 
blame for the scattering cannot be placed on any one 
of these factors. On the other hand, there is consider¬ 
able evidence that slight variations in whetlerizing 
technique, in the length of time elapsing between the 


preparation of the whetlerites and their testing, and 
in the nature of the surface of the charcoals in them¬ 
selves, account for a considerable scatter in the CK 
80-80 activity tests. Juhola 17 calls attention to two 
examples in which leaching the initial whetlerite and 
rewhetlerizing increased the CK 80-80 life from 0 to 
27 min in one case, and from 57 to 90 min in another. 
Obviously, this change is not connected with pore 
alteration in the charcoal. Accordingly, the agree¬ 
ment indicated by the data in Figure 28 is probably 
as good as could be expected. It is certainly suffi¬ 
ciently good to indicate the extreme importance of 
macropore volume as a criterion for selecting base 
charcoals for making ASC whetlerites. 

6.5.4 Pore Size in Relation to the PS, 

AC, SA, and CG Life of a Charcoal or 
Whetlerite 

In a previous section (Figure 8) attention has al¬ 
ready been called 23 to the apparent relation between 
the PS life of a charcoal and the amount of nitrogen 
adsorbed at a relative pressure of 0.4. Since this is a 
pressure that probably will form from one to one and 
a half monolayers of adsorbed nitrogen on the char¬ 
coal, it may be considered as a rough estimate of the 
surface area. It would be even better to plot the PS 
life against the surface area values for the various 
charcoals but, unfortunately, this is made difficult by 
the lack of precision in obtaining surface area values 
for adsorbents with pores as small as those of char¬ 
coal. An even better correlation was pointed out be¬ 
tween the PS life and the adsorption of PS or other 
molecules of similar size. 

Juhola 17 has plotted the micropore volume of a 
number of charcoals against the PS life with the re¬ 
sult shown in Figure 29. As he points out, there is 
considerable doubt as to whether a plot of this kind 
is significant in view of the fact that almost certainly 
PS will be adsorbed as at least a monolayer on the 
entire charcoal surface at the relative pressure of 
0.25 (47 mg of PS per liter) at which most PS life 
tests are made. 

Insufficient work has been done to draw very defi¬ 
nite conclusions relative to the relation existing be¬ 
tween pore volume, pore distribution, and the activ¬ 
ity of a charcoal toward the removal of AC and SA. 
From the study of activity vs time of activation of 
PCI charcoals, Blacet and Skei 68 obtained data 
which indicate that SA activity is very low for the 

























PORE SIZE ALTERATION 


121 



0 O.t 0.2 0.3 0.4 0.5 


MICRO PORE VOLUME-CC PER CC OF GRANULE 

Figure 29. Micropore volume of various charcoals vs 

PS life. 

first 100 min of activation and then rises sharply, 
almost linearly, with time of activation. Unfortu¬ 
nately, pore size measurements were not made on 
the samples in this series of runs. However, accord¬ 
ing to a similar series reported by Juhola 17 (Figure 19 
of his June 1945 report) the pore size that increases 
abruptly at about 100 min of activation is the range 
18 to 2000 A diameter. Presumably, therefore, pores 
in this range are essential to SA removal. In contrast 
to this, AC activity, according to Blacet’s and Skei’s 
results, increases from the start and for the 80-80 
tests has reached about 60% of its maximum by the 
end of 100 min of activation. This suggests that per¬ 
haps the smaller pores and capillaries (those under 
18 A in size) are especially necessary for AC removal. 
Doubt is thrown on both of these conclusions, how¬ 
ever, by the fact that the 80-80 CK activity behaves 
quite differently as a function of the time of activa¬ 
tion in Blacet’s and Skei’s 18 tests and in those re¬ 
ported by Juhola. 17 In the former, the CK activity 
begins rising abruptly after about 30-min activation 
and reaches a life that is, at least, 80% of the 
smoothed maximum by 100-min activation. In con¬ 
trast to this, according to Juhola’s report, 17 the CK 
80-80 activity is very low during the first 90-min 
activation and then rises linearly with time to an 
activation of 300 min, the longest activation period 
employed. This makes one believe that conditions 
during the activation of the two series were not the 
same and that, accordingly, the pore size measure¬ 
ments, as a function of time, on the series reported by 
Juhola may not be the same as on the series reported 
by Skei. It should be emphasized, however, that with 


the completion of the methods for measuring pore 
distributions in charcoals and whetlerites it is now 
possible to carry out experiments that should throw 
more light on the mechanisms of removal of the vari¬ 
ous gases by charcoal than has been possible in the 
past. 

The CG test data reported by Zabor and Juhola 64 
indicate that macropore volume is as important to 
the removal of CG (80-80 test conditions) as it ap¬ 
pears to be to the removal of CK under 80-80 test 
conditions. In both cases, according to these authors, 
there is a minimum macropore volume below which 
the CK and the CG lives are substantially zero. No 
further information is available relative to the CG 
activity as a function of macropore volume. The pre¬ 
ponderance of evidence certainly indicates the im¬ 
portance of macropore volume for CG as well as for 
CK removal. 

6.6 PORE SIZE ALTERATION 

When it appeared that pore size distribution might 
be largely responsible for the failure of certain char¬ 
coals to make good whetlerites, work was under¬ 
taken 69 with a view to altering the pore size of the 
base charcoals that would not make good whetler¬ 
ites. In particular, it appeared that the charcoals 
made at that time by the ZnCl 2 process were good ad¬ 
sorbents but very poor supports for making whetler¬ 
ites. A typical nitrogen isotherm of such a charcoal is 
illustrated in Figure 5. On the other hand, charcoals 
made from coal by certain procedures were excellent 
both as an adsorbent and as a base charcoal for mak¬ 
ing whetlerites. The intensive work on pore altera¬ 
tion, accordingly, originated with the idea of trying 
to alter the product of the ZnCl 2 process so as to per¬ 
mit the large plant capacity producing charcoal by 
this process to be usable. 

The alteration in pore size has been judged mostly 
by the change in the appearance of the nitrogen ad¬ 
sorption isotherms up to relative pressures of 0.99. 
Furthermore, most of the discussion will be centered 
upon the actual pore alteration rather than on the 
improvement in the whetlerized product-result from 
such alteration. The procedure in making these whet- 
lerite tests was not up to the usual standard of whet- 
lerization and testing because all samples of the base 
charcoal had to be shipped, and because whetlerizing 
technique and whetlerite testing were in the process 
of change during the period of this work, making it 
impossible to compare adequately one group of sam¬ 
ples with another. 


SECR E 






















122 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 




p 

P. 


Figure 30. Effects of treating CWSN 19: (1) Normal 
CWSN 19; (2) Steamed at 750 C, 43% loss; (3) H 2 at 
1000 C, 74% loss; (4) 5% Fe 2 0 3 , steam at 750 C, 37% 
loss; (5) 5% Fe 2 0 3 , H 2 at 600 C, 50% loss; (6) 5% Fe 2 O s , 
air at 350 C, 48% loss. 

In discussing the influence of various factors on the 
shapes of the isotherms, it will be convenient to dif¬ 
ferentiate between the total adsorption in the region 
up to 0.4 (called AB), the slope of the isotherm be¬ 
tween 0.4 and 0.7 (called BC; this is roughly the pore 
size that would be filled with water vapor by capil¬ 
lary condensation at 80% RH if cos 6 for water is 
about 0.6), and the slope of the isotherm between 
0.7 and 0.99 (called CD; this region is the portion of 
the macropore region lying between about 60 and 
2000 A). 

It is also important to differentiate between 
changes in isotherms per gram of charcoal and 
changes per cubic centimeter of granules (this means 
per cubic centimeter of actual charcoal volume as 
measured by mercury pycnometers at 1 atmosphere 
pressure). 

In a general way it can be said that it is possible 69 
to tailor-make the pore distributions in charcoals by 
a combination of steaming and hydrogenating (with 
and without impregnants), that is, to change char¬ 
coals having flat sotherms of the type shown in Fig¬ 
ure 5 for CWSN 19 to isotherms having steeper 
slopes. The region AB can be increased or decreased 




p_ 

p 0 


Figure 31. Effects of treating CWSN S5: (1) Normal 
CWSN S5; (2) Heated in pure N 2 to 1200 C then 
steamed at 750 C to 69% loss; (3) Heated for 2 hours in 
pure N> at 1200 C; (4) H 2 treated at 1000 C to 37% loss; 
(5) 5% Fe 2 0 3 , tank N 2 at 1000 C to 25% loss; (6) 5% 
Fe 2 0 3 , Ho treated at 500 C to 30% loss. 


on either a per gram or a per cubic centimeter basis; 
both BC and CD can be left unchanged in slope or 
can be increased in slope. An increase in slope of 
either of these last two regions is interpreted as an 
increase in pore volume in these respective ranges. 
On the other hand, an increase in AB might mean an 
increase in the number of small pores, or it might 
mean an increase in the total surface area caused pos¬ 
sibly by increases in the number of pores n the BC 
region. 

A few typical examples 69 of the effect of steaming, 
air oxidizing, hydrogenating and, to a limited extent, 
treatment with impregnants are shown in Figures BO- 
34. For more examples, the reader is referred to the 
original report 69 where a total of 17 figures show all 
the results that were obtained on pore alteration. 
Below are discussed the influence of a few of the op¬ 
erations on the shape of the isotherms in so far as 
any general conclusions can be drawn. 


9IHHH 

































































































PORE SIZE ALTERATION 


123 




Figure 32. Effects of treating coconut charcoal. (1) 
Normal coconut charcoal; (2) Steamed at 750 C to 40% 
loss; (3) 0.2% O 2 O 3 , steamed 750 C, 33% loss; (4) H 2 
treated at 1000 C to 31% loss; (5) 5% Cr 2 Oa, H 2 at 
1000 C to 38% loss. 

6.6.1 Steaming without Impregnating 

Moderate steaming at 750 C on standard charcoal 
samples increased the adsorption in region AB. This 
presumably means that added steaming beyond the 
point usually used for steam-activated charcoals con¬ 
tinues to open up small pores. This was always true 
on a weight basis for the four charcoals studied, 
CWSN 19,CWSN 55, coconut charcoal, and PCI P58. 
The adsorption per cc was increased in the AB region 
for the first of these four but decreases slightly for the 
other three. Examples are given by curves in Fig¬ 
ures 30 to 34. There is nothing unusual in these 
steaming results since new small pores can certainly 
be opened up by the treatment with a resulting in¬ 
crease in adsorption per gram. If the steaming is car¬ 
ried too far, of course, the adsorption per cubic centi¬ 
meter of granules must start to decrease because of 
overlapping of the small pores. 




£ __ 
p o 


Figure 33. Effects of treating PCI P58. (1) PCI P58; 

( 2 ) Steamed 750 C to 31% loss; (3) 5% O 2 O 3 * steam 
750 C, 36% loss; (4) H 2 at 1000 C to 48% loss; (5) 5% 
Cr 2 Oo, H 2 at 1000 C, 43% loss. 

6.6.2 Hydrogenation without Impregnation 

It does not seem to be generally recognized in the 
literature that hydrogenation can alter pore sizes and 
distribution just as effectively as can steaming. Usu¬ 
ally, however, a somewhat higher temperature is 
needed for hydrogenation than for steaming. Fig¬ 
ures 30 to 34 show curves illustrating the effect of 
hydrogenation of the four charcoals studied. For all 
of them, the adsorption in the AB region per gram 
either increases or remains constant; the slope of the 
adsorption in the intermediate BC region remains 
unchanged, and the slope of the adsorption in the 
CD region increases sharply with an especially rapid 
increase close to a relative pressure of 0.99. In fact, 
the rapid rise in the adsorption between 0.9 and 0.99 
relative pressure is rather characteristic of hydro¬ 
genation in the absence of impregnants. 

Only for charcoal CWSN 19 is there an increase in 
the total adsorption per cubic centimeter of granules 
during mild hydrogenation. Presumably, the major 
attack is on pores in the CD region. 


























































































124 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 




£ 

p o' 


Figure 34. Effects of hydrogenation of CWSN 19. 

(1) CWSN 19; (2) 5% NiO. H 2 at 1000 C to 27% loss 
Ni(N0 3 ) 2 ; (3) 5% NiO, H 2 at 1000 C to 25% loss 
(NiCl 2 ); (4) H 2 treated at 1000 C to 26% loss. 

6.6.3 Partial Combustion in Nitrogen 
Containing Limited Amounts of Oxygen 

and No Impregnants 

Mild oxidation of CWSN 19 increased the adsorp¬ 
tion in the A B region (Figure 30) by a small amount 
both on a per gram and a per cubic centimeter basis. 
On the other hand, it had little influence on the slope 
of the isotherm above 0.4 relative pressure. Presum¬ 
ably such oxidation primarily effects the formation 
of new small pores. 

6.6.4 Influence of Impregnants on Steaming, 
Hydrogenation, and Partial Oxidation 

In the course of the work, the action of Cr 2 0 3 , 
Fe 2 0 3 , Mo 2 0 3 , Na 2 C0 3 , and NiO on the various proc¬ 
esses for altering pore size were studied. These com¬ 
pounds were formed in amounts ranging from 0.2 to 
5.0% by various procedures. 69 It is sometimes diffi¬ 
cult to generalize because the impregnant produced 


results at times that differed as a function of the 
particular compounds used in getting the given oxide 
on the sample. However, in a general way the results 
were as follows. 

1. Fe 2 0 3 gave definite evidence of catalyzing the 
attack on the charcoal. For example, at 600 C in the 
presence of 5% Fe 2 0 3 impregnant a 50% weight loss 
of CWSN 19 was brought about by hydrogenation, 
whereas in the absence of the impregnant practically 
no loss occurred. Another evidence is the fact that 
even on a weight basis, the adsorption up to 0.4 rela¬ 
tive pressure decreased in a majority of treatments 
with Fe 2 0 3 as impregnant. This is definite evidence 
of an attack on the smaller pores greater in extent 
than any formation of small pores that is taking 
place. The iron oxide invariably causes a consider¬ 
able rise in the isotherms between 0.7 and 0.99 re¬ 
gardless of the gas being employed for activation. 

One result with iron oxide is especially puzzling. 
In a run using 5% iron oxide and carried out with 
tank nitrogen at 1000 C to a 13% weight loss, the 
total pore volume on both the per gram and per 
cubic centimeter basis dropped about 20%. Unless 
some error in calculation was involved (the original 
notebooks are not available at this writing) this 
means that the closing up of enough small pores by 
the 1000 C treatment more than compensates for the 
increase in the number of pores indicated by the 
0.7 to 0.99 relative pressure region. This is the only 
instance in which positive evidence was obtained of 
a pore closing effect on CWSN 19. 

2. Cr 2 0 3 impregnation combined with steaming 
on CWSN 19 seems to have little added effect over 
steaming by itself. On hydrogenation, however, the 
effect is similar to that of the iron in that a consider¬ 
able decrease in the A B region occurs on a volume 
basis with a marked increase in the CD region. 

The results on CWSN S5 are confused by the fact 
that heating this charcoal to 1200 C even in pure 
nitrogen causes a shrinkage as a result of which the 
adsorption per unit weight decreases more than the 
adsorption per unit volume (Figure 31). In other 
words, the apparent particle density increases. At 
750 C, steaming after impregnation with chromium 
oxide produces a very different effect than steaming 
alone. The low-pressure adsorption decreases per 
cubic centimeter of charcoal, whereas the slopes of 
both the BC and CD regions are increased by about 
15%. The hydrogenation at 1000 C with Cr 2 0 3 pres¬ 
ent seems to produce the same sintering effect caused 
by heating this charcoal to 1200 C but in addition 
















































OXYGEN SURFACE COMPLEXES ON CHARCOALS 


125 


causes a 20% increase in the slope of the CD portion 
of the isotherm. 

On coconut charcoal, impregnation with 0.2% 
Cr 2 0 3 caused nearly a 100% increase in the adsorp¬ 
tion up to 0.4 relative pressure on a weight basis, a 
30% increase on a volume basis and a 15% slope in¬ 
crease in the CD region (Figure 32). Strangely 
enough, 5% Cr 2 0 3 and steaming produced very little 
more effect than straight steaming to a similar weight 
loss, though the slope of the BC and CD regions were 
10 to 20% greater than those resulting from steaming 
alone. Hydrogenation of coconut charcoal impreg¬ 
nated with 0.2 or 5% Cr 2 0 3 caused none of the slope 
change characterizing similar runs on CWSN 19 or 
CWSN S5, the slope of the isotherms being identical 
to that of the original charcoal; in fact, the marked 
turn-up of the isotherm between 0.9 and 0.99 pro¬ 
duced by straight hydrogenation is absent when 
Cr 2 0 3 is present (Figure 32). 

PCI P58, impregnated with Cr 2 0 3 , behaved little 
differently on steaming from samples not impreg¬ 
nated as regard the slope of the isotherms; however, 
the larger (5%) Cr 2 0 3 content caused a drop in the 
absolute adsorption of 15 or 20% on both the weight 
and volume basis (Figure 33). Hydrogenation after 
impregnation with Cr 2 0 3 produced the same slope 
increase in the CD region that was obtained without 
any impregnation; the total pore volume, however, 
of this charcoal was decreased by the impregnation 
both on the weight and volume basis (Figure 33), 
much as though a sintering effect had taken place 
that shifted the adsorption to smaller values on both 
a weight and volume basis. 

It is apparent that Cr 2 0 3 as an impregnant can 
effect marked changes in charcoals when combined 
with steaming and hydrogenation, and that the ef¬ 
fects are apparently quite specific and dependent on 
the kind of charcoal used. 

3. On steaming, NiO on CWSN 19 produces no 
change in slope of the isotherms, just as was true of 
straight steaming; however, it appears to drop the 
total pore volume on both a weight and volume basis 
by about 35% compared to the volume after steam¬ 
ing in the absence of NiO. For hydrogenation, the 
nickel results are especially noteworthy in that they 
show a decided specificity upon the particular nickel 
salt used in impregnation. For example, if the nitrate 
is used together with precipitation by NH 4 OH, hy¬ 
drogenation to a weight loss of 29 % results in a nitro¬ 
gen isotherm that is a straight line from 0.4 to 1.0 
relative pressure with an increase in volume of 20% 


over this range. In contrast to this, the same per¬ 
centage of NiO produced from NiCl 2 plus NH 4 OH 
caused no change in slope and only a few per cent 
decrease in total adsorption compared to the initial 
CWSN 19 (Figure 34). In fact, the NiO from the 
chloride appeared to have little effect on the hydro¬ 
genation. 

The single experiment tried on CWSN 5 indicated 
that impregnation with 5% NiO combined with 
hydrogenation at 1000 C resulted in no change in 
slope of the isotherm compared to the original, and a 
decrease of about 15% total adsorption on both a 
weight and volume basis. 

4. Impregnation (5%) with Mo 2 0 3 produced no 
specific effects in either steaming or hydrogenating 
CWSN 19 other than those observed without the 
impregnation. Likewise, 5% Na 2 0 from sodium car¬ 
bonate produced no noticeable modification to the 
hydrogenation of CWSN 19 at 1000 C. 

The two experiments on steaming Type A whetler- 
ites (Cu impregnation) behaved quite differently. On 
CWSN 19, steaming a whetlerite to a 26% loss at 
750 C resulted in an isotherm unchanged in slope 
from that of the original charcoal but about 35% 
smaller in volume than would have resulted from a 
steaming to a 40% weight loss in the absence of the 
impregnant. On the other hand, steaming a Type A 
whetlerite made from CWSN S5 caused the slope of 
the BC and CD section of the isotherm to increase 
greatly, the adsorption at 0.99 relative pressure being 
about 20% greater than at 0.4 relative pressure. 

6.7 OXYGEN SURFACE COMPLEXES ON 
CHARCOALS 

6.7.1 Introduction 

It has long been known 33> 38> 70-72 that charcoals 
and activated carbons are covered with carbon-oxy¬ 
gen complexes, the composition of which varies as a 
function of the method of treatment of the sample. 
Research on surface complexes of charcoal during the 
war has been carried out primarily because of the 
help it might furnish in (1) showing the proper sur¬ 
face treatment to give maximum adsorption of cer¬ 
tain gases such as ammonia that are apparently very 
sensitive to the nature of the charcoal surface; (2) in¬ 
terpreting the aging of base charcoal that from time 
to time was thought to be taking place on storage 
under humid conditions; (3) interpreting the aging 
of ASC whetlerites that is known to occur under high 







126 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


humidity; and (4) indicating the type of surface 
complex that might be most effective in minimizing 
the adsorption of water vapor by the whetlerites. 

The actual results obtained that are applicable to 
the four main objects of the work are, for the most 
part, restricted to item (1) above. The surface com¬ 
plex studies failed to throw much light on items (2) 
and (3). 27 This may be due in part to the fact that 
the surface complex work was carried out in a differ¬ 
ent laboratory from that in which the whetlerization 
and aging work was done. Consequently, the delay 
in getting samples whetlerized, the uncertainties sur¬ 
rounding the treated base charcoals during shipment 
for whetlerization, and the changing of whetlerizing 
procedures in the course of this work, all tended to 
complicate the drawing of any rigorous conclusions 
as to the influence of surface complexes on the aging 
of either the base charcoals or the whetlerites. As for 
(4), the behavior of whetlerites toward water vapor 
appears to be much more dependent on the pore size 
distribution in the region between that correspond¬ 
ing to capillary condensation at 0.8 relative pressure 
and that at 1.0 relative pressure than it does on the 
nature of the surface complex. The latter is more 
likely to influence the amount of water adsorption 
occurring at low relative pressures but is less influ¬ 
ential on the adsorption at high relative pressures. 

The work that has been done on the surface com¬ 
plexes divides itself rather naturally into two parts: 
(1) the study of oxygen adsorption by the charcoal 
in relation to the adsorptive properties toward am¬ 
monia, acids, and bases; and (2) the measurement of 
the gas evolution as a function of the temperature to 
which the various charcoals have been heated. The 
first of these two groups of experiments were carried 
out chiefly by Young 24 * 73 and his co-workers; the 
second, by Anderson. 27 These two research studies 
contribute a great many useful data and correlations 
that will now be briefly summarized even though 
they fail to give a definite answer to the question of 
the relation between the surface composition and the 
aging of charcoals and whetlerites. 

6.7.2 Oxygen Adsorption by Charcoals 
and its Influence on their Properties 

As pointed out by Young, 73 it has long been 
known 74 * 75> 75a - 79a - 80a that several different carbon- 
oxygen surface complexes may exist on charcoal and 
carbon black. Two 76-78 of these appear to be formed 
by the picking up of oxygen at room temperature; 


another is claimed to be formed by exposure of char¬ 
coal to oxygen at about 400 C; and a fourth 79 is sup¬ 
posed to form above 850 C in the presence of oxidiz¬ 
ing gases. Oxygen complexes have been reported for 
graphite and diamond 80 as well as for charcoal and 
carbon black. The experiments reviewed and sum¬ 
marized in the present section were directed not so 
much toward the verification of these various com¬ 
plexes as toward the study of the influence of the 
complexes formed at 400 C in free oxygen upon the 
properties of the various charcoals as adsorbents for 
acids, bases, ammonia, HC1, and water vapor. A few 
experiments were also made upon the rate of oxygen 
pickup by various charcoals at room temperature. 
These various results and observations made during 
this work may be summarized as follows. 



O 50 100 150 200 250 

T IN HOURS 

Figure 35. Oxygen sorption at 25 C on charcoals. 


1. Oxygen pickup by charcoals: Lowry 38 pointed 
out that oxygen is slowly picked up by charcoals at 
room temperature in the form of a chemical adsorp¬ 
tion. In addition, there is a rapid physical adsorption 
which is easily reversible and which amounts to about 
10% of a monolayer at one atmosphere pressure. The 
slow chemical adsorption varies in amount and rate 
with different charcoals. Figure 35 shows the results 
obtained by Young 24 on a typical group of charcoals. 
The total oxygen picked up irreversibly by even 
CWSN 44 is apparently only a small fraction of a 
monolayer. 

By exposing charcoals to oxygen at 400 C, Young 
has succeeded in building up an oxygen content of as 



















OXYGEN SURFACE COMPLEXES ON CHARCOALS 


127 



0 0.1 0.2 0.3 0.4 0.5 0.6 

HCL ADSORBED-ME PER GRAM 



0 10 20 30 4 0 50 60 


PER CENT WEIGHT LOSS 

Figure 36. Influence of oxygen treatment on the base 

and acid adsorptive properties. 

much as 18% on the charcoals. This oxygen coating 
was accompanied by a 56 % weight loss. It should be 
noted that even 18% oxygen corresponds to only a 
monolayer of oxygen on the surface of the carbon. 

2. Influence of oxygen treatment on the base and 
acid adsorptive properties: CWSN 19, upon which 
most of the early oxygen complex work was done, ad¬ 
sorbed 73 0.27 milli-equivalents of HC1 per gram and 
no NaOH. The time allowed for equilibration in ad¬ 
sorption in these experiments was 30 min and the 
original concentration of the adsorbate solution was 
0.03A r . Oxygen-treating the charcoal increased the 
base adsorption and decreased the acid adsorption. 
The results are shown in Figure 36 taken from the 
paper of Young. 73 In the same figure is shown the 
NaOH adsorption as a function of the weight loss in 
the oxidation process. 

In Figure 37 is shown the variation of the rate of 
NaOH pickup with time, temperature, and the 



HCI ADSORBED ME PER GRAM 

Figure 37. Variations of the rate of NaOH pickup with 
particle size. 


amount of crushing to which the sample has been 
subjected. Evidently, crushing the sample and in¬ 
creasing the temperature increases the rate of adsorp¬ 
tion greatly. Neither temperature increase nor crush¬ 
ing has any effect on the final equilibrium value of the 
adsorption. Figure 37 also shows the adsorption 
curve obtained by allowing 24-hour equilibration and 
by using adsorption solutions that were 0.5N. As 
pointed out by Young, the slope of this curve indi¬ 
cates that for every equivalent of acid-forming power 
lost by the charcoal, four to five equivalents of base¬ 
forming power are gained. 

Experiments by King 79 and also by Young 73 lead 
to the conclusion that both the H + and the Cl~ are 
adsorbed from solutions by the charcoals. Also, both 
Na + and OH - are adsorbed. It is still unknown 
whether the alkali adsorption is a process by which 
the Na + , by base exchange, displaces a H + from the 
surface which then reacts with the OH - or whether 
the Na + and OH - are actually adsorbed. 

Washing experiments showed that most of the HCI 
adsorbed by the untreated CWSN 19 and most of the 
NaOH adsorbed by the oxygen-treated samples were 
irreversibly adsorbed. In other words, they were not 
removed by thorough washing. However, these quan¬ 
tities of irreversibly held adsorbates could be titrated 
with base and acid respectively, washed, and caused 
to re-adsorb the original amount of adsorbate. For 
example, the original CWSN 19 held 0.24 milli-equiv- 



























































128 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 



Figure 38. Typical curves of effects of oxygen coating 
on NH 3 adsorption. 


alent of HC1 irreversibly. This, on titration, picked 
up 0.24 milli-equivalent of NaOH with the evolution 
of this amount of NaCl into the solution. The sample, 
after washing, could then again pick up 0.24 milli- 
equivalent of HC1 and the process could be repeated. 

3. Influence of surface complex on the adsorption 
of water vapor: It has already been pointed out in 
the section on water adsorption that adding oxygen 
complex to a charcoal increases the low pressure ad¬ 
sorption of water vapor and displaces the desorption 
hysteresis loop to lower relative pressures. Con¬ 
versely, treating charcoals with hydrogen or with 
steam at high temperature tends to shift the adsorp¬ 
tion curves to higher relative pressure and decreases 
markedly the adsorption below 0.5 relative pressure. 
It should also be noted that similar effects have been 
observed for carbon black samples as shown in 
Figure 14. 

4. Influence of surface complex on the adsorption 
of ammonia and of HC1 gas: Oxygen-treating a char¬ 
coal at 400 C increases its tube life for ammonia ten 
to forty fold and increases the ammonia adsorption 
over the entire relative pressure range. 23, 73 In Fig¬ 
ure 38, two typical curves that illustrate the effect of 
oxygen coating are shown. The extra ammonia 
pickup would appear to be due to a kind of chemical 
adsorption of ammonia since the increase in adsorp¬ 
tion is between 75 and 100 cc throughout the entire 
pressure range. However, the heat of binding of such 
chemisorption is not great, as is evidenced by the 
fact that the extra ammonia will pump off slowly at 


25 C, and completely in a short time at 100 C. 23 It 
should also be recorded that nitrogen isotherms prove 
that this enhanced ammonia adsorption is definitely 
not the result of an increase in surface of the charcoal 
resulting from the oxygen treatment. It is due to the 
specific nature of the surface containing the oxygen 
complex. 

The adsorption of HC1 gas by CWSN 19 is not 
altered 81 in any marked way by oxygen coating. The 
changes in the adsorption are small and apparently 
no greater than the corresponding changes in the 
nitrogen adsorption. 

5. Heat of binding of oxygen to carbon in the sur¬ 
face complex: By a series of careful measurements of 
the heat of combustion of charcoal as a function of 
the amount of oxygen complex on the surface, 
Young 73 has been able to show that the oxygen is 
held to the surface of a carbon by a heat of about 
60,000 to 65,000 calories per mole of oxygen. The heat 
of adsorption at 400 C thus estimated appears to be 
independent of the fraction of the surface covered by 
complex. These heat of adsorption values are in good 
agreement with the value 70,000 calories found by 
Keyes and Marshall 82 for charcoal at 0 C, 60,000 
calories reported by Blench and Garner 83 for ad¬ 
sorption at room temperature, and 70,000 to 129,000 
calories reported by Marshall and Maclnnes. 84 There 
can be no doubt that the oxygen is held to the carbon 
surface by very strong chemical bonds. 85, 86 

6.7.3 Gas Evolution from Charcoals as a 
Function of the Temperature 
to Which They are Heated 

Lowry 38 has described the apparatus used and the 
results obtained in degassing a series of charcoals 
which at the end of World War I could be considered 
as typical of those used by the United States, Great 
Britain, and Germany. In general, he showed that all 
charcoals evolved considerable quantities of CO, 
CO 2 , and water vapor up to about 900 C. Between 
900 and 1200 C, increasingly large quantities of hy¬ 
drogen were given off. Part of this hydrogen ap¬ 
peared to come from the surface of the charcoal 
though it is also possible that part of it resulted from 
decomposition of hydrogen-carbon complexes that 
were not located at the actual surface of the charcoal. 

Using a very similar apparatus, Anderson 27 has 
made an extended series of experiments on various 
charcoals of interest in the recent research work in 

































OXYGEN SURFACE COMPLEXES ON CHARCOALS 


129 


Table 6. Degassing experiments on charcoals — total gas evolved ml (STP) per g. 


Sample 

25-300 C 

300-600 C 

600-900 C 

900-1200 C 

CO 

d 

o 

h 2 o 

h 2 

CO 

C0 2 

HoO 

h 2 

CO 

C0 2 

H 2 0 

h 2 

CO 

ch 4 

co 2 

HoO 

CWSN 19 

0.2 

0.3 

0.4 

0.3 

3.8 

1.5 

1.3 

10.4 

11.7 

0.5 

0.4 

46.4 

1.0 

2.1 

1.0 

0.0 

CWSN S5 

0.5 

2.0 

2.3 

1.0 

4.6 

2.3 

5.3 

92.0 

21.7 

1.4 

6.0 

36.9 

0.6 

0.6 

0.0 

0.0 

CWSN S5 

















Extracted with HF 

0.9 

3.0 

5.8 

2.5 

87.2 

39.9 

1.9 

66.9 

27.7 

1.2 

2.0 

21.58 

0.4 

0.6 

0.7 

0.1 

CWSN 44 

0.7 

3.3 

3.5 

1.4 

6.6 

3.2 

4.6 

97.5 

22.8 

1.1 

4.0 

51.8 

2.6 

3.3 

0.1 

0.0 

CWSN 196 B1 

0.5 

2.7 

3.3 

1.4 

5.5 

3.0 

4.6 

93.0 

29.5 

0.5 

1.8 

36.5 

0.5 

0.8 

0.2 

0.0 

CWSN 196 BIX 

0.2 

1.5 

1.6 

1.0 

3.3 

6.8 

1.6 

53.1 

11.8 

0.2 

0.1 

33.8 

0.4 

0.8 

0.2 

0.1 

PCI P58 

0.1 

0.2 

0.9 

0.1 

1.2 

0.7 

0.7 

16.2 

11.4 

0.5 

0.2 

38.3 

97.8 

4.7 

0.0 

0.0 

CWSC 1242 

0.3 

0.6 

0.9 

0.0 

0.7 

1.2 

1.1 

5.8 

4.0 

0.3 

0.2 

19.3 

0.9 

0.1 

0.2 

0.1 

CFI “CC” 

0.1 

0.2 

1.2 

0.0 

0.7 

0.3 

1.1 

7.8 

5.5 

0.2 

0.2 

38.5 

63.4 

0.8 

0.2 

0.0 

CWSB-X2 

0.2 

3.1 

2.3 





13.4* 

7.8* 

2.2* 

1.9* 

36.3 

5.4 

0.6 

0.3 

0.1 


25-120 C 

120-600 C 










PCI P25 

0.0 

0.0 

0.5 

0.5 

2.0 

1.0 

3.0 

10.5 

9.9 

0.4 

0.5 

35.3 

88.5 

2.7 

0.3 

0.0 

PCI 1042 

0.0 

0.2 

0.6 

0.3 

2.6 

1.2 

1.3 

7.5 

9.6 

0.3 

0.3 

43.2 

93.1 

2.3 

0.4 

0.0 

PCI 1042 

















Extracted with HF 

0.0 

0.0 

0.7 

0.6 

51.2 

9.4 

4.3 

20.8 

20.9 

3.0 

0.3 

22.3 

0.8 

0.8 

0.4 

0.0 


* 300-900 C. 


Table 7. Degassing experiments on charcoals — total gas evolved ml (STP) per g. 


Sample 


25-900 C 



25- 

-1200 C 



h 2 

o 2 

o 2 

h 2 

CO 

C0 2 

h 2 o 

h 2 

CO 

ch 4 

O 

O 

H 2 0 

evolved 

evolved 

in ash 

CWSN 19 

10.7 

15.7 

2.3 

2.1 

57.1 

16.7 

2.7 

3.3 

2.1 

0.58 

1.81 

0.04* 

CWSN S5 

CWSN S5 

93.0 

26.8 

5.7 

13.5 

129.9 

27.4 

1.4 

5.7 

13.6 

1.31 

3.74 

2.0f 

Extracted with HF 

69.4 

115.8 

44.1 

9.7 

91.2 

116.2 

1.8 

44.8 

9.8 

0.93 

16.10 


CWSN 44 

98.9 

30.1 

7.6 

12.1 

147.5 

32.7 

8.3 

7.7 

12.1 

1.58 

4.30 

0.8* 

CWSN 196 B1 

94.4 

35.5 

6.2 

9.7 

130.9 

36.0 

1.8 

6.4 

9.8 

1.29 

4.18 

0.6* 

CWSN 196 BIX 

54.1 

15.3 

8.5 

3.3 

87.9 

15.7 

1.5 

8.7 

3.4 

0.84 

2.59 

1.0* 

PCI P58 

16.3 

12.7 

1.4 

1.8 

54.6 

110.5 

5.0 

1.4 

1.8 

0.59 

8.22 


CWSC 1242 

5.8 

5.0 

2.1 

2.1 

25.1 

5.9 

0.2 

2.3 

2.3 

0.25 

0.91 


CFI“CC” 

7.8 

6.3 

0.7 

2.5 

49.7 

13.4 

0.8 

5.6 

4.3 

0.50 

2.06 


CWSB X2 

13.4 

8.0 

5.3 

4.2 

46.3 

69.7 

0.8 

0.9 

2.5 

0.45 

5.28 


PCI P25 

11.0 

11.9 

1.4 

4.0 

46.3 

100.5 

2.8 

1.7 

4.0 

0.40 

7.70 


PCI 1042 

PCI 1042 

7.8 

12.2 

1.7 

2.2 

51.0 

102.3 

2.5 

2.1 

2.2 

0.58 

7.76 


Extracted with HF 

21.4 

72.1 

12.4 

5.3 

43.7 

72.9 

1.2 

12.8 

5.3 

0.46 

7.42 



* Ash was assumed to be zinc oxide in computation of these values, 
t Reported by Wiig and Flagg (Informal Report 10.1-26 June 11, 1943). 


World War II. The evolved gas was collected during 
periods of about seven hours for each temperature 
interval studied. The experiments were grouped to 
cover the range 25 to 300 C; 300 to 600 C; 600 to 
900 C; and 900 to 1200 C. The variables studied in¬ 
cluded the nature of the charcoal, the ash content 87 
of the charcoal, and the type of treatment to which 
the charcoal had been subjected. The principal re¬ 
sults 27 obtained may be briefly summarized as 
follows. 

1. In Table 6 are shown the volumes of CO, H 2 , 
C0 2 , CH 4 , and H 2 0 evolved from a number of typical 
charcoals as a function of the temperature to which 
they were heated. In Table 7 the results are summa¬ 


rized to cover the region up to 900 and up to 1200 C; 
also in this latter table are shown the results of gas 
evolution to 1200 C calculated in terms of equivalent 
per cent of hydrogen and oxygen in the original char¬ 
coal. For comparison, Table 7 also shows the per cent 
oxygen present in the ash wherever ash analysis was 
available or could be guessed from the method of 
preparation of the charcoal. 

Several general conclusions can be drawn from 
the results in these two tables. In the first place it 
should be noted that the CO and C0 2 evolution is 
smaller from the PCI, CWSC, CFI, and CWSB-X 
(nutshell) than from the National samples prepared 
by the ZnCl 2 process. However, a detailed study of 
































130 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


the gas evolution from one of the National samples, 
CWSN 5, at 60-degree intervals showed that most of 
the CO and H 2 0 were evolved in the temperature 
range 600 C to 800 C. Concomitantly with the gas 
release, a deposit of zinc was formed on the cooler 
part of the reaction vessel. In all probability, there¬ 
fore, the excessive evolution of CO and H 2 0 from the 
National samples in the temperature range up to 
900 C may be attributed to a large extent to the re¬ 
duction of ZnO ash by C and by H 2 . Consistent with 
this interpretation is the fact that CWSN 19, which 
had only 0.04% ash, yielded volumes of CO and H 2 0 
in the temperature range up to 900 C approximately 
the same as obtained from charcoals not made by the 
ZnCl 2 process. 

At temperatures above 900 C, a burst of CO was 
obtained from all the charcoals that had appreciable 
percentages of ash other than ZnO. There seems to 
be little doubt that this higher temperature CO evo¬ 
lution is caused by the reduction of the ash com¬ 
ponents by C. Ash for the most part on analyzed 
samples was found to consist of Si0 2 and A1 2 0 3 . 87 
Data in the literature 88 indicate that for the reduc¬ 
tion of Si0 2 by C to form silicon carbides and CO, 
the partial pressure of evolved gas at 900 C at equi¬ 
librium is about 0.1mm, and at 1200 C is about 

10.7 mm. Accordingly, since the maximum pressure 
in the present experiments was about 0.02 mm, it is 
entirely possible that the higher temperature (at 
temperatures in excess of 900 C) CO evolution could 
have come from the reduction of silica components 
in the ash. In line with this conclusion is the fact that 
the gas evolved from a sample of PCI that had been 
rendered substantially ash free by extraction with 
HF contained practically no CO. 

One other peculiarity of these results should be 
noted. Two different samples that had been ex¬ 
tracted by HF evolved excessive amounts of CO and 
C0 2 in the region between 300 and 900 C. Thus, 
CWSN S5 after extraction evolved 115.8 ml of CO 
and 44.1 ml of C0 2 compared to 26.8 ml of CO and 

5.7 ml of C0 2 from the sample that had not been ex¬ 
tracted. Corresponding results for PCI 1042 showed 
72.1 ml of CO and 12.4 ml of C0 2 after extraction, 
compared to 12.2 ml of CO and 1.5 ml of C0 2 before 
extraction. The cause of this excessive gas evolution 
from the extracted samples is not clear. Possibly, the 
reagents used have a catalytic effect on the oxidation 
of the surface by air during extraction or drying. 

Strong hydrogen evolution from certain charcoals 
was noted a number of years ago. 38 The runs in 


Tables 6 and 7 show that some of the charcoals 
evolve as much as 147 ml of H 2 per gram on being 
heated to 1200 C. In general, it appears that the 
ZnCl 2 charcoals evolved much more hydrogen than 
the others. Furthermore, with the exception of 
CWSN 19, all of the ZnCl 2 charcoals tested appeared 
to evolve most of their hydrogen in the 600 to 900 C 
region rather than the 900 to 1200 C region. CWSN 
19, for some unknown reason, evolved the normal 
amount of hydrogen in the higher temperature region 
but very little hydrogen up to 900 C. The amount of 
hydrogen present in the charcoals is probably related 
to their pretreatment since it is known that the higher 
the temperature of calcining of the various charcoals 
in the course of preparation and activation, the 
smaller the percentage of hydrogen that they con¬ 
tain. There is some evidence that steaming at 900 C 
will put hydrogen onto a charcoal. Thus, a sample 
of CWSN BIX that had been heat-treated in nitro¬ 
gen at 1000 C until it would evolve only 15.6 ml of 
hydrogen to 1200 C, was found to evolve 47 ml of 
hydrogen after being steamed at 900 C to a 56% 
weight loss. In contrast to this, short steaming to a 
few per cent weight loss at 300, 400, and 750 C 
caused no appreciable increase in the hydrogen evo¬ 
lution above the 15.6 ml of the original sample. 
There is a chance, of course, that the excessive steam¬ 
ing made possible the escape of some hydrogen that 
originally was buried so deep in the charcoal as not to 
be able to escape at temperatures up to 1200 C. 
Hence, the interpretation of this result must remain 
uncertain until more work is done. 

2. Heat treating samples of charcoal to 1000 C in 
a stream of nitrogen was found 27 to remove practi¬ 
cally all the CO, C0 2 , and H 2 0 from the surface and 
about two-thirds of the hydrogen. This would be ex¬ 
pected on the basis of the degassing experiments 
shown in Tables 6 and 7 and hence needs no special 
comment. 

3. It is interesting to note 27 that exposure to air 
at room temperature for a week of a sample of 
CWSN BIX that had been treated with nitrogen at 
1000 C and cooled in a stream of nitrogen, restored 
the original complex to such an extent that the C0 2 
evolution on heating to 1200 C was as large as the 
original untreated sample, and the CO was two- 
thirds as large. Exposure of a heat-treated sample of 
this charcoal to oxygen at 300 C for 30 min put on 
more complex than was characteristic of the original 
charcoal as shown in Table 8; the CO and C0 2 con¬ 
tent was still, however, much smaller than that of 







OXYGEN SURFACE COMPLEXES ON CHARCOALS 


131 


Table 8. Effect of heat treatment on National charcoals — gas evolved ml (STP) per g of sample. 












Total gas evolved 



[H 2 . O 2 ,] 

%o 2 

Sample 

25-300 C 

300-600 C 


600-900 C 

900-1200 C 



25-900 C 

25-1200 C 


evolved 

in ash 


COCO 2 H 2 O 

H 2 COCO 2 H 2 O 

H> 

CO CO 2 H 2 O 

H 2 CO co 2 

CH 4 

H 2 0 

H, 

CO 

O 

.9 

0 

8 

co cm 

O 

.9 

h 2 o 




7. CWSN 196BlXheated 

















in N 2 to 1000 C, cooled 
in Ni and transferred 
in N 2 

0.0 0.0 0.1 

2.1 0.3 0.2 0.8 

2.7 

0.7 0.1 0.1 

33.2 1.3 0.6 

0.1 

0.0 

4.8 

1.0 

0.3 1.0 38.0 

1 

^2.3 0.6 

0.4 

1.0 

0.36 

0.29 

1.0* 

8. Same as No. 7 exposed 
to air for one week 

11. CWSN 196 BIX ex¬ 

0.3 3.5 3.9 

1.2 1.5 5.6 2.6 

4.5 

6.0 0.3 0.1 

33.2 1.2 0.7 

0.3 

0.1 

5.7 

7.8 

9.6 6.6 38.9 

9.0 0.8 

9.9 

6.7 

0.41 

2.54 

1.0* 

posed to O 2 at 300 C 

0.1 0.4 0.7 

0.2 4.1 9.5 1.8 

42.9 22.9 1.0 0.4 

35.0 0.4 0.4 

0.1 

0.0 

43.1 

27.1 

10.9 2.9 78.3 

27.5 0.6 

11.0 

2.9 

0.73 

3.74 

1.0* 


* Ash assumed to be zinc oxide in computations of these values. 

some of the National samples treated with oxygen 
at 400 C by Young. 

4. In view of the fact 89 that aging base charcoals 
by exposing them to a high relative humidity for a 
long period of time was believed to render the char¬ 
coal less useful for making whetlerites, a few experi¬ 
ments were carried out to compare the surface com¬ 
plex of aged and un-aged samples. Also, because heat¬ 
ing an aged sample to 110C for an hour was re¬ 
ported 89 to restore it to a condition in which it would 
then make a good whetlerite, a sample of aged char¬ 
coal was examined after it had been evacuated at 
115 C. The oxygen content of the charcoals increased 
during aging in all cases by 2% in absolute value 
(33 to 100% relative increase in oxygen). The in¬ 
crease in oxygen 27 found by our degassing experi¬ 
ments on charcoals CWSN S5, CWSN 44, and 
PCI P58 was 2.12, 1.85, and 1.43 compared to values 
of 2.6, 2.3, and 1.2 found by ultimate analyses by 
Young. It should be noted that the 3-hour heating at 
115 C of the aged CWSN S5 sample produced no de¬ 
tectable change in composition or amounts of evolved 
gas. If the improvement in whetlerizability resulting 
from heating an aged charcoal to 110 C as claimed by 
Blacet 89 was real, then either his heating conditions 
were critically different from ours or else the surface 
complex is not related in an important way to the 
whetlerizability of a charcoal. 

5. English workers 90-95 have reported results which 
indicate that in the process of adsorbing such vapors 
as CC1 4 on charcoals, part of the surface complex is 
driven off into the gas phase. The displaced gases 
were reported to be equal in some cases to the equi¬ 
librium partial pressure of the adsorbate and to cause 
marked changes in the adsorptive characteristics of 
the charcoal. The actual volumes of displaced gas 
were not mentioned. To check this important factor, 
several experiments shown in Table 9 were carried 
out 2? on a charcoal made by the ZnCl 2 process and 


Table 9. Displacement of complex by adsorption of 
vapors at 25 C. 


Charcoal 

Vapor 

Vol of 
liquid 
ml per g 
charcoal 

Time 
of ads 
in hr 

Gases evolved 
ml (STP) per g 

CO 

C0 2 

CWSN 196 B1 

CC1 4 

0.5 

18 

0.0028 

0.0036 

CWSN 196 B1 

C 6 H 5 C1 

0.4 

5 

0.00036 

0.00039 

CWSN 196 B1 

h 2 o 

0.4 

4£ 

0.0014 

0.495 

CWSN 196 B1 

h 2 o 

0.2 

2^ 

0.0024 

0.205 

CWSN 196 B1 

h 2 o 

0.1 

16 

0.0016 

0.235 

PCI P58 

c 6 h 5 ci 

0.15 

3 

0.0016 

0.00003 

PCI P58 

h 2 o 

0.08 

1 

0.0025 

0.0094 


on a PCI sample made from coal. The samples were 
evacuated at 120 C before the run in each instance, 
at temperature that should cause practically none of 
the CO or C0 2 in the complex to be removed. The 
results clearly indicate that the amount of complex 
evolved by the adsorption of either CCI4 or C6H5CI 
is very small, being equivalent in all cases to less 
than 0.01 ( /( of the complex known to be present. 
Only water vapor displaced an appreciable amount 
of gas from the charcoals; the gas evolved by water 
was entirely C0 2 and was limited almost entirely to 
the sample made by the ZnCl 2 process. It seems 
likely that most of this evolved C0 2 may have re¬ 
sulted from the attack on the ZnC0 3 ash content by 
water condensed in capillaries. The total C0 2 evo¬ 
lution in one case amounted to about 8% of that 
which would have been evolved by heating the sam¬ 
ple to 1200 C. The results as a whole fail to check the 
English work and certainly give no indication that 
physical adsorption of vapors is capable of seriously 
altering the composition of the surface complex on 
typical charcoals. 

6. In view of the fact that most charcoals are acti¬ 
vated by steam, it seemed worth while to ascertain 
the effect of steam activation on the surface com¬ 
plex. In Table 10 the results are shown for such a 
series of experiments on charcoal CWSN 191 BIX 


























132 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


Table 10. Complex formed during steam activation. 


A. CWSN 196 BIX sample extracted with HF and heated 
in N 2 at 1000 C for 3 hr. 


Temp 
range C 

Gases evolved during degassing ml (STP) 
per g charcoal H 2 0 

H 2 CO CH 4 C0 2 vapor 

25-300 

0.0 

0.0 

0.0 

0.0 

0.6 

300-600 

0.3 

0.0 

0.0 

0.1 

0.2 

600-900 

1.2 

0.1 

0.1 

0.1 

0.1 

900-1200 

14.2 

0.2 

0.3 

0.4 

0.0 

Total 

15.7 

0.3 

0.4 

0.6 

0.9 

B. Treated as in A, then exposed to water vapor at 300 C for 
33^ hr (weight loss = 0.4%). 

25-300 

0.0 

0.0 

0.0 

0.1 

0.8 

300-600 

0.2 

0.1 

0.0 

0.9 

0.8 

600-900 

1.1 

0.6 

0.1 

0.2 

0.1 

900-1200 

11.4 

0.4 

0.2 

0.2 

0.0 

Total 

12.7 

1.1 

0.3 

1.4 

1.7 


C. Treated as in A, then exposed to water vapor at 600 C for 
3H hr (weight loss = 1.0%). 


25-300 

0.0 

0.1 

0.0 

0.0 

1.3 

300-600 

0.1 

0.0 

0.0 

0.3 

0.6 

600-900 

1.5 

1.8 

0.0 

0.1 

0.2 

900-1200 

12.3 

2.3 

0.2 

0.3 

0.1 

Total 

13.9 

4.2 

0.2 

0.7 

2.2 

D. Treated as in A, then exposed to water vapor at 750 C for 

1 hr (weight loss = 1.6%). 





25-600 

0.2 

0.0 

0.0 

0.3 

1.7 

600-900 

2.7 

2.3 

0.1 

0.3 

0.4 

900-1200 

16.9 

1.9 

0.2 

0.1 

0.0 

Total 

19.8 

4.2 

0.3 

0.7 

2.1 

E. Treated as in A, then exposed to water vapor at 900 C for 

3^ hr (weight loss = 56%). 




25-300 

0.0 

0.0 

0.0 

0.4 

0.6 

306-600 

0.6 

0.1 

0.0 

1.1 

1.1 

600-900 

5.8 

1.3 

0.2 

0.2 

0.2 

900-1200 

40.5 

2.2 

0.5 

0.1 

0.1 

Total 

46.9 

3.6 

0.7 

1.8 

2.0 


after it had been extracted with HF and heated 3 hr 
in nitrogen at 1000 C. In general, the results obtained 
agree with those of Muller and Cobb 96 who studied 
the chemisorption of water vapor on an acid-ex¬ 
tracted wood charcoal at temperatures ranging from 
300 to 1100 C. Steaming at temperatures up to and 
including 750 C produced only a slight increase in 
the amount of adsorbed water and a total fixation of 
only 4.1 ml of water vapor in a form evolved as CO 
and CO 2 on heating. Over this temperature range, 
the hydrogen fixed was no greater than that calcu¬ 


lated from the amount of oxygen fixed. The sample 
that was steamed at 900 C to a 56% weight loss 
clearly fixed more hydrogen than oxygen. This is in 
agreement with the experiments of Muller and 
Cobb 97 who noted more hydrogen than oxygen be¬ 
ing fixed by steaming in the range 700 to 900 C. The 
total oxygen fixed at 900 C was no greater than on 
steaming at 750 C. In view of these results, it is easy 
to understand why the CO and CO 2 complex is so 
low on samples of charcoal made by steaming at high 
temperature and not exposed excessively to air be¬ 
fore cooling. 

6.8 SPECIAL SURFACE COATINGS ON 
CHARCOAL 

There are statements in the literature 93 to indicate 
that the relative amounts of different gases adsorbed 
may well depend upon the exact nature of the surface 
coating of the charcoal. Because of the obvious im¬ 
portance of knowing the nature of any such changes 
that might be produced, a few experiments were car¬ 
ried out in an effort to coat charcoals with complexes 
other than carbon-oxygen complexes. Specifically, 
the influence of covering the surface with nitrogen, 
with chlorine, and with sulfur were investigated. The 
principal results obtained on samples with these 
coatings will now be considered. 

6 . 8.1 Treatment of Charcoals with 
Nitrogen 

References in the literature 98> 99 indicate that 
high-temperature treatment of charcoals with am¬ 
monia is capable of forming carbon-nitrogen com¬ 
plexes that are more stable than carbon-oxygen com¬ 
plexes. Accordingly, two sets of experiments were 
carried out 27 in which an acid-extracted, degassed 
sample of CWSN BIX charcoal was heated in am¬ 
monia at 750 C and at 900 C. The samples were then 
analyzed by being heated by Anderson to various 
temperatures up to 1200 C and the evolved gases 
analyzed. The results as shown in Table 11 confirm 
the previously published work. A nitrogen complex 
is formed that is evolved only on heating in the 900 to 
1200 C region. Most of the nitrogen comes off as free 
nitrogen, though some is evolved as HCN, C 2 N 2 , 
and NH 3 . It will also be noted that the hydrogen 
content of the charcoal is increased by the ammonia 
treatment from a value of 15.6 for the original sample 
to values of 30.5 and 39.3 ml for the ammonia treat- 




























SPECIAL SURFACE COATINGS ON CHARCOAL 


133 


Table 11. Complex formed during ammonia activation. 


A. Sample exposed to NH 3 at 750 C for three hr. Weight 
loss = 0.4%. 


Gases evolved during degassing ml (STP) per g char 


Temperature 

of 

degassing 

h 2 

CO 

n 2 

c 2 n 2 

HCN 

nh 3 

H 2 0 

25-600 

0.6 

0.0 

0.1 

0.2 

0.1 

0.5 

600-900 

3.3 

0.1 

0.2 

0.1 

0.1 

0.5 

900-1200 

26.6 

0.4 

5.2 

2.3 

0.3 

0.1 

Total 

30.5 

0.5 

5.5 

2.6 

0.5 

1.1 

B. Sample exposed to NH S 
loss = 17.1%. 

at 900 C for three hr. 

Weight 

25-300 

0.0 

0.0 

0.0 

0.0 

0.0 

0.6 

300-600 

2.3 

0.0 

0.1 

0.2 

0.2 

0.6 

600-900 

5.2 

0.1 

0.1 

0.2 

0.2 

0.3 

900-1200 

31.8 

0.7 

6.3 

2.5 

0.8 

0.2 

Total 

39.3 

0.8 

6.5 

2.9 

1.2 

1.7 


ments at 750 C and 900 C respectively. Unfortu¬ 
nately, time did not permit further work with these 
ammonia-treated samples. 

6.8.2 Treatment of Charcoals with Chlorine 

Chlorine complexes which are so stable that the 
chlorine cannot be removed by evacuation at tem¬ 
peratures as high as 600 C, nor by the action of boil¬ 
ing 10% NaOH over the period of an hour, have been 
reported 100 in the literature. For the present work 27 
charcoal has been made to retain as much as 17 % of 
its weight of chlorine after evacuation for an ex¬ 
tended period at 400 C. The results are shown in 
Table 12 and in Figure 39. Apparently the amount 
of stable chlorine held by the charcoal increases with 
the temperature of treatment because the amount 



p 0 

Figure 39. Treatment of charcoals with chlorine. 


retained at room temperature after evacuation is 
greater when the temperature of the original treat¬ 
ment is high. This is also true of the fraction of the 
total chemisorption that is retained on evacuation 
to 400 C. 

Insufficient nitrogen adsorption runs were carried 
out on the chlorinated sample to answer the question 
as to the location of the chemisorbed chlorine. In 
general, it may be said that the chemisorbed chlorine 
did not decrease the volume of nitrogen held by the 
charcoal at 0.99 as much as one would expect though 
conclusions are uncertain until more runs are made. 
Figure 39 indicates that on treating a sample at 
200 C with chlorine and then evacuating it at 200 C 
a drastic pore size change occurs. If these few experi¬ 
ments are to be believed, the change occurs during 
the long evacuation at 200 C rather than during the 
original treatment since evacuation at 100 C left an 


Table 12. Adsorption of chlorine by CWSN BIX. 


Weight of chlorine* adsorbed per gram of charcoal at various temperatures 


Temperature of experiment 
used in adsorption. 

Flow system employed. 

Physical adsorptionf 
at room tempera¬ 
ture and 1 atm 

Chemisorption re¬ 
tained after evacua¬ 
tion at room temper¬ 
ature 

100 C 

200 C 

400 C 

Room temp flow expt No. 1 

0.6262 

0.2523 



.... 

Room temp flow expt No. 2 

0.719 

0.202 

0.081 

.... 

.... 

100 C flow expt No. 3 

0.6338 

0.2502 

0.2152 

0.142 

0.0976 

200 C flow expt No. 4 

0.665 

0.352 

0.2734 

0.239 

0.178 

400 C flow expt No. 5 

0.722 

0.342 

0.317 


.... 


* Weights of Ch adsorption in columns 3-6 are the weights of CI 2 retained by sample after extended evacuation at successively higher temperatures 
from 25 to 400 C. 

t Column 2 represents physical adsorption at room temperature when sample was cooled in stream of CI 2 at 1 atm from T of experiment indicated in 
column 1. 































































134 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


isotherm similar to, but 11% smaller, than the one of 
the untreated sample. The attack on the charcoal is 
not especially surprising in view of the fact that one 
proposed method of producing active charcoal 104 
involvesburning hydrocarbon sin chlorine under such 
conditions as to deposit a considerable portion of the 
hydrocarbon as free carbon. 

6.8.3 Treatment of Charcoals with Sulfur 

Young and his co-workers 24 prepared a number of 
samples of charcoal coated with sulfur by heating 
charcoal and sulfur together at 400 C in a rotating 
furnace. Comparatively little work was done on the 
properties of the coated charcoals though the follow¬ 
ing facts were established: 

1. As much as 41% sulfur by weight could be in¬ 
corporated into the charcoal. The amount of sulfur 
picked up was proportional to the amount included 
in the original mix. 

2. The 41% sulfur content of one of the charcoals 
was reduced to 29 % by extraction with either of two 
different solvents. Apparently some of the sulfur is 
present in an extractable form and part of it in a more 
tightly bound form. 

3. The hydrogen content of the charcoal decreases 
to about one-third of its original value as the sulfur 
content increases to 40%. 

4. Water adsorption isotherms show that if the 
sulfurized sample was protected from oxidation it 
picked up very little water below 0.5 relative pres¬ 
sure. The samples are definitely still hydrophobic. 
The sulfur, however, apparently decreases the pore 
volume of the charcoal considerably as evidenced by 
the fact that the sample containing 41% sulfur had 
only about 0.12 ml water sorptive capacity at satu¬ 
ration. 

5. There seems to be no relation between the acid 
and base adsorptive properties and the sulfur con¬ 
tent. 

6.9 RELATION BETWEEN ADSORPTION 
AND MOLECULAR STRUCTURE 

Before considering the work that has been done on 
the measurement of the adsorption of gases such as 
chloropicrin, pyridine, CC1 4 , and other vapors, it 
seems well to summarize the results that have been 
obtained by Kummer 105 and are being reported here 
for the first time on the relation existing between the 


adsorption of a gas and the structure and properties 
of the adsorbate. In view of the fact that the effi¬ 
ciency of removal of war gases by gas mask charcoal 
is known to depend upon a rate factor and upon a 
capacity factor N 0 , it seemed worth while to carry 
out a study with a view to predicting the sorption 
capacity of a given charcoal for a gas at various rela¬ 
tive pressures as a function of the properties of that 
gas. It would be especially helpful to be able to pre¬ 
dict approximately the shape of the adsorption iso¬ 
therm of a gas on charcoal if only a few of the funda¬ 
mental properties of the adsorbate gas are known. 
The analysis of the problem and the experimental re¬ 
sults presented here give us a much better insight into 
the factors upon which the adsorbability of a gas de¬ 
pends than we have ever had before and enables us 
to predict with a fair approximation whether a gas 
will be adsorbed strongly, medium strongly, or 
weakly by a sample of charcoal. 

Experimental measurements relative to this study 
were made on a single charcoal CWSN 19, one of the 
early samples made by ZnCl 2 . (See Chapter 3.) It 
had an apparent density of 0.482, a particle density 
of 0.792, a carbon density (as determined by helium 
at 25 C) of 2.09; an ash content of about 0.3% made 
up mostly of ZnO and ZnCl 2 ; a heat of wetting in 
benzene of 22.69 cal per g, and a PS service life of 
about 66 min. As indicated in one of the earlier sec¬ 
tions, the charcoal is characterized by a comparatively 
low amount of surface complex; 27 on being heated to 
1200 C it evolved 57 ml H 2 , 7 ml CO, 2.7 ml CH 4 , 3.3 
ml of C0 2 and 2.1 ml of water vapor. 

6.9.1 Experimental Data for the Adsorp¬ 
tion of Gases on CWSN 19 

Figure 40 shows the adsorption isotherms for 
a large number of gases. The data are plotted in the 
manner suggested by Polanyi 34 as the fraction of the 
total sorption capacity taking place as a function of 
RT times the logarithm of the relative pressure. A 
few regular isotherms plotted with relative pressure 
as the abscissa are given in Figure 41. The adsorption 
data are summarized in Table 13. It will be noted 
that the total liquid volume of gas adsorbed at satu¬ 
ration pressure is substantially constant and inde¬ 
pendent of the nature of the adsorbate. We shall now 
turn to the theoretical part of his work and summa¬ 
rize his derivation of relationships that will enable 
one to predict the general nature of the adsorption 



RELATION BETWEEN ADSORPTION AND MOLECULAR STRUCTURE 


135 





p 

RT LOG ~ IN CALORIES 


Figure 40. Adsorption isotherms for various gases on 
CWSN 19. 

of any adsorbate from its physical properties and the 
behavior of some other one adsorbate on the same 
charcoal. 

6.9.2 Theory 

In deriving the desired relationship, a number of 
equations will be used. To begin with, we have the 



Figure 41. Some regular isotherms vs relative pressure 
for gases on CWSN 19. 


Table 13. Adsorption data for various gases on 
CWSN 19. 


Gas 

Temp 
of run 
C 

Adsorption at 
a relative 
pressure of 
0.99. ml of 
gas STP per 
gram of 
charcoal 

Adsorption at 
a relative 
pressure of 
0.99. ml of 
liquid ad¬ 
sorbate per 
g of charcoal 

n 2 

-194 

397 

0.616 

A 

-194 

490 

0.600 

ch 4 

-160 

360 

0.610 

bf 3 

- 78 

291 

0.600 

ph 3 

- 78 

298 

0.615 

HC1 

- 78 

442 

0.613 

C0 2 

- 78 

355 

0.554 (liquid 
density) 

H 2 S 

- 78 

371 

0.566 

cf 2 ci 2 

- 20 

166 

0.609 

nh 3 

- 46 

526 

0.572 

cos 

- 46 

262 

0.608 

CH 3 C1 

- 20 

264 

0.600 

c 2 n 2 

- 21 

245 

0.595 

Cyclopropane 

- 39 

216 

0.590 

CH 3 NH 2 

0 

296 

0.596 

S0 2 

0 

298 

0.595 

COCl 2 

0 

193 

0.596 

CNC1 

0 

267 

0.598 

HCN 

25 

350 

0.607 

cs 2 

25 

216 

0.585 

h 2 o 

40 

644 

0.520 

n-Heptane 

25 

87 

0.567 

Toluene 

25 

120 

0.574 

CC1 3 N0 2 

25 

128 

0.570 

2-methylpentane 

25 

95 

0.560 

Isooctane 

25 

76.5 

0.563 


(2,2,4-trimethylpentane) 


Polanyi 34 relationship to account for the dependence 
on temperature of adsorption of a given adsorbate 

7\log p = r 2 log§- (12) 

A H 

where T i and T 2 are the two different temperatures 
of the adsorbent, Pi and P 2 are the isotherm pres- 


SECRET 


e 

i 

m 































































































136 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


sures, and P 0l and P Q ., are the vapor pressures of the 
adsorbate at the two temperatures. This equation is 
derived to hold for a constant fraction of the total 
adsorption. In other words, the pressure required to 
produce the same fractional saturation of a given 
adsorbate would vary with the temperature in the 
way indicated. 

It will be convenient also to use an empirical equa¬ 
tion for the relation between the amount of adsorp¬ 
tion and the pressure of the adsorbate. If 6 represents 
the fraction of the saturation value of the adsorption 
that is occurring at pressure P, the relation 

RT log e ^ = K(1 - d) 1 - B log e 6 (13) 

is found to hold fairly well for all adsorbates on 
CWSN 19. It gives an isotherm in which the slope 
dV/dP decreases monotonously as the pressure in¬ 
creases and equals zero when P = P 0 . For those char¬ 
coals which give an S-shaped isotherm it would not 
hold above P/Po = 0.5 but it is to be noted that a 
mask is rarely called upon to afford protection from 
gases which have attained a partial pressure in the 
air equal to one-half the vapor pressure of the liquid 
adsorbate. 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

_P _ 

P o 

Figure 42. Isotherm shape as a function of AHi —AHl. 

If constants K and B could be evaluated from 
molecular data for the adsorbate, the given problem 
would be completely solved. It is extremely difficult 
to do this with exactness. Accordingly, in this section 
a way will be pointed out to make a somewhat sim¬ 
pler but useful approach to the problem. Specifically, 
a way will be outlined for calculating the difference 
between the integral heat of adsorption — A Hi, and 
the heat of liquefaction — AHl, for the adsorbate on 
the basis of the fundamental properties of the ad¬ 


sorbate molecule. Since it is well established that 
adsorption isotherms follow curves of types 1, 2, or 3 
in Figure 42, depending upon whether the heat of 
adsorption is greater than, equal to, or less than the 
heat of liquefaction, then it will be obviously possible 
to indicate the general nature of adsorption. 

A thermodynamic equation for the adsorption of a 
gas on a solid is 


at log. / = 



+ A H l + T 



(14) 


which relates the relative pressure P/Po of the ad¬ 
sorption to the differential enthalpy of adsorption 
for the gas going to the adsorbed phase, d(A H a )/dn, 
and the differential entropy change <9 (A S)/dn when 
the bulk liquid is transferred to the surface layer. 

Now, if equation (12) holds, it can be shown that 
the entropy term disappears and that 


RT log^-° 


djAHa) 

dn 


- A H l . 


(14a) 


Coolidge’s data 39 show that the organic gases follow 
equation (12) very closely, whereas water does not. 

In order to estimate the entropy term, some as¬ 
sumptions are necessary. For one thing, it is neces¬ 
sary to assume some shape factor for the capillaries 
in order to be able to know the fraction of liquid ad¬ 
sorbate which is in contact with the surface of the 
charcoal. The exact form of the assumption is not too 
important because with a variety of choices the final 
answer as to the calculated difference between the 
integral heat of adsorption and heat of liquefaction 
does not change much. For simplicity, it will be as¬ 
sumed that the charcoal pores have plain parallel 
walls and are four molecular diameters apart. Fur¬ 
thermore, usually the entropy term is written in the 
form RT In 0/1 — 4> where <f> represents the fraction 
of the surface covered by adsorption. However, it 
appears simpler for physical adsorption to assume 
that the rate of condensation on the surface is pro¬ 
portional to the total surface rather than to 1 — <t> 
and, hence, for <f> < 1, the entropy term can be 
written 


d(AS) 

dn 


— R\n<f). 


(14b) 


For </> > 1, the entropy term is 0 since there is the 
same surface for evaporation as for condensation. 
If, as is likely, most of the first layer will form before 
the second begins, then <f> = 2d. 






























RELATION BETWEEN ADSORPTION AND MOLECULAR STRUCTURE 


137 


Combining equations (13), (14), and (14b), we have 

— ) +AH l = K(1 - 8) 1 - B\n6 - RTln2 8. 
dn /T 

(15) 

The integrahheat of adsorption can be found by in¬ 
tegrating the entire expression including the last 
term from 6 = 0 to 0 = 0.5; and, without the last 
term, from 0.5 to 1. The integral heat of adsorption 
— A Hi obtained in this way is 

—AHi = -AH l + } K + B - ±RT 

= — AH l + AH X . (16) 



We deal with the integral heat of adsorption up to 
complete filling of the pores because complete filling 
represents a definite physical state which is the same 
for all gases and which lends itself to theoretical cal¬ 
culations. 

In order to calculate the integral heat at satura¬ 
tion, we can consider the following simple process: 

1. Condense one mole of gas into a bulk liquid; 
the enthalpy change will be AH l- 

2. Next, spread this bulk liquid out into a sheet 
four molecules thick; the enthalpy change will be 
one-half the energy required to bring a mole of water 
from the interior or bulk liquid to the surface of the 
liquid, or AH s /2. 

3. Allow both sides of this sheet to come in con¬ 
tact with a charcoal surface, giving an enthalpy 
change of AH c /2, where AH C is the heat that would 
be evolved if all the molecules in the mole of ad¬ 
sorbate were brought as a sheet of liquid into contact 
with the carbon surface. Then 


AHr = A H L +±f + ±f 


(17) 


Next, we shall proceed to find a means of evaluat¬ 
ing A H c and A H s that depends upon the physical 
properties of the adsorbate molecule. The enthalpy 
change when a molecule is brought from the interior 
of a liquid to the surface is largely independent of the 
temperature and can be calculated by 

A H s = +2.22 k e (T c - 6) (18) 


where k e is Eotvos* constant and T c is the critical 
temperature. One, therefore, has a ready means of 
calculating AH s /2, the heat required to form a mole 
of liquid into a sheet four molecules thick. 

The heat quantity A H c can be evaluated by means 
of the theory of London 105 to be 


3Na c a g (2)V 0c V % 

mVo c + V % ) 


(19) 


where a c is the polarizability of the carbon surface, 
a g is the polarizability of the gas molecules, V 0c is 
the fundamental frequency of the carbon surface, 
V % is the fundamental frequency of the gas mole¬ 
cules, N is Avogadro’s number, and h is the distance 
between the carbon surface and the molecules of ad¬ 
sorbate when the sheet is at its equilibrium position. 
Since we intend to evaluate all the right-hand side of 
the equation by some given adsorbate, we can write 

— AH C = Ca g V % . (20) 

We evaluate C from some one adsorbate and then 
neglect any change in C produced by possible changes 
in h involved in using other adsorbates. By substi¬ 
tuting (17), (18), and (20), in (16) we now have 

iLCa g Vo a - 2.22 (T c - fc.)] = \K + B — ±RT 

= +AH X . (21) 

This equation can be rearranged in the form 

<+ v % = -Aff. + 1.11 (T e - 6)fc e 

= +AH x +iAH s . (22) 

Tables 14A and 14B show values of K, B, and A H x 
calculated from the isotherms together with A H s and 
physical data for the various adsorbate molecules. 
Figure 43 is a plot of a g V 0g against A H x + \AH s . 
The value of C turns out to be 3.75 and is equal to 
twice the slope of the plot. 

As pointed out above, complete solution of the 
problem requires a method for evaluating the abso¬ 
lute values of K and B. Several procedures for doing 
this are now being worked on but have not yet been 
completed. However, at the present stage of develop¬ 
ment, it is possible to evaluate A Hr — A H L for any 
adsorbate from the experimental adsorption values 
for some standard adsorbate on a charcoal, together 
with fundamental data for the adsorbate for which 
A Hi — AH l is sought. For the standard adsorbate 
one can calculate K and B for the given charcoal 
from an isotherm. Knowing A H L for this standard 
adsorbate one can then calculate A H x as per equa¬ 
tion (21). But AH X is really AHJ2 + AH s /2 andAH s /2 
is known from the Eotvos equation. 108 Consequently, 
from the experimental data and the Eotvos equa¬ 
tion, a value for A H c can be calculated and used to 
evaluate the constant C. The value of a g can be 
readily calculated by the method of Denbigh 110 from 
the structure of the molecule, and the value of V 0(t 
for organic molecules 109 lies within ±20% of the 
value 286 kcal per mole. For other adsorbates, then, 
on the same charcoal, one has merely to insert values 








138 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


Table 14A. Fundamental data on the adsorbate gases. 

Gas 

Mol wt 

Density 
g per ml 

Temp 

C 

-A H l 
cal per 
mole 

Molal 
vol ml 

Average 
liquid 
radius, A 

Dipole 
moment 
n X 10 18 
Debyes 

Polariz¬ 
ability 
c* 0 ml X 10 24 


n 2 

28.02 

0.805 

-194 

1335 

34.9 

2.16 

0.0 

1.74 


A 

39.94 

1.454 

-194 

1590 

27.4 

2.00 

0.0 

1.63 


ch 4 

16.04 

0.422 

-160 

2040 

38.0 

2.23 

0.0 

2.54 


bf 3 

67.82 

1.47 

- 78 

4620 

43.0 

2.32 

0.0 

2.40 


ph 3 

34.04 

0.736 

- 78 

3489 

46.3 

2.37 

0.55 

3.50 


HC1 

36.46 

1.174 

- 78 

3860 

31.1 

2.08 

1.03 

2.63 


C0 2 

44.01 

1.26 liq. 

- 78 

4130 

34.9 

2.16 

0.0 

2.57 


H 2 S 

34.08 

0.993 

- 78 

4463 

34.3 

2.15 

1.10 

3.64 


COS 

60.07 

1.154 

- 46 

4423 

52.0 

2.47 

0.65 

5.05 


C 3 H 6 

42.05 

0.688 

- 39 


61.1 

2.61 

0.0 

4.55 


NH 3 

17.03 

0.697 

- 46 

5720 

24.4 

1.92 

1.49 

2.14 


CH 3 C1 

50.5 

0.99 

- 20 

5170 

51.0 

2.45 

1.86 

4.41 


c 2 n 2 

52.02 

0.953 

- 21 

5576 

54.6 

2.51 

0.0 

4.65 


so 2 

64.06 

1.432 

0 

5960 

44.7 

2.35 

1.67 

3.76 


COCl 2 

98.92 

1.428 

0 

5990 

69.3 

2.72 


6.51 


CNC1 

61.48 

1.226 

0 

6300 

50.1 

2.44 


4.58 


HCN 

27.02 

0.695 

25 

6027 

38.9 

2.24 

2.6 

2.46 


cs 2 

76.13 

1.256 

25 

6490 

60.6 

2.60 

0.0 

8.03 


n-Heptane 

100.2 

0.684 

25 

7650 

146.1 

3.49 

0.0 

13.7 


H 2 0 

18.02 

0.995 

40 

10400 

18.1 

1.74 

1.85 

1.48 


Toluene 

92.13 

0.862 

25 

7980 

107.0 

3.14 

0.4 

12.3 


CH 3 NH 2 

31.06 

0.687 

0 


45.2 

2.36 

0.99 

3.88 


2-methylpentane 86.1 

0.654 

25 

7000 

132.0 

3.37 


11.8 


Isooctane 

114.1 

0.692 

25 

8200 

165.0 

3.63 


15.5 


CC1 3 N0 2 

164.4 

1.641 

25 


100.0 

3.08 


10.82 


cf 2 ci 2 

120.9 

1.47 

- 20 

4760 

82.1 

2.88 


6.55 





Table 14B. 

Fundamental data 

on adsorbate gases. 




Gas 

Fundamental 
frequency 
Vo kcal 

Isotherm constant 

K B 

Total surface 
energy A H s 
cal per mole 

A H x cal 
per mole a g Vo g 

A H x + 1A H s 


n 2 

402 



561 


700 

v:> 


A 

396 



643 


645 


: A 

ch 4 

324 

240 

1210 

817 

1268 

822 

1677 


bf 3 

435 

295 

1555 

1460 

1581 

1043 

2311 


ph 3 

(300) 

650 

1485 

1410 

1778 

1050 

2483 


HC1 

311 

394 

1300 


1401 

818 



C0 2 

357 

292 

816 

1320 

840 

916 

1500 


H 2 S 

257 

1060 

608 


1208 

935 



COS 

313 

765 

1417 

1740 

1741 

1580 

2620 


c 3 h 6 

307 

1170 

1451 


2061 

1675 



nh 3 

271 



1290 


580 



ch 3 ci 

312 

1117 

1081 

1910 

1667 

1380 

2622 


c 2 n 2 

285 

870 

1290 

1840 

1689 

1322 

2609 


so 2 

272 

1020 

915 

2050 

1407 

1022 

2432 


COCl 2 

274 

1465 

1429 

2100 

2256 

1785 

3306 


CNC1 

(300) 

938 

1150 


1581 

1372 



HCN 

321 

552 

765 

1100 

881 

790 

1431 


cs 2 

188 

1610 

1192 

2520 

2102 

1510 

3362 


n-Heptane 




2490 





H 2 0 

311 

360 

10 

1520 

0 

460 

760 


Toluene 




2870 





ch 3 nh 2 

294 

1110 

990 

1145 

1549 

1140 

2121 


2-methylpentane 









Isooctane 









CC1 3 N0 2 

(280) 

2620 

2000 

3640 

3667 

3030 

5487 


cf 2 ci 2 

(300) 

1160 

1910 

1850 

2530 

1970 

3455 


















RELATION BETWEEN ADSORPTION AND MOLECULAR STRUCTURE 


139 



0 2000 4000 6000 ! 


&H x -*--5AH s IN CALORIES 

Figure 43. Plot of equation (22) for determining the 

constant C. 

for a g and F 0fl in equation (20) and obtain a value for 
A H c . Knowing A H s from the Eotvos equation, one 
can then calculate A H x and hence by equation (17) 
obtain a value for A Hi — A H L - In other words, by 
knowing a single adsorption of any one adsorbate on 
a given charcoal and by knowing the polarizability 
and fundamental frequency of the molecules of the 
adsorbate whose adsorption one wishes to evaluate, 
one is able to tell whether the difference between the 
integral heat of adsorption and the heat of liquefac¬ 
tion is a large positive quantity, zero, or a negative 
quantity. From this knowledge, one can by equa¬ 
tion (3) or equation (4) tell whether the adsorbate 
will be strongly adsorbed as in curve 1, weakly ad¬ 
sorbed as in curve 2, or very weakly adsorbed as in 
curve 3, Figure 42. 

To show the usefulness of this method of pro¬ 
cedure, there are listed in Table 15 values for 
— (AHi—AHl) for the various adsorbates as de¬ 
termined experimentally and as calculated using the 
isotherm for CH3CI for evaluating the constant C. 
It is readily apparent that one would not be misled as 
to the nature of the adsorption isotherm of any of the 
gases listed by the calculated value for the difference 
between the integral heat of adsorption and the heat 
of liquefaction of the adsorbate. 

The question naturally arises as to the extent to 
which the results in Table 15 are dependent upon the 
nature of the assumption made as to the shape of the 
pores in the capillary. If one assumes that the ad¬ 
sorption is taking place in pores that are cylindrical 
and four molecules in diameter, one obtains an equa- 


Table 15. Calculation of —(A Hi — AHl) for various 
adsorbates on CWSN 19, assuming adsorbate is in 
capillaries with parallel walls four molecular diameters 
in size. 


Gas 

Temp of 
isotherms 
C 

-(A H t - AH l ) 
from actual 
isotherms by 
equation (16) 

-(A Hi - AHl) 
calculated from 
constant C 
and values for 
atgVog and AH, 

ch 4 

-160 

1269 

1131 

bf 3 

-78 

1589 

1230 

ph 3 

-78 

1778 

1255 

co 2 

-78 

840 

1050 

cos 

-46 

1750 

2080 

CH 3 C1 

-20 

1667 

1625 

c 2 n 2 

-21 

1689 

1560 

so 2 

0 

1407 

895 

C0C1 2 

0 

2256 

2290 

HCN 

25 

881 

925 

cs 2 

25 

2102 

1570 

ch 3 nh 2 

0 

1549 

1568 

cci 3 no 2 

25 

3667 

3860 

cf 2 ci 2 

-20 

2530 

2755 

h 2 o 

40 

0 

-23 

Table 16. 

Calculation of —(A Hj — A H£) for various 

adsorbates 

on CWSN 

19, assuming adsorbate is in 

cylinders four molecules 

in diameter. 





—(AH 1 - AH l ) 




calculated from 


Temp 


constant C 


of 

-(A Hj - AH l ) 

for CH 3 C1 and 

isotherms 

from actual 

values for 

Gas 

C 

isotherm data 

ocgV 0 g and AH § 

ch 4 

-160 

1232 

1155 

bf 3 

- 78 

1524 

1185 

ph 3 

- 78 

1713 

1230 

C0 2 

- 78 

775 

1020 

COS 

- 46 

1684 

2110 

ch 3 ci 

- 20 

1584 

1584 

c 2 n 2 

- 21 

1606 

1514 

so 2 

0 

1316 

760 

C0C1 2 

0 

2165 

2290 

HCN 

25 

781 

965 

cs 2 

25 

2002 

1440 

ch 3 nh 2 

0 

1459 

1582 

cci 3 no 2 

25 

3567 

3854 

cf 2 ci 2 

- 20 

2457 

2438 

h 2 o 

40 

-113 

-64 


tion similar to (16), except that the constant 2 is 
changed to about 1.5. Evaluation of the difference 
between the heat of adsorption and the heat of lique¬ 
faction calculated for a cylindrical capillary from the 
absolute physical constants for the adsorbate and the 
difference between these two heat quantities as cal¬ 
culated by the proper modification of equations (17, 
20, 21, and 22) is shown in Table 16; it is evident that 
to a close approximation, one can estimate the magni¬ 
tude of the difference between the heat of adsorption 









































140 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


and the heat of liquefaction without too much error 
being entailed by the nature of the assumption that 
has to be made relative to the shape of the pores of 
the charcoal. The procedure here presented should, 
therefore, be very useful in quickly evaluating the 
probable adsorption characteristics of any adsorbate 
if only the polarizability, the fundamental frequency, 
and surface energy of the adsorbate molecule are 
known. If one wished to estimate the adsorption at 
room temperature, one should divide A Hi — A H L by 
298 and then solve for V at the particular partial 
pressure being used by inserting e~ iAHl ~ AHl ^ rt for 
C in equation (3) or (5), and using an estimated V m 
based on a comparison of the size of the molecules 
being studied with the V m and size of the molecules 
used in the standard isotherm. Since actual ad¬ 
sorption usually deviates at low relative pressure in 
the direction of being greater than that estimated 
from equation (3) or (5), the above method of esti¬ 
mating the adsorbability of an adsorbate is conserva¬ 
tive and would give adsorption values that, if any¬ 
thing, would be too low. 

6.10 ADSORPTION OF PS, PYRIDINE, 
PICOLINE, CC1 4 AND OTHER VAPORS 
ON CHARCOAL 

Most of the adsorption work has been done upon 
typical war gases such as PS 111 as a function of the 
kind of charcoal and the amount of moisture present 
during adsorption, upon gases such as pyridine and 
picoline 27 that appear to be useful for improving the 
quality of whetlerites, or upon gases such as CCI 4 112-114 
which have been used in studying pore size and 
rates of adsorption. Other examples of adsorption 
have already been included in the discussion of the 
adsorption of nitrogen and water vapor as they are 
related to surface area and pore size measurements. 
Additional data on adsorption, which will be included 
in the section on retentivity, have been taken pri¬ 
marily with a view to judging the danger of desorp¬ 
tion of gases into a stream of vapor-free gas. 

6 . 10.1 Adsorption of PS on Charcoal 

The adsorption of chloropicrin on CWSN 19 was 
determined 111 at 15, 25, and 35 C by passing a gas 
stream charged with a known amount of PS through 
a tube of charcoal and determining the increase in 
weight at steady state. The results are shown as a 
Polanyi plot in Figure 44. The detailed data are 



0 100 200 300 400 500 600 700 800 900 1000 1100 1200 
-T LOG P. 

P o 

Figure 44. Polanyi plot of CC1 3 N0 2 on CWSN 19. 

given in the original report. It is evident that the 
data all fall, as would be expected, on the same curve. 
Hence, at a given relative pressure the fraction of the 
total adsorption occurring changes only slightly. 
The isotherm is of the strong adsorption type, large 
adsorption occurring at low relative pressures. A 
typical isotherm is shown in Figure 45. 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.0 0.9 

P 


Figure 45. Chloropicrin isotherm on CWSN 19 at 

25 C. 

The influence of water vapor on PS adsorption was 
also determined. 111 In Table 17 are shown data taken 
on CWSN 19 in the presence and absence of water 
vapor equivalent to adsorption equilibration at 0.75 
RH. Similar data for the Type A whetlerite CWSN 
Type 1 are also included in the table. 

It will be noted that for high relative pressures of 
PS the water vapor has little effect on the adsorption. 
Presumably the water is quickly expelled by the more 
strongly adsorbed PS. This is true regardless of 
whether the experiment was started with dry char- 


















































ADSORPTION OF VAPORS ON CHARCOAL 


141 


coal or with charcoal that had already been equi¬ 
librated with water vapor at 75% RH. However, for 
small partial pressures of PS, the presence of water 
vapor equivalent to 75% RH had a marked inhibiting 
effect on the PS adsorption. This is consistent with 
the well known fact that under the test conditions 
usuallj" employed for PS, the presence of water vapor 
causes a marked decrease in the break time of the 
mask or charcoal tube. 


Table 17. Weight of PS adsorbed in the presence of 
water vapor on charcoal CWSN 19 and whetlerite 
CWSN 19 Type 1. 


Initial condition 
of charcoal or 
whetlerite 

P/Po for 

PS 

P/Po for 
H 2 0 

Adsorption Adsorption 
of PS grams of H 2 0 
per g grams per g 

Dry 

0.75 

0.00 

0.925 


Wet 

0.75 

0.75 

0.92 

0.0 

Dry 

0.75 

0.75 

0.90 

0.0 

Dry 

0.045 

0.00 

0.77 


Wet 

0.045 

0.75 

0.465 

0.24 

Dry 

0.031 

0.00 

0.72 


Wet 

0.031 

0.75 

0.41 

0.28 

Dry 

0.034 

0.75 

0.58 

0.11 

Dry 

0.00 

0.75 


0.50 

Dry whetlerite 

0.017 

0.00 

0.57 


Dry whetlerite 

0.017 

0.75 

0.32 

0.24 

Dry whetlerite 

0.022 

0.00 

0.59 


Wet whetlerite 

0.022 

0.75 

0.19 

0.33 

Dry whetlerite 

0.00 

0.75 


0.409 


6 .10.2 Adsorption of Pyridine and 
4-Picoline 

In view of the widespread interest shown in the 
possible use of pyridine and related materials for im¬ 
proving the aging characteristics toward CK under 
80-80 tests, some measurements have been made 27 
of the adsorption of both pyridine and 4-picoline. The 
results are illustrated by the isotherms in Figure 46. 

The isotherms are of a standard strong adsorption 
type and indicate that both of these gases would be 
strongly held by the charcoals. The rates of adsorp¬ 
tion observed were extraordinarily low. As much as 
20 hr was required in the equilibration of each 
adsorption point. The extreme slowness is probably 
connected with the slowness of surface migration of 
molecules of this molecular weight and strongly polar 
character into the tiny capillaries of the charcoal. 
The cause of the slowness cannot be stated with cer¬ 
tainty until further studies on similar molecules are 
made, but there can be no doubt of the reality of the 
slow nature of the gas pickup. One sample of a Type 
A whetlerite prepared from a BC charcoal showed 



0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 



Figure 46. Adsorption of pyridine and picoline by 

CWSN 196 BIX at 23 C. 

strong adsorption of pyridine contrary to the obser¬ 
vation made at Edgewood Arsenal to the effect 1 hat 
this whetlerite would not adsorb this vapor. The 
cause of the disagreement is not known. 

6.10.3 Adsorption of CC1 4 and Other 
Vapors by Charcoals 

Most of the adsorption work dealing with the 
pickup of CC1 4 by charcoals has been done with a 
view to studying the pore size, sorption capacity, 
and rate of equilibration of various charcoals. The 
Canadian workers have employed an isopiestic tech¬ 
nique 112-114 in their work that seems to simplify 
greatly the making of comparisons of the sorptive 
capacities of the various charcoals. By their pro¬ 
cedure, a series of charcoals together with some 
standard charcoal is exposed to CCI 4 or other vapors 
at various but unknown partial pressures in a desic* 
cator. The samples are left until equilibrium is 
attained. By knowing the adsorption isotherm for 
the standard charcoal, they are able to establish the 
dependence of adsorption of the other charcoals on 
the partial pressure of adsorbate. Their proce dure 
affords a rapid and easy means of establishing the 
relative sorptive characteristics of a large number of 
charcoals. They find a certain correlation between 
the isopiestic isotherms and the volume activity 
(weight of adsorbate picked up by the charcoal in a 
standard tube test up to the break point). 

In a report by Heise and Slyh, 115 it was stated that 
an unusually large variation in the capacity and the 
rate of CCI4 adsorption was observed for a number of 


































142 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


base charcoals. The saturation values in the tem¬ 
perature range 20 to 23 C were reported to be only 
about one-third to one-half as large as those of 25 C, 
and the charcoal was four times as slow in equi¬ 
librating. Since there seemed to be no reasonable 
explanation of this behavior, the results were re¬ 
peated by Holmes. Measurements on four National 
samples, CWSN S5, CWSN 19, CWSN 196 BIX, 
and CWSN BIX TH 410, gave results that contra¬ 
dicted the experience of Heise and Slyh and gave 
normal adsorption values both as regards the rate 
of equilibration and the total adsorption. A later 
recheck by the National workers indicated that the 
early report was in error. In view of this fact, the 
results are not being included in the present report, 
but are merely being called to the attention of the 
reader. 

Canadian workers have studied the adsorption of 
a number of vapors other than CC1 4 by various char¬ 
coals. 112 Most of their work had been done by their 
isopiestic method and a great deal of it is concerned 
with determining the saturation adsorption values of 
charcoals toward miscellaneous vapors. The amount 
of various vapors taken up by a series of five char¬ 
coals at saturation are given in Table 18, the results 


Table 18. Isopiestic volume activities* at saturation. 
Weight of adsorbate per 100 cc char. 


Vapor 


Carbon numbers 


1 

7 

8 

9 

0 

Carbon 

tetrachloride 

24.4 

26.2 

30.2 

38.2 

39.4 

Phosgene 

20.6 

24.3 

28.2 

33.5 

34.0 

Mustard gas 

19.8 

21.8 

25.7 

31.9 

32.9 

Water 

14.1 

15.9 

18.9 

23.0 


Amyl chloride 



18.0 

22.6 


Benzene 

13.6 

15.5 

17.3 

22.0 


Methyl alcohol 

12.0 

13.5 

15.7 

19.5 


n-hexane 



13.3 

16.8 



* From Report No. 2 Project CE 107 by Ferguson Shelter, and Waldock, 
April 10, 1942. 


being expressed as weight of adsorbate taken up by 
100 cc of the charcoal. The same group of experiments 
showed that the volume activities of any charcoal 
toward eight different adsorbate vapors bears a 
constant ratio for all adsorbate vapors against the 
volume activities of a standard charcoal. For ex¬ 
ample, the volume activity of charcoal No. 1 in 
Table 18 was approximately 0.62 that of the volume 
activity of charcoal No. 9 for all of the vapors shown 
in Table 18. Such measurements are accordingly 


very useful for comparing different charcoals and for 
predicting their behaviors toward adsorbates upon 
which they have not been tried. 

6.11 HEATS OF ADSORPTION AND 
IMMERSION 

Comparatively few measurements have been made 
as part of the NDRC program on the heats of im¬ 
mersion of charcoals, aside from the standard routine 
testing of charcoal by measuring the heat evolved 
when a sample is immersed in benzene. Young has, 24 
however, employed an accurate calorimeter and com¬ 
pared his results with those obtained by the standard 
CWS test method. The heat evolved will increase as 
the sample being used is made more nearly gas free. 
Thus, a sample measured in air evolved 28.2 cal 
per g, one measured in helium evolved 30.2 cal per 
g; and one measured in vacuum produced 30.85 cal 
per g. These values are to be compared with 26.5 cal 
obtained by the usual CWS heat of immersion 
technique and 29.1 cal when the CWS calorimeter is 
calibrated by electrical heating technique. He con¬ 
cludes that the usual crude measurements are quite 
satisfactory and within 3 to 6% of more accurately 
determined values, depending upon the method used 
in calibrating the calorimeter. 

Young 24 also obtained a few values for the heat of 
immersion of charcoal in water. For CWSN 19, the 
evolved heat was 59 cal per g. It was given off over a 
period of 48 hr and required a special technique and 
method of calculation for its determination. On the 
other hand, CWSN 19 TUC 87, which was prepared 
by oxidizing CWSN 19 in air until it had 15% 
oxygen, yielded a value of 24.6 cal per g but liberated 
this heat rapidly. It is easy to understand why the 
heat should be liberated more rapidly from the 
oxygen-coated sample. The adsorption at low rela¬ 
tive pressures is much greater and, therefore, the 
rate of saturation in all probability is also greater for 
the oxygen-treated than for the original CWSN 19. 
However, the average or integral heat of adsorption 
would, if anything, be greater on the treated than 
on the untreated sample. It is, therefore, difficult to 
account for the smaller heat evolved on immersing 
the oxygen-treated sample than on immersing the 
original CWSN 19. 

Trost and Morrison 116 measured the heat of ad¬ 
sorption of butyric acid from aqueous solution onto 
the surface of charcoal. On a series of charcoals that 
had been activated to different degrees, they found 













RETENTIVITY OF CHARCOALS 


143 


that the heat of adsorption of the butyric acid was 
constant at 2.2 kcal per mol of butyric acid ad¬ 
sorbed. It was concluded that within the accuracy 
of the measurements, the activity of the surface- 
per-unit area did not change during activation. In 
other words, the quality of the surface was constant 
even though the absolute surface area was increasing. 

In connection with measurements being made on 
retentivity, Wiig 117 has determined the heat of 
wetting in ethyl chloride for various charcoals. 
The results are shown in Table 19 in comparison 


Table 19. Heats of wetting in ethyl chloride at 0 C 
for various chars. 


Char 

Av heat 
of 

wetting 
cal per g 

Density 

of 

char 

Heat Heat of 

of wetting in 

wetting benzene 
cal per cc cal per cc 

PCI-1143 

11.5 

0.533 

6.13 

9.37 

DX-134 

11.3 

0.539 

6.09 


DX-166 

11.6 

0.515 

5.97 


DX-184A 

12.4 

0.482 

5.97 


DX-86 

12.7 

0.472 

5.99 


PC-518 

10.9 

0.545 

5.94 


EASC on PCI-1143 

10.7 

0.617 

6.61 


N-204A-2X 

17.4 

0.324 

5.63 

8.45 

N-291AY-1 

17.8 

0.283 

5.04 


NY-165 

14.3 

0.380 

5.43 


EASC on N-204A-2X 

14.2 

0.412 

5.85 


Seattle 

13.9 

0.351 

4.88 

7.95 

H-1366 

10.4 

0.438 

4.56 


H-960 

' 14.7 

0.356 

5.23 


EASC on Seattle 

12.0 

0.456 

5.47 



with a few scattered values for the heats of ad¬ 
sorption in benzene. The measurements were made 
with the same type of calorimeter employed by 
Young in the work described in preceding text. 
Wiig concluded that no consistent correlations be¬ 
tween the data on heats of wetting and the amount 
of ethyl choride adsorbed at the break point or re¬ 
tained during desorption could be made. 

6.12 RETENTIVITY OF CHARCOALS 

It has long been recognized that a complete ap¬ 
praisal of the performance of a mask in removing 
a poison gas must concern itself with the relative ease 
with which the adsorbed gas is given up to a stream 
of poison-free air as well as with the length of time 
the mask will give protection when used against a 
stream of gas containing a definite concentration of 
the poisonous component. The ability of an adsorbent 
to retain the gas which it has picked up is generally 
called the retentivity of the adsorbent. 


The exact method of determining the retentivity and, 
hence, of defining its true meaning has varied a great 
deal. The history of work done is given by Volman, 
Doyle, and Blacet 118 and by Stevens 119> 120 and need 
not be reviewed here. It will suffice for present con¬ 
siderations to point out that there are really two 
extreme cases with which one has to deal in approach¬ 
ing the problem. If a mask is used against a poison gas 
for only a fraction of its break time and is then per¬ 
mitted to stand unused for a sufficient length of time, 
it is known that the adsorbed gas will eventually 
redistribute itself uniformly throughout the mass of 
adsorbent. When the redistribution is complete and 
the mask is again put into service, the first bit of air 
passing through will remove the adsorbed gas at a 
gaseous concentration corresponding to the adsorp¬ 
tion isotherm of the particular adsorbate being used. 
The seriousness of such redistribution and desorption 
will then depend primarily upon the shape of the 
adsorption isotherm. The other extreme case is the 
one in which the mask is used continuously, but the 
poison content of the entering air drops to zero before 
the break time is reached. The question then arises 
as to how long the mask can be kept in continuous 
service on poison-free air before the slug of adsorbed 
gas works itself along the canister bed and into the 
exit gas stream. 

A complete solution of the problem would involve 
measuring adsorption isotherms for all the known 
and potential poison gases that are removed by ad¬ 
sorption on all Service charcoals, both under dry and 
moist conditions, and also measuring the retentive 
time for all gases as a function of moisture content, 114a 
and fraction of the service time during which the 
sample was being gassed before the beginning of the 
passage of poison free air through the sample. Many 
such data have been accumulated and are available 
for numerous gases and charcoals but the specific 
results on actual poison gases are not available at 
the present writing. In this section we shall restrict 
our attention to two papers by Stevens 119,120 and 
one by Volman, Doyle, and Blacet 118 dealing with 
the adsorption and retentivity of a number of non¬ 
toxic organic vapors as a function of moisture content 
of the charcoal and gas stream, and the relative 
miscibility of the gas being used and water vapor. 
Wiig 117 has also been carrying on an extensive study 
of the retentivity of ethyl chloride but the final 
report of his work has not yet been received. 

By saturating a sample of charcoal Avith given 
partial pressures of vapors and then noting the 











144 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


change in concentration of the effluent gas when 
vapor free air is passed into the sample, it is possible 
to construct an approximate adsorption isotherm 
giving the amount of adsorbate left on the sample as 
a function of the exit partial pressure of the adsorbate. 
Ordinarily, the approximate isotherms so obtained 
will be somewhat lower than a true isotherm because 
the charge left on the charcoal at any stage in the 
desorption is not uniformly distributed but is con¬ 
centrated more at the exit than the entrance to 
the bed of adsorbent. Nevertheless, such approxi¬ 
mate isotherms serve as a useful means of predicting 
the initial exit concentration of vapor that one could 
expect in a mask as a function of the amount of 
adsorbate that had been taken up and permitted to 
redistribute itself. This technique also permits one to 
determine the influence of moisture on the reten- 
tivity. 

By employing such technique, the approximate 
isotherms were constructed for CC1 4 , CHC1 3 , CS 2 , 
ethylene dichloride, methyl ethyl ether, 118 neopen¬ 
tane, 118 acetone, and4nethanol. 118 It was concluded 
that water vapor decreased the amount of adsorbate 
that could be held at equilibrium and decreased the 
retentivity very markedly for all vapors that were 
insoluble in water. For those that were slightly solu¬ 
ble, the effect was less pronounced and for those that 
are miscible in all proportions with water, no appreci¬ 
able decrease in the total sorption capacity or re¬ 
tentivity of the charcoal was found to occur. As a 
matter of fact, it was shown that the isotherm for 
methanol could be derived in the presence of water 
from the dry isotherm and the water isotherm. 

Time required for the effluent gas to build up to 
the break value depends upon the length of the 
gassing time and the relative humidity. This is 
illustrated in Table 20 taken from the reports of 
Stevens. 119 The gas time in column 3 refers to the 
number of minutes during which the vapor CHCI 3 
was passed through the adsorption tube. The re¬ 
tentive time in column 6 is measured from the be¬ 
ginning of the gassing period. Columns 4 and 7 
represent the percentage of the service time during 
which the sample was gassed, and the percentage of 
the service time to which the retentive time is 
equivalent, respectively. It is evident that the ratio 
of the retentive time to the service time depends both 
upon the gassing time and upon the relative humidity 
during the runs. 

The suggestion has been made 118 that retentivity 
experiments carried out with an organic vapor of 


medium molecular weight might enable one to antici¬ 
pate the behavior of unknown poison gases that 
would have to be removed by adsorption. It may be 
well to point out that this would be true only in the 
event that the unknown poison gas had the same 
adsorptive characteristics as the organic vapor. If 
one could predict the isotherm of the poison gas from 
the structure and physical properties of its molecule, 
one could also anticipate fairly well the retentivity 
of the gas. Progress has been made in this direction 
as outlined in Section 6.12 though it cannot be said 
that the exact shape of the isotherm can yet be pre¬ 
dicted with sufficient detail to be very helpful in 
calculating the retentivity. 


Table 20. Retentive time* of charcoal SBT 350 in re¬ 
lation to gassing time and relative humidity. CHCI 3 , 9 mg 
per min. 


Relative 

humidity 

Service 
time T 
in min 

Gas 

s time 
min 

%of 

T s 

Retentive 
Charge time 
mg min 

%of 

T, 

0 

143 

100 

70 

900 

158 

no 



71 

50 

639 

235 

164 



50 

35 

450 

550 

385 

60 

50 

35 

70 

315 

58 

116 



30 

60 

270 

60 

120 



25 

50 

225 

78 

156 



20 

40 

180 

108 

216 



17 

35 

153 

230 

460 

70 

32 

20 

62 

180 

36 

113 



15 

47 

135 

42 

130 



10 

31 

90 

60 

187 



6.5 

19 

59 

96 

300 



5.0 

15.5 

45 

150 

470 

80 

22 

11 

50 

99 

25 

114 



7.2 

25 

65 

30 

136 



4.0 

18 

36 

40 

182 



2.2 

10 

20 

55 

250 


* From C. E. 161 III-1-1806 by W. H. Stevens, September 9, 1944. 


6.13 CHEMISORPTION ON THE CuO IN 
TYPE A WHETLERITES 

In order to obtain some idea as to the extent of 
surface of the inorganic material added to base char¬ 
coals in the course of making Type A whetlerites, a 
search was made for a gas that would not be strongly 
adsorbed on charcoal and that would form only a 
layer of chemically bound adsorbate on the CuO 
attached to the charcoal. At the same time, measure¬ 
ments were made on two different samples of CuO of 
known surface areas. 

The detailed results of the work need not be given 







STRUCTURE OF CHARCOAL 


145 


here. 121 It will suffice to point out that H 2 S, PH 3 , 
CNC1, BF 3 , HC1, C 2 H 2 and NO all appear to react 
at room temperature with the CuO in Type A whet- 
lerites to a depth in excess of a monolayer and hence 
will not serve for measuring the surface area of the 
whetlerizing ingredients. H 2 S, CNC1, BF 3 , and 
HC1 seem especially reactive and probably combine 
almost stoichiometrically with the copper oxides 
present. NO reacts extensively even with the base 
charcoal. CO, S0 2 , H 2 0, C 2 N 2 , and NH 3 are all 
chemisorbed in amounts that do not exceed a mono- 
layer. They combine to indicate that on the three 
Type A whetlerites investigated, CWSN 19 TP 1, 
CWSN 19 TU 8, and CWSC 10 TI 15, about 3 ml of 
gas is required to form a monolayer on the copper 
oxides of the whetlerite. This corresponds to a parti¬ 
cle size of about 100 A for the CuO crystals. 

6.14 STRUCTURE OF CHARCOAL 

There are very few things about which we can be 
sure as regards the structure of charcoal. Perhaps 
one of the few things we can say with certainty is 
that an active charcoal must contain a network of 
capillaries, some large and some small. This seems 
essential in order to provide avenues by which the 
molecules that are to be adsorbed can gain entrance 
to the interior of the charcoal particles and to the 
large surface area that must necessarily be located 
in small pores. When, however, we come to a dis¬ 
cussion of the pore shape and ask whether we should 
consider charcoal as a honejTomb structure of 
approximately cylindrical pores, or as a collection of 
platelets more or less parallel to each other and 
forming boxlike capillaries of rectangular cross sec¬ 
tion, or some combination of these, or some arrange¬ 
ment involving pores of still different shapes, we 
find ourselves in the realm of speculation and unable 
to speak with certainty. Perhaps the best procedure 
to follow in summarizing the evidence is to con¬ 
sider the results obtained from each of the principal 
tools and types of measurement through which we 
can hope to obtain information as to the pore shape 
and the general structure of charcoal. These various 
approaches will include (1) X-ray diffraction studies, 
(2) microscopic studies, (3) electron microscope 
studies, (4) area and pore volume measurements and 
calculations, (5) chemical behavior of charcoal, 

(6) expansion of charcoal during adsorption, and 

(7) measurements of the true density of the carbon 
in charcoal. These will now be discussed in turn. 


6.14.1 X-ray Structure Work on Charcoal 

In an extended series of papers, Johnstone and 
Clark 122 - 123 have reported the results of their study 
of the structural characteristics of some 1,200 
samples of carbons, cokes, activated charcoals, 
resins and gas mask adsorbents of all kinds. A num¬ 
ber of their observations relating to the charcoals 
are as follows. 

1. Charcoals sinter and turn into graphite much 
less readily than does petroleum coke. 

2. The value of c (twice the spacing between 
planes in the c direction) is about 7.72 A for a coco¬ 
nut charcoal and 7.47 A for a National charcoal 
made by the ZnCl 2 process, provided the samples 
have not been heated over 1100 C. This compares 
with 6.70 A for graphite. 

3. The value of a is about 2.45 A for both these 
charcoals and for graphite. 

4. These charcoals appear to contain a number of 
platelets which in the c direction are about 10 A in 
thickness; for a few other charcoals this thickness is 
as high as 12 A. 

The disks or platelets of carbon revealed by the 
X-ray studies are broader than they are thick. 
For coconut charcoal they range from about 20 A for 
samples that have been heated to no more than 
500 C, to 39 A for samples that have been heated to 
1000 C. Values for this L a dimension for National 
charcoals start at 20 A for the coconut charcoal 
but extend up to 45 A on samples heated to 900 C 
and to 63 A for samples heated to 1100 C. 

The X-ray results, taken as a whole, constitute 
strong evidence that much of the carbon in charcoal 
is arranged in platelets. The preferential growth of 
these in one direction seems to be especially con¬ 
vincing evidence of their reality. Johnstone and 
Clark conclude 123 that “the data obtained from the 
X-ray study evidently gives credence to the idea that 
activation is essentially a process of cleaning out 
capillaries in changing their size, and perhaps their 
shape without greatly effecting the matrix structure 
of carbon.” 

6.14.2 Microscopic Studies 

During World War II no extensive microscopic 
studies of charcoals were reported. However, it is 
well known from published reports 124> 124a that it is 
possible to show the presence of large capillaries in 
the surface of charcoal particles by photomicro¬ 
graphs. Necessarily, the limit to such studies is 




146 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


about 05 micron so that capillaries smaller than 
about 5000 A will not be observable. These micro¬ 
scopic studies, accordingly, will merely confirm the 
presence of the large connecting channels by which 
the gases that are to be adsorbed gain access to the 
interior of the particles. They show nothing about 
the shape or distribution of the fine pores. 

6.14.3 Electron Microscope Studies 

Electron microscope pictures push the microscopic 
observations out to capillaries smaller by perhaps a 
factor of 50 than those observable in the ordinary 
light microscope. The results have been well ex¬ 
pressed in a summary of the paper by Johnstone, 
Clark and Le Tourneau: 125 

Thirty-six electronmicrographs of various charcoals are 
presented. While they do not reveal the ultimate pore structure 
of the charcoal, they do show a larger pore structure between 
several hundred and 1000 A in diameter, in the nut shell char¬ 
coals as ordinarily prepared, in Carlisle charcoal, in low density 
National Carbon Company charcoals, and in highly activated 
(steamed) Saran charcoals. The importance of these large 
pores is not fully established, but they may effect the rates of 
adsorption of gases by the charcoal. 

6.14.4 Area and Pore Size Measurements 

In earlier work, Young 126 calculated the diameter 
and length of a cylindrical capillary that would be 
required to be equivalent to the area and pore 
volumes of typical charcoals. For CWSN 19 using a 
value of 1,338 sq m per g for the area, he concluded 
that 2.05 X 10 13 cm of pores 20.8 A in diameter would 
be needed. To illustrate the enormous length of 
capillary thus involved, he pointed out that the 
length in a 1-g sample would be equivalent to 40,000 
times the circumference of the earth. If one assumes 
that these cylindrical capillaries are arranged as a 
honeycomb in a particle of charcoal, it turns out that 
the minimum wall thickness between the cylinders 
would be only about 4 A. It is a little difficult to 
reconcile such a picture with the X-ray observations 
of platelets 10 A thick and 20 to 60 A wide as making 
up most of the charcoal. Even though cylindrical 
capillaries have been used for convenience in calcu¬ 
lating pore diameters from water desorption iso¬ 
therms, the X-ray results, if they can be relied upon, 
certainly would dictate the use of caution in formu¬ 
lating any such picture of the charcoal structure. 

Young also calculated that if all of the capillary 
space consists of rectangular parallelepiped capil¬ 
laries with parallel walls, the distance between the 


walls would, on an average, have to be 10.4 A for 
CWSN 19, in order to account for the observed area 
and pore volume. Such a picture would be entirely 
consistent with the X-ray data. As a matter of fact, 
it was found that on one particular sample of 
National charcoal, the apparent area dropped from 
2,040 sq m per g to 1,670 sq m per g as the sample 
was heat treated up to 1100 C. During this heat- 
treating the L a dimension of the disks or platelets 
increased from 20 to 63 A in size. It is entirely 
reasonable on a platelet structure to explain such 
particle growth with comparatively little change in 
surface area. It would be much more difficult to 
explain if the charcoal consisted of a honeycomb 
structure of cylindrical capillaries. 

6.14.5 Chemical Behavior of Charcoal 

It is well known that standard charcoals can all be 
converted by proper chemical treatment into com¬ 
pounds that appear to have a central nucleus of 
carbon atoms arranged much as though they were 
in a plane of graphite. Thus mellitic acid has been 
reported 127 to be formed in good yield by controlled 
oxidation with nitric acid. This certainly indicates 
that much of the carbon is arranged in two dimen¬ 
sional graphite-like sheets or platelets and again is 
consistent with the X-ray picture of the structure 
of charcoals. 

6.14.6 Expansion of Charcoals During 

Adsorption 

At least two different observers 401128 have noted 
that when charcoal picks up water vapor it expands. 
This has been construed as evidence against capillary 
condensation and in favor of an adsorption inter¬ 
pretation of the water vapor picked up by charcoal. 
It should be noted, as pointed out by Kummer, that 
it is much easier to imagine the expansion of charcoals 
if they are made up of platelets capable of being 
pried apart to some extent by entering water mole¬ 
cules in much the same way that various molecules 
can pry apart the planes of monotmorillonite and 
certain other clays. If the pore structure consists of a 
honeycomb of cylinders the possibility of expansion 
seems much more limited. 

6.14.7 True Density of Carbon in Charcoal 

The true density of carbon in graphite is about 
2.25 g per cu cm as determined both from X-ray 




SUMMARY 


147 


work and from actual density measurements. If the 
c dimension in charcoal is as large as 7.5 A as indi¬ 
cated by the X-ray work, and the a dimension is 
substantially the same as for graphite, it would 
seem to follow that the apparent density of the 
carbon in charcoal cannot be as high as 2.25 g per 
cu cm since the c distance for graphite is only 6.7 A. 
On the basis of the X-ray measurements the density 
should be somewhere between 2.0 and 2.1 g per cu 
cm. Carbon densities determined by helium have 
been reported over the entire range from 1.77 to 
2.36 g per cu cm for various charcoals; a large number 
of the apparent densities are in the range 1.95 to 
2.15 g per cu cm. Accordingly, it may be said that the 
density values of the carbon in charcoals are also 
consistent with the X-ray data. It should be noted 
in this connection that an interplanar distance of 
7.5/2 that one would deduce from the c dimension is 
probably too small to permit the entrance of helium 
atoms between planes during density measurements. 
Hence, the helium density determinations would 
really yield values for the density of the platelets. 

6.14.8 General Conclusion as to Structure 

As stated in the introduction to this section, it is 
not possible to speak with certainty as regards the 
structure of charcoal. When all of the evidence listed 
above is taken as a whole, however, it seems to speak 
in favor of capillaries of rectangular cross section for 
the most part, rather than cylindrical capillaries. 
Immediately, one is confronted with the question as 
to what happens to the pore diameter calculations 
made by Juhola in the event that the pores are really 
boxlike structures rather than cylinders. The answer 
is that the distance between parallel walls that one 
calculates from the Kelvin equation is just one-half 
as great as the diameter calculated from cylindrical 
capillaries. Accordingly, capillaries which with a cos 
0 of 1.0 appeared to be about 36 A in diameter, if 
present as cylinders, would calculate to be 18 A be¬ 
tween parallel platelets. However, the calculation 
of the distance between parallel planes from the rela¬ 
tion of the increment of surface area A covered up 
by each increment of volume V is given by the 
equation 


Hence if cos 0 were taken as 0.53, the measurement 
of the slope of the surface area vs volume of water 


curve Avould lead to a value of about 9 A for the dis¬ 
tance d. This is too small a size to permit the occur¬ 
rence of what we might call capillary condensation. 
On the other hand, if one assumes that the charcoal 
is made up of platelets and accepts the distance d as 
18 to 20 A the surface area per g of charcoal is com¬ 
puted as about 800 sq m per g; this is to be compared 
to values ranging from 1,300 to 1,700 sq m per g ob¬ 
tained by different methods of estimating the area. 
Possibly the answer to the dilemma is to be found by 
assuming that the capillaries are for the most part 
rectangular in cross section and for CWSN 19 about 
18 to 20 A between platelets, and that even smaller 
crevices leading off the 20 A openings become covered 
with adsorbed water only when the larger 20 A 
openings are full. In desorption, this would mean 
that the water in the very small cracks and crevices 
would disappear at the same time that the water 
was desorbed by capillary condensation from the 
hemicylindrical surface at the edge of the rectangular 
capillary opening. Furthermore, this explanation is 
not inconsistent with the value of d obtained from 
equation (23) because such a calculation is necessarily 
an average for the main capillaries and any smaller 
side capillaries that fill and empty at the same time 
that the main 20-A capillaries fill and empty. It does, 
however, entail assuming cos 0 = 1, an assumption 
that does not seem very reasonable at relative pres¬ 
sures at which water vapor is only slightly adsorbed. 

Possibly the capillaries are neither cylinders nor 
rectangular parallelepipeds, but some irregular collec¬ 
tion of openings of odd shapes that will not permit 
any simple presentation. The final answer still seems 
obscured. As stated above, however, if the choice 
were between cylindrical capillaries and rectangular 
capillaries, the bulk of the evidence would, in the 
writer’s opinion, favor the latter. 

6.15 SUMMARY 

Measurement of Surface Area 

By measuring the adsorption of nitrogen at 
—195 C it is now possible to determine the relative 
surface area of non-porous, finely divided solids or of 
porous solids having large pores, to an accuracy of 
about 5% and the absolute area to an accuracy of 
about 25%. The method is also applicable to fine pore 
adsorbents such as charcoal, but for such materials 
it is attended with considerably more uncertainty 
than for the non-porous or large pore adsorbents. 






148 


MEASUREMENTS ON CHARCOAL AND WHETLERITES 


Application of Area Measurements in Predict¬ 
ing the Performance of Charcoals 

The nitrogen adsorption isotherms used in surface 
area measurements can be employed to obtain an 
approximate estimate of the PS life of a charcoal and 
to give some indication as to the utility of the base 
charcoal for making ASC whetlerite. 

Adsorption of Water Vapor 

Water vapor is adsorbed only slightly by most 
charcoals at relative humidities below 50%; at 
higher relative pressures, the adsorption rises rapidly 
and reaches a final saturation value which is about 
the same as that of other vapors when calculated as 
volume of liquid. Desorption of water vapor from 
activated charcoals is almost always accompanied by 
marked hysteresis, the equilibrium pressure for a 
given volume of gas adsorbed being much less on de¬ 
sorption than on adsorption. Desorption appears to 
take place as though the water were held in the 
capillaries by capillary condensation; adsorption of 
water vapor seems best explained as a combination 
of adsorption and capillary condensation. 

Pore Size and Pore Size Distribution 

Methods for measuring pore size include (1) use of 
molecules of increasing size in adsorption studies; 
(2) application of the Kelvin equation to adsorption 
isotherms of gases other than water vapor; (3) appli¬ 
cation of the Kelvin equation to water vapor ad¬ 
sorption and especially desorption isotherms; 
(4) measurement of the relation between the residual 
surface area and the amount of water held in the 
capillaries of a charcoal; and (5) measurement of the 
pressure required to force Hg into capillaries. By a 
combination of (3), (4), and (5), pore size distribu¬ 
tion curves have been obtained on more than a 
hundred charcoals. 

Influence of Pore Size and Distribution on 
Charcoal Performance 

A necessary prerequisite to a good base charcoal 
for making ASC whetlerites to remove CK under 
80-80 test conditions appears to be the possession of 
a macropore volume in excess of about 0.2 cc per cc 
of charcoal granule. Micropores suffice for removal of 
PS provided enough large capillaries are present to 
permit gas to enter the particle readily. The same 
pore size criteria appear to apply to the removal of 
CG that apply to CK. The pore size requirements 
for the removal of SA and AC are less exactly de¬ 


termined as yet, but are susceptible to determina¬ 
tion by methods now available. 

Pore Size Alteration 

By a suitable combination of steaming, hydro¬ 
genation, or partial oxidation in the presence or 
absence of impregnation with inorganic materials, 
it is possible to tailor-make charcoals to give any 
desired distribution of pore sizes. Cr 2 0 3 , Fe 2 0 3 , NiO, 
Mo 2 0 3 , Na 2 C0 3 and CuO have all been studied as 
impregnating agents to assist in pore size alteration. 

Carbon-Oxygen Complexes 

The pickup of oxygen at temperatures up to 400 C 
has been studied in relation to its influence on the 
properties of charcoal. The adsorption of base from 
solution, of ammonia from the gas phase, and of 
water vapor at low relative pressure are all increased 
by oxygen treating. The surface complexes formed 
during the treating can all be removed from charcoal 
as CO and C0 2 by evacuation to 1200 C together 
with large quantities of hydrogen and smaller 
amounts of water vapor and methane. No correlation 
between the nature of the surface complex and the 
whetlerizability of a base charcoal has been estab¬ 
lished. 

Special Surface Coatings on Charcoal 

Samples have been prepared that are coated with 
partial layers of chemically bound nitrogen, chlorine, 
and sulfur. The influence of these coatings on the 
whetlerizability or sorptive capacity toward poison 
gases has not been measured. 

Molecular Structure and Adsorption 

Adsorption isotherms of about twenty different 
gases on CWSN 19 have been used as a basis for 
working out a theory for predicting the adsorption 
isotherm of a gas from its structure and physical 
constants. It has been found possible to predict 
whether a given adsorbate will be strongly, weakly, 
or very weakly adsorbed by a charcoal if the surface 
energy of the liquefied adsorbate, and the polariz¬ 
ability, and fundamental frequency of its molecules 
are known together with the adsorption isotherm for 
any known gas on the sample of charcoal to be used. 

Adsorption of Vapors by Charcoal 

Data are presented for the adsorption of PS in the 
presence and absence of water vapor and for the 



SUMMARY 


149 


adsorption of pyridine, picoline, and carbon tetra¬ 
chloride. Adsorption volumes at saturation are 
shown, in addition, for phosgene, mustard gas, amyl 
chloride, methyl alcohol, benzene, and n- hexane. 

Heats of Adsorption and Immersion 

Heat of immersion values have been measured for 
benzene on one charcoal under various conditions; for 
water on a charcoal before and after treating it with 
oxjrgen at 400 C, and for ethyl chloride on a series of 
charcoals. 

Retentivity 

The importance of the retentivity of a charcoal for 
a poison gas has been emphasized as a prerequisite 
for gas mask use. Detailed studies have been made 
on the retentivity of a number of vapors that are not 
miscible with water, of some that are partially mis¬ 
cible, and of several that are completely soluble. 
Water vapor on the charcoal or in the gas stream 
used in desorption was found to greatly decrease the 
retentivity of the first class of vapors, to influence to 
a smaller extent the desorption of the second class, 
and to have little influence on the desorption of those 
vapors that are miscible with water vapor. 


Chemisorption of Gases by Whetlerite Com¬ 
ponents 

On Type A whetlerites H 2 S, PH 3 , CNC1, BF 3 , 
HC1, C 2 H 2 , and NO appear to react with the CuO 
at room temperature to a depth in excess of a mono- 
layer and hence were not useful for measuring the 
particle size of the CuO particles deposited by 
whetlerization. CO, S0 2 , H 2 0, C 2 N 2 , and NH 3 all 
give promise of being useful for such measurements. 
On several typical whetlerites the average size of the 
CuO crystals appeared to be about 100 A. 

Structure of Charcoal 

It has not been possible to decide definitely as to 
the structure of the charcoal. Many pore size meas¬ 
urements have been made on the assumption that the 
pores are cylindrical capillaries. This is almost cer¬ 
tainly an over-simplification. Many of the properties 
of charcoals seem best explained by assuming that 
the charcoal is made up of sheets of carbon atoms 
only a few atoms thick, the pores having plain walls 
and being so crisscrossed as to provide sufficient 
strength for the particles. In any case, it is certain 
that a good gas mask charcoal must include a net¬ 
work of large and small pores; the large pores permit 
ready access to the molecules being adsorbed; the 
small pores provide the large surface area that is 
essential for removing gases by adsorption. 


I 



Chapter 7 

MECHANISM OF CHEMICAL REMOVAL OF GASES 

By J. William Zabor 


7.1 PURPOSE AND SCOPE OF THE 
INVESTIGATIONS 

uring the past four years a considerable amount 
of time and effort has been expended in studies 
of the mechanism of chemical retention or destruction 
of the various types of chemical warfare agents on 
base or impregnated charcoals. The research was 
undertaken in the hope that a better understanding 
of the mechanisms might lead to such advances as 
the following. 

1. Ideas for new impregnants, which by virtue of 
stoichiometric or catalytic action, would increase the 
protection afforded by gas mask absorbents for each 
type of gas. 

2. Clues to the mechanism of deterioration of im¬ 
pregnated charcoals now in use and to possible 
methods of reduction or elimination of such deleteri¬ 
ous aging. 

3. Information to guide the search for new war 
gases toward types which would most readily pene¬ 
trate enemy gas masks. 

4. Suggestions for gaseous agents which might be 
employed tactically as catalyst poisons — that is, 
agents designed to reduce the protection afforded by 
enemy gas masks against standard war gases to such 
a point that the enemy would be rendered vulnerable 
to subsequent gas attack; and, conversely, to dis¬ 
cover and eliminate such vulnerability in the gas 
masks of our Armed Forces. 

Among the references used in the compilation of 
this chapter are many reports of studies which were 
originally directed toward objectives other than the 
discovery of the mechanism of retention of the gases. 
Even from these, however, some information perti¬ 
nent to this subject may be gleaned. 

Considerable knowledge of the mechanisms for 
removal of the more common gases had been accumu¬ 
lated prior to 1940 by the Chemical Warfare Service 


and by independent workers. Much of the work, or 
similar investigations, leading to this knowledge was 
purposefully repeated in order to ascertain whether 
the more recently developed charcoals and whetler- 
ites behave similarly. Because this chapter does not 
represent a chronological treatment of the subject, 
only the more recent evidences are given in cases of 
duplication. 

It is obvious from consideration of the purpose of 
these investigations that a complete knowledge of the 
mechanisms, including all minor side reactions, is 
unnecessary; and understanding of only the principal 
reactions should suffice in most instances. For this 
reason, as well as for lack of time and because of the 
comparative importance of other methods of ap¬ 
proach to the general problems at hand, the con¬ 
clusions to be drawn are fragmentary and in some 
cases only tentative, pending the results of further 
investigation. 

7.2 CLASSIFICATION OF AGENTS 

There are many criteria upon which to base the 
classification of agents. For the purposes of this dis¬ 
cussion it is most convenient to classify them pri¬ 
marily according to their chemical properties. In 
general, such a classification system naturally 
separates the mechanisms into general types as well. 

On this basis the agents are considered in the fol¬ 
lowing order: 

1. Gases retained primarily by physical adsorp¬ 
tion. 

2. Acidic or acid-forming gases. 

3. Basic or base-forming gases. 

4. Readily oxidizable gases. 

5. Readily reducible gases. 

As in any classification system, there is some over¬ 
lapping of types; some agents exhibit properties 
characteristic of two or three of the classes. 



150 


SECRET 


CLASSIFICATION OF AGENTS 


151 


7.2.1 Gases Retained Primarily by Physical 
Adsorption 

Chloropicrin 

It has always been assumed that chloropicrin 
(trichloronitromethane; CC1 3 N0 2 ; PS) is physically 
adsorbed. A large volume of work has been done on 
the nature of this adsorption, its dependence on 
numerous variables, and its reversibility. Only a few 
of the experiments and conclusions supporting the 
assumption of physical adsorption need be quoted in 
this section; the bulk of the research is beyond the 
scope of this discussion. 

Nature of the Product Desorbed} Base charcoals and 
whetlerites were brought half way to the break point 
in standard tube tests with chloropicrin, and de¬ 
sorption was effected by passing dry air through the 
absorbent bed at 25, 35, 50, and 95 to 100 C. The 
boiling point, freezing point, and index of refraction 
of the desorbed gas were determined, alcohol solu¬ 
tions of the desorbed gas were analyzed polaro- 
graphieally, and chloride analyses were made of the 
pyrolytic products of the gas. All analyses indicated 
that chloropicrin was at least the chief, if not the 
only, substance desorbed from either type of ad¬ 
sorbent. 

Effect of Humidity of the Gas Mixture. 2 ' 3 Studies of 
effluent concentration versus time curves and of the 
weight-gains of dry charcoal tested with chloro- 
picrin-air mixtures at 0% and 50% RH showed that, 
within experimental error, the results of either type 


Table 1 . Comparison of standard PS tube lives of 
12-16 mesh base charcoals and Type ASC whetlerites. 


Service time (min) 


Base charcoals 

Whetlerites 

39 

34 

50 

45 

56 

51 

64 

57 


of test were independent of humidity. Though no 
attempt was made to ascertain the fraction of the 
gain in weight due to water adsorption, it is safe to 
assume on the basis of other experimental data that 
little or no water was adsorbed. Thus, at least during 
the course of dynamic tests, it is probable that hy¬ 
drolysis plays a negligible role in the retention of 
chloropicrin. Water originally adsorbed by the char¬ 
coal does effect adsorption of PS or other gases by 
rendering part of the charcoal surface inaccessible. 

Comparison of Base Charcoal and Whetlerite. The 


reference 2> 3 quoted is only one of many in which 
chloropicrin lives of base charcoals and whetlerites 
are compared. Typical performance data extracted 
from this reference and summarized in Table 1 show 
that the normal effect of whetlerization is to reduce 
slightly the amount of PS adsorbed. 

Occasionally a sample is found in which the life of 
the whetlerite is slightly longer than that of the base 
charcoal. Such infrequent phenomena are best ex¬ 
plained either on the basis of additional activation 
during the drying of the whetlerite, or change of 
mesh size due to attrition during the whetlerization 
process. In general, however, the reduction of PS 
service times by impregnation indicates that the 
impregnant occupies space on the adsorbent, or in 
some other way makes this adsorption space inac¬ 
cessible to chloropicrin. It further indicates that 
during the course of dynamic tests no beneficial re¬ 
action takes place between chloropicrin and the 
impregnant. 

Mustard Gas 

By virtue of their low volatilities and high molecu¬ 
lar weights persistent agents are adsorbed tenaciously 
by dry charcoals and whetlerites. As a consequence 
the protection of the respiratory tract against such 
agents does not present a problem and little work has 
been done to determine Avhether chemical reaction 
plays any appreciable role in the retention. 

One series of experiments 5 on the performance of 
the M10 canister against H—mustard gas, 2,2'- 
dichlorodiethyl sulfide; (C1CH 2 CH 2 )2S—under humid 
tropical conditions is of interest. Canisters filled with 
humidified Type A and Type AS whetlerites were 
tested at 50 1pm against H at 40 to 50 C. Even 
under these extreme conditions the protection 
afforded is more than ample. Examination of the 
weight changes during the tests offers the most inter¬ 
esting and conclusive evidence that the adsorption 
is primarily physical in nature. In all tests, the weight 
of H adsorbed exceeded the weight gain; indeed, in 
some of the experiments the canisters lost weight 
while adsorbing as much as 34 g of H. Because it is 
improbable that any volatile decomposition products 
other than HC1 would be formed and since HC1 
would be retained by the adsorbed water and the 
impregnants, these observations are best explained 
on the premise that H, being much more strongly 
adsorbed than water, displaces the latter from the 
adsorbent. 

Some hydrolysis of H undoubtedly takes place on 


SECRET 








152 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


the adsorbent, but the evidence for the displacement 
of water by mustard gas suggests that physical 
adsorption is of prime importance in dynamic tests. 

Similar results and conclusions 6 have been 
obtained with HN-3—tris /3-chloroethyl amine, 
(C1CH 2 CH 2 ) 3 N. 

Many other gases which are held by physical ad¬ 
sorption have been studied during the past two 
decades. In general, however, except for carbon 
monoxide, these gases have little or no promise as 
toxic agents; those which are toxic are nonvolatile 
and are well adsorbed by charcoal. 

7.2.2 Acidic or Acid Forming Gases 

The majority of the nonpersistent gases fall in this 
classification. The three standard agents, phosgene, 
hydrogen cyanide, and cyanogen chloride, are ex¬ 
amples of this type as well as the many fluorides upon 
which considerable time and energy were expended in 
search for new agents during the early part of World 
War II. Other gases which have been investigated to 
a moderate extent and which are members of this 
group are nitrogen dioxide, hydrogen sulfide, sulfur 
dioxide, and the halogen acids. 

Needless to say, the largest bulk of research in the 
field of reaction mechanism has been directed at the 
problems arising from consideration of the more im¬ 
portant agents of this group. An effort is made, 
therefore, to summarize the experimental evidence 
and conclusions with reference to summary reports 
whenever feasible. 

Phosgene 

The main features of the mechanism of CG (car¬ 
bonyl chloride; COCl 2 ) removal by charcoals have 
long been known. 7 The conclusions from early tube 
tests with unimpregnated charcoal are briefly sum¬ 
marized as follows. 

1. In contact with charcoal, phosgene is hydro¬ 
lyzed by moisture in the air or in the charcoal; hy¬ 
drochloric acid and carbon dioxide result. 

2. Whichever substance (phosgene or water) is 
present in deficient amounts is completely used up. 

3. For dry charcoal and dry gas mixtures the 
phosgene is held by physical adsorption. 

4. If water is present in deficient amount, hydro¬ 
chloric acid will penetrate the charcoal before phos¬ 
gene since hydrochloric acid is less tenaciously ad¬ 
sorbed than is phosgene. 

5. If water is present in excess, phosgene will 


penetrate the charcoal before the hydrochloric acid 
because hydrochloric acid is very soluble in the excess 
adsorbed water while phosgene, being relatively in¬ 
soluble, must be retained principally by adsorption 
on the surface of the charcoal. 

6. The service times of deep layers of charcoal are 
considerably longer in the presence of excess mois¬ 
ture (either in the gas mixture or in the charcoal) 
than in absence of excess moisture, by virtue of the 
increased capacity of the charcoal for HC1 at high 
humidities. 

7. The carbon dioxide formed by the hydrolysis of 
phosgene appears in the effluent stream shortly after 
the start of the test under any set of conditions. 
Large excess of water may delay the appearance 
slight^, but in any case most of the carbon dioxide 
appears eventually in the emergent gas. 

These conclusions have been verified by more 
recent tests. 8 The results indicate that the phosgene, 
under dry conditions, is held principally by physical 
adsorption. 

C*OCl 2 = C*OCl 2 (Adsorbed), (1) 

C*OCl 2 (Adsorbed) + O(Surface) = C*0 2 + 2C1 
(Adsorbed), (2) 

2C1 (Adsorbed) + C + O(Surface) - COCl 2 . (3) 

Studies 9 with radioactive carbon a as a tracer 
suggested the possibility that reactions (2), and (3) 
might take place to a minor extent following re¬ 
action (1) on dry charcoal. This series of reactions 
seemed necessary to explain the presence of C0 2 in 
the emergent stream in excess of the amount ex¬ 
pected from reaction with the small amount of 
water available. Verification with thoroughly dried 
charcoal and gas streams is necessary. In any case, 
however, these reactions are of little interest in the 
overall mechanism inasmuch as they play a negli¬ 
gible role in the usual circumstances when some 
water is present ; the principal reaction must then be 
hydrolysis: 

COCl 2 + H 2 0 = C0 2 + 2HC1. (4) 

On whetlerites this reaction is followed by neutral¬ 
ization of the HC1 

CuO + 2HC1 = H 2 0 + CuCl 2 , (5) 

and regeneration of the water. Thus in the presence 
of deficient amounts of water the life to the pene¬ 
tration of HC1 is considerably lengthened by whet- 
lerization. 

a Radioactive carbon atoms are indicated by an asterisk. 


SECRET 




CLASSIFICATION OF AGENTS 


153 


The observation 9 of considerable C*0 2 in the 
effluent gas in tests with relatively dry whetlerite and 
gas may be explained on the basis of reactions (2) 
and (3) or by the chain set up in (4) and (5) or 
possibly by direct reaction with the copper oxide: 

CuO + C*OCl 2 = C*0 2 + CuCl 2 . (6) 

This reaction is also probably of little significance in 
the usual circumstances. 

Thus the catalytic hydrolysis [equation (4)] fol¬ 
lowed by neutralization [equation (5)], or by solu¬ 
tion of the HC1 in adsorbed water, probably represent 
the overall mechanism adequately. Other basic con¬ 
stituents of the impregnant may enter into reactions 
similar to equation (5) as well. 

The rate 9> 10 of removal of phosgene from the gas 
stream decreases with increasing moisture content 
of the whetlerite while the capacity of the adsorbent 
for the products increases. This is illustrated in the 
life vs thickness plots in Figure 1 for a Type AS 
whetlerite prepared from an extruded, zinc chloride- 



activated wood charcoal. This effect on the rate of 
removal of phosgene, together with other evidence, 
suggests that the reaction mechanism discussed 
above must be preceded by physical adsorption. 
This suggestion is deduced from the fact that the 
rate of physical adsorption must be a function of the 
accessible adsorptive surface area and consequently 
should decrease as the moisture content of the ad¬ 


sorbent increases; on the other hand, the rate of 
hydrolysis should be a function of the amount of 
accessible water and should increase with increasing 
moisture content. The extent of this effect depends 
to a large degree on the pore size distribution of the 
adsorbent as discussed in Chapter 6. 

The CG capacity of dry whetlerites increases with 
decreasing temperature; 9 at the same time the 
critical bed depth first increases, probably because of 
changes in the diffusive properties of the gas, and 
then decreases as the rate of rise of capacity in¬ 
creases. This is typical of systems in which reversible 
adsorption is the predominating process. The ca¬ 
pacity of whetlerites having a high moisture content 
remains essentially unchanged with decreasing tem¬ 
perature 9 - 12 until approximately — 20 C is reached; 
at this point the capacity of most samples studied 
drops sharply. This may indicate a change in physi¬ 
cal state of the adsorbed water and consequent 
transition to a mechanism of primarily physical ad¬ 
sorption. The critical bed depth increases at first 
partially because of the decrease in temperature and 
because of a reduction in the rate of hydrolysis. 
Below — 20 C there is indication of a rise in rate of 
adsorption as in the case of dry adsorbents. 

The experiments to determine the effects of tem¬ 
perature are only cursory in nature and are quoted 
only to complete the picture and to show that by 
reasonable speculation they may be qualitatively 
interpreted on the basis of the proposed mechanism. 

The copper content of a whetlerite is in the range of 
5 to 8 % on a weight basis and the apparent density is 
approximately 0.5 g per ml; thus the copper content 
may be expressed as 0.025 to 0.040 g per ml. In tests 
of whetlerites as received with 50% RH CG-air 
mixtures, the capacities of the adsorbents expressed 
in millimoles of CG lie in the range of 0.6 to 0.9 
millimole per ml. Similar tests with base charcoals 
indicate that excess of the observed range of capaci¬ 
ties of whetlerites over the range calculated from the 
copper content and the proposed mechanism, repre¬ 
sents a reasonable capacity for the charcoal base. 
The critical layers for the whetlerites under these 
conditions lie in the range of 0.5 to 1.5 cm at a 
linear flow rate of 500 cm per min and are nearly 
independent of flow rate over the range of 250 to 
1,000 cm per min. 

For whetlerites or base charcoals equilibrated at 
80% RH, the capacities are in the range of 1.5 to 2.5 
millimoles per ml and the critical layers in the range 
of 1.0 to 2.3 cm at a flow rate of 500 cm per min. 


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154 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


Preliminary tests 13 with monofluorophosgene 
(COC1F) are compatible with the mechanism dis¬ 
cussed above. The protection afforded by dry wliet- 
lerites against dry gas mixtures is less for COC1F 
than for COCl 2 . This would be predicted on the 
basis of the effect of reduced molecular weight and 
increased vapor pressure on physical adsorption. 
The protection afforded in moist systems, on the 
other hand, is greater against COC1F than against 
COCl 2 presumably because of the greater ease of 
hydrolysis of COC1F. 

Acids 

None of the acids HF, HC1 or H 2 S are of interest as 
war gases, but studies of protection afforded against 
these gases and of the mechanism of the retention 
lend insight to the expected behavior of new agents 
of this general classification. 

Life vs thickness studies 14 with dry Type A whet- 
lerite and dry HF-air mixtures demonstrated that 
at 25 C and an influent concentration of 1.5 mg per 1, 
the capacity of the whetlerite was 1.75 millimoles per 
ml of adsorbent while the critical bed depth was 1.2 
cm; at 40 C and an influent concentration of 1.65 mg 
per 1, the capacity was reduced to 1.45 millimoles per 
ml while the critical bed depth remained unchanged. 
The fact that part of the HF is held by physical ad¬ 
sorption is shown by the reduction in capacity with 
increase in temperature and by desorption trials. 
Nevertheless, the amounts of HF retained by 3-cm 
layers of dry whetlerite taken to the break point 
were found to be independent of the influent concen¬ 
tration over the range from 0.4 to 2.2 mg per 1 at 
25 C; base charcoal on the other hand not only shows 
a smaller retention under these conditions, but also a 
retention which increases with increasing influent 
concentration. These observations may be considered 
as good evidence for the predominance of a chemical 
reaction, presumably 

CuO + 2HF = CuF 2 + H 2 0. (7) 

The equality of critical layers for the whetlerite at 
these two temperatures is an indication that re¬ 
action (7) is probably preceded by adsorption and 
that adsorption may be the rate-governing step. On 
the basis of equation (7) and approximate calcula¬ 
tions such as were made in the section dealing with 
phosgene, the capacity due to chemical reaction 
should lie in the range of 0.8. to 1.3 millimoles per ml 
as compared with the observed capacity of 1.45 
millimoles per ml. 

The presence of moisture increases the tube lives of 


either whetlerite or base charcoal several fold, indi¬ 
cating additional retention by solution of HF in the 
adsorbed water. 

If dry or moist adsorbents are exposed to or be¬ 
yond the HF break point in a tube test and an air 
stream is subsequently passed through the tube, 
some of the HF will desorb. 15 The desorption from 
base charcoal is much greater than from Type A 
whetlerite. If the desorption curves 15 are extrapo¬ 
lated to the point where the concentration becomes 
essentially zero, a rough estimate may be made of 
the amounts of HF retained chemically. Estimates 
made in two trials with dry Type A whetlerite were 
0.7 and 1.1 millimoles per ml; the first estimate may 
be low since the test was carried only to the break 
and insufficient time was given to permit redistribu¬ 
tion of the slight excess of adsorbed gas in the 
influent layers to the effluent layers so that reaction 
(7) could proceed to complete utilization of the CuO 
or of the HF. Though these estimates are only 
approximate, the fact that they fall in the range of 
capacities predicted for this mechanism constitutes 
additional substantiation. A similar desorption ex¬ 
periment with base charcoal was not conducted over 
a sufficiently long period to permit an extrapolatory 
estimate of the retentivity, but it is certain from the 
data that the retentivity would be less than that of 
the whetlerite by a large factor. 

When 1 g (approximately 2 ml) of thoroughly dried 
whetlerite was exposed to 21.6 ml (STP), or ap¬ 
proximately 1 millimole of HC1 gas, the gas was 
completely and irreversibly adsorbed. 16 Water equiva¬ 
lent to 70% of the HC1 was removable. This result 
is compatible with the proposition of equation (5) as 
the principal mechanism for removal of HC1 by 
whetlerites in the absence of water. The predicted 
irreversible capacity is 0.8 to 1.3 millimoles of HC1 
per ml of whetlerite. 

Canister tests with HC1 17 are likewise compatible 
with this mechanism. MIXA1 canisters tested to the 
break point failed to evolve any HC1 during 6 hr of 
subsequent passage of air. At the break point the gas 
input was less than the capacity computed on the 
basis of chemical reaction. 

Hydrogen sulfide behaves in a manner similar to 
hydrochloric acid when brought in contact with 
thoroughly dried whetlerite. 16 Even at — 78 C the 
H 2 S reacts within a few minutes with all the CuO 
present in the whetlerite to form H 2 0 and CuS. 
Tube tests of whetlerite in comparison with base 
charcoal 18 substantiate this chemical removal. 


SECRET 



CLASSIFICATION OF AGENTS 


155 


Nitrogen Dioxide (N0 2 ) 

By virtue of its oxidizing properties, N0 2 might be 
classified as a readily reducible gas. However, a study 
of its behavior in contact with charcoal or whetlerite 
leads rather to classification as one of the more or 
less unique members of the acidic group. 

No data have been obtained in systems entirely 
free of water. Since such circumstances are never met 
in actual practice this lack of information is of little 
concern except for the light which might be shed on 
the mechanism of removal of N0 2 by studies of its 
behavior under these conditions. 

In tube and canister tests 19> 20 in the presence of 
some moisture charcoals and whetlerites exposed to 
N0 2 are penetrated first by NO. In general, the 
greater the amount of moisture present, the more 
rapidly NO forms and penetrates the adsorbent. 
Charcoals and whetlerites equilibrated at 50 to 80% 
RH transmit NO immediately when exposed to N0 2 . 

N0 2 is reduced to NO on the surface of other solids 
such as silica gel and soda lime, which are not re¬ 
ducing agents. Water is the only substance present 
capable of accounting for the reduction. It was, 
therefore, concluded that the reaction 

3N0 2 + H 2 0 = 2HN0 3 + NO (8) 

is catalyzed by these surfaces at room temperatures; 
when uncatalyzed this reaction is unimportant com¬ 
pared with the reaction 

2N0 2 ± H 2 0 = HN0 3 + HN0 2 . (9) 

That water is involved in the removal of N0 2 is also 
shown by the observation that the time before pene¬ 
tration of N0 2 increases with increasing moisture 
content while the time to penetration of dangerous 
dosages of NO decreases. NO must result mainly 
from direct reaction with water and not from de¬ 
composition of HN0 2 inasmuch as the production of 
NO takes place on soda lime and whetlerite where no 
appreciable quantities of HN0 2 may exist in the early 
stages of the test because of reaction with the bases 
present. 

That reaction (8) is preceded by activated ad¬ 
sorption is suggested by the necessary catalytic 
nature of the reaction as well as by the observation 
that NO is produced less rapidly on soda lime 
than on charcoal. 

Reactions (8) and (9) followed by solution or 
neutralization of the HN0 3 and HN0 2 suffice to ex¬ 
plain the material balance of influent and effluent 
gases observed over fairly long periods of time. After 


extended periods of time, however, three times the 
NO concentration in effluent gas plus the penetrating 
concentration of N0 2 becomes greater than the 
influent N0 2 concentration. This may be due to 
reaction between the HN0 3 and the charcoal, re¬ 
sulting in the formation of either NO or N0 2 , or 
both; 

4HN0 3 + 3C = 4NO + 3C0 2 + 2H 2 0. (10) 
4HN0 3 + C = 4N0 2 + C0 2 + 2H 2 0. (11) 

When moist whetlerite is tested with NO immedi¬ 
ate penetration of a relatively high concentration of 
NO is observed, but after continued exposure N0 2 is 
likewise found in the emergent gas; the service time 
to the penetration of N0 2 increases with increasing- 
moisture content of the adsorbent. Numerous re¬ 
actions could be postulated to account for these ob¬ 
servations, but it seems most likely that the mecha¬ 
nism consists primarily of the adsorption and catalytic 
oxidation of the NO: 

NO + 0 (Surface) = N0 2 , (12) 

and that the effect of moisture is to retain the N0 2 by 
reactions (8) and (9) as well as to reduce the rate of 
(12) by reducing the accessible adsorptive surface 
area. 

While many side reactions are conceivable and 
may play minor roles, the overall mechanism of 
adsorption followed by reactions (8), (9), (10), (11), 
and (12) is adequate to explain the observations on 
the removal of N0 2 by charcoals and whetlerites in 
dynamic systems. 

Sulfur Dioxide (S0 2 ) 

Only a few experiments have been performed with 
S0 2 and these are too few to permit speculation as to 
the exact nature of the chemical removal. In the 
absence of sufficient data on the mechanism of re¬ 
action, S0 2 is merely mentioned because of the 
additional evidence it affords for the conclusion that, 
in general, the first step in the mechanism of removal 
of gases is that of physical adsorption. 

At 25 C the S0 2 tube test lives of Type A whet¬ 
lerite, considered as a function of humidity, display 
a maximum at intermediate humidities. The initial 
increase in life with increasing humidity is in the range 
where the adsorbed moisture has little or no effect on 
the rate of physical adsorption. Such behavior indi¬ 
cates that the mechanism definitely involves solution 
of the S0 2 in water adsorbed during the exposure or 


SECRET 



156 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


chemical reactions in which water plays an important 
role. The subsequent fall in life with increase in 
humidity is in the range in which water renders a 
considerable fraction of the surface inaccessible to 
the S0 2 and, therefore, suggests that adsorption is 
the initial step and a limiting process in the mech¬ 
anism. 

At intermediate humidities the amount of S0 2 re¬ 
moved at the break point decreases with increasing 
concentration. Because the capacity, regardless of 
the mechanism, must either remain constant or in¬ 
crease as the influent concentration is increased, this 
is considered as evidence that even under these con¬ 
ditions the rate of removal is a limiting factor in 
determining the service time. At higher humidities, 
the rate of removal should become more dominant 
as the limiting process. 

While the few tests with S0 2 do not permit an un¬ 
ambiguous conclusion as to the mechanism, they are 
most readily interpretable on the basis of the assump¬ 
tion that the first step in the removal is physical 
adsorption, followed by chemical reaction and solu¬ 
tion of S0 2 in the water condensed in the pores. 

Reaction of S0 2 with the CuO, et cetera, of the 
impregnant in the absence of moisture may or may 
not occur. Preliminary investigation 16 showed that 
such reaction may be sensitive to small amounts of 
alkali. 

Fluorides 

A considerable research program has been con¬ 
ducted in search for new toxic agents among the 
compounds containing fluorine. One of these, COC1F, 
has already been mentioned in this chapter. Because 
of their lower boiling points and molecular weights 
such compounds are less readily adsorbed physically 
than the corresponding chlorine derivatives. Never¬ 
theless, most of the toxic fluorides are readily hy¬ 
drolyzed or decomposed in contact with charcoal 
and hence under normal conditions the protection 
afforded by gas mask canisters containing moist 
charcoals or whetlerites is adequate. 

Phosphorus Trifluoride (PF 3 ). In tube tests 22 in 
the absence of moisture, the total input of PF 3 to 
the break points of Type A whetlerites was found to 
be independent of the influent concentration over the 
range of 0.5 to 13.4 mg per 1. The tube lives at 
— 30 C were longer than those at 25 C under these 
conditions. These results indicate that physical ad¬ 
sorption is the principal means of retention; reaction 


with the CuO of the whetlerite can play only a minor 
role. 

With addition of moisture to the adsorbent the 
service time increases at first and then decreases when 
more than an optimum amount of water is added. 
The lives of whetlerites tested with a 50% RH gas 
stream are longer than those with dry gas when the 
moisture content of the whetlerite is less than about 
10% on a dry basis. The tube life for tests with dry 
gas decreases with decreasing temperature if the 
moisture content of the whetlerite is greater than 
about 10%. 

On the basis of these and previous observations it 
is concluded that the hydrolysis of PF 3 plays a major 
role in the mechanism of removal of this agent. As in 
the case of other gases considered, it is probable that 
this reaction takes place on the surface of the ad¬ 
sorbent and must be preceded by physical adsorption. 

Selenium Hexafluoride (SeF$) . The experiments 
performed with selenium hexafluoride 23 > 24 are not 
as complete as those with phosphorus trifluoride. 
Nevertheless, the data are consistent with the con¬ 
clusions drawn above. The mechanism probably con¬ 
sists principally of physical adsorption followed by 
hydrolysis and subsequent retention of the products 
by neutralization by the impregnants, solution in 
the adsorbed water, and physical adsorption. The 
fact that the service time continues to rise at least 
to the highest moisture content (75% RH; 30% 
moisture on the whetlerite) employed, suggests that 
the initial step is not dominant as the rate controlling 
step. This conclusion is confirmed by the observation 
that the dry life does not go through a minimum, but 
shows a continuous increase as the temperature is 
decreased. 

Sulfuryl Chloro-fluoride ( S0 2 CIF ). A limited num¬ 
ber of tube tests with sulfuryl chloro-fluoride 25 
yielded interesting results. In tests with dry Type A 
whetlerite and dry air, S0 2 was the first substance 
to penetrate the adsorbent; this product probably 
results from the catalytic decomposition of S0 2 C1F 
following adsorption: 

S0 2 C1F = S0 2 + C1F. (13) 

C1F is presumably more strongly adsorbed than 
S0 2 . S0 2 C1F was the second gas to penetrate under 
these conditions 

In the presence of moisture, S0 2 C1F was found in 
the emergent stream before S0 2 . In all cases the 
chloride and fluoride in the effluent gas were small 


SECRET 



CLASSIFICATION OF AGENTS 


157 


in amount compared with the S0 2 C1F. The chloride 
and fluoride probably appear as HC1 and HF formed 
by hydrolysis: 

SChClF + 2H 2 0 = H 2 S0 4 + HC1 + HF, (14) 
or 

2C1F + 2H 2 0 = 2HC1 + 2HF + 0 2 . (15) 

Competition of (14) with (13) probably accounts par¬ 
tially for the precedence of S0 2 C1F before S0 2 in 
tests in the presence of moisture. H 2 S0 4 , HC1, and 
HF are retained by reaction with CuO and by solu¬ 
tion in the adsorbed water; 0 2 may either be chemi¬ 
sorbed by the charcoal or appear unnoticed in the 
emergent gas. 

S0 2 C1F preceded S0 2 and the halogen acids by 
longer time intervals when tests were performed 
with moist whetlerite at —29 C, indicating a prob¬ 
able reduction in rate of reactions (13) and (14). 

Sulfur Pentafluoride; (*S 2 Fi 0 ); 1120 or Z. When 
charcoal or whetlerites are exposed to sulfur penta- 
fluoride-air mixtures, 26 a mixture consisting chiefly 
of SF 6 and S0 2 F 2 generally penetrates the adsorbent 
first; in some cases, however, S0 2 is the first pentrat- 
ing gas. This initial penetration is followed con¬ 
siderably later by penetration of HF and finally by 

s 2 f 10 . 

Insufficient experimental data are at hand to as¬ 
certain the importance of the role played by mois¬ 
ture, but the presence of sulfuryl fluoride and hydro¬ 
fluoric acid in the effluent stream and some evidence 
for an increase in the tube life in the presence of mois¬ 
ture suggest that hydrolysis plays a major role in the 
mechanism of removal. 

Because SF 6 , S0 2 F 2 , and S0 2 are relatively innocu¬ 
ous, penetration of these gases is of little concern. 
While not very toxic, HF is irritant, and penetration 
of this gas would probably mark the conclusion of the 
period of usefulness of the canister. Under all condi¬ 
tions of test, protection to the HF break appears to 
be adequate. Whetlerite and Type D mixtures are 
more effective than base charcoal in removing the 
HF. There is some evidence for transmission of small 
concentrations of toxic substance prior to the S 2 Fi 0 
break; this may be due to slow leakage of this agent 
at concentrations which appear too small to be 
effective. 

These many observations demonstrate a very com¬ 
plicated mechanism. Nevertheless, with the aid of 
the results obtained with other fluorides, it is possible 
to speculate as to the more important reactions in 
the overall mechanism. 


The first step is probably adsorption followed by 


decomposition: 

S 2 F 10 = SF 6 + SF 4 . (16) 

Adsorption of SF 6 and SF 4 may then be followed by 
catalytic hydrolysis: 

SF 6 + 2H 2 0 = S0 2 F 2 + 4HF. (17) 

SF 4 + 2H 2 0 = S0 2 + 4HF. (18) 

Another source of S0 2 in the effluent gas may be a 
decomposition similar to reaction (13): 

S0 2 F 2 = S0 2 F 2 . (19) 

F 2 and S0 2 F 2 probably undergo hydrolysis similar to 
(14) and (15): 

2F 2 + 2H 2 0 = 4HF + 0 2 . (20) 

S0 2 F 2 + 2H 2 0 = H 2 S0 4 + 2HF. (21) 


Boron Trifluoride Acetonitrile (CH Z CN-BF 3 ). 
Tests 25 with CH 3 CN • BF 3 were insufficient in num¬ 
ber to permit much speculation in regard to the 
mechanism of removal. No tests were made for 
acetonitrile in the emergent stream because it is rela¬ 
tively innocuous. Moist whetlerite afforded longer 
service time to the penetration of fluorides than dry 
whetlerite. Thus the mechanism probably consists of 
the catalytic decomposition yielding acetonitrile and 
boron trifluoride, followed by hydrolysis of the BF 3 
(and possibly CH 3 CN as well). Protection appears to 
be adequate in any case. 

Arsenic Trifluoride (A sF 3 ). The results of tests 25 
with arsenic trifluoride, though inconclusive, indicate 
strong adsorption followed by rapid hydrolysis. 
Protection against this gas appears to be excellent 
under all conditions. 

1,2-Dinitro-tetrafluoro-ethane. Investigations of 
1,2-dinitro-tetrafluoro-ethane (C 2 F 4 [N0 2 ] 2 ) show no 
evidence for reaction or decomposition of the gas 
either on dry or moist Type A whetlerite. 25 Indeed, 
the results of all experiments with this agent indicate 
reversible adsorption, and adequate protection ex¬ 
cept at high moisture content of the adsorbent. Being 
relatively innocuous, dinitro-tetrafluoro-ethane sup¬ 
ports the generalization that fluorides sufficiently 
toxic to be of interest as war gases must be reactive 
and hence subject to hydrolysis and/or other decom¬ 
position on moist whetlerites as exemplified by the 
other fluorides considered in this section. 

Phosphoryl Trifluoride (POF 3 ) . The few experi¬ 
ments performed with phosphoryl trifluoride 25 indi¬ 
cate direct reaction with the CuO of Type A whet- 


SECRET 



158 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


lerite as well as with adsorbed water in line with the 
general mechanisms discussed above. 

Hydrogen Cyanide (HCN; AC) and Cyanogen 
(C 2 N 2 ) 

Hydrogen cyanide was used on a minor scale dur¬ 
ing World War I and today is one of the three 
standardized nonpersistent agents produced by the 
Chemical Warfare Service. Among the advantages of 
this agent are its low molecular weight and high 
volatility which result in inadequate protection by 
physical adsorption on activated charcoal. As a con¬ 
sequence, considerable effort has been expended in 
search for suitable impregnants which enhance the 
protection by chemical retention or destruction, in 
study of the mechanism of removal, and in con¬ 
sideration of tactics for use of AC against protected 
enemy troops. 

Because of the volume of work and reports dealing 
with the removal of AC, it is impossible to discuss all 
of the experimental results in this brief treatment of 
the subject. Only some of the more important aspects 
of the research are mentioned. For detail, the reader 
is referred to summary reports 28 - 29 and to the original 
reports of the research. 

Cyanogen is considered concurrently with hydro¬ 
gen cyanide because of the similarities in many of 
the reactions in the mechanisms of removal of these 
two gases. No implication of equal importance is 
intended. 

The AC tube lives of dry base charcoals are short 
at room temperature, but increase rapidly with de¬ 
creasing temperature, indicating that physical ad¬ 
sorption is the principal mechanism of retention. 
The presence of moisture either in the gas stream or 
on the charcoal effects a small increase in life, prob¬ 
ably due to retention by reaction of HCN with the 
adsorbed water, with possible hydrolysis to am¬ 
monium formate. Only HCN is found in the effluent 
gas. 

The C 2 N 2 tube test lives of base charcoals are gen¬ 
erally somewhat longer than the AC lives under 
similar conditions. This observation and the effect 
of temperature on C 2 N 2 service times in dry systems 
indicate that the gas is held primarily by physical 
adsorption at room temperature. At high humidities, 
equilibrated charcoals tested at various temperatures 
exhibit minimum service times at about 25 C, indi¬ 
cating that a chemical reaction occurs in the presence 
of water. The presence of HCN in the effluent gas 
under these conditions suggests that hydrolysis is a 


probable reaction. In the absence of evidence pro or 
con, however, other reactions such as polymerization 
must be admitted as additional possibilities. 

At high humidities the C 2 N 2 lives decrease with in¬ 
creasing humidity of equilibration and test. Such a 
decrease is probably due, at least partially, to the 
slowness of the chemical reactions in the destruction 
of the cyanogen and consequent regeneration of ad¬ 
sorptive surface of the charcoal. The possibility of 
desorbing cyanogen and observations of recovery of 
life on standing after initial test lend further support 
to the thesis that physical adsorption is the primary 
step and that this is followed by slow reaction of the 
cyanogen. 



Figure 2. Typical effluent concentration-time curve 
for tube tests of Type A whetlerite against HCN. 


It has long been recognized 30 that cyanogen ap¬ 
pears in the emergent gases from whetlerites exposed 
to hydrogen cyanide. Typical effluent concentration- 
time curves 31 for tube tests of Type A whetlerite at 
AR-50 and 80-80 humidity conditions appear in 
Figures 2 and 3, respectively. By passage of gas-free 
air through a whetlerite following an HCN exposure, 
varying amounts of C 2 N 2 can be desorbed depending 
on the extent of the original exposure and the humid¬ 
ity conditions. The greatest amount of C 2 N 2 is de¬ 
sorbed under relatively dry conditions, but even in 
such cases the amount desorbed is not proportional 
to the amount of HCN adsorbed. 


SECRET 




CLASSIFICATION OF AGENTS 


159 



Figure 3. Typical effluent concentration-time curve 
for tube tests of Type A whetlerite against HCN. 


Since the removal of HCN or C 2 N 2 by whetlerite 
involves the absorption of both, the mechanisms for 
the removal of these gases cannot be discussed sepa¬ 
rately. The reactions postulated apply to the ab¬ 
sorption of either. 

As in all previous instances, it is believed that 
physical adsorption of the toxic gas is the first step in 
the mechanism. The AC protection afforded by im¬ 
pregnated resins and soda lime indicate that this step 
is probably not the major rate-governing process in 
the case of whetlerites. On the other hand, the in¬ 
effectiveness of catalytic cuprous or cupric oxide in 
granular form, or whetlerized sodium silicate, or 
exploded mica, are evidence supporting the con¬ 
clusion that adsorption is a prerequisite to satis¬ 
factory removal. Temperature and adsorption studies 
with C 2 N 2 show that it can be appreciably adsorbed 
without chemical reaction. The short life of whet¬ 
lerite at 80-80 is evidence that adsorption of cyanogen 
is the primary step in its retention by whetlerite. 

The presence of C 2 N 2 in the emergent gases from 
whetlerites exposed to HCN necessitates the presence 
of an oxidizing agent on the charcoal surface; oxygen 
has been found to be unnecessary for the removal of 
HCN and production of C 2 N 2 . Furthermore, a 
stoichiometric reaction with the copper is indicated 



Figure 4. Effect of copper content on HCN and C 2 N 2 
lives of whetlerite. 



% Cu ON CHARCOAL 

Figure 5. Effect of copper content of whetlerite on 

HCN and C 2 N 2 lives. 

by the facts that (1) saturation data show that 1.5 
to 2.0 moles of HCN are adsorbed per mole of copper 
and (2) the HCN life is proportional to the copper 
content of the whetlerite (see Figures 4 and 5). The 
nitrogen in the HCN is not oxidized, but remains in a 
form which can be hydrolyzed to ammonia (as nitrile, 
amide, or ammonia salt). At 100 C about 50% of the 
absorbed HCN remains on the whetlerite as cyanide, 
tentatively identified as cuprous cyanide. This 
abundance of evidence supports the theory that the 
main reaction for HCN removal is 

4HCN + 2CuO = 2CuCN + 2H 2 0 + C 2 N 2 . (22) 

This is not the only form of chemical removal. In 
addition to CuO, cuprous oxide and basic copper 
carbonate have been identified on whetlerites by 


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160 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


X-ray diffraction studies. Tube tests indicate that 
cupric oxide is more reactive than basic copper car¬ 
bonate. Nevertheless, the evolution of considerable 
C0 2 in the reaction of HCN is best explained on the 
basis of reaction with the carbonate: 

4HCN + 2CuC 0 3 = 2CuCN + 2H 2 0 + C 2 N 2 

+ 2C0 2 . (23) 

It is possible that some C0 2 comes from other 
sources, but the observations supporting equation 
(23) as the principal reaction involved are that (1) 
sufficient carbonate was present to account for all the 
C0 2 , (2) C0 2 was found in the absence of water and 
to a greater extent from HCN than from C 2 N 2 and 
thus does not arise to an appreciable extent from 
hydrolysis of these gases, and (3) all of the HCN ab¬ 
sorbed was found as cyanide or cyanate. 

Cu 2 0 and HCN most likely undergo a straight 
metathetical reaction: 

2HCN + Cu 2 0 = 2CuCN + H 2 0. (24) 

Whetlerites containing copper in the form of Cu 2 0 
instead of CuO exhibit lives slightly more than half 
those of standard whetlerite. 

Polymerization of HCN is possible, but there is no 
evidence available to substantiate the occurrence of 
such a reaction; moreover saturation experiments 
indicate that it does not occur to any great extent. 

British investigators claim ammonium formate as 
the main end-product on their adsorbents. This 
product has not been found on whetlerite and the 
general stoichiometric nature of the HCN adsorption 
with the formation of C 2 N 2 precludes the possibility 
that hydrolysis to the formate plays a very important 
role on whetlerite. 

Cyanogen is held irreversibly on whetlerite 16 in 
the same amounts as S0 2 , CO, and H 2 0. This chemi¬ 
sorption or chemical reaction may be represented by : 

/ /OCN\ 

C 2 N 2 + CuO —> CuO • C 2 N 2 (Perhaps Cu<^ CN j • 

(25) 

Such a reaction would explain the greater C 2 N 2 life of 
whetlerite in comparison with base charcoal tested 
at 0-0 RH. It also would afford at least a partial ex¬ 
planation for the reduction of HCN life of a whet¬ 
lerite by previous exposure to C 2 N 2 . Such reduction 
of HCN life is greater under dry conditions than in 
the presence of moisture. This may be due to the 
decomposition of the product of reaction (25) by 


hydrolysis or to the fact that a greater proportion of 
the cyanogen maybe destroyed by direct hydrolysis: 

C 2 N 2 + H 2 0 = HCN + HOCN, (26) 
or 

C 2 N 2 + 2H 2 0 = (CONH 2 ) 2 . (27) 

The appearance of HCN in the emergent stream in 
C 2 N 2 tests on whetlerite as well as base charcoal is 
evidence for reaction (26). The HOCN may undergo 
polymerization to cyanuric acid, a probable reaction 
in the absence of strong acids. Since some ammonia 
has been identified on whetlerite exposed to HCN, 
it is also possible that HOCN is hydrolyzed to NH 3 
and C0 2 . However, insufficient NH 3 is found to ac¬ 
count for more than one-tenth of the HOCN being 
destroyed by this hydrolysis, if all the C 2 N 2 is re¬ 
moved by reaction (26). Some of the ammonia, how¬ 
ever, could be removed by side reactions leading to 
formation of ammonium cyanate, urea, ammonium 
carbonate and copper ammonium complexes. 

That the oxamide formed by reaction (27) may also 
undergo hydrolysis is indicated by the identification 
of both ammonium oxalate and oxamide among the 
products. 

There is no direct evidence for or against the poly¬ 
merization of cyanogen on whetlerite, but it must be 
considered as a possibility until such evidence is ob¬ 
tained : 

zC 2 N 2 (CN) 2 *. (28) 

Impregnation of charcoal with chromium or mo¬ 
lybdenum oxides alone improves only slightly its 
ability to remove HCN or C 2 N 2 . However, in con¬ 
junction with copper oxide, they are effective in 
removing these gases (particularly cyanogen). That 
reaction (22) occurs with Cu-Cr-Ag and Cu-Mo-Ag 
adsorbents is indicated by the saturation data, the 
effect of copper content on the life, and the presence 
of small quantities of C 2 N 2 in the effluent gas. 
Catalytic hydrolysis of the C 2 N 2 with destruction of 
the CuO may be responsible for the longer lives of 
these adsorbents. A mole ratio greater than two for 
HCN to Cu indicates that Cr must give the ad¬ 
sorbent some additional ability to remove HCN. 
The mole ratio of adsorbed cyanogen to copper and 
chromium on the char is too great for the reaction 
to be stoichiometric. Lack of a direct relationship 
between the life and the copper or chromium contents 
supports this conclusion. 

Reaction (26) cannot be the major reaction, for 
the amount of HCN generated would be too great 
to be completely adsorbed. Even after being run to 


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CLASSIFICATION OF AGENTS 


161 


the C 2 N 2 break point, Type ASC whetlerites display 
long service times against HCN. 

Inasmuch as water is necessary to make Type ASC 
whetlerite effective in removing C 2 N 2 , but oxygen of 
the air is not, a catalytic reaction is indicated. The 
most likely reactions are hydrolysis [reaction (27)] 
to oxamide and then to ammonium oxalate, or poly¬ 
merization [reaction (28)]. Qualitative identifica¬ 
tion of oxalate favor the hydrolysis as the major 
reaction. 

Adsorbents impregnated with zinc, cadmium, and 
nickel have appreciable HCN lives and probably 
react to form stable metal cyanides or cyanide 
complexes. No cyanogen is generated. 

Lives of charcoals impregnated only with silver are 
short in comparison with lives of whetlerites. Hy¬ 
drolysis to ammonium formate is said to be the major 
reaction in the removal of HCN. The silver, however, 
is rapidly attacked; small amounts of HCN poison 
the catalyst, destroying its action in arsine removal. 

Cyanogen Chloride 

Cyanogen chloride (CNC1; CK) was standardized 
and produced by the Chemical Warfare Service as 
the third nonpersistent gas largely because of the 
vulnerability of enemy canisters to this agent (see 
Chapter 11). Prior to 1945 it was known as CC. A 
considerable amount of time and effort has been ex¬ 
pended by Division 10 of NDRC and by the Tech¬ 
nical Division of the Chemical Warfare Service in 
search for new impregnants for charcoal or new ad¬ 
sorbents which would afford ample protection against 
CK under all conditions. This research culminated in 
the standardization of Type ASC whetlerite (see 
Chapter 4). Considerable thought and experimenta¬ 
tion was devoted simultaneously to the mechanism 
of removal of CK for clues such study might uncover 
toward possible improvements in the impregnation 
of charcoal, elimination of the deterioration of the 
proposed impregnants, and optimum tactical em¬ 
ployment of the gas as an offensive weapon. 

Though the research was prodigious and quite 
fruitful, the mechanism of retention of CK has proved 
to be complex and an unambiguous or unique solution 
has not been found. This was true in the cases of the 
other gases considered in this chapter, but to a lesser 
degree. Nevertheless, a brief summary of pertinent 
observations and tentative conclusions is warranted 
at this point. 28 - 32 

The CK tube test lives of dry or moist base char¬ 
coals decrease with increasing temperature over the 


range of 0 to 100 C. Studies of the kinetics of the 
adsorption in dry systems 33 show that, at least in the 
absence of water, this observation is due to a re¬ 
duction in the capacity of the charcoal which more 
than compensates for a simultaneous increase in the 
first-order rate constant for the adsorption. The 
presence of moisture reduces both the service times 
at any temperature studied and the capacities of base 
charcoals (at least at 25 C). Such observations are 
indicative of physical adsorption as the principal 
process of retention. 

Additional validation of this hypothesis is obtained 
in the observation that all of the adsorbed chloride 
can be desorbed from dry charcoal by the passage of 
air. About 12% of the chloride in one test failed to 
desorb in 20 min from charcoal tested at 80-80. It is 
possible that this fraction of the absorbed gas is held 
by solution in the water condensed in the pores and 
is thus less readily desorbed; however, part of the 
remaining absorbate might be destroyed by a slow 
reaction which can play only a minor role in the 
overall mechanism. Thin layers of charcoal which 
appear to be saturated in 5 or 6 min at 80-80 and high 
flow rates, continue to pick up CK slowly, giving rise 
to an increase in apparent capacity. For one sample, 
an increase from 10 to 14.3 mg of CK per ml of 
charcoal was noted after 180 min. This may indicate 
a slow displacement of water, a slow rate of reaction, 
or both. At any rate, the slowness of this removal 
eliminates it as an important step in the mechanism 
and hence does not invalidate the conclusion that 
physical adsorption is the major process involved in 
dynamic tests. An increase in the CK input to the 
tube-test break point with increase in influent con¬ 
centration in the presence or absence of moisture 
lends further support of this thesis. 

Type A and AS whetlerites yielded similar results 
in regard to the effects of humidity and influent con¬ 
centration on the tube lives, indicating that the 
mechanism of rapid removal in dynamic tests at room 
temperature is essentially the same (physical ad¬ 
sorption) as in the case of base charcoal. The CK 
tube test lives at AR-50 were found to be practically 
independent of the amount of copper in the impreg- 
nant. Hence it seems that copper oxide does not 
react to an appreciable extent with CNC1 or at least 
in a rapid stoichiometric reaction. However, whet¬ 
lerites broken to CK in air streams at various humidi¬ 
ties and temperatures recover considerable fractions 
of their original lives upon standing; furthermore, 
this regeneration process may be repeated several 


SECRET 



162 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


times. It is thus apparent that a slow chemical re¬ 
action occurs which removes some of the CNC1, 
permitting additional physical adsorption in subse¬ 
quent tests. Since this phenomenon was not observed 
on base charcoal, it must be concluded that the 
copper oxide plays a role (either catalytic or stoi¬ 
chiometric) in the reaction during recovery. Such a 
slow reaction is further evidenced by the fact that 
the amount of desorbable chloride decreases if the 
exposed whetlerite is permitted to stand before de¬ 
sorption is attempted. Furthermore, preliminary 
studies seem to indicate that the dry tube lives may 
pass through a minimum as the temperature is in¬ 
creased and then rise with further increase in tem¬ 
perature, substantiating the conclusion that a slow 
reaction may be taking place at room temperature. 

Cupric chloride has been identified by means of 
X-ray diffraction on a whetlerite exposed to CNC1. 
Such a compound could be formed by reaction with 
HC1 produced by CNC1 hydrolysis or with Cl 2 from 
CNC1 oxidation. Similarly the presence of C0 2 in the 
effluent gas long before the CK break point may be 
explained either by hydrolysis or by oxidation of the 
CK. However, as pointed out in the section dealing 
with HCN, much of the C0 2 may result from re¬ 
action of HC1 with copper carbonate which is likely 
to be present in the whetlerite. Only faint qualitative 
tests for cyanate have been found; this may be due to 
predominance of destruction of CK by oxidation over 
that by hydrolysis, or it may be explained by further 
hydrolysis of HOCN. 

To increase the protection against CK, particu¬ 
larly in the presence of moisture, the Chemical War¬ 
fare Service developed E6 whetlerite, a standard 
whetlerite treated with sodium thiocyanate and 
sodium hydroxide (see Chapter 4). This additional 
impregnation increases the lives of all whetlerites at 
low humidities, and at high humidities it increases 
the lives of whetlerites having the proper distribution 
of pore sizes and characteristics (see Chapter 6). 
No desorption is observed from E 6 whetlerites which 
have been exposed to CK. Upon aging, the E 6 
whetlerites lose a considerable fraction of their 
original lives. Such deterioration in protection ap¬ 
pears to be due to the oxidation of part of the thio¬ 
cyanate to sulfate. From these observations it has 
been concluded that the CNC1 reacts directly with 
the nitrogen of SCN~. 

An increase in C 0 t with increasing C 0 is generally 
taken as an indication of physical adsorption as the 
major step in the removal of a gas. Such behavior 


should also be manifested in cases in which reactions 
subsequent to adsorption are slow and fail to remove 
the gas from the adsorptive surface rapidly enough to 
make appreciable additional adsorption possible; 
any change in conditions which tends to accelerate 
the chemical reaction in such cases should decrease 
this trend of C 0 t. The presence of moisture on thio¬ 
cyanate whetlerites appears to decrease this tendency 
of C 0 t to increase with increasing C 0 , probably by 
accelerating the reactions of adsorbed CK, and hence 
offers some additional validation to the conclusion 
that adsorption, the primary step, is followed by a 
relatively slow chemical reaction. 

Search for impregnants affording greater original 
protection and stability led to the investigation of 
many metal oxides. Of these chromium, vanadium, 
and molybdenum were most promising. Study has 
been concentrated mainly on chromium impreg¬ 
nated charcoal inasmuch as this impregnant offered 
the best overall characteristics. Many of the specula¬ 
tions and conclusions for chromium impregnated 
charcoals and whetlerties, however, apply equally to 
those containing vanadium and molybdenum as 
well. 

Impregnation by copper or chromium alone yields 
poor adsorbents for cyanogen chloride. Both Cu +2 
and Cr+ 6 are necessary for optimum protection. The 
decrease in protection during aging is apparently due 
to loss of Cr+ 6 by reduction to Cr+ 3 , presumably by 
oxidation of the charcoal to C0 2 . A similar reduction 
of Cr +6 occurs during exposure to CK. In samples of 
ASC whetlerite exposed to less than the break time, 
4.7 equivalents of CK were absorbed per equivalent 
of chromium reduced; in long exposures, far beyond 
the normal service time, this ratio was found to be 
11.4, although 27% of the Cr+ 6 still remained after 
the longest exposures attempted. Thus it would seem 
that there is no direct relationship between the 
amount of Cr +6 reduced and the total amount of CK 
absorbed; this may be partially due to reaction of 
CK with CuO, though it is unlikely that such a 
reaction could afford a complete explanation. It is 
therefore doubtful that CNC1 reacts stoichiometri- 
cally with the impregnant. Thus while Cr +6 is neces¬ 
sary for rapid reaction, reduction of the chromium 
may not be a part of the primary process, but of a 
secondary or side reaction. It is possible that at least 
part of the reduction is due to oxidation of carbon; 
this reaction is known to be accelerated in the 
presence of acid. 

The initial rates of sorption of CK are approxi- 


SECRET 



CLASSIFICATION OF AGENTS 


163 


mately the same for base charcoal and ASC whet- 
lerite; however, the rate falls off more rapidly with 
time in the case of the base charcoal. This observa¬ 
tion would suggest that the first step in the removal 
of CK by ASC whetlerite is physical adsorption be¬ 
cause only with such a mechanism could the initial 
rates be equal on base charcoal or ASC whetlerite. 
This conclusion is validated by indirect evidence that 
the rate of destruction of CIv on ASC whetlerite in¬ 
creases at first during the period when the concentra¬ 
tion of adsorbed CK is probably increasing and then 
decreases during the extended period when the 
impregnant is being destroyed and part of the ad¬ 
sorptive surface is being utilized or made inaccessible 
by reaction products. 

In tube tests taken to the break point, CK satura¬ 
tion values are never reached in any part of beds of 
moderate thickness. Under standard test conditions 
life vs thickness plots are curved and estimates of 
capacities from such studies yield low values. This 
is apparently due to the slowness of chemical reaction 
of the adsorbed CK. The apparent capacities of 
present ASC whetlerites are within the range of 
40 to 100 mg of CK per ml of whetlerite (as compared 
with 0 to 15 mg of CK per ml of charcoal at 80-80) 
and are essentially independent of moisture con¬ 
ditions. Longer test lives at low humidities are due to 
the greater rates of sorption. Calculations based on 
comparison of results of tests with ASC whetlerites 
and base charcoals indicate that the specific chemical 
reaction rate for CK on ASC whetlerite is greater at 
high than at low humidities. Thus water plays an 
important part in the mechanism. This naturally 
suggests hydrolysis as a major step, but catalytic 
action of water may be important as well. CO 2 , 
NH 3 , Cl - , and small amounts of HOCN are known 
to be among the products of the reaction; other 
products may also be present. Practically no CNC1 
can be desorbed from ASC whetlerite within short 
periods of time after exposure to the break point. 
Thus all of the CK must be either destroyed or 
chemisorbed. 

All the chloride ion in CK taken up by charcoal 
or whetlerite can be recovered by acid distillation; 
about 90% can be recovered by extraction with 
water. On the average, less than 40% of the nitrogen 
can be recovered as NH 3 by basic distillation; some¬ 
what larger percentages can be recovered if the 
whetlerite was made acid for a period prior to the 
basic distillation. Approximately 70 to 75% can be 
recovered as NH 3 by extraction with water and sub¬ 


sequent basic distillation of the extract. From a 
comparison of NH 3 blanks for these two methods, it 
is apparent that part of the ammonia originally on 
the whetlerite is not removable by extraction $ it is 
possible that part of the CK which was not extract- 
able as NH 3 was lost by similar retention. It is also 
possible that loss is partially due to failure of inter¬ 
mediate products to hydrolyze. HOCN hydrolyzes 
slowly in basic m^dia whereas urea hydrolyzes less 
readily in acid media. A third possibility is that CK 
is destroyed by some other reaction which does not 
yield NH 3 . 

The amounts of C0 2 recovered in the effluent gas 
and from the adsorbent are large but irreproducible. 
This may be caused in part by variability of original 
C0 2 on the whetlerite due to different degrees of 
aging or to varying amounts of C0 2 picked up during 
equilibration. As mentioned above, part of the CO 2 
may arise during the test from oxidation of carbon by 
the Cr +6 . This oxidation may be accelerated by the 
temperature rise due to the heats of adsorption and 
reaction of CK and by increased acidity. 

In view of these observations, it is possible only to 
speculate as to the mechanism of reaction of CK on 
various whetlerites. All reactions are open to some 
question and need additional verification. Un¬ 
doubtedly the primary process is physical adsorption. 
This may be followed by hydrolysis, oxidation, or 
polymerization catalyzed by CuO and Cr 2 0 3 or a 
complex salt of these metals. 

CNC1 + HoO = HOCN + HC1, (29) 

2CNC1 + 20 2 = 2C0 2 + N 2 + Cl 2 , (30) 

3CNC1-(CNCl) 3 (Cyanuric chloride). (31) 

Hydrolysis to yield HC1 and HOCN is favored by 
change of free energy over the alternative reaction 
yielding HOC1 and HCN. Furthermore, reaction 
(29) is necessary to explain the observation of OCN - . 

Oxidation according to reaction (30) has been ob¬ 
served to take place fairly rapidly in experiments 
with CK and metal oxides on asbestos at 75 C. The 
fact that the capacity of ASC whetlerite is approxi¬ 
mately the same at 0-0, 0-50, and 80-80 RH 
would seem to indicate that the reaction can go to 
the same extent in the presence or absence of water 
and hence that water is merely a catalyst and 
hydrolysis is excluded as the major reaction. How¬ 
ever, there was, undoubtedly, some water present in 
the 0-0 RH tests because drying procedures em¬ 
ployed do not remove all the water either from the 


SECRET 



164 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


adsorbent or the gas stream and small amounts of 
additional water may possibly be picked up by the 
gas in passage through the flowmeters; furthermore, 
some water may be formed by neutralization re¬ 
actions such as in equation (5). Thus neither reaction 
(29) nor (30) can be excluded. 

No direct evidence for or against polymerization 
(31) on the adsorbent has been found. It must, there¬ 
fore, be included as a possible reaction of minor 
importance in the mechanism. 

The HOCN can undergo further hydrolysis or re¬ 
action with NH 3 : 


HOCN + H 2 0 = NH 3 + C0 2 , (32) 

HOCN + NH 3 = CO(NH 2 ) 2 , (33) 


and the urea could be hydrolyzed: 

CO(NH 2 ) 2 + H 2 0 = C0 2 + 2NH 3 . (34) 

Urea has not been identified as a final or intermedi¬ 
ate product, but reaction (34) is known to be possible. 

The ammonia would be retained by reaction with 
HC1 or with the metal impregnants, forming com¬ 
plexes. Cl 2 and HC1 should be retained by mecha¬ 
nisms similar to those postulated in previous sections. 

It has long been known that cyanogen chloride 
undergoes an addition reaction with amines: 34 


R—NH 2 + CNC1-> 


/H + 

R— NCN + Cl- (35) 
\H 


That such reactions take place on charcoal ad¬ 
sorbents is evidenced by an increase in rate of 
removal and of capacity of the adsorbent, 34 ’ 35 upon 
addition of amines to the impregnant. The nitrogen 
bases evidently react directly with the CK and do not 
merely activate the other catalysts, since an efficient 
adsorbent is formed when pyridine is put on base 
charcoal; in such cases the life is proportional to the 
amount of pyridine added. 

Pyridine and other bases do not appear to affect 
the aging of the inorganic catalyst, but merely raise 
the final life of aged whetlerite. 

Use of this additional impregnant has not been 
standardized since (1) the hazards of deterioration of 
ASC whetlerite have been found to be much less 
serious than was originally feared, (2) the addition of 
organic bases does not appreciably affect the initial 
overall performance of ASC whetlerite, and (3) many 
of the organic bases give off objectionable vapors on 
aging. Hence no detailed mention is necessary at this 
point. 


Because ASV and ASM whetlerites have not been 
standardized they need not be considered separately 
nor in detail in this discussion. It is sufficient to say 
that vanadium and molybdenum, like chromium, 
probably act as catalysts in conjunction with copper. 

For comparison purposes, the ranges of 80-80 CK 
capacities achieved with variously impregnated 
charcoals are summarized in Table 2. These values 
were obtained from the slopes of life vs thickness 
curves and hence are probably below the true satura¬ 
tion values. Nevertheless, they offer a good com¬ 
parison of the capacities effective during the useful 
lives of these adsorbents. 


Table 2. Ranges of 80-80 CK capacities of variously 
impregnated charcoals. (Influent concentration = 
4 mg per 1; flow rate = 500 cm per min). 


Impregnation 

No range (mg per ml) 

None 

0-15 

P* or Pi* 

15-35 

ASP or ASPi 

25-55 

ASM 

30-50 

ASMP or ASMPi 

40-100 

ASC 

40-100 

ASCP or ASCPi 

40-100 


* P = pyridene; Pi = picoline (/3— y mixture). 


General Conclusions for Acidic or Acid- 
Forming Gases 

It has been concluded that the first step in the re¬ 
moval of acidic or acid-forming gases by gas mask 
adsorbents is physical adsorption. This conclusion 
probably applies generally, as shown in the succeed¬ 
ing sections of this chapter. 

Acid gases, such as the halogen acids, undergo a 
rapid metathetical reaction with the metal oxides of 
the impregnant or, since most of them are very solu¬ 
ble in water, are retained by solution in the water 
condensed in the pores of the charcoal. 

The majority of the probable nonpersistent war 
gases are halides of one sort or another. The toxicity 
usually bears some relation to the reactivity of the 
molecule; the more reactive, the more toxic. Such 
gases are readily hydrolyzable and acid producing. 
The second step in the mechanism of removal is, 
therefore, hydrolysis, followed by reaction of the acid 
products with the impregnant or by solution of these 
products in the adsorbed water. Both the charcoal 
and the metal oxides are effective catalysts for hy¬ 
drolysis. Frequently, agents of this type react di¬ 
rectly with the metal oxides in the absence of water, 
but this is not an important feature because the 


SECRET 











CLASSIFICATION OF AGENTS 


165 


adsorbent in use in the field always contains some 
moisture, as does the air. 

HCN and CNC1 are exceptional members of this 
group. The mechanism of HCN reaction is compli¬ 
cated by the fact that Cu(CN) 2 , formed by meta- 
thetical reaction with the copper, is unstable, decom¬ 
posing to CuCN and C 2 N 2 . The resulting cyanogen 
is less readily destroyed than HCN; nevertheless, 
chromium in conjunction with copper acts as an 
effective catalyst for the destruction; probably by 
hydrolysis. In the case of CNC1 it is the original 
hydrolytic reaction which is the limiting process. 

The metal oxides are present in sufficient quanti¬ 
ties in the U. S. gas mask adsorbents to afford ample 
protection against gases of this group by metathetical 
reaction. Thus a catalyst “poison” designed to de¬ 
stroy the possibility of chemical reaction and render 
the mask vulnerable to subsequent attack must be 
employed in sufficiently large dosages to react with 
most of the impregnant; dosages are comparable to 
those necessary for penetration of the mask by a 
lethal agent. Partial destruction of the impregnant 
produces only a partial loss of protection against the 
lethal agent, whether it be removed by catalysis or 
by direct reaction with the impregnant. Thus the 
tactical use of a nonpersistent catalyst poison prior 
to attack by a lethal agent, in general, has little 
advantage except perhaps one of ease of procure¬ 
ment of such poison. A disadvantage in use of a gas as 
a poison is the resultant complications of logistics 
and the uncertainty of the result. 

However, in cases where the rate of removal of a 
gas is the limiting factor and the presence of large 
amounts of adsorbed water reduces the rate to a 
dangerous level, the use of a persistent agent to en¬ 
force prolonged masking during a period of high 
humidity prior to attack with the nonpersistent 
agent would be effective. 

It is improbable that continued research will pro¬ 
duce any new acidic or acid-forming gas which 
simultaneously is very toxic and readily able to 
penetrate U. S. gas masks. 

7.2.3 Basic or Base-Forming Gases 

Little attention has been paid to the nonpersistent 
basic gases. At one time ammonia was considered by 
some as a possible harassing agent because of the low 
dosage required for canister penetration. However, 
the only basic gases which have been standardized by 
the armed forces of any country are the nitrogen 


mustard gases; these amines are persistent agents 
and, by virtue of their relatively high molecular 
weights and low volatilities, are strongly adsorbed. 

A limited number of experiments have been per¬ 
formed to determine the protection afforded by char¬ 
coal adsorbents against NH a and a few amines. 
Though the results of these experiments are inade¬ 
quate to permit a complete evaluation of the 
mechanisms of rembval, a brief discussion at this 
point has some value as a guide to future work. 

Ammonia (NH 3 ) 

In tests with an influent concentration of 6.8 mg 
of NH 3 per 1, saturation values 36 obtained from the 
slopes of life vs thickness for five Type A whetlerites 
ranged from 2.0 to 15 mg of NH 3 per ml of whetlerite 
under 0-0 conditions; at 80-0 the capacities were 
increased to 22 to 70 mg per ml. A larger, critical bed 
depth was found for the equilibrated whetlerites 
than for the same whetlerites when dry. 

Large percentages of the ammonia are desorbable 
from all types of whetlerites both in the presence and 
absence of water. 36 - 37 In tests with Type AS whet¬ 
lerite in M10 and MIXA1 canisters taken to the break 
points immediately previous to the desorption, 63 to 
75% of the ammonia was desorbed from the dry 
whetlerite in 22 min and 51% was desorbed from 
equilibrated whetlerite in 41 min. The effluent de¬ 
sorption concentration had not fallen to zero by the 
conclusion of the experiment in any of the trials; 
hence these percentages are minimum values and it 
is possible that all the adsorbed NH 3 could have been 
desorbed. Type ASC whetlerite affords considerably 
greater protection than Types A or AS whether dry 
or moist, and the desorption from ASC whetlerites 
proceeds much more slowly; only 33 % of the NH 3 is 
desorbed in 43 min from a previously broken dry 
Type ASC whetlerite, and the rate of desorption 
from the moist whetlerite is even slower. Again, these 
are minimum values, and it is possible that all or 
nearly all the NH 3 can be desorbed by the prolonged 
passage of air. Lowering the temperature increases 
the amount of ammonia adsorbed by canisters filled 
with Type A or AS whetlerites. 

These observations clearly indicate that the major 
process involved in the retention of NH 3 by dry char¬ 
coal or whetlerites of Types A or AS is physical 
adsorption. On equilibrated adsorbents of these types 
this process is followed by solution of the ammonia 
in the adsorbed water. The enhanced protection 
afforded by ASC whetlerite would seem to indicate 


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166 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


that chemisorption on or reaction with the chromium, 
probably to form complexes, may play an appreciable 
role in the mechanism as well as adsorption and 
solution. 

Other Amines 

Though a considerable amount of work has been 
done with ethylenimine [EN], this gas may be dis¬ 
missed very briefly by a comparison with ammonia. 

In the case of a whetlerite which had a 0-0 capacity 
of 2 mg of NH 3 per ml at an influent concentration 
of 6.8 mg per 1, the capacity for EN at 0-0 and an 
influent concentration of 3 mg per 1 was found to be 
50 mg per ml. EN, having a higher molecular weight 
and lower volatility than NH 3 , is much more strongly 
held. Indeed EN is more strongly held by the char¬ 
coal than by solution in water and consequently the 
capacity decreases as the moisture content of the 
adsorbent is increased. 

Like ammonia, EN can be desorbed from whet¬ 
lerite, but the desorption is slow. The effect of tem¬ 
perature on the performance of a whetlerite against 
EN is similar to its effect in the case of NH 3 . No 
volatile products are evolved during the adsorption 
of ethylenimine and there is no regeneration of the 
adsorbent upon standing. Thus it is reasonable to 
postulate that physical adsorption is the principal 
process in the removal of this gas. It is possible that 
polymerization takes place to a minor extent on the 
adsorbent, but at best this could only play an insig¬ 
nificant role in the retention. 

Other amines whose tube lives have been deter¬ 
mined for comparison are t rime thy lenimine, piperi¬ 
dine, N-methyl ethylenimine, methyl ethylenimine, 
pyridine, diethyl amine, and allyl amine. The pro¬ 
tection against all these amines is greater than that 
against ethylenimine. 

General Conclusions for Basic or Base- 
Forming Gases 

Because of the nature of the impregnation now 
employed on gas mask adsorbents, basic gases are 
retained primarily by physical adsorption. However, 
of all of the basic gases studied to date, only ammonia 
is inadequately removed from the gas stream. The 
limitations of molecular weight and volatility for 
gases of this type to penetrate the gas mask are quite 
stringent. Even if these limitations were to be cir¬ 
cumvented, the resultant gas would probably have 
to be hydrolyzable in order to be toxic. In such an 


event the agent would most likely behave more 
nearly like the acidic gases than like the basic gases 
even though the intact molecule were basic. Thus it 
seems unlikely that a gas of this class will be found 
which at the same time will be very effective against 
protected troops. 

Nevertheless, ammonia is deserving of some con¬ 
sideration. Aside from its potentialities as a harassing 
agent, it is conceivable that it might be used to good 
advantage preceding attack with an odorless lethal 
gas. Poorly disciplined troops might be expected to 
remove their masks during subsequent attack rather 
than endure the irritation of the desorbing ammonia. 
It must be remembered, however, that the presence 
of NH 3 on the adsorbent increases, rather than de¬ 
creases, the protection against acid gases. 

7.2.4 Readily Oxidizable Gases 

Oxidation has been postulated as a possible reaction 
in the mechanisms of removal of phosgene [reaction 
(2)], nitric oxide [reaction (12)], and cyanogen 
chloride [reaction (30)]. The oxidation of phosgene 
plays an insignificant part in the presence of water. 
It seems also probable that oxidation of cyanogen 
chloride is of secondary importance in comparison 
with hydrolysis under usual conditions. The primary 
process in the mechanism of chemical removal of 
nitric oxide, no doubt, is oxidation to N0 2 . The lack 
of adequate protection against NO is probably due, 
first, to the weakness of the physical adsorption 
which must precede oxidation, and second, to the 
regeneration of NO by reactions (8) and (10). At any 
rate the nature of the reaction products from CG, 
CK, and NO and the nature of the reactions other 
than oxidation which these gases undergo, leads to 
their classification as acid-forming gases. 

Arsine is the best known of the gases which are re¬ 
moved solely by oxidation. Since World War I it has 
been one of the standard test gases used by the 
Chemical Warfare Service to evaluate gas mask ad¬ 
sorbents. In addition to the innumerable specification 
tests which have been run, a considerable amount of 
research has been devoted to the study of the mecha¬ 
nism of its removal. It is possible that other arsenicals 
undergo similar oxidation on whetlerites. The arseni¬ 
cals that have been considered as possible war gases, 
however, have high molecular weights and low vola¬ 
tilities and are consequently strongly adsorbed. 
Furthermore, they are generally readily hydrolyzed, 
yielding nonvolatile products. Thus, such gases do 


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CLASSIFICATION OF AGENTS 


167 


not constitute a hazard to the respiratory tracts of 
masked men regardless of the nature of the gas mask 
adsorbent, and hence they have not been studied 
and are not considered in this discussion. 

Carbon monoxide should also be considered a 
member of this class. A slow oxidation of CO to CO 2 
is known to occur on whetlerites. 16 Nevertheless, 
because of the weakness of adsorption of CO on 
charcoal and of the slowness of the oxidation, the 
protection afforded by the gas mask is entirely in¬ 
adequate. It has been necessary to design special 
canisters and adsorbents to care for this gas; the 
research along these lines is discussed in Chapter 12. 

Arsine (AsH 3 ; SA) 

When whetlerites are exposed to SA-air mixtures, 
large rises in temperature are observed. 40 If the whet- 
lerite is exposed to SA in the absence of oxygen, no 
great thermal effect is observed until air is ad¬ 
mitted. 41 

The arsine tube life of Type A whetlerite, 39 both 
dry and moist, decreases with decrease in tem¬ 
perature until a minimum is reached at about 

— IOC after which the life increases markedly. Base 
charcoal exhibits a continued increase in life with 
decrease in temperature until the life becomes 
identical with that of the whetlerite at and below 

— 30 C. An important difference between the two, 
however, is that even at — 45 C the passage of pure 
air through the bed soon after the break point and at 
the same temperature failed to remove any appreci¬ 
able amount of arsine from the whetlerite while 
considerable quantities could be desorbed from the 
base charcoal. 

These observations clearly indicate the occurrence 
of a rapid oxidation reaction on the whetlerite. At 
temperatures below — 30 C the physical adsorption, 
which must precede the chemical reaction, becomes 
the characterizing step because the removal of ad¬ 
sorbed SA by reaction is too slow to appreciably alter 
rate or effective capacity of adsorption; the whet¬ 
lerite therefore behaves like the parent base charcoal. 

Calorimetric studies of the removal of arsine indi¬ 
cate that the energy production is not the result of a 
single unique reaction. 42 One of the simplest ways to 
interpret the observed facts is to postulate that two 
or more reactions are occurring and that the relative 
amounts depend on the experimental conditions. 
Such postulation had been offered previously in ex¬ 
planation of the fact that C 0 t to the break point 
increases with increasing Co. There are a number of 


possible reactions which might occur in this system. 
The three most probable ones are: 

2AsH 3 + 40 2 = As 2 0 5 + 3H 2 0; (36) 

2AsH 3 + 30 2 = As 2 0 3 + 3H 2 0; (37) 

4AsH 3 + 30 2 = 4As + 6H 2 0. (38) 

H 2 0, As 2 0 3 41> 42 and As 2 0 5 42 have been identified 
as the major products of reaction of arsine on char¬ 
coals and whetlerites. Though As has not been 
specifically identified it is possible that reaction (38) 
plays a minor role in the removal. 



Figure 6. Effect of humidity on SA lines of silver-im¬ 
pregnated charcoal and whetlerites of Type A and AS. 


For Type A whetlerites prepared from most types 
of base charcoals, the SA tube lives 39 increase at first 
with increasing humidity of gas mixture and char¬ 
coal, pass through a maximum between 30 and 50% 
RH and then decrease rapidly. These observations 
are consistent with the postulates that physical ad¬ 
sorption is the first step and that water catalyzes the 
oxidation; at high humidities the adsorbed water 
causes a reduction in the rate of adsorption to the 
point that this becomes the limiting process. Type A 
whetlerites made from some charcoals show a con¬ 
sistent decrease in life with increase in humidity at all 
humidities; in such cases the rate of adsorption is 


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168 


MECHANISM OF CHEMICAL REMOVAL OF GASES 


probably the limiting factor throughout the whole 
range of humidities because of the structure of the 
charcoal. 

Silver-impregnated charcoals are quite ineffective 
against SA at low humidities, but display high maxi¬ 
mum lives in the vicinity of 80% RH. Metallic 
silver, in conjunction with water, is an excellent 
catalyst for one or more of the oxidation reactions. 

Type AS whetlerites exhibit the additive proper¬ 
ties of the two separate impregnants (see Figure 6). 
Type ASC whetlerite behaves like Type AS. 

Because the whetlerite in the influent end of a bed 
does not become saturated 38 during a tube test the 
life vs thickness plots are definitely curved. Indeed 
it is difficult to define a saturation value for SA. 
After a period of relatively rapid removal of SA, 
whetlerite continues to absorb the gas very slowly 
over long periods of time. This phenomenon seems to 
be due to two factors; 41 (1) some of the product 
oxides are apparently chemisorbed on the catalyst, 
thus reducing its effectiveness, and (2) the initial 
rapid reaction takes place near the entrance of each 
pore and the products partially block the channels, 
making diffusion into the active inner surfaces and 
catalyst very slow. At any rate, the amounts of SA 
absorbed per milliliter of whetlerite are so excessive 
over the amount required for reaction with the CuO 
present in Type A whetlerite that it is obvious that 
the impregnant acts primarily as a catalyst and does 
not participate solely in a metathetical reaction. 


This conclusion is in accord with the observation that 
oxygen is necessary for the reaction to proceed. 

General Conclusions for Readily Oxidizable 
Gases 

Because of the insurmountable difficulties involved 
in the storage and dispersion of arsine, due mainly 
to its instability, it is not considered as a likely war 
gas. Therefore, observations made in the preceding 
section merely serve to indicate the possibility of 
attaining adequate protection against readily oxi¬ 
dizable gases by suitable impregnation of charcoal, 
provided that the gas is so strongly adsorbed physi¬ 
cally by the charcoal that this necessary initial step 
does not become the limiting process in the removal. 

It seems unlikely that any other nonpersistent gas, 
which could be removed by such oxidation processes, 
would be sufficiently stable to undergo dispersion 
from explosive munitions without chemical change. 
Such circumstance would present a serious limita¬ 
tion to its use. 

7.2.5 Readily Reducible Gases 

The only reducible gases which have been studied 
to date are N0 2 and Cl 2 . N0 2 was considered in de¬ 
tail in a previous discussion because it behaves as an 
acid-forming gas. Chlorine was not used or considered 
as a war gas in World War II and therefore its be¬ 
havior was not studied in any of the laboratories 
dealing with absorbents. 


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Chapter 8 

THE ADSORPTION WAVE 


By Irving 

8.1 INTRODUCTION 

he general object in the study of the ad¬ 
sorption wave has been to obtain an under¬ 
standing of the various factors which determine the 
variation in concentration of a toxic gas efflilent 
from a bed of charcoal. The study of the adsorption 




Figure 1. A. Distribution curve for the concentration 
of air above various points in the bed of adsorbent. 
B. Flow of gas through an adsorbent. 


wave includes the consideration, from an experi¬ 
mental and theoretical point of view, of the distribu¬ 
tion of toxic gas throughout a bed both on the ad¬ 
sorbent and in the air above the adsorbent. 

A typical distribution curve showing the concen¬ 
tration of gas in the air above various points in the 


M. Klotz 

bed of adsorbent is shown in Figure 1A. The curve 
for the concentrations which would be in equilibrium 
with the adsorbed gas at various points in the bed 
would be similar in shape but displaced slightly to 
the left. The term adsorption wave is generally ap¬ 
plied to the movement of these distribution curves 
(to the right in Figure 1A) during the continuous 
passage of gas-laden air through the bed of ad¬ 
sorbents. 

A complete mathematical description of the wave 
would effect a number of important consequences. It 
would be possible to predict the performance of a 
particular canister from a minimum of experimental 
data and without exhaustive tests on the canister 
itself. It would also be possible to devise the best 
test procedures from which to obtain the information 
necessary for the prediction and evaluation of can¬ 
ister behavior. A complete understanding of the 
adsorption wave would lead also to the design of 
the most efficient type of canister. Equally important 
would be the elucidation of the mechanism of the 
adsorption process for various gases on different 
types of charcoal. Such an understanding would sug¬ 
gest additional treatments for the improvement of 
the adsorbent and would also indicate when the 
natural limit to such improvement had been at¬ 
tained. 

The problem of the adsorption wave has not been 
solved in its most general form, primarily because of 
the prodigious mathematical difficulties entailed. In 
connection with a similar problem of correlating the 
performance of small-scale and large-scale reactors 
in chemical engineering processes, the opinion has 
been expressed 6 that the correlation is impossible to 
attain in a truly rigorous manner. Nevertheless, a 
number of simplified special cases of the adsorption 
wave have been considered and, with these results as 
guides, it has been possible to develop several semi- 
empirical approaches to the problems of performance 
and mechanism of reaction. 



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169 










170 


THE ADSORPTION WAVE 


It is recognized generally that the removal of a 
toxic gas from air by a porous adsorbent may involve 
one or more of the following steps: 

1. Diffusion (mass transfer) of the gas from the 
air to the gross surface of the granule. 

2. Diffusion of the molecules of gas into (or along 
the surface of) the large pores of the adsorbing 
particle. 

3. Adsorption of the molecules on the interior 
surface of the granule. 

4. Chemical reaction between the adsorbed gas 
and the charcoal or adsorbed oxygen, water, or 
imp regnant. 

The relative importance of each of these four steps 
may vary widely with the particular conditions 
under which the removal is taking place. The rate of 
mass transfer is influenced strongly by the flow rate 
of the gas stream, by the diffusion coefficient of the 
gas, and by the particle size of the adsorbent, but is 
relatively unaffected by temperature. The impor¬ 
tance of diffusion in the pores is determined by such 
factors as the particle size, the structural character¬ 
istics of the pores, certain diffusional properties of the 
system, and the rate of reaction at the internal sur¬ 
face. The speed of adsorption at the interface depends 
on the nature and extent of the surface as well as on 
the activation energy for the adsorption of the par¬ 
ticular gas under consideration. Chemical reaction is 
also determined by the properties of the surface, but 
much more specific effects will be obtained than in 
adsorption. Since large activation energies may be 
expected in steps (3) and (4), these processes will be 
highly sensitive to temperature. 

Usually, all four steps in the removal process may 
proceed with rates of approximately the same mag¬ 
nitude, and hence a problem of extreme mathe¬ 
matical difficulty is presented. On the other hand, in 
many situations one particular step may be much 
slower than the others, and hence it may be con¬ 
sidered the rate-controlling process. For a single rate¬ 
controlling process, a number of mathematical ap¬ 
proaches have been developed. A few attempts have 
also been made to treat situations with more than 
one rate-controlling step, and for certain special cir¬ 
cumstances, partial success has been attained. 

8.2 THEORIES PREDICTING EFFLUENT 
CONCENTRATION AS A FUNCTION 
OF TIME 

The ultimate aim of the mathematical analysis is 
an expression for the dependence of the effluent con¬ 


centration on time. Even without such an expression, 
however, some qualitative description of the shape of 
an effluent-time curve can be given. Figure 2 illus¬ 
trates a number of interesting cases. If the reaction 
on the charcoal were instantaneous and if the ad¬ 
sorbent were infinitely fine-grained, none of the 
adsorbable gas would penetrate until some time t, 
when the charcoal would be saturated, and then the 
gas would penetrate at full influent concentration. 


o 



Figure 2. Transmission of a gas by an adsorbent. 

Such an adsorbent would exhibit a transmission curve 
such as A in Figure 2. On the other hand, if the re¬ 
action is not instantaneous, a curve such as B would 
be exhibited. This curve would be symmetrical only 
for certain simple rates of adsorption. In addition to 
these two examples, cases may be encountered (for 
example, in the removal of carbon monoxide) where 
the charcoal, or its imp regnant, acts as catalyst for 
a reaction involving the toxic gas. As a result, 
the effluent-concentration curve C may rise very 
slowly; and if the catalyst remains at least partially 
unpoisoned, the transmission of gas may never reach 
the full influent value. It is also conceivable, although 
no such case has been yet encountered, that the rate 
of catalysis may be very high compared to the rate of 
supply of gas. In such circumstances the transmis¬ 
sion curve would be the time axis, that is, none of the 
gas would penetrate. 

8.2.1 Theories in Which One Step is Rate- 
Controlling 

The General Differential Equation 

Consider a stream of gas and air flowing through 
a bed of adsorbent as indicated in Figure IB. 
Each layer of the adsorbent removes a portion of the 
gas from the air, and hence the concentration of gas 
drops from an influent value of c 0 to an effluent 
value of c e . A cross section of infinitesimal thickness 
dz will reduce the concentration from c to c + dc 


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EFFLUENT CONCENTRATION AS A FUNCTION OF TIME 


171 


{dc is negative). From the principle of conservation 
of mass it follows that: 

Quantity of gas entering = quantity of gas picked up 
by charcoal + quantity of gas leaving. (1) 

The quantity of gas entering the infinitesimal sec¬ 
tion of bed will be equal to the concentration c times 
the volume rate of flow L times the interval of flow 
dt: 

Quantity of gas entering = cLdt. (2) 

The amount of gas picked up by the charcoal will 
be given by the rate of pickup per unit volume dn/ dt 
times the volume of the infinitesimal section of the 
bed (area A X depth), multiplied by the interval of 
exposure: 

Quantity picked up by the charcoal = — (Adz)dt. 

dt 

(3) 

The quantity of gas leaving the section dz will be 
given by: 

Quantity leaving = (c + dc)Ldt. (4) 

Setting up the equality demanded by the conserva¬ 
tion principle, one obtains: 

dfi 

cLdt = — ( Ad,z)dt + (c + dc)Ldt, (5) 


which can be rearranged to give: 

A dn 

— dc = —r — dz. (6) 

L dt V 

Since c is a function of the variables z and t, the 
total differential is: 


dc 


= (s),* + (S) 


— ) dt. 


and since 
and 


dz/ dt — V 
L = VAa 


(7) 

(8) 
(9) 


where V is the linear velocity through the interstices 
between the particles of the adsorbent, and a is the 
porosity (that is, the fraction of voids per unit gross 
volume of bed) one obtains: 


(dc , dc \ 1 
1 — dz + — dt) = — 
\dz dt / al 


* dn 
— —dz 
V dt 


( 10 ) 


which can be rearranged to give 


1 dn _ dc dc 

a dt dt+ dz 

It is implicitly assumed in the derivation 


(ID 

of this 


equation that the concentration of gas is small and 
that diffusion in the direction of flow is negligible. 

The solution to equation (11) depends on the 
mathematical relation one assumes for dn/dt , the 
local rate of removal of the toxic gas by the granules. 
The particular mathematical form to be chosen de¬ 
pends on the mechanism of the removal process. No 
matter which mechanism is visualized, the local rate 
of removal would be dependent in general on the 
following variables: 

1. The nature of the adsorbent. 

2. The nature of the gas to be removed. 

3. The geometrical state of the adsorbent. 

4. The temperature. 

5. The local concentration of the toxic gas, as 
well as of other gases in the air. 

6. The relative amount of the toxic and other 
gases already adsorbed by the granules. 

7. The velocity of the gas-air stream. 

In all cases which have been considered, it has been 
assumed that the first four variables are maintained 
constant, but that dn/dt may depend on one or 
more of the remaining three. 

Diffusion as the Rate-Controlling Step 

Case A. In some cases, one may encounter a gas 
which has no back pressure on charcoal, but which 
ceases to be removed by the granules when the 
moles of gas on the granules n approaches N 0 , the 
saturation capacity of a unit gross volume of ad¬ 
sorbent for the toxic gas. Under these conditions the 
local rate of removal would be given by the relation: 

±5-^, (12) 

a dt ap 

where F is the mass transfer coefficient, a the super¬ 
ficial surface per unit volume of granules, and p the 
density of the air-gas mixture. 

The solution of the differential equation may be 
resolved into two cases. For all times up to to when 
n = N 0 at the entrance face, the concentration at a 
given point in the bed is given by the equation: 

c \ Fa z~\ 

- = exp-- • (13) 

Co L ap VJ 

For times greater than to, the following relation holds: 

Case B. If a gas is adsorbed reversibly on charcoal, 
the equation obtained for c/c 0 depends on the char¬ 
acter of the adsorption isotherm. One of the simplest 


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172 


THE ADSORPTION WAVE 



Figure 3. Relation of gas unremoved to time and position. 


cases that has been considered is that of the linear 
isotherm, for which 

c* = bn (15) 


where c* is the concentration of the gas in air stream 
at a given point in the bed in equilibrium with the 
charcoal at that point, and b is a constant. With a 
linear isotherm governing the back pressure of the 
gas, the equation for the local rate of removal be¬ 
comes : 


1 dn 
a dt 


~ Fa i *■» 

-(c - c*) . 

ap 


( 16 ) 


The solutions of the differential equations, for the 
boundary conditions encountered in charcoal, are 
well known because completely analogous equations 
have been encountered in the problem of heat ex¬ 
change in granular beds. Analytical expressions, in 
terms of Bessel functions, for the solutions are 
cumbersome to handle, and hence the results are 
given best in the form of reference curves of c/c 0 as 
a function of the important variables. The curves 
worked out by Furnas 14 are very incomplete in 
regions of low concentrations, the regions of great 
interest in work on gas transmission. Consequently a 
semi-logarithmic plot taken from a report by Hougen 
and Dodge 17 is given in Figure 3. For values of c/c 0 
below 0.01 see reference 10. 

Case C. Most gases do not exhibit a linear isotherm 
on charcoal. A better approximation is the Langmuir 


isotherm which may be expanded in a power series of 
the form 

c *=b + ih n2+ "- (17) 

where K is a constant. Using the first two terms in 
equation (17) as a parabolic approximation to the 
isotherm, one may substitute for c* in equation (16). 
The solutions of the resultant equations in terms of 
standard graphical procedures have been worked 
out. 10 

Adsorption or Reaction on the Surface as the 
Rate-Controlling Step 

Case A. The earliest analysis of the adsorption 
wave was made by Bohart and Adams 4 on the as¬ 
sumption that the toxic gas is adsorbed irreversibly 
and at a local rate of removal governed by the 
equation: 

1 dn 

~ — = kic(N 0 - n), (18) 

a dt 

where Aq is a constant. 

A similar treatment has been carried out more 
recently. 7 Both groups of investigators have derived 
the following expression for the variation of the con¬ 
centration of gas in the air stream: 

^ 7=1 + [exp (- AqcoO] £ ex P ^r~ )“ 1 J' 


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EFFLUENT CONCENTRATION AS A FUNCTION OF TIME 


173 


This equation in its various forms has been used very 
widely to interpret and to interpolate data on the 
performance of various charcoals. Unfortunately, 
present indications are that there are few cases where 
the rate of removal of a gas by charcoal is governed 
primarily by adsorption or reaction at the surface. 
Diffusion, or mass transfer, seems to make some con¬ 
tribution to the slowness of removal of almost all 
gases by charcoal, and hence equation (19) is not 
strictly applicable. 

Case B. An attempt has been made by Lister 25 to 
consider the relations obtained when adsorption on 
the surface is the rate-controlling step but for the 
special case where the adsorption is reversible and 
the adsorbed gas exerts a back pressure. For such 
conditions, the equation for the local rate of ad¬ 
sorption becomes 

- — = kic(N 0 — n) — k 2 n, (20) 

a dt 

where ki and k 2 are constants. 

No complete solution of the resultant differential 
equations has been given. Approximations have been 
given for the conditions obtained with fresh char¬ 
coal, but the general validity of these has been 
questioned. 10 

8.2.2 Theories in Which More Than One 
Step Contributes to Rate of Removal 

Diffusion in Air and Deposition on Surface 
Contributing 

It has been possible to construct 10 a differential 
equation for the local rate of removal on the as¬ 
sumption that the diffusion of the toxic molecule 
from the air to the charcoal and the subsequent de¬ 
position process, whether chemical or adsorptive in 
nature, both contribute to the slowness of removal. 
The general equation for this process has not been 
solved. Nevertheless, certain special cases have been 
considered, but each of them reduces to one of the 
single-step processes discussed in the preceding text 
and hence does not warrant further elaboration. 

Diffusion in Air and Processes Within the 
Granule Contributing 

A very detailed consideration of the nature of the 
processes involved in the removal of gases by ad¬ 
sorbents has been made. 37 Emphasis has been given 
particularly to diffusion within the pores and to the 
various factors which influence the cross-sectional 
and longitudinal mixing in the intergranular spaces. 


Where the equilibrium adsorption of a gas follows a 
linear isotherm, the differential equations have been 
solved and have been shown to be applicable to the 
experimental data on the removal of C0 2 at 100 C. 
For gases with curved isotherms, however, the 
general solution to the differential equation has not 
been obtained though certain special cases have been 
considered. 

8.2.3 Comparison of Theories with 
Experiment 

None of the theoretical approaches gives a satis¬ 
factory correlation of the experimental data on the 
removal of a toxic gas by charcoal. Even with gases 
such as chloropicrin, where (as is shown later) mass 
transfer seems to be the rate-controlling step, the 
observed dependence of effluent concentration on 
time does not agree over any appreciable range with 
the curves given in Figure 3. The primary cause of 
the deviation, for other gases as well as for chloro¬ 
picrin, is the curvature of the adsorption isotherm, 
a condition which so far has not been incorporated 
into the wave equations, except in an approximate, 
empirical manner. 29 In addition to the curvature of 
the isotherm, a further difficulty that arises with 
most other toxic gases of interest is the combina¬ 
tion of mass transfer with one or more of the suc¬ 
ceeding steps in controlling the rate of removal of 
the gas by the adsorbent. Minor discrepancies may 
also arise from thermal factors. Temperature changes 
in the removal process, which in some cases are 
many degrees, may raise the back pressure of the 
adsorbed gas or may affect the rate of mass transfer 
in the carrier stream. 

Sufficiently fundamental differences exist in the 
differential equations for the local rate of removal 
in the mass-transfer and surface adsorption mecha¬ 
nism so that one can determine the presence or ab¬ 
sence of a slow, diffusion step. In equation (18), based 
on surface adsorption as the rate-controlling step, 
the velocity V does not appear, and hence, in the 
integrated equation for c/c 0 , V will enter only as 
z/V as can be verified by glancing at equation (19). 
Similarly, on expanding and rearranging (19) to ob¬ 
tain an equation for the instantaneous break time, 
4, an expression is obtained in which V enters only 
as z/V. In contrast, when mass-transfer (diffusion) is 
the controlling step, the velocity of flow enters the 
equation for the local rate of removal, inasmuch as 
F, the mass-transfer coefficient, depends on the rate 
of flow. In consequence, the instantaneous break 


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174 


THE ADSORPTION WAVE 


time depends on V as well as on z/V, and a plot of 
tb vs z/V gives different curves for different rates of 
flow. (It should be emphasized that the cumulative 
break time, that is, the time in which a total quantity 
of gas sufficient to produce a change in some indi¬ 
cator has escaped from the bed, depends on V and 
z/V whether or not V enters the expression for the 
local rate of removal. Therefore, the cumulative 
break time cannot be used to distinguish between 
mechanisms of removal.) Thus, a criterion has been 
established for detecting the presence of a slow 
diffusional step. In Figure 4, this criterion is applied 



Figure 4. Effect of rate of flow on rate of removal of 
chloropicrin. Time (of contact) = z/V X 10 3 min. 


to some data on chloropicrin. 38 It is obvious from the 
graph that % depends on V as well as on z/V, and in 
consequence, that diffusion contributes to the slow¬ 
ness of removal of chloropicrin by charcoal. Conse¬ 
quently, it is unlikely that the theories based on 
surface adsorption or surface reaction as the rate¬ 
controlling process will be applicable to any charcoal 
which has sufficient activity to make it useful in 
protection against toxic gases. 


Unfortunately, these relationships were not real¬ 
ized in much of the early work and many extrapola¬ 
tions were made on the basis of the Bohart-Adams- 
Hinshelwood equation, 4 - 7 which is based on a surface- 
deposition, rate-controlling mechanism. The par¬ 
ticularly misleading fact is the observation that in 
many circumstances a plot of log (co/c — 1) is 
linear with time, a necessary condition derivable 
from equation (19). Unfortunately, such linearity is 
not a reliable test of the applicability of equation 
(19), for all the other mechanisms will also lead to 
such linear equations over wide ranges if suitable 
values are chosen for the constants. When constants 
for equation (19) are determined from plots of log 
(cq/c — 1) vs time, one finds that both ki and N 0 
vary with the rate of flow of the air stream. Such be¬ 
havior is completely at variance with the postulates 
of the mechanism and illustrates the inapplicability 
of the equation to the removal of gases by the usual 
charcoal adsorbents. 

8.3 SEMI-EMPIRICAL TREATMENTS 

In the absence of a satisfactory comprehensive 
theory of the adsorption wave, investigators have 
been forced to develop semi-empirical methods of 
treating data. Primary emphasis has been given to 
equations which relate break time to the common 
variables such as bed depth, rate of flow, particle 
size, and concentration of influent gas. With the 
accumulation of results from different modes of ap¬ 
proach, it has also been possible to correlate certain 
relations with particular mechanisms of removal. 

8.3.1 Factors Affecting Break Time 

Nature of Flow in Charcoal 

The flow of fluids through beds of granular solids 
is very complicated in nature because the channels 
are very tortuous and nonuniform. It is impossible 
to fix the dimensions or number of channels, as two 
streams may frequently merge or a single stream may 
redistribute itself into several new paths of flow. 
Since sudden contractions or enlargements in the 
intergranular spaces may occur, it is quite possible 
to have both streamlined and turbulent flow occur¬ 
ring simultaneously in different portions of a granular 
bed. In consequence, there is a much slower transi¬ 
tion from conditions of laminar flow to those of turbu¬ 
lent flow in the passage of gas through an adsorbent 
bed than there is in the flow of fluid through pipes. 


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SEMI-EMPIRIC AL TRE ATMENTS 


175 


Usually the nature of the flow of fluids is studied 
by measuring the pressure drop in the bed or pipe. 
Correlations are then made with the dimensionless 
parameter known as the Reynolds number, D p Vp/p. 
When a graph of a function of the pressure drop 
known as the friction factor 15> 16 is plotted against 
the Reynolds number, two linear portions are 
observed which intersect at the critical Reynolds 
number, a value corresponding to conditions under 
which laminar flow is transformed into turbulent 
flow. 

In studies made of the flow of fluids through porous 
carbon, 16 a critical Reynolds number of about 4 has 
been found. Extensive work has also been carried 
out on the flow of gases through beds of charcoal. 24 
Two representative curves are shown in Figure 5. 



Figure 5. Relation of flow rate to pressure drop in 
charcoal beds. 


From these curves and other data, it has been con¬ 
cluded that the critical Reynolds number is about 
10 in the charcoals investigated. The Service labora¬ 
tories 33 and two English workers 20 have found a 
transition in the same region. But it cannot be cer¬ 
tain that the same critical value will be observed 
with all charcoals of any possible shape since it is 
quite conceivable that curious shape factors may 
occasionally be encountered in view of the rather 
arbitrary use of particle diameter D p in place of 
pore size in the Reynolds number. In all the work 


described here, however, it has been assumed that 
the critical region is in the neighborhood of a Reyn¬ 
olds number of 10. 

The Effect of Bed Depth 

The dependence of canister or tube life on the 
depth of charcoal has been investigated more widely 
than has the dependence on any other variable. The 
reason for such emphasis is perhaps obvious, for the 
amount of adsorbent necessary determines very 
largely the bulk of the canister. Life-thickness curves 
have become, therefore, the most common method 
of representing the performance of a charcoal. In 
consequence, the interpretation of performance in 
terms of the mechanisms of removal has revolved 
around the elucidation of life-thickness curves. 

General Character of Life-Thickness Curves. A sur¬ 
vey of performance data shows that two types of 
life-thickness curves are encountered. The simplest 
case is a linear relation such as is shown in curve A 
of Figure 6. Most organic gases when tested in a dry 



DEPTH OF BED 

Figure 6. Life-thickness curves. 


condition against dry charcoal exhibit linear life¬ 
thickness curves. In principle, a break-time test using 
a cumulative indicator should not show a linear re¬ 
lation with bed depth, at least not at small depths, 
but this lack of linearity is frequently overlooked 
because few tests are carried out at very small 
depths. Curve B exhibits a very common observation 
of curvature at low lives with a tendency to linearity 
at high break times. Such behavior should always be 
encountered in cumulative tests of the break time. 
It is also usually observed when tests are carried out 
with humidified gases and charcoal, and in some 
cases occurs in tests under dry conditions. 


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176 


THE ADSORPTION WAVE 


Whether or not curvature occurs, the life-thickness 
curve intersects the bed-depth axis at a finite value. 
It follows then that there exists a critical bed depth 
below which the life is zero. This critical length 
varies with the conditions of flow, concentration, 
mesh size, sensitivity of the detector, and the 
nature of the charcoal. It is this manifold dependence 
which has engaged much attention. Numerous at¬ 
tempts have been made to correlate these variables 
in some convenient analytic expression, for in small 
beds as in canisters, it is the critical bed depth which 
primarily determines the degree of protection. 

The Mecklenburg Equation. A very convenient ex¬ 
pression for the linear life-thickness curve has been 
derived by Mecklenburg 28 from elementary con¬ 
siderations of conservation of mass. At the break 
time a negligible portion of the toxic gas has pene¬ 
trated the bed, and hence one can assume that: 

Weight of gas supplied = Weight of gas 

picked up by adsorbent. (21) 

The weight of gas supplied by the air stream is equal 
to the time of flow (the break time in minutes) times 
the rate of flow L (in liters per minute) times the 
concentration (in grams per liter). In turn, the 
pickup by the charcoal may be arbitrarily considered 
as occurring in a certain portion of the bed instan¬ 
taneously and up to the saturation value, while the 
remainder of the bed, defined by Mecklenburg as the 
dead layer, remains completely free of gas. As was 
emphasized by Mecklenburg, the dead layer is a 
purely fictional concept devised merely to facilitate 
the derivation of the following equation and to obvi¬ 
ate the necessity of considering in detail the distribu¬ 
tion of gas in the bed of adsorbent. With this arbi¬ 
trary division it follows that the amount picked up by 
the charcoal is equal to the saturation value per 
unit volume times the area, times the difference be¬ 
tween the bed depth and the depth of the dead 
layer h. In algebraic terms the equality in (21) may 
be expressed as follows: 

tbLco = N 0 A(z - h). (22) 

This equation may be rearranged readily to give an 
expression for the break time, 

t b = ^(z-h)- (23) 

Leo 

As has been pointed out previously (Chapter 2), 
the slope of the life-thickness curve for a fixed rate 
of flow, input concentration, and bed cross-section is 
a measure of the capacity (No) of the charcoal. For a 


system which obeys this equation throughout the 
complete life-thickness curve, the dead layer h and 
critical bed depth I must be equal, so that 

k = ~ (2 - I). (24) 

LCq 

The great deficiency of equation (24) is that it 
cannot be used to extrapolate information from one 
set of flow or concentration conditions without 
further information on the dependence of the critical 
bed depth on these variables. The wave theories dis¬ 
cussed in preceding paragraphs set certain require¬ 
ments for the variation of critical bed depth, and 
where these theories are applicable they may be used 
to extend equation (24). Further details are con¬ 
sidered in a subsequent section. 

Curvature Due to Cumulative Method of Test. If the 
break time is defined in terms of the period necessary 
for a total cumulative amount of gas to penetrate 
the bed, it can be shown that the life-thickness curve, 
even in the simplest mechanism of removal, would 
obey an expression of the form 


= y^k 3 V k 4 In I"- 
Leo L 


5 exp ( z/k z V k «) 
NoAk s V k * 


+ 1 • (25) 


In general, equation (25) would not be linear; how¬ 
ever, for large bed depths, the first term inside the 
brackets becomes large in comparison to the second 
term and the equation as a whole approaches the 
linear relation: 


t c = 


NpAz 

Lcq 


+ k$. 


(26) 


These predictions are in agreement with the behavior 
observed in cumulative tests. 

Curvature in Systems Using Instantaneous Tests. 
In the testing of Type ASC charcoals with cyanogen 
chloride, it has always been observed that the life¬ 
thickness curves for humidified gas streams and 
humidified charcoal show pronounced curvature at 
small bed depths but approach linearity with deep 
beds. Curve B of Figure 6 is a typical example. The 
increasing slope of this curve with increase in bed 
depth implies an increasing capacity, per unit vol¬ 
ume, of adsorbent for the toxic gas. This expec¬ 
tation has been verified by an examination of the 
distribution of gas adsorbed on the bed at various 
time intervals. For a substance such as chloropicrin, 
which exhibits a linear life-thickness curve on dry 
charcoal, the amount of gas taken up by a unit 
volume of charcoal reaches a maximum which is not 
surpassed by increasing the time of exposure of the 


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SEMI-EMPIRICAL TREATMENTS 


177 


bed to the toxio gas. As a result, the distribution 
curves behave as shown in Figure 7A. In contrast, a 
humidified ASC charcoal shows a continuously in¬ 
creasing capacity, per unit volume, for cyanogen 
chloride and in consequence exhibits a set of distribu¬ 
tion curves such as is shown in Figure 7B (Wiig). 
The capacity of the influent end of the bed ap¬ 
proaches, but never quite reaches, a true saturation 
value, probably because a second slow reaction 
follows an initial rapid one. Consequently, the dis¬ 
tribution curve is displaced upward as well as to 
the right toward the inside of the bed. 


< 

o 

o 

tr 

< 

1 

o 

2 
< 
tr 
o 

tr 

UJ 

CL 

</) 


</) 

2 

< 

ce 

o 


< 

o 

o 

CL 

< 

X 

o 

2 

< 

tr 

o 

tr 

ui 

o. 

tfi 

< 

<s> 

o 

2 


(A) CHLOROPICRIN 



BED DEPTH (CM) 


(B) CYANOGEN CHLORIDE 



Figure 7. Distribution of gas on absorbent. 


In a number of cases, tests carried out with dry 
gases on dry base charcoal have also shown curva¬ 
ture in their life-thickness curves. A typical example 
would be methyl alcohol or ethyl chloride. The 
curvature in all such cases, however, is less than that 
observed with cyanogen chloride. Although no dis¬ 
tribution curves were obtained for these dry ex¬ 
amples, it seems likely that in these cases also some 
slow secondary reaction occurs in addition to the 
initial rapid one. For methyl alcohol it is possible 
that an oxidation process is being catalyzed by the 
charcoal. With other inert gases, and perhaps also r 
with methyl alcohol, it seems likely that the slow 
reaction is a diffusion process within the pores of the 
granule. 


The Effects of Velocity of FLOw r , Concentra¬ 
tion, and Particle Size 

It can be shown 23 from considerations similar to 
those discussed by Hurt 19 for the design of catalytic 
reactors, that if more than one step contributes to the 
rate of removal of a gas from the carrier stream, the 
critical bed depth I will be the sum of two terms 1 1 
and I r . It represents the portion of the critical bed 
depth due to the slowness of diffusion of gas from the 
air stream to the surface of the charcoal, whereas 
I r represents the fraction due to processes occurring 
within a charcoal granule. Since the critical bed 
depth can be thought of as the distance which the 
gas may penetrate the bed before its concentration 
is reduced to the break value, it seems reasonable to 
expect a certain minimum value of I for a fixed set 
of conditions, which would represent the smallest 
penetrable depth possible, even if every process in 
the granule were instantaneous and the rate were de¬ 
termined entirely by the speed with which the gas 
diffuses to the particle. This limiting value of I for a 
fixed set of conditions would be I t . Any critical bed 
depth above I t must be the contribution of the 
processes within the granule. That this contribution 
should be an additive term, rather than a multi¬ 
plicative factor, has been shown in principle by 
Hurt. 19 

The critical bed depth due to diffusion, I t , can be 
expressed 23 in terms of a number of familiar param¬ 
eters, independent of the nature of the charcoal, but 
dependent on the properties of the air-gas mixture 
and on the granular characteristics of the bed. Con¬ 
siderations of dimensional analysis lead to the con¬ 
clusion that at a fixed ratio of influent to effluent 
concentration, 1 1 should be a function of the particle 
size of the granules, and of two dimensionless param¬ 
eters DpG/n and n/pD v , the Reynolds number and 
Schmidt number, respectively. The specific function 
which has been adopted is essentially that of Gamson, 
Thodos, and Hougen: 


It = 


2.303 v- fVo. 

a \ p / \pD„/ Cb 


(27) 


In the derivation of this equation, it is assumed that 
co/cb is very large. Strictly speaking, this equation 
should be applicable only in cases of turbulent flow, 
but it has been found that in the region of laminar 
flow in charcoal, 1 1 is approximated satisfactorily by 
equation (27). For a fixed ratio of influent to effluent 
concentration, the equation expresses the variation 
of the critical bed depth with particle size D p , rate of 


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178 


THE ADSORPTION WAVE 


flow G, and diffusion coefficient of the gas D v . The 
factor a , the superficial surface of the granule (ig¬ 
noring pore structure), depends on the particle size 
and on the percentage of voids in the bed. Values of a 
have been calculated and are tabulated. 15 Where 
the absolute value of I t is not desired but only the 
form of the equation is necessary, one can substitute 
the following approximate equation: 

a = Constant X D s p . (28) 

The power $ takes into account the variation of per¬ 
centage voids with particle size and generally has a 
value slightly less than 1. 

For convenience in comparing data on critical bed 
depths with analogous performance data in chemical 
engineering processes, the following transformation is 
useful: 

Ht = _ h _i/mYVjlY ' 67 . (29) 

2.303 log Co/c b a \ n / \pD v / 

H t is called the height of a transfer unit. 

In contrast to I t , I r would be a complex function 
of the structure and nature of the charcoal and would 
be specific for the particular gas being removed. 
While it would be independent of the Reynolds 
number, it should [judging from consequences of 
equation (19)] vary directly with the rate of flow of 
of the gas-air stream, and it may be quite sensitive 
to temperature. Since many of these variables cannot 
be estimated in any general way, it is only possible 
to suggest the following relation for I r (on the as¬ 
sumption that cjcb is large and that the reaction 
is first order): 

I r = hV\ n-°. (30) 

Cb 


The total critical bed depth, therefore, should be 
given by the expression 


/ = /, + /,= 


i/D P v p y-«( m y- 67 ln 

a V u / \pD v / 


T k s V In 


(31) 


To determine the relative contributions of I t and 
7 r , one may proceed in at least two ways. One ap¬ 
proach would be to calculate I t from equation (27) 
and obtain I r by difference from the total critical bed 
depth. To facilitate these calculations a series of 
graphs has been prepared in which 1 1 is plotted as a 
function of the common variables. 22 A second ap¬ 
proach is to obtain data on I as a function of the 
linear velocity V, and then to plot the data against 


F -0 59 . It is obvious from equation (31) that for all 
conditions, except flow rate, fixed, I/V may be 
expressed as 

L = k,V -+ ho, (32) 

where k 9 and k w are constants. The intercept of the 
line obtained is a relative measure of I r and the 
value of the first term in equation (32) at any 
particular linear velocity is a relative measure of 1 1 . 

The variation of the critical bed depth with particle 
size depends on the relative importance of the two 
terms in equation (31), that is, on the mechanism of 
the removal process. If the slow step in the granule 
is some surface reaction, I r will be independent of 
particle size, whereas I t will vary as some power of 
D p , usually near 1.4. If diffusion in air and surface 
reaction contribute about equally, a plot of I against 
D p will approach a finite limiting value as D p ap¬ 
proaches zero. This is illustrated by curve A in 
Figure 8. If mass transfer alone is rate-controlling, 
one obtains a similar curve (B in Figure 8) but with 
an intercept at the origin. In contrast, if the surface 
reaction were rate-controlling, I would be inde¬ 
pendent of granule size, as is illustrated in curve C 
of Figure 8. 



Figure 8. Effect of mesh size on critical bed depth, for 
various mechanisms of gas removal. 


Where both terms contribute appreciably to the 
critical bed depth, one obtains an interesting graph 
in a plot of break time versus particle size. For large 
sizes, the life is less than that for small particles, but 
as the granule size decreases the life rises and ap¬ 
proaches a limiting value, corresponding to condi- 


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SEMI-EMPIRICAL TREATMENTS 


179 



Figure 9. Dependence of break time on particle size 
(for phosgene). 



Figure 10. Dependence of critical bed depth on ratio 
of influent to effluent concentration. 


tions where the surface reaction becomes the im¬ 
portant factor and mass transfer has been effectively 
eliminated. A typical curve is shown in Figure 9. 

The variation of the critical bed depth with ve¬ 
locity of flow also depends on the relative importance 
of the two terms in equation (31). If the slow step is 
a reaction in the granule, I will vary directly with 
the velocity. In contrast, if mass transfer is rate¬ 
controlling I will vary with the 0.4 power of the 
velocity. Where the two processes contribute, I can 
usually be expressed in terms of some power of the 
velocity between 0.4 and 1.0, although it must be 
realized that such a function would be merely an ap¬ 
proximation to the fundamental one of equation (31). 

The available evidence indicates that the critical 
bed depth is a logarithmic function of c 0 /cb. 
According to equation (31), the logarithmic relation 
should hold for any mechanism of removal. Sufficient 



v IN CM/MIN 

Figure 11. Critical bed depths for chloropicrin. 



Figure 12. Water removal by charcoal. Deviation of 
observed from computed values of H. 


data on effluent concentration as a function of time 
are available only for a few gases, so that the pre¬ 
dicted relation has not been tested adequately. That 
it does hold for chloropicrin is shown in Figure 10. 

Mechanism of Removal of Some Gases. The criteria 
described for estimating the relative contributions of 
diffusion in air and physical or chemical reactions in 
the charcoal to the critical bed depth have been 
applied to a number of gases with the aim of eluci¬ 
dating the mechanism of their removal. 23 

Chloropicrin is an example of a gas whose rate of 
removal is governed primarily by the rate of diffusion 
to the particle surface. In Figure 11 the observed 
values of the critical bed depth are plotted as a 
function of the linear velocity, and for comparison 
the curve calculated for I t is also shown. The ob¬ 
served values do not deviate significantly from the 
calculated curve. Such behavior indicates no appre¬ 
ciable contribution of any factors other than mass 
transfer (diffusion in air) to the removal of chloro¬ 
picrin, at least not in the initial stages of the process. 


SECRET 







180 


THE ADSORPTION WAVE 


In direct contrast to chloropicrin is water, whose 
rate of removal seems to be governed primarily by 
some slow surface process. Experimental data on the 
rate of removal of H 2 0 5 have been expressed in 
terms of a quantity H which may be defined by the 
equation 


Values of H on a sample charcoal are shown in Fig¬ 
ure 12. In comparison to the values to be expected if 
diffusion in air were the controlling process, the ob¬ 
served values are very high and indicate the large 
contribution that is made by factors which appear 
within or on the granule. 

Other gases, such as cyanogen chloride, are inter¬ 
mediate in behavior between water and chloropicrin, 
in that diffusion in air and surface factors contribute 
almost equally to the rate of removal of the gas. 

Dependence of Critical Bed Depth on Nature of 
Adsorbent. It must be realized that the relative con¬ 
tributions of various steps to the rate of removal will 
be very sensitive to the nature of the adsorbent. 
This dependence is well illustrated in the case of 
water where different base charcoals, having differ¬ 
ent pore structures and surface complexes, can react 
with water with different speeds and hence strikingly 
influence the critical bed depth or the value of H. 
Similarly, charcoals treated with impregnants usu- 
ually react more rapidly with water, apparently be¬ 
cause of their ability to form hydrates, and hence the 
magnitude of H is reduced considerably. In adsorb¬ 
ents such as silica gel, where the combination with 
water vapor at low pressures is probably due to 
hydrogen-bonding rather than primarily to van der 
Waals’ forces, the removal reaction is extremely 
rapid and H approaches the limiting value due to 
diffusion in air alone. These factors are illustrated 
by the values of H listed in Table 1. 


Table 1. Dependence of H on adsorbent. 5 


Adsorbent 

H (in cm) 

Charcoal, base, CWSN-19 

38-64 

Charcoal, base, CWSC-11 

20-30 

Charcoal, impregnated, CWSE1-TE1 

7-15 

Silica gel 

0.5-2.5 


The measurement of critical bed depths for char¬ 
coals which have been subjected to various treat¬ 
ments is a useful method of analyzing the results 
obtained. For gases such as chloropicrin, at least 


some of the available charcoals can react so rapidly 
that the limiting factor in the removal of gas (the 
rate of diffusion to the granule) has been reached, 
and it is futile to attempt to improve the adsorbent 
any further toward these particular toxic materials. 
On the other hand, toward most possible toxic agents 
there is still sufficient room for additional treatments 
or impregnations which may speed up processes 
which occur within the granule. 

The Effect of the Capacity of the Charcoal 

A clear statement of what is meant by capacity of 
a charcoal is not as readily available in a flow type of 
experiment as it is in the static case. In the latter 
situation, capacity refers to the amount of gas 
picked up by a unit weight of charcoal after sufficient 
time has elapsed for equilibrium to have been 
attained. The inapplicability of such a definition is 
particularly evident for a gas such as cyanogen 
chloride where, as is illustrated in Figure 7B, the 
influent end of a bed still has not reached a static 
state even after 200 min. 

The primary value of a measure of capacity is in the 
prediction of the dependence of life on bed depth. 
Consequently, it is customary to define A 0 in terms 
of the slope of a life-thickness curve [see equation 
(23)]. In this manner, two samples which show 
linear life-thickness curves can be compared re¬ 
liably in their performance under a set of conditions 
requiring a slight extrapolation from the measured 
ones. It is realized of course that such a capacity may 
be far different from the final equilibrium value, 
even for gases removed by adsorption alone. Never¬ 
theless, it is more useful than a definition based on a 
static experiment. 

For small bed depths, the break time is determined 
primarily by the critical bed depth of the adsorbent, 
inasmuch as the critical bed depth is a large fraction 
of the total bed. On the other hand, as the bed is 
made deeper, the critical bed depth becomes less im¬ 
portant, whereas the capacity becomes increasingly 
significant and in large depths is the determining 
factor. These relations became evident in a com¬ 
parison of the lines A and C in Figure 6. 

The capacity is also a useful function for esti¬ 
mating the maximum possible life one can obtain 
from a sample. By assuming a critical bed depth of 
zero, one can calculate the total amount of gas that 
could be picked up by the bed and, from the flow 
conditions, the maximum limit for the break time 
(see “Efficiency of Canister,” Chapter 2). 


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SEMI-EMPIRICAL TREATMENTS 


181 


8.3.2 Equations for Canister Life 

To predict the performance of canisters under any 
set of conditions other than those used in routine 
tests, it is necessary to have convenient analytic re¬ 
lations for life as a function of the common variables. 
This problem has not been solved satisfactorily 
except in a few special cases. Where the life-thickness 
relations show distinct curvature, no suitable ana¬ 
lytical method has been evolved for extrapolating 
data. Since many tests are carried out under humid 
conditions, in which curvature is generally observed, 
this large field of testing still remains to be con¬ 
sidered. However, in testing under dry conditions, 
where linear life-thickness curves are obtained, use¬ 
ful equations for the break time have been de¬ 
veloped. 


Cases in which Diffusion in Air is the Rate- 
Controlling Step 


Under these conditions it is a simple matter to 
combine the Mecklenburg relation for t b and equa¬ 
tion (27) for I t . The result is the expression: 


h = 


N q A 
Lc o 


imri-j-Y**]. 

L a\ ijl / \pD v / c b J 


(34) 


It allows the prediction of the complete break-time 
history for any gas whose removal is controlled by 
mass transfer after the determination of one constant 
No, the capacity of the charcoal for the particular 
toxic material. The diffusion coefficient D v of the gas 
can be estimated readily from relations available in 
the literature, or in most cases can be estimated 
sufficiently from the molecular weight curve illus¬ 
trated in Figure 13. Tables of a, the superficial area, 
for various particle sizes and percentage of void 
spaces are listed. 15 All other constants may be 
evaluated from the conditions of flow and from the 
dimensions of the adsorbent bed. 


Cases in which More Than One Step Con¬ 
tributes to Rate 

It has been shown that under these conditions the 
critical bed depth may be expressed as a sum of two 
terms, each of which contains the linear velocity Fto a 
different power. Equation (31) for / could be inserted 
into the Mecklenburg relation but the resultant ex¬ 
pression is not as convenient for manipulation as an 
alternative developed. 23 

It has been observed in most experiments that a 
plot of the critical bed depth versus the logarithm 
of the rate of flow can be approximated sufficiently 
well by a straight line. Because of the large errors 



MOLECULAR WEIGHT 

Figure 13. Relation between diffusion coefficient and 
molecular weight. 

inherent in the determination of the critical bed 
depth, the relation 

I = Constant X V d , (35) 

where d is a constant, can be used in place of the two- 
term expression of equation (31). The insertion of 
this simple relation into the Mecklenburg equation 
gives: 



in which g is a constant which depends on the mesh 
size of the charcoal and the particular gas being- 
removed, d is a constant determined by the test gas, 
A b is the open area of the baffle at the effluent end of 
the canister and L e is the steady flow rate equivalent 
to the pulsating rate of flow actually used. As has 
been described in a previous chapter, canister tests 
are made with a breather apparatus, designed to 
simulate respiratory conditions, in which the flow 
may vary from a high peak rate down to zero. The 
equivalent steady flow may be determined by meas¬ 
uring critical bed depths for a series of different 
constant flow rates and plotting I vs V. Then in a 
subsequent experiment with pulsating flow, the value 
of 7 is determined and from the reference graph a 
corresponding equivalent steady flow is read off. 
The reference curve may vary with the test gas as 
well as with large changes in the shape factor of the 
charcoal. 


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182 


THE ADSORPTION WAVE 


The use of equation (36) requires the evaluation of 
three constants, A r 0 , g, and d. The other parameters 
would be fixed by the conditions of flow and the 
geometric properties of the bed. 

The equation has been applied 33 to five test 
gases (arsine, chloropicrin, cyanogen chloride, hy¬ 
drogen cyanide, and phosgene) and to a number of 
different charcoals and found to be reliable within 
the precision of the experimental data. Thus, it 
affords a very convenient interpolation formula for 
the prediction of the performance of axial-flow 
canisters. 

The principles used in the derivation of equation 
(36) have been applied to the radial-flow canister 
also. The result depends on the geometrical configura¬ 
tion of the canister. 33 

8.4 CONCLUSIONS 

In examining the whole of the theoretical and ex¬ 
perimental results of the work on the adsorption 
wave, it is seen that progress has been attained in the 
following respects. The nature of the steps involved 
in the removal of a toxic gas from air by a granular 
adsorbent has been clearly stated. Where the rate¬ 
controlling process is a single one of these steps, it has 
been possible within recognized restrictions to de¬ 
velop a complete analytical expression for the adsorp¬ 
tion wave. Where two steps contribute to the rate of 
removal, a complete theory is still lacking, but it has 
been possible to develop criteria for the evaluation 
of the relative importance of diffusion in air and re¬ 
actions in the granule in the removal process. These 
criteria have been applied to a number of different 
gases and the mechanism of their removal has been 
elucidated. From the general nature of the various 
equations for the adsorption wave it has been possible 
to develop semi-empirical relations for the prediction 
of canister lives under dry conditions and to predict 
qualitatively the effects of mesh size, flow rate, and 
concentration under dry or wet conditions. 

The great gap in the present work is a suitable 
analytical treatment of results obtained under humid 
conditions or in other cases where non-linear life¬ 
thickness relations are obtained. Related to this is the 
absence of a complete treatment of the adsorption 
wave where many steps contribute to the rate of re¬ 
moval. These failures, however, are bound very 
closely to the general obscurity of the structural char¬ 
acteristics of granular adsorbents and of the nature 
of catalytic reactions. As fundamental relations in 


these latter fields are gradually evolved, one may 
anticipate further progress in the treatment of the 
adsorption wave and in canister design. 

SYMBOLS 

a superficial surface of the granule (ignoring pore structure) 
per unit volume of bed 
A cross section of adsorbent bed 

A b open area of the baffle at the effluent end of the canister 
b constant in equation for linear adsorption isotherm 
c concentration of toxic gas in air stream at any point in 
bed of adsorbent 

c* concentration of toxic gas in air stream at any point in 
the bed in equilibrium with the charcoal at that point 
Cb concentration of toxic gas in air stream chosen as the 
break value 

concentration of toxic gas in air stream at exit face of bed 
c 0 concentration of toxic gas in air stream at entrance face 
of bed 

d constant in equation for critical bed depth 
D P diameter of granule 

D v diffusion coefficient of the toxic gas (units of area per unit 
time) 

exp notation for the exponential e 
F mass transfer coefficient 
g constant in equation for canister life 
G mass velocity, that is, weight per unit time per unit cross 
section of bed 

h depth of the “dead layer” 

H height of a removal unit; 7/ln c 0 /c.b 
Hi height of a transfer unit; It fin Co/o> 

I critical bed depth, that is, the actual intercept of a life¬ 
thickness curve on the thickness axis 
Ir fraction of critical bed depth due to slowness of processes 

occurring within a charcoal granule 
It fraction of critical bed depth due to slowness of diffusion 
of gas from air stream to the surface of the charcoal 
ki constant in rate equation 

ki constant in rate equation 

ki constant in equation for t c 

ki constant in equation for t c 

kb constant in equation for t c 

k 6 constant in equation for t c 

k 7 constant in equation for critical bed depth 
ki constant in equation for critical bed depth 
K constant in the expanded form of the Langmuir isotherm 
L rate of flow in liters per minute 

L e rate of steady flow equivalent to rate of pulsating flow 
n moles of toxic gas on or in the granules contained in a 
unit volume of bed 

N 0 saturation capacity of a unit gross volume of adsorbent 
for the toxic gas 

s constant in equation for superficial area 
t time 

tb instantaneous break time, that is, the time at which the 
effluent concentration reaches a value specified as the 
break concentration 

t c cumulative break time, that is, the time necessary for a 
given total amount of gas to penetrate the adsorbent 
V linear velocity through the interstices between the par¬ 
ticles of the adsorbent; G/ap 
z distance from the entrance face of the bed 
a porosity, that is, the volume of intergranular voids per 
unit gross volume of bed 
u viscosity of gas-air stream 
p density of gas-air stream 


SECRET 



Chapter 9 

CANISTER DESIGN 

By W. Conway Pierce 


9.1 INTRODUCTION 

T he factors that govern the amount of gas pro¬ 
tection which can be obtained from a given 
volume of adsorbent (of given capacity, No) have 
been discussed in Chapter 8. In this section, the 
factors of practical importance which must be con¬ 
sidered in the development of a gas mask canister are 
discussed. These are: 

1. Amount of gas and smoke protection sought. 

2 . Weight and size permitted for the canister. 

3. Resistance of canister. 

4. Effect of mesh size on resistance and protection. 
The factors listed above are so interrelated that, 
in practice, it is usually necessary to effect a com¬ 
promise to obtain the desired protection; an under¬ 
standing of the way in which they are related one to 
another is necessary in the development. 

9.2 AMOUNT OF PROTECTION 

There is, to date, no general agreement as to the 
amount of gas and smoke protection which the gas 
mask canister should provide. Moreover, it is im¬ 
probable that a general agreement will ever be reached 
on this question even if gas is actually used, since it 
is not possible to increase protection without in¬ 
creasing weight, bulk, and pressure drop. Two some¬ 
what opposing views are held. One group thinks 
chiefty in terms of protection and strives for the 
maximum safety, while the other group would sacri¬ 
fice protection to achieve lightness and compactness 
and would take a considered risk of some casualties 
to obtain the lightest possible mask. 

Several years ago a standard was empirically set up 
at Edge wood Arsenal of 6-g protection for all gases. 
This was based upon the 32-lpm flow rate used for 
testing at that time and for a gas concentration of 
10 mg per 1. It corresponded to a minimum life of 
19 min. It was an easy matter to achieve this degree 
of protection for H, CG, and dry SA and AC but 
prior to the introduction of Type ASC whetlerite the 
80-80 protection for SA, AC and CK was much less 
than 6 g for all canisters. 

In 1943, a joint committee representing the British, 
Canadians, CWS and NDRC was set up to consider 
the question of how much protection is needed. This 


committee set up as the desired standard a protection 
against a gas dosage ( Ct ) of 100 mg min per 1 (100,000 
mg min per cu m). No reference was made to the 
breathing rate except for the statement that this 
protection should be afforded under all conditions 
likely to be encountered. While this approach is more 
realistic than the previous value of 6-g protection it is 
necessarily empirical. 

The ASC filled canisters of today will easily meet 
the desired protection, even when badly aged, except 
at high breathing rates which correspond to vigorous 
sustained exercise. When new, and tested at 25 1pm, 
an Mil canister will protect against a Ct of several 
hundred mg min per 1 (see data of Chapter 11). 

On the basis of field experiments with gas argu¬ 
ments may be found in favor of almost any desired 
degree of gas protection. In the open, a high Ct 
rarely can be obtained except under certain restricted 
conditions. On the other hand, in the jungle, one can 
obtain a Ct of several thousand with reasonable 
munition expenditures. It is characteristic of these 
high dosages, however, that the gas cloud hugs the 
ground and tends to flow down slopes or ravines like a 
liquid. Under most conditions of terrain, and with 
most gases, simple evasive action could materially 
reduce the dosage to which a man is exposed. 

Protection against a dosage of 50 to 100 is 
probably almost as good as one against a dosage ten¬ 
fold greater. That is, Army canisters that protect 
against a dosage of 50 to 100 mg min per 1 will proba¬ 
bly not have much greater percentage of gas casual¬ 
ties than canisters that protect against a Ct of 500. 
The arguments favoring this hypothesis are as fol¬ 
lows: 

1 . Exposures to very high dosages will probably 
be very rare since a high dosage can be obtained 
only under such specialized conditions: 

a. In woods or heavy vegetation, where wind 
velocities are very low. 

b. Under inversion conditions. 

c. On level ground or in ravines and depressions. 

d. In enclosed places such as caves. 

2 . Unless a gas attack can be accompanied by 
sustained heavy fire to force troops to remain under 
cover, it is usually possible to escape from a region 


SECRET 


183 


184 


CANISTER DESIGN 


of high concentration by moving to an elevated posi¬ 
tion. Since large gas concentrations over large areas 
can be laid down only by aerial bombs, it is not very 
feasible to provide covering-fire during the period of 
gas attacks. Friendly troops must be kept at a safe 
distance from the area under attack. Therefore, it is 
probable that in a heavy gas attack the majority of 
individuals can seek the comparative safety of higher 
ground. 

3. In view of the difficulties attendant upon setting 
up high dosages over large areas the use of nonper- 
sistent gas, except against enclosures is likely to be 
for the purpose of surprise rather than for canister 
penetration. If so, a small degree of protection will 
be sufficient since alertness rather than the degree of 
protection is important. 

4. Whenever it is possible to exceed dosages of 50 
to 100 by large margins, canister penetration is a 
possibility. With properly chosen weapons, the use of 
gas against caves, pill boxes and other enclosures can 
lead to casualties by canister penetration. 

5. When high dosages are achieved, there will be 
casualties from leaky valves, poorly fitting facepieces 
and causes other than canister penetration, but the 
number is difficult to predict and would decline as 
troops became accustomed to gas warfare. Heavy 
canisters with large protection may even increase the 
danger of casualties from facepiece leakage for those 
gas masks with canisters attached directly to face- 
pieces. 

If the above premise is accepted (that protection 
against a dosage of 50 to 100 is adequate) it does not 
follow that better protection is undesirable. Every 
effort should be made to get the maximum protection 
consistent with other features such as weight and 
resistance. Low protection should be accepted only 
when it is not feasible to aim for higher values. 

Filter protection should be made as high as possi¬ 
ble, consistent with breathing resistance and canister 
design. Present filters will permit penetrations of the 
order of 0.01 to 0.1% of the incident aerosol. 

The relation of pressure drop to protection in filters 
is such that it is not feasible to lower protection from 
the present level in order to obtain decreased resist¬ 
ance. As the thickness of filter is reduced, the resist¬ 
ance is decreased linearly but the protection de¬ 
creases logarithmically. 

9.3 WEIGHT AND SIZE OF CANISTER 

The weight and size permissible for a gas mask 
canister depend upon how the canister is mounted 


and used. The trend today is toward developing face¬ 
piece-attached canisters but there are still large 
numbers of hosetube masks with the canister 
mounted in a knapsack carrier. In the facepiece 
canister models both the weight and size are of im¬ 
portance but in the hosetube type, weight is of 
secondary importance. 

Choice of Type 

It should be pointed out that, despite the present 
trend of facepiece canister masks, data on the relative 
merits of the two types are very meager. Neither the 
British nor the U. S. gas defense organizations have 
adequate facilities for testing the field behavior of 
gas masks. Present opinions as to the relative merits 
of hosetube and facepiece canister models are based 
upon limited wearing trials under non-gas warfare 
conditions and there is no real knowledge regarding 
the relative merits of the two types. If gas warfare 
were initiated, the choice would depend upon the 
conditions found to prevail in the field. It is believed 
that if it is found necessary to wear masks for long 
periods the hosetube type may be superior because 
of greater comfort but if gas attacks are infrequent 
and of short duration the facepiece attached type 
may be superior because of lightness and decreased 
interference with other activities. Much more pro¬ 
tection can be built into a hosetube-type canister 
since weight is not important and this type can be of 
far more rugged construction than the facepiece type. 
On the other hand it is easier to waterproof the face- 
piece type and easier to wear it in active combat. 

It is fortunate that in the absence of real knowl¬ 
edge of the relative merits of the two types, the 
British and U. S. Armies had large supplies of both. 
In the event that gas warfare had been started, all 
combat troops could have been readily equipped with 
the type of mask which proved to be most desirable 
as new conditions were encountered. 

Hosetube Canisters 

It is much easier to design a canister which is at¬ 
tached by a hosetube and carried in a knapsack than 
one which is directly carried on the facepiece. The 
only important limitation of the knapsack canister is 
that of bulk, or more specifically, of diameter. It is 
undesirable to have a canister of diameter greater 
than about 3 in. since the amount of interference 
depends upon the distance the canister projects from 
the body. Weight is not important, within limits, 
since a change of a few ounces is not noticeable and 


SECRET 



WEIGHT AND SIZE OF CANISTER 


185 


as much as 2 lb (the weight of the M9 A2 canister) can 
be tolerated. 

For many years the U. S. canisters of the hosetube 
type have been of a radial-flow design. There are 
several advantages in this construction, which is 
possible only when weight is not a limiting factor. 

1. Charcoal bed resistance is low. For large canis¬ 
ters the filter resistance may be kept quite low. 

2. Radial-flow canisters are more rugged than flat¬ 
bed, axial-flow types because the chemical container 
is a separate can mounted within an outer jacket 
which furnishes protection. 

3. In a radial-flow design as compared to a flat-bed 
type, it is easier to pack the absorbent tightly so that 
it does not loosen or channel. Baffles at the top and 
bottom of the inner tube of the chemical container 
effectively prevent any channeling if the granules 
become loosely packed. 

4. The large surface area on the outside of the 
chemical container provides for large filter area. 

The weights of these radial-flow canisters vary 
from about 1 lb for the M10 to 2 lb for the M9A2. 
Nearly half this weight is in the metal parts. If de¬ 
sired, the weight might be materially lightened by 
use of aluminum or light alloys in place of steel parts. 
This, however, has not been thought necessary. 

The ultimate in low resistance and high protection 
has not been attempted in the hosetube canisters 
since there has been no apparent need for further im¬ 
provement. An obvious change that could be made 
without making the canister more bulky or increasing 
the weight too much is to increase the length of the 
M10A1 canister which is the most efficient of the 
radial-flow models. An increase in length of 1 in. 
would lower the resistance at least 20% and increase 
the protection by much more than 20%, perhaps by 
as much as 50%, because of decreased critical depth 
at the lower flow rate. This is mentioned to illustrate 
the possibility but is not recommended since the 
protection of the M10A1 canister already seems 
adequate for all needs. 

Facepiece Canisters 

There are two general methods of attaching canis¬ 
ters to the gas mask facepiece, at the chin and on the 
left cheek. The former method is used in German 
masks and the latter in British and U. S. masks. Each 
has advantages and disadvantages. 

Both weight and size of the canister are important 
considerations. More weight can be tolerated in a 
chin-mounted canister than in a cheek-mounted be¬ 


cause the unbalanced weight on the cheek tends to 
break the face seal. Tests conducted by the CWS 
development laboratory indicate that the weight of a 
cheek-mounted canister should not be much greater 
than 250 g and that above this weight there is far 
greater tendency to break the face seal when the head 
is moved quickly. A weight oif nearly a pound can be 
tolerated in a chin-type canister, since the pull is 
exerted on the head harness and does not break the 
face seal. 

Because of the necessity to conserve weight it is not 
feasible to use a radial-flow canister for mounting on 
the facepiece. The U. S. training mask is the only 
case of such a usage and this mask is not satisfactory 
for field use. All other facepiece-attached canisters of 
this and other nations are of the flat-bed, axial-flow 
type. To conserve resistance the diameter is made as 
large as can be tolerated, usually about 4 in. The 
volume of charcoal ranges from about 225 ml in the 
British canister and 250 ml in the U. S. Mil to over 
410 ml in the latest model German canisters (FE42). 

Relation of Weight and Protection 

Since weight and protection vary somewhat in¬ 
versely with one another, it is necessary in designing 
a canister to know the relation of the two for a given 
type. This relation may be discussed for the Mil 
canister to illustrate the general principles involved. 



DRY WEIGHT OF CANISTER IN GRAMS 

Figure 1 . The relation of weight and protection against 

CK in Mil canisters. 

The Mil canister with steel parts (now discon¬ 
tinued, but with several million in stock) weighs 
about 350 to 400 g. Of this, only about 175 g is taken 
up by the adsorbent when the canister is dry and 
200 g when humidified. An increase or decrease of 


SECRET 





186 


CANISTER DESIGN 


10% of the charcoal volume (which does not affect 
the weight appreciably) may cause a large change in 
protection. This is illustrated in curve A of Figure 1 
which shows protection against CK as a function of 
weight. Similar curves can be drawn for other gases 
but with the inflection points located somewhat dif¬ 
ferently, depending upon the critical bed depths for 
the gases in question. The protection of the present 
canister, with a volume of 250 ml is indicated by an 
arrow. It is noted in Figure 1 that if the weight is re¬ 
duced by 30 g (1 ounce) the gas life drops from 27 to 
11 min. Conversely an increase in weight of 30 g more 
than doubles the gas life. The reason that this is not 
done is that the corresponding increase in the amount 
of charcoal makes the bulk too great for a canister 
worn on the cheek (one argument for a snout canister 
is that greater bulk can be tolerated). 



Figure 2. Scheme of apparatus used to measure peak 
resistance. 


Since it is not feasible to reduce the weight by using 
less absorbent, the onty other possibility is in the use 
of lighter metal parts. The CWS development labora¬ 
tory has designed a satisfactory Mil canister which 
uses aluminum components, thereby affecting a ma¬ 
terial weight reduction. A life-weight curve for such 
an aluminum canister is shown in Figure 1, curve B. 
There is a weight saving of about 100 g for the same 
protection. This is the canister now in production. 

Similar relations hold for weight and protection in 
the radial-flow canisters. The M10A1 canister with 
340 ml absorbent gives a much higher gas protection 
than the M10 with 275 ml absorbent, although 
weighing only 40 to 50 g more; as mentioned in a 
preceding section, a still further increase in protec¬ 
tion could be obtained by an increase in the length. 

The present aluminum body Mil canister is still 
not the ultimate that can be expected in reduction of 
weight but is near the ultimate in bulk. Using present 
grade charcoal and the present mesh size it is im¬ 
practical to reduce the charcoal volume materially 
since protection falls off much more rapidly than 
weight. It might be possible to effect a small saving 
in volume by using finer mesh charcoal, but it would 


not be safe to go far below the present volume of 
250 ml. Use of a charcoal of lower apparent density 
is feasible and has been done experimentally. The 
present PCC charcoal when impregnated has an 
apparent density of about 0.65. It is possible to 
obtain good whetlerites with an apparent density of 
0.40 to 0.45. The weight saving in 250 ml is therefore 
near 50 g. 


9.4 CANISTER RESISTANCE 

The first impression received on wearing a gas mask 
is that it is difficult to breathe, particularly if vigorous 
exercise is attempted. From the start of gas warfare 
one of the most important considerations in gas mask 
design has been to keep the breathing resistance low. 
This section reviews the factors which cause resist¬ 
ance and their effect on canister design. 

Measurement of Resistance 

For many years it has been customary to express 
the resistance of a gas mask canister as the pressure 
drop in millimeters (or inches) of water when air is 
passed through the canister at a flow rate of 85 1pm. 
The choice of flow rate is purely empirical since this 
rate is higher than average flow but lower than the 
peak flow for men at vigorous exercise. 

During World War II devices have been developed 
to measure peak resistance for canisters and complete 
masks worn by men at heavy exercise. One of these 
is shown schematically in Figure 2. It consists es¬ 
sentially of a bottle G to which a water manometer C 
is attached, connected by rubber hose to the gas 
mask facepiece. Valve A permits air to be drawn from 
the bottle until an equilibrium pressure is attained; 
the pressure is then read from the manometer. The 
valve A must open at low resistance and have low 
leakage characteristics. The same apparatus may be 
used for expiratory resistance by arranging the valve 
so that pressure is built up in the reservoir to equal 
the static pressure of the gas mask valve. 

Typical results for several subjects at heavy exer¬ 
cise and for a standard mechanical breather pump 
are given in Table 1. 

These data show that the peak resistances vary 
over wide ranges for different subjects, because of 
different breathing rates. The mask for which the 
data are given was of poor design and had an un¬ 
usually high expiratory resistance. In the better 
masks peak expiratory resistances were much less 
than the inspiratory resistances; this is achieved by 


SECRET 






















CANISTER RESISTANCE 


187 


proper design of the outlet valve. Incidentally, it may 
be pointed out, as shown in Table 1, that the sub¬ 
jects at heavy exercise showed peak flow rates of the 
order of twice that for the mechanical pump, which 
had a flow rate of 50 1pm and a peak of near 155 1pm. 
The exercise conditions were chosen as the most 
severe that the subjects could endure for a few 
minutes. 


Table 1 . Maximum inspiratory and expiratory re¬ 
sistance for a gas mask. 



Max. resistance in in. of water 

Subject 

Inspiratory 

Expiratory 

1 

2.7, 2.7, 2.9 

2.7, 2.8, 2.7 

2 

3.1, 3.2, 3.4, 3.2 

5.0, 4.5, 4.9, 5.1 

3 

5.7, 5.8, 6.3, 6.2 


4 

3.3, 3.4, 3.4, 3.3 

3.1, 3.3, 3.3, 3.2 

5 

5.5, 4.7, 4.9, 5.3 

5.1, 5.0, 5.5 

Mechanical pump 
(50 Imp) 

2.6, 2.9, 2.8, 2.9 

2.8, 3.2, 3.3 


Physiological Effects of Canister Resistance 

It is not easy to arrive at definite conclusions re¬ 
garding the amount of resistance that can be per¬ 
mitted in a gas mask. Tests conducted at the Depart¬ 
ment of Physiology, Harvard School of Public Health, 
indicate that for subjects at exercise no marked differ¬ 
ence is found in physical stamina up to resistances of 
nearly 75 to 100 mm of water (measured at 85 1pm 
flow). These tests were made on the basis of measure¬ 
ments of pulse, temperature, et cetera, for subjects 
who did not know how much resistance was inter¬ 
posed. Tests by Medical Division CWS indicate also 
that there is no marked impairment of efficiency so 
long as the breathing resistance does not exceed 75 to 
100 mm water. (Reports from Division 11 NDRC 
and Medical Division CWS should be consulted for 
details.) On the other hand, experience with troops 
wearing gas masks in field trials tends to indicate that 
the efficiency of the average man is markedly lowered 
by wearing a gas mask of resistance near 75 mm 
water and that the endurance at heavy work is 
greatly decreased. Some claim that in field tests with 
mustard gas the comfort of the mask is increased by 
removing the particulate filter, thereby halving the 
resistance. How much of the handicap of the mask is 
due to its discomfort in binding the face, how much 
to the breathing resistance, and how much to psycho¬ 
logical factors, is not known. The writer feels that the 
subject warrants a more thorough study than has yet 
been made and that in particular more data should be 


obtained on the ability of men to become acclimated 
to wearing the mask. Possibly a rigorous training pro¬ 
gram might enable men to be as efficient when breath¬ 
ing through a 75- to 100-mm resistance as when no 
resistance is present. 

Lacking good data on the effect of resistance, cur¬ 
rent practice is to permit masks to have a resistance 
as high as of 75 mm water. Efforts are made to keep 
the resistance as low as is compatible with the amount 
of protection desired, but in general, the 85 1pm re¬ 
sistance of M3-10A1-6 masks is near 60 mm and that 
of the M5-11-7 mask near 70 mm. The fact that no 
serious objections have been raised to these resist¬ 
ances is not proof that they are satisfactory since, to 
date, masks are worn by the average soldier only for 
a few hours in training. 

Sources of Resistance 

In a complete gas mask assembly the inspiratory 
resistance is the summation of the following: 

1. Particulate filter of canister. 

2. Chemical container. 

3. Fittings, connections and facepiece. 

In a properly designed mask most of the resistance 
is in the canister, divided between the filter and 
chemical container. The proportion due to each de¬ 
pends upon the type of construction. In the radial- 
flow models the filter resistance is about three-fourths 
the total, while in axial-flow canisters of the Mil 
type the resistance of the filter is usually less than 
that of the chemical container. 

The chemical container resistance is due to the 
intergranular resistance within the charcoal bed and 
to the retaining screens and dust filter. In early stages 
of the Mil development, the interfacial resistance 
between charcoal and screen was high but suitable 
pad and screen combinations were later found to give 
a low canister blank. The effect of screens and pads 
cannot be determined from the resistance of an 
empty container but must be measured with charcoal 
present by plotting pressure drops vs volume of char¬ 
coal and extrapolating to zero volume. 

Since the chemical container resistance of radial- 
flow canisters, like the M10A1, is inherently small no 
difficulty is met in holding within tolerances in the 
assembly plant. Such is not true of the flat-bed Mil 
canister. Unless the operation of filling machines is 
carefully controlled and care is taken to avoid ex¬ 
cessive amounts of fine-mesh charcoal the resistance 
may go very high. Normally the resistance of the 
assembled Mil chemical container is about 35 to 


SECRET 













188 


CANISTER DESIGN 


40 mm. It varies somewhat with the different char¬ 
coals now on procurement. 

The resistance of complete canisters shows some 
variations as filter materials and charcoal from dif¬ 
ferent sources are used, but in general it is: 


Source 


Resistance 


MIXA1 or M9A2 
Ml or M1A1 
M10 or M10A1 
Mil 


50 mm 
60-65 mm 
60-70 mm 
60-70 mm 


Relation of Resistance to Size of Canister 

In the development of the Mil canister certain 
simple principles were noted, relating resistance to 
cross section of the canister. These are: 

1. The resistance of the filter is inversely propor¬ 
tional to the area or to the square of the diameter. 

2. The resistance of the chemical container is, for a 
given charcoal volume, roughly inversely propor¬ 
tional to the square of the cross-section area or the 
fourth power of the diameter. This relation is based 
upon the fact that both the flow rate and the bed 
depth depend upon the cross section. Protection, 
however, is almost constant, within certain limits, 
for a given charcoal volume. Data to show this point 
are given in Table 2. The calculated resistances are 
based on the relation 

Ri = (A )_ 4 
A (A ) 4 ’ 

These are net values, corrected for the container 
blank. 

Although it is not likely that an increase in the 
diameter of the Mil canister will ever be used, these 
data show why it was not possible to use a smaller 
canister than the present 4-in. size. In a 3-in. can the 
chemical container resistance would be for the same 
charcoal volume about three times that for the 4-in. 
can. 


tolerance is given the manufacturer in the distribu¬ 
tion of sizes but in general this distribution is ap¬ 
proximately 20-50-30 (20% 12-16; 50% 16-20; 30% 
20-30). The British, Canadians and Australians em¬ 
ploy a more uniform mesh distribution. 

There is no theoretical basis for the mesh size now 
used; rather the requirements are based upon prac¬ 
tical considerations of what the manufacturers can 
supply without undue wastage and how much pres¬ 
sure drop can be tolerated in the chemical container. 
A more efficient ratio of protection to resistance could 
be obtained by use of a narrower mesh spectrum but 
at present the wastage in producing such a charcoal 
renders a change inadvisable. 

Considerable work has been done on the relation 
of resistance in the charcoal bed to the size and distri¬ 
bution of granules, and tests of gas lives have been 
performed with various mesh distributions. The re¬ 
sults of such tests can be qualitatively summarized 
in a curve of the form shown in Figure 3, which repre¬ 
sents gas life as a function of resistance for a given 
volume of charcoal. 



RESISTANCE 

Figure 3. Relation of gas life and resistance for given 
volume of charcoal. 


Table 2. Effect of variation in diameter on resistance 
and gas protection for 250 ml adsorbent. 


Diameter 

Resistance 

Gas lives 

Observed Calculated CK 

CG 

AC 

10.6 cm (4^ in.) 

25 

32 

42 

53 

11.2 cm (4H in.) 

21 20 

33 

40 

47 

11.8 cm (4f£ in.) 

17 16 

26 

39 

51 


Effect of Mesh Size on Resistance and Protec¬ 
tion 

It is present U. S. practice to use 12-30 mesh (U. S. 
standard) for gas mask adsorbents. Considerable 


A curve of this type is readily explained from the 
considerations given in the preceding chapter. At a 
low resistance, or with large particles, the protection 
is low because the critical depth is large. As the 
particle size is decreased, protection increases more 
rapidly than resistance, due to the fact that when the 
critical depth is near the total bed depth a slight de¬ 
crease in the critical depth may cause a dispropor¬ 
tionate increase in the thickness of the saturated 
layer. At still higher resistances, which correspond to 
smaller intergranular distances, the critical depth be¬ 
comes a small fraction of the total bed depth. When 


SECRET 










CONCLUSIONS 


189 


this occurs, any further increase in resistance causes 
little increase in protection since the bulk of the 
absorbent is in the saturated zone already. At this 
point the curve flattens out. 

From such considerations it is obvious that for a 
given canister design it is desirable to obtain the 
resistance-protection curve for typical gases, in order 
to select the optimum mesh size of absorbent. These 
tests should be made both with gases whose I r values 
are small and large to cover the extremes which may 
be encountered. The curves for small l r values may 
be quite unlike those for large I r values. 


9.5 CONCLUSIONS 


In light of present knowledge as to the require¬ 
ments for the gas mask canister it is felt that the two 
most modern U. S. canisters, the M10A1 and Mil 
models, represent about the best overall performance 
that can be obtained with present charcoals and 
filters. Both canisters have high efficiencies of the 
order of 50 to 75% when new. 

Weight of gas retained at break 


Efficiency = 


Weight of gas at saturation 


It is felt that an increase in efficiency at the expense 


of weight or bulk is not now justified. Conversely, it is 
felt that a reduction in weight or bulk at the expense 
of protection is not justified unless it can be shown 
by large scale field trials that such a reduction is 
urgently needed. Should such needs develop, the 
principles of design are now well understood and if 
new requirements are set up it, is a simple matter to 
redesign the canister to meet them. At the present 
time canister design is ahead of facepiece design and 
extensive canister development is not needed until 
the designers of facepieces demand something dif¬ 
ferent. 

Attention should be called to one weakness in 
present canister design; that is, in the lack of rugged¬ 
ness. The M10A1 and other radial-flow canisters 
were so rugged in construction that they could be 
carried in a cloth knapsack without damage. The 
Germans have used a fragile canister for years but 
keep it in a sturdy metal carrying case. It is not at all 
certain that a fragile canister like the Mil aluminum 
model can be safely carried in a cloth knapsack. It is 
quite probable that many canisters will be dented 
and the bottoms mashed in so that the rubber plug 
cannot be used for waterproofing, thereby sacrificing 
one of the advantages of this type of canister. 


SECRET 




Chapter 10 

THE AEROSOL FILTER 

By W. Conway Pierce 


10.1 INTRODUCTION 

t the end of World War I the development of 
aerosol filters for gas masks was well under way. 
The Germans had first realized that a gas mask 
canister could be penetrated by airborne particles, 
which are not absorbed by charcoal. They had de¬ 
veloped the use of diphenylchloroarsine smoke for 
this purpose and, in the latter days of the war, this 
agent was used on a rather large scale. Dispersion was 
effected by placing solid diphenylchloroarsine in high 
explosive shells. The smoke so obtained was poorly 
dispersed, according to modern standards, and al¬ 
though it was effective against masks which had no 
filter the smoke could be stopped by a very crude 
filter pad. By the end of the war all masks were 
equipped with some type of filter to stop smoke 
particles. 

In the period between World War I and II the 
smoke protection of gas masks was greatly improved 
and at the start of the present war the gas masks of 
all nations provided at least moderately good pro¬ 
tection against all known toxic and harassing aerosols. 
A variety of types was used. 

10.1.1 United States 

The filter of the MIXA1 and Ml canisters was 
composed of several sheets of porous paper impreg¬ 
nated by aspiration of carbon black (from a smoky 
flame) through the paper. The filtering action was 
due to deposition of carbon filaments of small 
diameter across the large pores of the cellulose fiber 
network of the paper. This filter was very effective 
against solid particle smokes, particularly at low 
humidity. It would, however, break down on ex¬ 
posure to liquid smokes. 

10.1.2 German 

The filter was a single sheet of asbestos-bearing 
paper, folded so as to present a large area with low 
resistance. It was the best of the prewar filters when 
both resistance to flow and protection were con¬ 
sidered. Later U. S. filters were based upon develop¬ 
ments resulting from studies of German and British 


filters. However, the theory underlying filter action 
was carefully studied as a basis for later develop¬ 
ments. 

10.1.3 British 

Two types were used. The large box canister con¬ 
tained pads of wool into which asbestos fibers had 
been carded. Later, w hen the assault mask was de¬ 
veloped, the asbestos w r as replaced by a resin w hich 
w r as carded into the wool. This filter functioned be¬ 
cause of electrostatic charges. Under optimum con¬ 
ditions it was very effective but it had the weakness 
that the charge might be dissipated with age, b\ r acid 
gases, or even high humidities. When this happened 
the filter permitted high penetration of aerosols. 

10.1.4 Japanese 

The filter w as made of cloth that was pleated so as 
to present a large surface to the air stream. The 
filters on some types of canisters w T ere excellent. 

10.2 DEVELOPMENTS OF THE WAR 
PERIOD 

The first chemical warfare problem to reach the 
NDRC w'as CWS-1. The Service directive requested 
that fundamental scientific information be obtained 
on the dissemination and filtration of aerosols. In¬ 
tensive work on this subject began in 1940-41, by 
both NDRC and CWS, and led to a more funda¬ 
mental understanding of the problem. The follow ing 
generalizations appear in early reports. 1-6 

1. An aerosol filter is a netw ork of fine fibers. It 
does not function as a sieve; all but the largest par¬ 
ticles may pass through the holes. 

2. A particle is caught by the filter only when it 
comes into contact w ith one of the fibers, w'here it is 
held by van der Waals’ forces and is not removed by 
air currents w hich flow' at moderate speeds. 

3. A mathematical theory w^as developed 5,6 that 
took account of the mechanism w hereby the particle 
reaches the fiber surface, and that predicted the effect 
of particle size, flow' rate, and other factors on filtra¬ 
tion. It w'as shown that the fiber diameter should be 



190 


SECRET 


DEVELOPMENTS OF THE WAR PERIOD 


191 


of the same order of magnitude as the particle diame¬ 
ter. The predictions of this theory were confirmed by 
experiments. 

4. Presence of an electrostatic charge on the filter 
fibers increases their interception radius and im¬ 
proves the efficiency of filtration. All filters display, 
under certain conditions, some electrostatic action 
but, in general, it is not safe to rely chiefly upon this 
effect which may be lost on exposure to humidity or 
to certain types of liquid aerosols. The safest filters 
are those which act by interception even when elec¬ 
trostatic charges are not present. Testing of filters 
should be carried out at high humidity to avoid 
spurious effects due to transient electrostatic charges. 
Liquid smoke (that is, the dispersed phase is liquid 
droplets) should be used for testing filters, since such 
smokes are more penetrating than smokes which 
contain solid particles. 

5. It was stated 1 that “Apparently the ideal filter 
would consist of a series of grids made up of proper 
sized filaments placed in series and staggered so that 
the stream lines will not pass straight through the 
filter.” This ideal filter must be of finite depth since 
a shallow grid is more readily clogged than a deeper 
one of the same resistance. 

6. The filter should contain fibers of 1 to 2 microns 
diameter but a support of heavier fibers may be 
necessary to prevent matting of the fine fibers. The 
cellulose fibers of alpha web paper used in the prewar 
mask are some 20 microns in diameter. Carbon im¬ 
pregnation of this paper presumably gives finer fila¬ 
ments which span the large pores in the cellulose 
network. 

Recognition of the above generalizations was fol¬ 
lowed by an intensive study of means for producing 
filters of optimum efficiency and low pressure drop. 
Several sources of fine fibers were investigated, in¬ 
cluding asbestos, glass wool, organic fibers, and rock 
wool. Excellent filterswere made from all of these, but 
asbestos combined with paper was found to be best 
suited to rapid, large scale production. All U. S. gas 
mask filters of the M9A2, M1A1, M10, M10A1 and 
Mil canisters were equipped with asbestos-paper 
filters. A brief account of the various fine fiber studies 
follows. 

10.2.1 Glass Wool 5 

This material is readily available and has small 
fibers, usually less than 10 microns in diameter. The 
first tests, with laboratory material of fiber diameter 


6 to 8 microns, appeared very promising but it was 
soon realized that fibers of this size were not ade¬ 
quate at high humidity. At low humidity, where 
electrostatic effects may aid the filtration, these fibers 
are excellent. In view of these findings, the Owens- 
Corning Fiberglas Company undertook to make an 
ultrafine glass wool with fibers 2 to 3 microns in 
diameter. Experimental lots appeared to be very 
good and in 1942 Rodebush reported 5 “It may be 
considered therefore that the glass wool research has 
been completed and that the problem is now in a 
development state.. . . Glass wool is superior to paper 
as a filter material for two reasons: (1) the small di¬ 
ameter of the fibers and (2) the better distribution in 
space. Paper is ill adapted to use as a filter because 
it is made of large fibers which are matted together 
with a minimum of open space between them. ... In 
glass wool the fibers are uniformly dispersed through¬ 
out the volume with a relatively large amount of free 
space and the glass wool, therefore, gives a very low 
pressure drop for a given degree of penetration.” 

Following the research studies on glass wool, a 
CWS contract was given to Owens-Corning Fiberglas 
Company for development of a filter suitable for 
wrapping on the M10 canister. Sheets were prepared 
which gave excellent filtrations with low pressure 
drop, but by the time development work had pro¬ 
ceeded far enough to warrant production, an excellent 
asbestos-bearing paper was in production and it was 
not deemed desirable to make a change which would 
involve retooling and bring about new problems in 
manufacture. 

It appears in retrospect that had the glass wool 
development been made earlier it might have won 
out in competition with asbestos. One of the peace¬ 
time studies needed is a thorough comparison of 
glass wool and absestos filters, particularly for the 
axial-flow type of canister. Theoretically, glass wool 
appears to be superior in structural make-up but it 
is not certain that it can replace asbestos paper in 
practical application (which involves questions such 
as mounting, handling, and uniformity of production 
material). 

10 . 2.2 Rock Wool 5 

The use of rock wool as an aerosol filter was sug¬ 
gested to the CWS in 1941. This suggestion was re¬ 
ferred to NDRC and extensive investigations were 
made. Rock wool is manufactured in large tonnage 
for use as a heat insulator. The fibers are very similar 


SECRET 



192 


THE AEROSOL FILTER 


to those of glass wool, with diameters ranging from 
1 to 2 up to about 7 microns, the average being about 
twice that of the ultrafine glass wool made experi¬ 
mentally. In commercial manufacture, a binder is 
added and the rock wool is felted into pads. The com¬ 
mercial product has several disadvantages for gas 
mask filter use: (1) the pads are often uneven, having 
thin and irregular spots; (2) it is difficult to control 
the fiber size; (3) the wool contains a considerable 
amount of shot or beads of fused glass which occupy 
space but contribute nothing to filter action; and 
(4) adequate protection could not be obtained with¬ 
out excessive bulk or pressure drop. 

Because of these disadvantages, no serious con¬ 
sideration was given to the use of rock wool for 
military canisters. However, its availability in large 
amounts and its quite excellent filtering power led to 
consideration of rock wool for use in canisters for 
civilian or noncombatant masks. In 1942 the Johns- 
Manville Company undertook, without charge, an 
experimental development of a civilian canister. 
Later, this was continued at Edgewood Arsenal. 
Some excellent and cheap canisters were made by 
placing a layer of charcoal between two rock wool 
pads. Before this development was completed all 
need of a civilian canister had ended and the study 
was discontinued. Should it ever become necessary 
to produce large numbers of noncombatant canisters 
quickly, rock wool might well be considered for use 
in the filter pad; it does not appear, however, to hold 
any promise for use in military canisters. 

10 . 2.3 Organic Fibers 

In the search for fine fibers for use in filters, it was 
a natural development to investigate organic ma¬ 
terials which could be prepared by the methods used 
in the rayon and nylon industry. Research contracts 
were set up with American Viscose Corporation, 
E. I. duPont de Nemours Company, and Tennessee 
Eastman Corporation. It was found that superfine 
fibers could be produced, with diameters ranging- 
down to 0.01 micron and that these fine fibers could 
be prepared in uniform sizes. By the time these re¬ 
sults were achieved, the asbestos filter program was 
proceeding so satisfactorily that no attempt was 
made to set up production facilities, to solve the many 
problems attendant upon changing over from a 
laboratory to a commercial scale, or to devise 
methods for the fabrication of these fibers into gas 
mask filters. Thus, beyond the production of fibers 


by a relatively expensive process, the field of organic 
fibers is practically untouched. 

Unfortunately only one report of the work on 
fibers has been distributed. 7 Contractors’ final re¬ 
ports in the Division 10 files should be consulted for 
details. 

10.2.4 Asbestos 

The first material to be investigated in the search 
for fine fibers was, of course, asbestos since this was 
known to contain fibers of the proper size. It was in 
use in British and German gas masks, and it was 
readily available. Early tests with laborator 3 r as¬ 
bestos of Gooch crucible grade showed that it made 
an excellent filter. Work was begun immediately by 
CWS and NDRC on methods for incorporating as¬ 
bestos into filters by combining it with paper. Two 
general lines of attack were made on the problem: 
(1) by impregnating an open structure paper with 
asbestos, much as the older type paper was impreg¬ 
nated with carbon black; (2) incorporating asbestos 
into the paper so that it was interspersed throughout 
the cellulose network. Papers made by the former 
process are designated asbestos impregnated and those 
in which the asbestos is incorporated in the paper as 
asbestos bearing papers. 

Methods for impregnating thin-sheet paper for 
use in wrap-on, multilayer filters were developed by 
the Services. In dry impregnation, shredded asbestos 
was aspirated through the paper by a method similar 
to that formerly used for carbon black impregnation. 
Apparently the fine asbestos fibers were pulled into 
the large holes of the cellulose network at the paper 
surface so as to form a network of fine fibers super¬ 
imposed upon the coarser cellulose fiber network. 
The filters made by wrapping on several layers of 
this paper gave excellent protection. Similar results 
were obtained by a wet impregnation in which the 
paper was treated with a thin coating of asbestos 
slurry which was allowed to dry, leaving a deposit 
of asbestos fibers. 

While asbestos-impregnated paper gave filters 
which were distinctly superior to carbon-impregnated 
paper, they were not wholly satisfactory and were 
never used on a large scale. Asbestos-bearing paper, 
when good manufacturing processes had been de¬ 
veloped, was used exclusively during the latter part 
of the war. 

Numerous problems had to be solved before a satis¬ 
factory asbestos-bearing paper could be produced. 
Among these were methods for preparing the asbestos 


SECRET 



DEVELOPMENTS OF THE WAR PERIOD 


193 


fibers of proper size, of removing dirt and foreign 
matter from the asbestos, of dispersing the asbestos 
uniformly throughout the paper pulp, and of retain¬ 
ing a satisfactory tensile strength in the finished 
product. Through close cooperation between the 
Services, the paper manufacturers, and the research 
group, all these problems were solved and several 
types of asbestos-bearing papers were developed. 8 
For multilayer, wrap-on filters, where tensile strength 
was of paramount importance, a reinforced paper 
backed by scrim was used. All later Model M10 and 
all M10A1 canisters were wrapped with this paper. 
In fact, the availability of this paper made possible 
the development of the M10A1 canister with the same 
outer dimensions as the M10 canister. The scrim- 
back paper was so efficient that the number of layers 
of paper was reduced and the space saved thereby 
was utilized for increasing the charcoal bed depth 
by %2 in- 


The development of effective procedures for in¬ 
corporating asbestos into the paper made possible the 
design of an axial-flow canister of the Mil type. Be¬ 
fore such a canister could be designed, a single-sheet 
paper was necessary that could be fluted to present 
a large filter area since in the axial-flow canister it is 
not feasible to use a wrap-ori multilayer paper. The 
single-sheet paper produced eventually was compa¬ 
rable to, and probably better than, the German filter 
in protection and resistance. 

During the filter paper development, extensive 
study was made 8 of the effect of cellulose fiber on the 
resistance and efficiency of the paper. The incorpora¬ 
tion of special fibers, such as esparto grass, and the 
development of methods for treating wood to obtain 
the best size and distribution of cellulose fibers, all 
contributed to the success of the asbestos-paper 
filter, particularly by giving the necessary mechanical 
properties. 


SECRET 



Chapter 11 

PERFORMANCE OF U. S. AND FOREIGN GAS CANISTERS 

By J. William Zabor 


ll.l INTRODUCTION 

T he purpose of this chapter a is to summarize 
the data on the protection afforded by allied and 
enemy canisters against nonpersistent agents under 
a variety of conditions simulating circumstances likely 
to be met on the battlefield. As indicated in Chapter 
7, the protection afforded by all canisters against 
persistent agents is more than adequate and, conse¬ 
quently, need not be considered in this resume. 

It is obvious that only those enemy canisters which 
have been captured and returned to allied nations 
are considered. These canisters do not necessarily 
represent the enemy canisters which would appear 
under gas combat conditions because the enemy may 
possess, or be able to produce in a short time, can¬ 
isters that afford better protection than those con¬ 
sidered herein. Furthermore, in comparing the pro¬ 
tection afforded by enemy canisters with that af¬ 
forded by allied canisters, it must be emphasized 
that many of the enemy canisters suffer the disad¬ 
vantage of having been carried by troops, or having- 
been subjected to climatic conditions causing cor¬ 
rosion, whereas most of the allied canisters were new 
and in their best condition. 

The general test methods employed have been de¬ 
scribed in Chapter 2. Concentrations, humidities, and 
flow rates were varied and are specified in each case. 
Only results with breather-type pumps are given. 
Whenever possible, the results of the following three 
types of tests are given: (1) absorption to initial 
penetration of physiologically significant concentra¬ 
tions, (2) absorption to the penetration of a dosage 
which is considered to be lethal, and (3) initial 
absorption followed by desorption. It must be re¬ 
membered in this connection, however, that penetra¬ 
tion of a lethal dosage during a given exposure in the 
laboratory does not insure that a casualty is produced 
in combat by a similar exposure; there is usually 
sufficient warning in the early stages of penetration 
to permit a change of canisters or of gas masks if 
such replacements are available. 

a This chapter was written before V-E Day but the con¬ 
clusions regarding enemy equipment have not been materially 
altered by developments of the immediate postwar period. 

—Ed. 


The agents to be considered are the three U. S. 
standard agents (CG, CK, and AC), plus PS, and 
N0 2 . As was pointed out in Chapter 7, these gases 
represent the typical as well as the exceptional non- 
persistent gases which are apt to be met on the battle¬ 
field. Sulfur pentafluoride, and any other fluoride 
which might conceivably be employed, behaves much 
like CG, and protection may be expected to be com¬ 
parable. The results obtained with PS offer an esti¬ 
mate of the protection which would be afforded 
against a semi-persistent agent whose destruction on 
charcoal by hydrolysis or other reaction is likely to 
be too slow to affect the dynamic retention. Though 
few tests have been made with N0 2 , it is considered 
because it has often been proposed as a potential war 
gas. SA is not discussed in this chapter; it is not 
under consideration by the U. S. Army as a possible 
war gas, and therefore performance data of enemy 
canisters toward SA would be of little interest. Allied 
canisters afford more than adequate protection 
against this agent and thus it is of little concern from 
a defensive point of view. Furthermore, any de¬ 
ficiencies in protection of enemy canisters against 
SA could very easily be remedied. Performance data 
are considered separately for each agent in order that 
a direct comparison of the several canisters may be 
drawn. 

The majority of the work done on foreign canisters 
has been done by the Chemical Warfare Service 
[CWS] laboratories and more complete data may be 
obtained by direct reference to the original technical 
reports of that Service. The summary given in this 
chapter gives a sketchy overall picture of gas mask 
performance and is intended only to render the first 
part of this book more complete. Reference is made 
only to summary reports whenever possible. 

11.2 GAS MASK CANISTERS 

All U. S. gas mask canisters, except the U. S. Army 
Mil canister, are radial-flow design. These canisters 
are adequately described in Chapter 1. All foreign 
canisters discussed herein are of the axial-flow design. 
It is unnecessary to describe these canisters in detail 
in this summary, but a few of the physical charac¬ 
teristics of the more important canisters should be 


194 


SECRET 



GAS MASK CANISTERS 


195 



Table 1. 

Physical characteristics of foreign canisters. 



Overall 

weight 

Resistance 
at 85 1pm 

Volume of 
adsorbent 

Wearing 

Moisture 

content 

Principal 

Canister 

(g AR) 

(mm H 2 0) 

(ml) 

position 

as issued 

impregnants 

British Mk II/L 

313 

63 

233 

Cheek 

ca 20% 

Cu, Ag (Pyridine) 

Canadian Mk II/L 




Cheek 

ca 20% 

| 

German FE41 

340 

59 

260 

Snout 

(or dry) 
Dry 

\ Cu, Ag, Cr 

K, Na, Zn, Cu, Ag 

German FE41P 

320 

68 

270 

Snout 

Dry 

Same as FE41; 

German FE42 

455 

75 

410 

Snout 

Dry 

also Pyridine or Picoline 
Same as FE41 

German FE42P 

455 

75 

420 

Snout 

Dry 

Same as FPM1P 

Japanese Army 99 

508 

47 

315 

Hose 

Dry 

Cu, Mn 

Japanese Army 95 

691 

55 

425 

Hose 

Dry 

Cu, Mn 

Japanese Navy 93 

918 

53 

610 

Hose 

Dry 



mentioned before consideration is given to the gas 
protection the canisters afford. A brief physical 
description is given in Table 1. 

It will be noted in Table 1 that British and some 
Canadian canisters are moistened before issue. This 
practice was started originally to provide added CG 
protection without impregnation. Inasmuch as the 
canisters soon become humidified in the field, the 


practice has been continued. All “AR” test-results 
summarized in succeeding sections were performed 
on the moist canisters as received. All other canisters 
are issued dry and “AR” represents a nearly dry 
canister. 

The German canisters have the adsorbent sepa¬ 
rated into two layers in the FE37, FE41,and FE41P, 
and three layers in the FE42 and FE42P models. 


Table 2. Comparison of CG protection afforded by allied and enemy canisters to the break points. 


Influent dosages required to the initial penetration of 
physiologically effective concentrations under various conditions 

Canister 

50 

50 

Flow rate (1pm) 

50 50 25 25 

10 

Influent concentration (mg per 1) 

10 20 50 10 10 

AR-50 

80-50 

Relative humidity 

80-50 80-50 AR-50 80-50 

U.S. Army Ml 

200 1 

160’ 



U.S. Army M1A1 

200 1 

150 1 



U.S. Army M10 

350 1 

320 1 

300 1 

200 1 

U.S. Army Mil 

430 1 

380 4 

360 4 

325 4 

U.S. Army M10A1 

450 1 

450 1 

440 1 

325 1 

U.S. Army M9A2 

1000' 

1000 1 



U.S. Navy (Old Type) 


200 1 



U.S. Navy Mark B 

330' 

250 1 



U.S. Navy Mark B1 

570' 

620 1 



British Mk II/L 

280 1 ’ 7 




Canadian Mk II/L 

300 1 

330 1 



German FE37 





German FE41 

100 1 

350 1 • 3 



German FE41P 


390 3 



German FE42 


790 :i 



German FE42P 


950 3 



German Civilian 




80-210 5 - 6 

Japanese Army 99 

20-170 1 - 2 



235 1 - 2 160'- 2 

Japanese Army 95 

80-400 1 - 2 



530 2 

Japanese Navy 93 


1160 2 


1310 1 1130 1 

Japanese Civilian 

350 1 



960 1 


Note. Superscript numbers refer to bibliographical references. 


SECRET 



















196 


PERFORMANCE OF U. S. AND FOREIGN GAS CANISTERS 


This permits the use of two or three different ad¬ 
sorbents without blending. It also facilitates the 
insertion of a specific absorbent in the advent of the 
use of a new gas. 

The Japanese Army 99 canister contains about 
28% by volume of a modified Hopcalite. The 
Japanese Army 95 and Navy 93 canisters, respec¬ 
tively, contain 26% and 17% by volume of soda 

Table 3. Comparison of CG protection to initial pene¬ 
tration and to lethal penetration. (Influent concentra¬ 
tion = 10 mg per 1; flow rate = 50 1pm; humidity = 
50-50.) 

Influent dosage 
(mg min per 1) 
Initial Lethal 
penetra- penetra- 

Canister tion tion 


U.S. Army M1A1 

195 

380 

U.S. Army M10 

290 

540 

U.S. Army M10A1 

500 

750 

U.S. Army M9A2 

820 

1000 

German FE41 

180 

220 

Japanese Army 95 

440 

730 

Japanese Civilian 

350 

475 


lime. The Navy canister is the latest type captured 
from Naval and Marine units; it is equipped with 
a carbon monoxide auxiliary canister containing a 
poor grade Hopcalite. 

11.2.1 Protection against Phosgene 

The comparative CG protection afforded by allied 
and enemy canisters to the break points is sum¬ 
marized in Table 2. The superscripts refer to the 
bibliography of this chapter and represent the sources 
of these data. Average values are given except in 
cases where the range of values is large. Such large 
discrepancies are due to the testing of a limited 
number of canisters which were probably subject to 
considerably varied treatment prior to receipt and 
test in this country. In such cases, the higher figures 
probably more nearly represent the average protec¬ 
tion to be expected in combat. 

A few tests have been conducted to determine the 
influent Ct’s required to produce a lethal effluent Ct 
(considered to be 7 mg min per 1). These tests 1 were 
all performed at 50 1pm, an influent concentration of 


Table 4. Comparison of CK protection afforded by allied and enemy canisters to the break points. 


Influent dosages (mg min per 1) required to the initial penetration of physiologically effective 

concentrations under various conditions 



50 

50 

50 

50 

Flow rate (1pm) 

50 32 32 

25 

25 

12.5 

12.5 






Influent concentration (mg per 1) 





4 

4 

4 

10 

20 4 4 

4 

4 

4 

4 






Relative humiditv 





Canister 

AR-80 

80-80 

AR-50 

AR-50 AR-50 AR-80 80-80 

AR-80 

80-80 

AR-80 

80-80 

U.S. Army Ml 

16 1 

4 1 



36 1 


8 1 



U.S. Army M1A1 


24’ 

90 1 







U.S. Army M10 

140 1 

80 1 

125 1 

120' 

110' 300 1 120' 





U.S. Army Mil 


140 1 

190 1 







U.S. Army M10A1 

300 1 

160 1 

200 1 

190* 

190 1 500 1 340* 


1000 2 ’ 3 



U.S. Army MIXA1 

30 1 

4 1 



16‘ 





U.S. Army M9A2 

400 1 

280 1 








U.S. Navy Mark B 

140 1 

70 1 



190 1 





U.S. Navy Mark B1 

290 1 

190 1 








British Mk II/L 

28 7 





85 7 




Canadian Mk II/L 


20 1 

140 1 







German FE41 

24 3 

41,3 

16 1 



55 3 

8 1 ’ 3 

130 3 

12 3 

German FE41P 

24 3 

4 3 




105 3 

32 3 


195 3 

German FE42 

40 3 

4 3 




125 3 

12 3 

315 3 

70 3 

German FE42P 

65 3 

8 3 




245 3 

70 3 



German Civilian 










Japanese Army 99 

12 2 

42 




24 2 

4 2 

55 2 

8 2 

Japanese Army 95 

60 2 

4 2 




80 2 

8 2 

240 2 

28 2 

Japanese Navy 93 

00 

8 2 



160 2 

225 2 

24 2 

535 2 

110 2 

Japanese Civilian 






85 1 

17 1 




Note. Superscript numbers refer to bibliographical references. 


SECRET 





















GAS MASK CANISTERS 


197 


Table 5. Comparison of CK protection to initial penetration and to lethal penetration. 


Canister 

%RH 

Flow Influent Influent dosage (mg min per 1) 

rate concentration Initial Lethal 

(1pm) (mg per 1) penetration penetration 

U.S. Army M1A1 

50-50 

50 

10 

40 

147 1 

U.S. Army M10 

50-50 

50 

10 

140 

340 1 

U.S. Army M10A1 

50-50 

50 

10 

180 

415 1 

U.S. Army M10A1 

80-80 

50 

4 

175 

550 2 

U.S. Army M10A1 

80-80 

25 

4 

1000 

1760 2 

U.S. Army MIXA1 

50-50 

50 

10 

40 

180 1 

U.S. Army M9A2 

50-50 

50 

10 

320 

547 1 

German FE41 

50-50 

50 

10 

20 

95 1 

German FE41 

0-80 

50 

4 

24 

85 3 

German FE41 

80-80 

50 

4 

4 

30 3 

German FE41 

0-80 

25 

4 

55 

150 3 

German FE41 

80-80 

25 

4 

4 

60 3 

German FE41 

0-80 

12.5 

4 

170 

290 3 

German FE41 

80-80 

12.5 

4 

12 

160 3 

German FE41P 

0-80 

50 

4 

24 

110 3 

German FE41P 

80-80 

50 

4 

4 

80 3 

German FE41P 

0-80 

25 

4 

105 

245 3 

German FE41P 

80-80 

25 

4 

32 

170 3 

German FE42 

0-80 

50 

4 

40 

145 3 

German FE42 

80-80 

50 

4 

4 

50 3 

German FE42 

0-80 

25 

4 

125 

255 3 

German FE42 

80-80 

25 

4 

12 

110 3 

German FE42 

0-80 

12.5 

4 

315 

490 3 

German FE42 

80-80 

12.5 

4 

70 

380 3 

German FE42P 

0-80 

50 

4 

65 

165 3 

German FE42P 

80-80 

50 

4 

8 

100 3 

German FE42P 

0-80 

25 

4 

245 

390 3 

German FE42P 

80-80 

25 

4 

70 

284 3 

Japanese Army 99 

0-80 

50 

4 

12 

90 2 

Japanese Army 99 

80-80 

50 

4 

4 

30 1 ’ 2 

Japanese Army 99 

0-80 

25 

4 

24 

170 2 

Japanese Army 99 

80-80 

25 

4 

4 

40 1 ' 2 

Japanese Army 99 

0-80 

12.5 

4 

55 

310 2 

Japanese Army 99 

80-80 

12.5 

4 

8 

85 1 ’ 2 

Japanese Army 95 

0-80 

50 

4 

60 

150 2 

Japanese Army 95 

80-80 

50 

4 

4 

40 2 

Japanese Army 95 

0-80 

25 

4 

80 

250 2 

Japanese Army 95 

80-80 

25 

4 

8 

100 2 

Japanese Army 95 

0-80 

12.5 

4 

240 

520 2 

Japanese Army 95 

80-80 

12.5 

4 

28 

170 2 

Japanese Navy 93 

0-80 

50 

4 

90 

205 2 

Japanese Navy 93 

80-80 

50 

4 

8 

70 2 

Japanese Navy 93 

0-80 

25 

4 

225 

395 2 

Japanese Navy 93 

80-80 

25 

4 

24 

130 2 

Japanese Navy 93 

0-80 

12.5 

4 

535 

785 2 

Japanese Navy 93 

80-80 

12.5 

4 

110 

345 2 

Japanese Navy 93 

0-80 

50 

1 

48 

120 2 

Japanese Navy 93 

80-80 

50 

1 

5 

57 2 

Japanese Navy 93 

0-80 

50 

20 

160 

320 2 

Japanese Navy 93 

80-80 

50 

20 

20 

120 2 


Note. Superscript numbers refer to bibliographical references. 


10 mg min per 1, and 50-50 humidity conditions. The 
results are tabulated in Table 3. It is noted that, on 
the average, the protection to lethal penetration is 
25 to 50% greater than the protection to the initial 
penetration. The data in Table 3 are for single tests; 


this explains the differences between the Ct’s to 
initial penetration given in Tables 2 and 3. 

No results on desorption are available. It is well 
to point out, however, that under normal conditions 
of high moisture content, it is unlikely that appreci- 


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PERFORMANCE OF U. S. AND FOREIGN GAS CANISTERS 


Table 6 . Time for penetration of a lethal dosage of CK including desorption after various 
exposures. (Flow rate = 50 1pm.) 


Canister 

%RH 

Influent 
concentration 
(mg per 1 ) 

Influent Time to penetration 
dosage of lethal dosage 

(mg min per 1 ) (min) 

German FE42 

0-80 

4 

88 

55 3 

German FE42 

0-80 

4 

100 

443 

German FE42 

0-80 

4 

128 

34 3 

German FE42 

80-80 

4 

32 

15 3 

German FE42 

80-80 

4 

38 

12 3 

German FE42 

80-80 

4 

44 

10 3 

Japanese Army 99 

0-80 

4 

45 

45 2 

Japanese Army 99 

80-80 

4 

19 

12 2 

Japanese Army 95 

0-80 

4 

46 

54 2 

Japanese Army 95 

80-80 

4 

21 

16 2 

Japanese Navy 93 

0-80 

4 

73 

84 2 

Japanese Navy 93 

0-80 

1 

80 

140 2 

Japanese Navy 93 

0-80 

20 

80 

130 2 

Japanese Navy 93 

80-80 

4 

31 

26 2 

Japanese Navy 93 

80-80 

1 

42 

60 2 

Japanese Navy 93 

80-80 

20 

29 

30 2 


Note. Superscript numbers refer to bibliographical references. 


able amounts of CG could be desorbed. Continued 
passage of air would probably remove only the 
hydrolysis products, HC1 and C0 2 . 

It is obvious from these data that all canisters 
provide adequate protection against phosgene under 
normal conditions. The element of surprise must 
therefore be relied upon to a large degree in the 
offensive use of this agent. 

n.2.2 Protection Against Cyanogen 
Chloride 

The comparative CK protection afforded by allied 
and enemy canisters to the break points is sum¬ 
marized in Table 4. Average values are given in all 
cases. The superscripts refer to the bibliography of 
this chapter and represent the sources of these data. 
It should be noted that, when humidified, German 
and Japanese canisters are penetrated by harassing 
concentrations of CK after short exposures even at 
breathing rates corresponding to moderate exercise. 

Comparisons of influent dosages required under a 
variety of conditions to produce initial penetration 
of harassing concentrations and those required for 
penetration of a lethal dosage (considered to be 
10 mg min per 1 at concentrations exceeding 0.2 mg 
per 1) are summarized in Table 5. In all cases the 
data under a given set of conditions are for single 
tests. In general, the protection to lethal penetration 
is several fold greater than the protection to initial 
penetration; this is particularly true at high humidi¬ 


ties where protection to initial penetration is at a 
minimum. 

Little or no desorption of CK is possible from ex¬ 
posed British Mk II/L, Canadian Mk II/L, German 
FE41P, or German FE42P canisters, or from exposed 
U. S. canisters which are filled with Type ASC whet- 
lerite; the impregnants in these canisters destroy the 
CK. Desorption is possible, however, from exposed 
German FE41 and German FE42 canisters and from 
all Japanese canisters tested to date. Tests have 
therefore been conducted to determine the rate and 
extent of the effective desorption (concentration ex¬ 
ceeding 0.2 mg per 1). In Table 6 the results are sum¬ 
marized of a few tests to determine the time for the 
penetration of a lethal dosage including desorption 
after various exposures under a variety of conditions. 
Such a situation could be met in combat only if a CK 
attack is accompanied or followed by an attack with 
an agent which is at least semi-persistent, in order to 
insure continued wearing of the mask. All the tests 
given in Table 6 were performed at 50 1pm; con¬ 
siderably longer periods would be required at breath¬ 
ing rates corresponding to rest or moderate exercise. 

It should be noted that the Germans were aware 
of the possibility of eliminating desorption of CK and 
increasing the protection against this agent by im¬ 
pregnation with pyridine or picoline. The canisters 
issued at the end of World War II contained pyridine. 
Some Japanese canisters are amenable to this method 
of improvement but it was not used by the Japanese. 
Both German and Japanese canister protections can 


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GAS MASK CANISTERS 


199 


Table 7. Comparison of AC protection afforded by allied and enemy canisters to the break points. 

Influent dosages (mg min per 1) required to the initial penetration of physiologically 
effective concentrations under various conditions 




Flow rate, 1pm 





50 

50 

50 50 

25 

25 

12.5 

12.5 




Influent concentration, mg per 1 




4 

4 

20 40 

4 

4 

4 

4 




Relative humidity 




Canister 

AR-80 

80-80 

80-80 80-80 

AR-80 

80-80 

AR-80 

80-80 

U.S. Army Ml 

60 1 

25 1 






U.S. Army M1A1 

90 1 

90 1 






U.S. Army M10 

130 1 

130 1 

80 





U.S. Army Mil 

155 1 

155 1 






U.S. Army M10A1 

180 1 

180 1 

160 1 160 1 





U.S. Army MIXA1 

140 1 

80 1 






U.S. Army M9A1 

300 1 

300 1 






U.S. Navy Mark B 

130 1 

140 1 






U.S. Navy Mark B1 

210 1 

210 1 






British Mk II/L 

28 7 







Canadian Mk II/L 

100 1 

90 1 






German FE41 

16 3 

10 13 


443 

24 3 

120 3 

36 3 

German FE41P 


8 3 



28 3 



German FE42 

443 

56 3 


235 3 

275 3 

425 3 

530 3 

German FE42P 


52 3 



235 3 



Japanese Army 99 

8 2 

4 2 


110 2 

12 2 

160 2 

75 2 

Japanese Army 95 

122 

8 2 


36 2 

30 1 ’ 2 

75 2 

70 2 

Japanese Navy 93 

32 2 

12 2 


55 2 

CO 

C£ 

160 2 

125 2 

Japanese Civilian 




24 1 

25 1 




Note. Superscript numbers refer to bibliographical references. 


likewise be improved and desorption eliminated by 
impregnation with copper and chromium. Thus, it is 
obvious that for this reason, as well as those listed 
in the introduction of this chapter, the figures quoted 
in Tables 4, 5, 6, represent minimum CK protection 
afforded the enemy soldier at the advent of gas. 
Nevertheless, it is apparent that it tvould be very 
difficult to obtain CK casualties by canister penetra¬ 
tion even at the present level of minimum protection, 
unless the enemy were attacked during periods of 
strenuous activity when his canisters were well 
humidified and replacement canisters were unavail¬ 
able. 

n.2.3 Protection Against Hydrogen Cyanide 

A comparison of AC protection afforded by allied 
and enemy canisters to the break points for various 
conditions is given in Table 7. The superscripts again 
refer to the sources of the data. In general, the protec¬ 
tion afforded by dry canisters to initial penetration is 
less against AC than against CK, and vice versa for 
humidified canisters; thus, the protection against AC 
is slightfy better balanced. The Japanese Army 99 


canister, containing Hopcalite, is an exception to this 
general rule; the protection afforded by this canister 
when dry is considerably greater than that afforded 
against CK. 

Table 8 shows AC protection to initial penetration 
and to lethal penetration. In general, the factor of 
difference between influent dosage to these two types 
of penetration is less in the case of AC than in the 
case of CK. In other words, the rate of increase of 
effluent concentration with time is generally more 
rapid for AC than for CK. In many instances, the 
protection to lethal penetration is lower for AC than 
for CK at moderate breathing rates. 

The results of a few penetration experiments, in¬ 
cluding desorption, are summarized in Table 9. De¬ 
sorption from the German FE42 and Japanese Army 
99 canisters is slow and limited. Desorption from 
German FE41 and Japanese 95 and 93 canisters is 
much more extensive and rapid. Little or no AC can 
be desorbed from Type ASC whetlerite or from char¬ 
coals impregnated with many other metal oxides, 
such as ZnO. Furthermore, as noted in the case of the 
Japanese Army 99 canister, Hopcalite eliminates or 
reduces this possibility and increases the protection. 


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200 


PERFORMANCE OF U. S. AND FOREIGN GAS CANISTERS 


Table 8. Comparison of AC protection to initial penetration and to lethal penetration. 


Canister 

% PH 

Flow Influent Influent dosage (mg min per 1) 

rate concentration Initial Lethal 

( 1 pm) (mg per 1 ) penetration penetration 

U.S. Army M1A1 

50-50 

50 

10 

90 

165 1 

U.S. Army M10 

50-50 

50 

10 

140 

215 1 

U.S. Army M10A1 

50-50 

50 

10 

200 

270 1 

U.S. Army M9A2 

50-50 

50 

10 

300 

415 1 

German FE41 

50-50 

50 

10 

30 

65 1 

German FE41 

0-80 

50 

4 

16 

40 3 

German FE41 

80-80 

50 

4 

8 

443 

German FE41 

0-80 

25 

4 

44 

75 3 

German FE41 

80-80 

25 

4 

24 

100 3 

German FE41 

0-80 

12.5 

4 

120 

176 3 

German FE41 

80-80 

12.5 

4 

36 

128 3 

German FE41P 

80-80 

50 

4 

8 

44 3 

German FE41P 

80-80 

25 

4 

28 

105 3 

German FE42 

0-80 

50 

4 

44 

76 3 

German FE42 

80-80 

50 

4 

56 

160 3 

German FE42 

0-80 

25 

4 

235 

300 3 

German FE42 

80-80 

25 

4 

275 

380 3 

German FE42 

0-80 

12.5 

4 

570 

665 3 

German FE42 

80-80 

12.5 

4 

705 

855 3 

German FE42P 

80-80 

50 

4 

52 

120 3 

German FE42P 

80-80 

25 

4 

235 

385 3 

Japanese Army 99 

0-80 

50 

4 

8 

56 2 

Japanese Army 99 

80-80 

50 

4 

4 

442 

Japanese Army 99 

0-80 

25 

4 

no 

240 2 

Japanese Army 99 

80-80 

25 

4 

12 

96 2 

Japanese Army 99 

80-80 

25 

1 

38 

258 2 

Japanese Army 99 

80-80 

25 

18 

18 

126 2 

Japanese Army 99 

0-80 

12.5 

4 

160 

340 2 

Japanese Army 99 

80-80 

12.5 

4 

75 

335 2 

Japanese Army 95 

0-80 

50 

4 

12 

40 2 

Japanese Army 95 

80-80 

50 

4 

8 

32 2 

Japanese Army 95 

0-80 

25 

4 

36 

80 2 

Japanese Army 95 

80-80 

25 

4 

24 

64 2 

Japanese Army 95 

0-80 

12.5 

4 

75 

135 2 

Japanese Army 95 

80-80 

12.5 

4 

70 

130 2 

Japanese Navy 93 

0-80 

50 

4 

32 

60 2 

Japanese Navy 93 

80-80 

50 

4 

12 

44 2 

Japanese Navy 93 

0-80 

25 

4 

75 

125 2 

Japanese Navy 93 

80-80 

25 

4 

40 

85 2 

Japanese Navy 93 

0-80 

12.5 

4 

160 

220 2 

Japanese Navy 93 

80-80 

12.5 

4 

135 

225 2 


Note. Superscript numbers refer to bibliographical references. 


The Japanese auxiliary CO canisters would provide 
ample protection against this agent. In view of these 
remarks, it must be concluded that the Japanese 
would soon be able to increase protection against AC 
amply if the present protection were found to be 
inadequate at the advent of gas warfare. 

11.2.4 Protection Against Chloropicrin 

As stated in the introduction to this chapter, PS is 
considered only because test results with this agent 
offer an estimate of the protection which would be 


afforded against a semi-persistent agent whose de¬ 
struction on charcoal by hydrolysis or other reaction 
is likely to be too slow to affect the dynamic reten¬ 
tion. 

Only a comparatively few breather tests have been 
performed with PS. The results of some of these tests 
are tabulated in Table 10 1 for a cursory comparison 
of canisters. Because the protection is substantial for 
all canisters in spite of the strenuous conditions of the 
tests, it is obvious that all Allied or enemy canisters 
would provide more than adequate protection against 
agents like PS under normal combat conditions. 


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GAS MASK CANISTERS 


201 


Table 9. Total AC penetration and time to the penetration of a lethal dosage including 
desorption after various exposures. (Influent concentration = 4 mg per 1.) 


Canister 

%RH 

Flow 

rate 

(1pm) 

Influent 

dosage 

(mg min perl) 

Time to 
penetration 
of lethal 
dosage 
(min) 

Total 

penetration 
at concentration 
>0.1 mg per 1 
(mg min perl) 

German FE41 

80-80 

25 

40 


8.1 

German FE42 

0-80 

50 

60 


1.9 

German FE42 

80-80 

50 

80 


0 

Japanese Army 99 

80-80 

25 

80 


3.0 

Japanese Army 99 

80-80 

25 

87 

55 

5.0 

Japanese Armj r 99 

80-80 

25 

100 


8.3 

Japanese Army 99 

80-80 

25 

120 


13.0 

Japanese Army 99 

80-80 

25 

140 


19.0 

Japanese Army 95 

80-80 

25 

20 


3.6 

Japanese Army 95 

80-80 

25 

24 

65 

5.0 

Japanese Army 95 

80-80 

25 

40 


15.0 

Japanese Army 95 

80-80 

25 

80 


41.3 

Japanese Navy 93 

80-80 

25 

20 


2.2 

Japanese Navy 93 

80-80 

25 

25 

38 

5.0 

Japanese Navy 93 

80-80 

25 

40 


15.0 

Japanese Navy 93 

80-80 

25 

60 


27.5 


Table 10. Comparison of PS protection afforded by 


enemy and allied canisters to the break points. 

Canister 

Influent dosages (mg min per 1) 
to initial penetration 

Flow rate (1pm) 

50 50 50 50 

Influent concentration (mg per 1) 

10 10 50 50 

Humidity 

AR-50 80-80 80-80 AR-50 

U.S. Army M1A1 
U.S. Army M10 

U.S. Army Mil 

U.S. Army M10A1 
U.S. Army MIXA1 
U.S. Army M9A2 
British Mk II/L 
Canadian Mk II/L 
German FE41 
Japanese Army 99 

580 100 

670 140 

720 160 

200 

800 200 

1200 350 

330 

160 

600 

450 ... 1200 


11.2.5 Protection Against Nitrogen Dioxide 

N0 2 has frequently been proposed as a war gas 
because of its reduction to NO on charcoal and the 
early penetration of this product. A few tests have 
been run on U. S. and enemy canisters to determine 
the protection to penetration of lethal dosages (con¬ 
sidered as 15 mg min per 1 at concentrations exceed¬ 
ing 0.24 mg per 1), inasmuch as the effluent concentra¬ 
tion of NO builds up slowly after initial penetration. 


Table 11 . Comparison of NO2 protection afforded by 


allied and enemy canisters to the penetration of lethal 
dosages of NO. 

Canister 

Influent NO2 dosage (mg min per 1) to 
penetration of a lethal dosage of NO 

Flow rate (1pm) 

32 32 16 32 32 16 

Influent concentration (mg per 1) 

4.3 4.3 4.3 21.4 21.4 21.4 

Humidity 

AR-50 80-50 80-50 AR-40 80-40 AR-40 

U.S. Army Mil 

U.S. Army M10A1 
U.S. Army M9A1 
German FE42 
Japanese Army 99 

800 500 750 . 

1000 550 1250 550 310 1200 

1450 950 1500 

750 400 

375 270 


The average results of these tests are summarized in 
Table 11. 

The protection afforded by all canisters at moder¬ 
ate breathing rates and influent concentrations less 
than 1.5 mg per 1 is practically unlimited if the thresh¬ 
old concentration considered is correct. At these low 
influent concentrations, the effluent concentration of 
NO will not exceed 0.24 mg per 1 for verj^ long periods 
of exposure. 

Naturally, the presence of NO even at low con¬ 
centrations will have a harassing effect, but the 
protection against serious injury to the respiratory 
tract is more than adequate for all canisters under 
normal conditions. 


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202 


PERFORMANCE OF U. S. AND FOREIGN GAS CANISTERS 


11.3 CONCLUSIONS 

All U. S. canisters that are filled with Type ASC 
whetlerite and that are issued at present for combat 
use provide adequate protection against all known 
nonpersistent war gases. Indeed, the U. S. canisters 


provide better all-around protection than any canis¬ 
ters now issued by ally or enemy. 

All Allied and enemy canisters afford ample pro¬ 
tection against CG, N0 2 , PS, or similar gases under 
normal conditions while German and Japanese canis¬ 
ters are most vulnerable against AC and CK. 


SECRET 



Chapter 12 

PROTECTION AGAINST CARBON MONOXIDE 

By Ralph N. Pease 


12.1 INTRODUCTION 

t hardly needs to be emphasized that carbon 
monoxide is a potential hazard wherever air is 
contaminated with the products of incomplete com¬ 
bustion. Fires that are in enclosed spaces (a ship’s 
hold, for example), gunfire (with high explosives gen¬ 
erally), products from flame-throwers, and engine ex¬ 
haust (particularly when rich mixtures are employed) 
may give rise to dangerous concentrations. 

The situation is the more serious since the gas, 
being colorless and odorless, gives no real warning of 
its presence. The first physiological effects (headache, 
drowsiness, dizziness, nausea) may easily go un¬ 
recognized. Even if a simple, reliable chemical or 
physical test were available, there would still remain 
the problem of specifying a critical concentration 
under each set of conditions since variables such as 
exposure-time, activity of the subject, oxygen partial 
pressure, and similar factors must be taken into 
consideration. For practical purposes 4 the following 
table gives critical concentrations. 

Concentration CO 


vol. % 

Effect 

0.01 

No symptoms for 2 hours 

0.04 

No symptoms for 1 hour 

0.06-0.07 

Headache and unpleasant 
symptoms in 1 hour 

0 .10-0.12 

Dangerous for 1 hour 

0.35 

Fatal in less than 1 hour 


Values as low at 0.0025 to 0.0050% (25-50 ppm) 
have been specified as permissible upper limits under 
extreme conditions (high-altitude flight). In these 
circumstances, the only safe procedure would be to 
supply complete protection for personnel wherever 
there is a chance of exposure. 

Such protection may be achieved in some cases 
either by efficient ventilation, provided this does not 
introduce new sources of the gas, or by the use of the 
relatively bulky oxygen helmet, especially when CO 
concentration may be high and oxygen concentration 
low, or where high oxygen content itself is essential. 
However, when mobility is a consideration and CO 
concentrations are not too great (less than 2%), the 
best solution is a suitable gas mask. 

Such a mask must depend for its effectiveness on an 


efficient canister filling material. The subject was 
widely investigated during World War I. 5 Direct 
adsorption is apparently out of the question with 
known adsorbents, though there seems to be no 
reason why a synthetic analogue of haemoglobin may 
not ultimately be prepared. (Dried blood is of no use.) 
Several oxidants have been evolved, such as “hoola- 
mite” (I 2 0 5 + fuming H 2 S0 4 ), silver permanganate, 
and some oxide mixtures. Most successful solution of 
the problem was the development of Hopcalite 
catalyst, which utilizes oxygen of the air for oxida¬ 
tion of CO. Hopcalite is a mixture of Mn0 2 with other 
oxides, particularly CuO. It has become a universal 
standard material in CO canisters. 

12 .1.1 Hopcalite 

Hopcalite is an extraordinarily active catalyst. 
Properly prepared and used, it can give almost com¬ 
plete protection at a space-velocity (hours) as high as 
50,000 at room temperature. This is roughly equiva¬ 
lent to passage of contaminated air (dry) at 2 1pm 
through a layer of 2.5 cc of catalyst. Unfortunately, 
Hopcalite has several undesirable characteristics. 
Since it is prepared from finely divided, precipitated 
hydrous oxides, the catalyst granules are often soft 
and friable. More serious is its high sensitivity to 
poisoning by water vapor, which necessitates the use 
of a pre-drier. Further, Hopcalite does not completely 
remove CO at temperatures below 0 degree C, 
though it still shows some activity as low as —79 C. 
Finally, as an inevitable consequence of the high 
heat of oxidation of CO (67,600 cal per mole) excep¬ 
tionally high-temperature rises result from its use 
(98 C for only 1% CO). Efforts have been directed 
at reducing some of these limitations. 

12 .1.2 Charcalite Drier 1 

The advantage in long life which might be expected 
to accrue from use of Hopcalite catalyst is largely 
lost in practice because of poisoning by water vapor. 
Effective life then depends on the efficiency of the 
pre-drier. For this purpose, CaCl 2 granules and silica 
gel have usually been employed. However, the former 


SECRET 


203 


204 


PROTECTION AGAINST CARBON MONOXIDE 


is unsatisfactory because drying is never complete, 
and liquefaction of the granules at high humidities 
leads to the danger of channeling. Silica gel, though 
more efficient initially, has relatively short life and 
tends to swell and crack on wetting. 

In searching for an improved pre-drier, advantage 
has been taken of the tremendous surface, per unit 
volume, of activated charcoal. Charcoal itself is not 
a good drying agent, though its ultimate capacity is 
large. A surface coating of high moisture retentivity 
is obviously needed. After several trials CaCl 2 was 
chosen for the purpose, with HP0 3 , MgCl 2 , or ZnCl 2 
as alternatives. Distributed thinly over the charcoal 
surface, (perhaps in a unimolecular layer) its residual 
aqueous tension is reduced far below that of the salt 
in bulk. The best charcoals for the purpose proved 
to be a series of ZnCl 2 -activated products manu¬ 
factured bjr National Carbon Company; for example, 
CWSN177 B3. These charcoals combine exceptionally 
large surfaces and pore volumes (average density 
about 0.25 to 0.30 g per cc). They take up not only 
a maximum quantity of impregnating solution, but 
also retain saturated solution satisfactorily during 
use in drying. That the salt is well dispersed through 
the charcoal is indicated by the fact that a product 
containing 40% by weight CaCl 2 is still coal-black 
except for occasional white flecks of effloresced salt. 

Charcalite has about twice the effective life of 
CaCl 2 granules, and 4 to 5 times the life of silica or 
alumina gel. In a layer 2.5 cm deep by a 4-sq cm sec¬ 
tion at 25 C, with air at 21pm, and 50% RH (11.5 mg 
H 2 0 per 1) there is no detectable escape (condensa¬ 
tion at — 79 C) for perhaps 30 min, a cumulative 
total of 50 mg H 2 0 in 70 min, and of 400 mg (the 
effective life) in 130 min. Overall, a total of nearly 3 g 
of water would have been retained by 10 cc apparent 
volume of Charcalite. Protection is proportionately 
as good over a range of conditions, except that at 
higher temperatures (toward 50 C) there is a con¬ 
siderable loss in retentivity, though not relative to 
either CaCl 2 granules or silica gel. At these higher 
temperatures, HP0 3 -impregnated charcoals have a 
marked advantage. 

Incidentally, it is of interest to find that Hopcalite 
catalyst itself is superior to silica gel as a drier. This 
is in harmony with the known poisoning action of 
water vapor. 

The general method of preparing Charcalite in¬ 
cludes soaking active charcoal in 40% by weight 
CaCl 2 solution and then draining, and drying. In the 
last operation the material is first oven-dried at 


HOC with frequent mixing to prevent efflorescence. 
Subsequently, it is heated to about 250 C in a large 
flask until the water content is 2% or less. (The 
charge catches fire in air at 180C or above.) An 
essentially similar process was employed successfully 
for large-scale production. 

12.1.3 Gel-Type Hopcalite 2 

The many shortcomings of Hopcalite have already 
been noted. The method of preparation developed 
during World War I involves the addition at 50 to 
70 C of solid KMn0 4 to a strong solution of H 2 S0 4 
containing MnS0 4 . This is said to form manganese 
disulfate. On pouring the solution into water, a 
finely divided precipitate of hydrated Mn0 2 (con¬ 
taining some excess oxygen) is formed. This is 
washed by decantation until free of sulfate. Copper 
(or other metal) basic carbonate or hydroxide is pre¬ 
cipitated in the suspension, or separately. After mix¬ 
ing and further washing, the precipitate is filtered off, 
dried, compressed, and meshed. 

It has been found that under certain conditions it 
is possible to obtain the product in the form of a gel. 
First experiments utilized solutions of NaMn0 4 , 
which is far more soluble than the potassium salt. 
When it became apparent that this salt was not 
available in quantity, the method was altered so that 
solid KMn0 4 could be employed. It was found that 
a similar hard product was obtained by the following 
procedure. 

To a solution of 4 moles H 2 S0 4 and 16 moles H 2 0 
one-quarter mole of MnS0 4 is added. This is heated 
to 50 to 70 C; then three-quarter mole of KMn0 4 
(solid) is added slowly (temperature tends to rise) 
with vigorous stirring. This mixture is poured into 
40 liters of cool, distilled water. A very bulky 
flocculent precipitate separates after a minute or two. 
The precipitate is washed free of sulfate and 
filtered. After drying, this yields hard granules of 
high activity without compressing. If copper is to be 
added, the basic carbonate is separately precipitated 
from Na 2 C0 3 and CuS0 4 solutions, and the suspended 
precipitates mixed after washing. Again a hard active 
product results. This catalyst shows less sensitivity 
to water vapor than commercial grades under certain 
conditions. 

One variant containing silver and palladium in the 
atomic ratio 3Mn:2Ag:lPd is exceptionally active, 
and was considered for use in detector equipment. 
Attempts were made to obtain large-scale prepara- 


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CANISTER DEVELOPMENT 


205 


tion but these failed to give active products. It was 
found that heat effects due to adsorption-desorption 
of carbon dioxide were especially troublesome with 
this catalyst (perhaps because of its silver content) in 
connection with detector operation, and the develop¬ 
ment was dropped. 

The question of thermal activation subsequent to 
actual precipitation and washing is an important one. 
It might be assumed that the sole requirement is 
reduction in water content, but this proves to be onty 
partially true. Samples dried at 110 C and containing 
as much as 20% of H 2 0 have appreciable activity, 
whereas samples heated to 400 C, and containing 
less than 1% of H 2 0 are relatively inactive. Further¬ 
more, a sample deliberately dried in a stream of 
humid air (50% RH at 25 C) at 350 C, is found to be 
inactive even though water content is low. Other 
samples dried in open flasks at 300 to 400 C are also 
of low activity. Optimum activity is obtained only 
when a lively stream of dry air is applied, or when the 
sample is thoroughly evacuated (Langmuir pump); 
this only when temperature is below 350 C. 

It seems fairly clear that the residual moisture 
content of the atmosphere surrounding the particles 
is a factor, though the reason is not obvious. Possibly 
it is a question of crystal growth. The available 
oxygen content (as Mn0 2 ) does not prove a satis¬ 
factory index of activity. Many active samples, 
especially after vacuum treatment, run as low as 
75% available oxygen. On the other hand, totally 
inactive commercial Mn0 2 powder registers 100%. 
Surface determinations (N 2 adsorption by the Em- 
mett-Brunauer method) show some correlation with 
activity (especially after higher temperature treat¬ 
ment) but not in any simple proportion. The precise 
sort of surface alteration involved remains a mysterjr. 

It seems quite definite that pronounced improve¬ 
ment in both the hardness and the activity of com¬ 
mercial Hopcalite can be attained. Formation of gel- 
tvpe products is merely a question of altering con¬ 
centrations in the preparation of Mn0 2 . As to ef¬ 
fectiveness of thermal activation and drying, com¬ 
mercial lots of Hopcalite sometimes contain as high 
as 5% of H 2 0. The customary oven-drying at 200 to 
250 C reduces this only moderately, depending on 
atmospheric humidity. For optimum activity a figure 
below 1% must be attained. This requires higher 
temperatures and closer control of drying conditions 
as well as subsequent protection from moist air in 
the canister filling operation. Just how much im¬ 
provement in practice may be made remains to be 


seen, but experience with break-down tests indicates 
there is a large margin. 

12.2 CARBON MONOXIDE REAGENTS 

Over against the Mn0 2 -base Hopcalite catalysts 
are substances which oxidize carbon monoxide at the 
expense of their own oxygen. Two such catalysts, 
silver peroxide and silver permanganate, have re¬ 
ceived some attention in England and Canada and 
merit consideration. 

Silver Peroxide 

This catalyst is prepared by adding silver nitrate 
to an alkaline solution of potassium persulfate con¬ 
taining a little manganous sulfate, which is said to 
act as a stabilizer. The precipitate may be combined 
with shredded asbestos for preparation of granules. 
These granules remove CO from air, for a time, at a 
rate comparable to that of Hopcalite. A marked ad¬ 
vantage is their insensitivity to water vapor. Dis¬ 
advantages are their thermal instability, and the ex¬ 
tremely large weights of silver required. 

Silver Permanganate 

This catalyst is easily prepared by precipitation 
from solutions of AgN0 3 and KMn0 4 . It has been 
combined with CaCl 2 and CaO, or with kieselguhr, 
before compressing into granules. Such granules also 
remove CO from air at a rate comparable to Hopcal¬ 
ite, and have the advantage of water insensitivity, 
although thermal instability is again a handicap. 

It may be noted that the preparation in which 
CaCl 2 and CaO are incorporated dry with AgMn0 4 
yields a markedly more active product, but one which 
is less stable at higher temperatures than that in 
which AgMn0 4 is mixed with kieselguhr. It remains 
to be seen whether a suitable compromise between 
activity and stability can be achieved. 

12.3 CANISTER DEVELOPMENT 

There was at one time a demand for an assault- 
type canister for use of LST personnel. Development 
was undertaken by the C WS Development Laboratory, 
Massachusetts Institute of Technology. Ultimately 
it was determined that about 160 cc Hopcalite and 
90 cc Charcalite in an Mil assault canister would 
give the protection required for a 30-min period. 

Another matter, at one time believed to be a press¬ 
ing one, concerned the protection of aircraft personnel. 
It was suggested by the Bureau of Navigation, U. S. 


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206 


PROTECTION AGAINST CARBON MONOXIDE 


Navy, that a unit might be developed as an adjunct 
to diluter-demand oxygen regulator equipment. 
Exact requirements were not specified but a long life 
(up to 5 hr) was indicated. Pressure drop had to be 
low, breathing rates and CO concentrations were not 
to be high, and allowance was to be made for a wide 
range of temperature. After some experimentation, 3 
it was concluded that a unit of 80 sq cm cross section 
(or larger) containing about 150 cc Hopcalite and 


300 cc Charcalite, would be suitable. It was also 
shown that a mixed filling might be employed, though 
with some loss in life. Such a canister would protect 
for 5 hr from —30 to 0 C up to 0.01 % of CO or less 
against an influent concentration of 0.05% of CO 
at 15 1pm. 

In both these cases it is understood that the 
problem was ultimately solved by improved ventila¬ 
tion. 


SECRET 



Chapter 13 

CRITICISMS AND RECOMMENDATIONS 

By W. Conway Pierce 


13.1 INTRODUCTION 

he preceding chapters of this report were 
largely written in the period February to June 
1945, and they reflect, therefore, the viewpoints held 
while World War II was still in progress. The present 
chapter is written in 1946, as the report goes to press. 
At this time it seems proper to review briefly the 
accomplishments in gas mask development made 
during the war period and to point out some of the 
things that were left undone. Such a resume may be 
of use at some future date, even though the problems 
of the future promise to be very different than those 
of the present because of the development of the 
atomic bomb. 

In this section the writer will, as in preceding sec¬ 
tions, treat the Service and NDRC work as a unit, 
since in many instances the problems were attacked 
jointly. 

In discussing the deficiencies of the program, the 
remarks will necessarily represent the writer’s per¬ 
sonal opinion, which in some instances at least will be 
conjectural, since gas warfare was not used. Excep¬ 
tion may be taken to some statements, since fre¬ 
quently the all-too-meager data are subject to various 
interpretations. These comments are offered, there¬ 
fore, as the basis for discussion and with the hope 
that such discussion may lead to further improve¬ 
ment in the U. S. gas mask. 

13.2 ACCOMPLISHMENTS 

A brief review may be made of the accomplish¬ 
ments in gas protection during the war period. 

1 . Two types of domestic charcoal, from wood and 
coal, were developed and put into large-scale produc¬ 
tion, replacing coconut charcoal. These domestic 
charcoals were not only more available and cheaper 
than nut charcoal; they were, after impregnation, 
decidedly superior in gas protection. 

2. New impregnants were developed which, when 
used with the domestic charcoals, gave an adsorbent 
that furnished complete protection against all known 
war gases, both dry and humidified. 

3. A lightweight mask was developed with the 


canister attached directly to the facepiece, thereby 
eliminating need for a hosetube. 

4. Lighter and more efficient canisters were de¬ 
veloped. 

5. Protection against aerosols was improved by 
development of asbestos-incorporated and asbestos- 
impregnated filters. All the later model canisters, 
M9A2, M10, M10A1 and Mil, had asbestos filters. 

6 . A single sheet, folded, asbestos-incorporated 
filter of high efficiency and low resistance was de¬ 
veloped. This made possible the development of the 
axial-flow Mil canister which was directly mounted 
on the facepiece. It is reported that the Germans 
considered the Mil to be the best canister they had 
examined. 

7. Many components of the gas mask, such as the 
eye lenses and the outlet valve, were improved. 

8 . Methods for testing the performance of ad¬ 
sorbents, filters and completed canisters were made 
more realistic and rigorous. As a result, the overall 
standards for procurement were raised. 

9. Advances were made in theoretical knowledge 
of the factors which govern the removal of gases and 
aerosols by gas mask canisters. 

10 . Useful studies were made of the relation of the 
surface structure of charcoal to adsorption, retentiv- 
ity, and effectiveness as a carrier for chemical agents. 
Knowledge was gained concerning the activation 
process and the variables which affect the nature of 
the charcoal surface. 

11 . Extensive studies were made of the aging of 
impregnated charcoal under a variety of storage and 
use conditions. These studies led to the development 
of adsorbents whose field life was increased, and to 
better methods for packaging masks and canisters. 
Improved laboratory methods for surveillance were 
developed. 

12. A better understanding was gained of the ex¬ 
tent to which water is adsorbed by impregnated char¬ 
coal and of the effect which this adsorbed water has 
on gas protection. 

13. Studies were made of the mechanism of re¬ 
moval of the important war gases by impregnated 
charcoal and of the possibility of “poisoning” the 
adsorbent by one gas so that the canister may be 



SECRET 


207 


208 


CRITICISMS AND RECOMMENDATIONS 


penetrated readily by a second gas. It was concluded 
that present ASC charcoal is not poisoned by any 
known gas and that the U. S. canisters are not vul¬ 
nerable to such a sequence of gas attacks. 

14. Extensive comparisons were made of the gas 
protection of U. S. and foreign gas mask canisters. 
It was found that, in overall protection under a 
variety of conditions, U. S. canisters are superior to 
corresponding types of foreign canisters. 

15. A superior drying agent, Charcalite, was de¬ 
veloped for use in carbon monoxide canisters to pro¬ 
tect the Hopcalite catalyst against the poisoning 
action of water vapor. 

13.3 CRITICISMS 

The accomplishments of the war period, listed in 
part in the preceding section, are a source of satis¬ 
faction to all who participated in the gas defense 
program. But despite these developments and im¬ 
provements, criticisms may be made of the overall 
program and of the status of gas protection at the 
close of the war. 

Perhaps the major criticism is that it has never 
been possible, because of manpower shortages and 
organizational difficulties, to provide truly adequate 
field tests of gas masks under conditions that might 
prevail if gas warfare were employed. The only field 
tests made during the war were limited in scope and 
usually designed to test some particular item. In 
combat operations, the gas masks were usually dis¬ 
carded as soon as it was found that the enemy was 
not using gas. 

It is felt that much useful information might have 
been gained by the establishment of a test unit whose 
sole duty was to use anti-gas equipment in field opera¬ 
tions under simulated gas warfare conditions. Such a 
unit was formed in 1918. Despite the fact that actual 
gas warfare was used then, the reports made at that 
time indicate that information gained from the field 
test unit was a great help in solving problems of 
design and use of masks. 

Because of the lack of adequate field testing, there 
are many questions concerning gas masks which are 
not yet completely answered. Some of these may be 
listed : 

1. Which is the better mask for all-round use, a 
hosetube or facepiece canister type? Certainly the 
latter is preferable on the basis of lightness and free¬ 
dom from interference. But if it becomes necessary 


to wear masks continuously for 12 to 36 hours, which 
mask is preferred? 

2 . For all-round use is it better to mount the 
canister on the cheek, as in the combat mask, or on 
the snout, as in the German mask? Each position 
may be superior for certain requirements. 

3. What degree of waterproofing of the canister is 
needed by combat troops operating under various 
conditions, such as living in the jungle and landing 
from boats? Will the waterproofing devices now pro¬ 
vided prove adequate under various field conditions? 
The writer suspects that they are not adequate, par¬ 
ticularly for the M3-10A1-6 mask. 

4. Does the M7 carrier for the combat mask pro¬ 
vide adequate protection for the canister? Will this 
carrier stand up under severe usage? Will it maintain 
its waterproofing? Should a fragile canister, such as 
the Mil, be provided with a metal carrier to protect 
it against damage? 

5. What is the tolerance of well-trained troops to 
prolonged wear of a mask under jungle warfare con¬ 
ditions? To what extent does the wearing of masks 
reduce the efficiency of trained men operating as in 
jungle warfare? Tests by the Medical Division indi¬ 
cate that under tropical conditions the tolerance for 
a mask is very limited. 

6 . How much of a handicap to vision is imposed by 
present masks, for men at various types of activity? 

7. Of how much importance is the canister breath¬ 
ing resistance? Will a reduction of resistance by 30 
to 40 mm decrease the amount of fatigue caused by 
wearing the mask? (It has been reported by partici¬ 
pants in the jungle trials at Innisfall that if the 
aerosol filter is removed from a British canister the 
mask is much more comfortable to wear.) What 
limits should be set for the breathing resistance of the 
mask, both for inhalation and for exhalation? 

8 . How important are the weight and bulk of the 
mask? 

9. If troops are forced to don masks after several 
days under combat conditions, what is the incidence 
of serious facepiece leakage because of dirt and 
beards? 

10. How important is it to have better speech 
transmission? Should all masks be of a diaphragm 
type? 

11 . Will freezing of valves cause trouble if masks 
are used intermittently by troops operating at sub¬ 
zero temperatures? 

12 . Are nose cups desirable? 

13. Is it possible to fight effectively in a tropical 


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RECOMMENDATIONS 


209 


climate while wearing a mask and full protective 
clothing? If not, the plans for distribution and use of 
clothing should be modified. 

When conclusive answers are obtained for these 
questions it will then be possible to delineate more 
definitely than at present the objectives which should 
be sought in the design of the gas mask and accessory 
equipment. 

13.4 RECOMMENDATIONS 

The whole question of gas and aerosol protection is, 
at this time, very much confused. The lack of gas 
warfare in World War II, the possibility of deadly 
aerosols such as bacteria or radioactive dusts, and the 
certainty that future wars will be fought with differ¬ 
ent weapons than in the past, all combine to make it 
impossible to make a clear statement of future ob¬ 
jectives. Some would advocate making the mask as 
impenetrable as possible, perhaps going so far as to 
recommend self-contained units with oxygen supply. 


Others feel that it is not possible to protect against 
all possible hazards and that a considered risk should 
be taken in order to make the mask as light and com¬ 
fortable as possible. 

In view of present uncertainty, it is believed that 
immediate development should be focused on im¬ 
proving the comfort of the mask, keeping the stand¬ 
ards of protection about as in the M4-11-7 unit. 
When a thoroughly satisfactory mask has been de¬ 
veloped along these lines, it will be possible to make 
a better evaluation of the overall policy regarding 
protection against hypothetical agents of future wars. 
If such a development is undertaken, the following 
points should be considered. 

1. Placement of canister, on cheek or snout. 

2. Improvement of vision. 

3. Improvement of speech transmission. 

4. Use of mustard resistant facepiece materials. 

5. Waterproofing. 

6. Light weight of complete assembly. 

7. Facepiece leakage. 

8. Ease of carrying the mask. 




SECRET 




PART II 


MICROMETEOROLOGY AND THE BEHAVIOR OF CHEMICAL 
WARFARE GAS CLOUDS 


SECRET 





Chapter 14 

GENERAL METEOROLOGICAL PRINCIPLES 

By Wendell M. Latimer 


14.1 ATMOSPHERIC STABILITY 


14 . 1.1 General Principles 


A ir is in a stable state of equilibrium when a 
volume of the air, which is displaced a small 
distance up or down, tends to return to its original 
position. Unstable air, when displaced upward, is 
acted upon by forces which tend to accelerate it in 
the direction of the impulse, while stable air is de¬ 
celerated. The acceleration, which acts upon a volume 
of unstable air, depends upon the difference in den¬ 
sity between it and its surrounding air; but since air 
is a compressible medium, changes in pressure and 
temperature occur, so that the difference in density 
of both the displaced volume and its surrounding air 
vary from the initial conditions. When resulting 
temperature changes cause condensation of aqueous 
vapor, the heat of vaporization is liberated and the 
density changes are further complicated by this heat. 

Atmospheric pressure decreases with increasing 
elevation and from the first law of thermodynamics 


dT 


dQ RT dp 
~C P ~C~ P ~p ’ 


( 1 ) 


where T is absolute temperature, Q the heat added 
to the system, R the gas constant, C p the specific 
heat of the air at constant pressure, and p is the air 
pressure. If no heat flows in or out of the system, 
dQ = 0 and the process is called adiabatic. Then 



( 2 ) 


where C v is the specific heat at constant volume. 
From the average decrease of pressure with altitude, 
the rate of change of temperature for the adiabatic 
transfer of air from low levels to higher levels is about 
1 degree C per 100 m or 5.4 degrees F per 1,000 ft. 
This is known as the adiabatic lapse rate. 

The condition for the stability of dry air is not 
that the density must decrease and the temperature 
increase with altitude, but that the temperature shall 
not decrease more rapidly than the dry adiabatic 
lapse rate. 

The normal lapse rate, that is, the normal decrease 
of temperature with altitude, is about 3.3 degrees F 


per 1,000 ft. An air mass with this lapse is stable, as 
is indicated in Figure 1. 

To interpret Figure 1, let a volume of air be taken 
from the level k to the level l. If it is dry air (or air 
which will not become saturated in the process) its 
temperature decreases by the adiabatic rate, that is, 
line Ik is parallel to line CD. Its temperature at l is 
less than that of the surrounding air which has a 
temperature corresponding to m. Therefore its den¬ 
sity is greater than that of the surrounding air, and 



Figure 1 . Relation of stability to lapse rate. 


the displaced mass tends to return to its original 
level. If the rate of decrease of temperature with in¬ 
crease in altitude for AB had been greater than for 
CD, the temperature at l would have been warmer 
than that of its environment and the air mass would 
have been unstable. 

The dependence of the lapse rate upon the rate of 
fall of pressure has been indicated in the last para¬ 
graph. However, there is an interdependence of the 
two factors as indicated by the following argument. 

The rate of fall of pressure with height is propor¬ 
tional to the density d. 


dp 

dz 


-gd , 


(3) 


where g is the acceleration due to gravity. But for a 


SECRET 


213 




214 


GENERAL METEOROLOGICAL PRINCIPLES 


gas d = p/RT, and if the temperature were constant 
at all heights, by integration 



Q*_ m 
RT ’ 


(4) 


Actually, however, temperature falls off and may 
be represented usually by a straight line function 

T = To - az, (5) 


where T 0 is the ground temperature (absolute). Hence 
p a . T — az a . T 


i g t 

log- = — log — 
Po aR 


-az _ g 
T 0 aR ° g T 0 


( 6 ) 


In dealing with air masses which are subject to 
changes in both temperature and pressure, it is con¬ 
venient to have some standard reference condition 
for the sake of comparisons. Such a factor is the 
potential temperature 0, which is defined as the tem¬ 
perature the air would have if brought adiabatically 
to a standard pressure (1,000 millibars). From equa¬ 
tion (2) 


0 = 


^ 1000 y’-wc. 


(7) 


At 25 C the specific heats of dry air are C p = 0.2396 
and C v = 0.1707 cal per g. Hence 


C p - C v 


0.288. 


(8) 


Atmospheric stability may be defined in terms of 
potential temperature. 

For stability, the potential temperature must de¬ 
crease with height. For instability, the potential 
temperature must increase with height. 


14.1.2 Moist Air Stability 

The criteria for the stability of dry air apply with 
sufficient accuracy to moist air, even though there is a 
slight difference in the specific heat values, as long as 
the movement of the air fails to produce saturation. 
The value for the saturated adiabatic lapse rate de¬ 
pends upon the temperature and pressure of the air 
but is not simply related to the altitude. A number 
of graphical thermodynamical methods are in use for 
solving problems involving ascending saturated air. 
An example of such is the aerogram. In this method 
log T as abscissa is plotted against T log p as ordinate. 
Isotherms are shown as vertical lines and isobars as 
nearly horizontal lines. The graph has three sets of 
lines: (1) constant, maximum, specific humidity (dew 
point lines), (2) dry adiabatic, and (3) moist adia¬ 


batic. At low temperatures and low pressures, lines 
(2) and (3) are nearly parallel but they diverge 
greatly at high temperatures and pressures. 

By means of such a diagram measurements of 
temperature and relative humidity permit the calcu¬ 
lation of the level at which ascending moist air will 
form a cloud and also the thickness of the cloud. 
Since the purpose of this discussion is to give a 
foundation for consideration of problems on the 
earth’s surface, it is not necessary to amplify the 
problem of saturated air and cloud formation. Refer¬ 
ence should be made to a standard text. 12 



TEMPERATURE 


Figure 2. Diurnal variation in air temperature near 
the ground; (A) night; (B) evening; (C) midday; (D) 
day-adiabatic. 

The arguments in the previous paragraphs have 
assumed that a volume of air could be displaced 
vertically without disturbing its environment. Actu¬ 
ally an ascending current is normally balanced by a 
descending current. The coexistence of such adjacent 
currents modify somewhat the conditions for stabil¬ 
ity. They give rise to solenoid-producing terms. These 
do not greatly affect dry air problems but do lead to 
slight changes in the criteria for the stability of 
saturated air. 

14.2 METEOROLOGY OF THE GROUND 
LAYER 

The layer of air near the ground tends to assume 
the ground temperature. The large diurnal heating 
and cooling of the earth’s surface is thus accompanied 
by corresponding changes in the air next to the sur¬ 
face. These effects are illustrated in Figure 2 and 
Figure 3. 


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TEMPERATURE GRADIENTS NEAR THE GROUND 


215 


0 1200 2400 0 1200 2 400 





Figure 3. Mean diurnal curves showing temperature differences over the height intervals 2.5 to 30 cm (full line) and 
30 cm to 1.2 m (dashed line) on clear and cloudy days in summer and winter (after Best). 


The very high ground temperatures in midday and 
early afternoon give rise to temperature gradients in 
the air which are in excess of the dry-adiabatic lapse 
rate. These conditions are referred to as super adia¬ 
batic lapse or often as high lapse or strong lapse. As 
the ground cools at night the temperature gradient 
of the air near the ground inverts from the normal de¬ 
crease with height to an increase with height. This 
condition is referred to as inversion. A cross-over 
occurs in the morning and evening where there are 
zero or normal lapse gradients; these are known as 
neutral conditions. 

14.3 FACTORS INFLUENCING TEMPER¬ 
ATURE GRADIENTS NEAR THE 
GROUND 

14.3.1 Radiation Effects 

The mean energy of solar radiation just outside the 
earth’s atmosphere is given as 1.93 cal per min per 


sq cm. On the average, 38% of the incoming radia¬ 
tion is scattered or reflected back into .space. This 
reflection is due to such surfaces as dust clouds or 
earth’s surface and for any region is subject to con¬ 
siderable variation. Thus, clouds and snow-covered 
ground may reflect 80% of the radiation, and the 
reflection from water surfaces is much greater than 
from the ground. 

Most of the sun’s radiation lies within the limits 
of wavelengths 0.2 to 3 u, about half within the 
visible range 0.4 to 0.7 u and half on the infrared side 
of the visible. The absorption by oxygen and nitrogen 
molecules is negligible except in the ultraviolet below 
0.3/x* Most of this appears to be due to atomic oxygen 
at 100-km levels and to ozone around the 40-km 
level. Carbon dioxide absorbs in a narrow band 
around 15 p. The absorption of water vapor lies in 
the region 5 to 8 m and 15 n to longer wavelengths. 

Since both the C0 2 and H 2 0 vapor absorption re¬ 
gions are so far out in the infrared, these absorptions 
do not remove an appreciable amount of energy from 


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216 


GENERAL METEOROLOGICAL PRINCIPLES 


the direct solar radiation, but they do play an im¬ 
portant part in both the emission and absorption of 
atmospheric-temperature radiation. 

Because the average yearly temperature of the 
earth is fairly constant and the amount of solar 
energy absorbed by vegetation is a small fraction, it 
follows that the energy of the temperature (black 
body) radiation of the earth’s surface and atmosphere 
must be approximately equal to the amount of solar 
radiant energy. 

From the Stefan-Boltzmann equation, 

E = 8.22 X 10- U T 4 , (9) 

the effective black-body temperature of the earth as 
a radiator to space may be calculated. Using 38% as 
the loss of solar energy by reflection and dividing by 
4, the ratio of the area of the surface of a sphere to 
the area of a circle, we have 


or 


0.62 X 1.93 
4 


= 8.22 x io- n r 4 


T = 246 K. 


This value is too low by about 40 degrees C. The as¬ 
sumption that the earth radiates as a black body is 
far from exact, and the actual value of the tempera¬ 
ture should be higher than that calculated. Moreover, 



WAVELENGTH U 


Figure 4. Energy distribution in black-body radiation 
at 300 K. Shaded portions are regions of water-vapor 
absorption. 

the earth’s temperature is dependent upon evapora¬ 
tion, condensation, and turbulent wind convection; 
these factors are also involved in the departure from 
black-body conditions. 

Since the wavelength of maximum energy in 
black-body radiation is inversely proportional to the 


absolute temperature, and since the ratio of the tem¬ 
peratures of the sun and earth is about 20 (that is, 
6,000/300), the maximum energy of the earth’s 
black-body radiation lies around 10 /x. This is in the 
region of the water vapor bands and much of the 
outward radiation from the earth’s surface is there¬ 
fore absorbed by the atmospheric water vapor (see 
Figure 4). However, it is noted that there is a trans¬ 
parent region in water vapor between 8 and 15 /x, and 
it follows that an appreciable fraction of the radia¬ 
tion is transmitted. 

The water vapor and carbon dioxide of the atmos¬ 
phere emit radiation in the same regions in which 
they absorb. This gives rise to an atmospheric radia¬ 
tion back to the earth’s surface which is highly im¬ 
portant. If the temperature of the atmosphere is 
much colder than the earth’s surface, the atmospheric 
radiation is small in comparison to that of the surface 
because of the 7 14 dependence of the energy, but if the 
temperatures are nearly the same, as they normally 
are, they differ only by the amount of radiation trans¬ 
mitted by the water vapor in the 8 to 15 n region. 

With clear skies the incoming atmospheric radia¬ 
tion (sky radiation) is between 50 and 85% of the 
black-body value corresponding to the temperature 
of the air near the ground. The variations are largely 
due to changes in the relative humidity or weight of 
water in the air, but the total pressure and tempera¬ 
ture differences in the upper atmosphere are also 
factors. 

Various formulas have been proposed to calculate 
the sky radiation. Angstrom gave 
R 

— = 0.806 - 0.236 X 10-°- 052e , (10) 

n 

where R is the incoming radiation, F b the black-body 
radiation at the temperature of the air near the 
ground, and e is water vapor pressure in millibars. 
Brunt found that the experimental data are quite 
accurately expressed by the equation 

— = 0.526 + 0.065 V^- 
F b 

Rabitzsch wrote 

R _ 0.135p + 6.0c . 

F b T 9 11 

where p is air pressure in millibars and T is absolute 
temperature. 

Taking as an example the set of conditions, 
p = 1,000, e = 15, and T = 300, one may calculate 
from equation (11) R/F b = 0.75. F b at 300 K is 0.60 


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GROUND TEMPERATURES 


217 


cal per cm per min. Hence R, the sky radiation, is 
0.45 cal per min per sq cm and the effective outward 
radiation of a black body on the earth’s surface would 
be 0.60 — 0.45 = 0.15 cal per min per sq cm. 

For the same set of data, Brunt’s equation would 
give: 

- = 0.526 + 0.065 V 15 = 0.78 . 

F b 

Angstrom and Asklof have shown that there is a 
simple linear relation between the effective outward 
radiation when the sky is clear, R 0 , and when the 
fraction wj 10 of the sky is overcast, R w ; 

“■-“•('-Tt)' <12) 

The value of k depends upon the type of cloud: for 
low clouds 1 to 2 km above the ground (stratus, 
nimbus, stratocumulus) k = 0.9; middle clouds (alto- 
stratus at 3 km) k = 0.7; very high clouds (cirro- 
stratus and cirrus, at about 7 km) k = 0.2. 



Figure 5. Heat balance of the free air over Ludenberg 
in June, clear sky (after Moller). 


The atmospheric counterradiation must depend 
upon the mass of the atmosphere and therefore de¬ 
crease with elevation. Angstrom gave the following 
data, but it should be kept in mind that they repre¬ 
sent average conditions and are subject to variation 
with changes in temperature and humidity. 

Elevation, meters 0 1,000 2,000 3,000 4,000 5,000 

Counterradiation, cal 

per min per sq cm 0.44 0.37 0.31 0.25 0.21 0.18 

The net outward radiation also depends upon eleva¬ 
tion. Absorption diminishes as the amount of water 
vapor in the atmosphere (above) decreases, but at 
the same time the outward radiation decreases as the 
water vapor decreases, and also as the temperature 



TEMPERATURE F 

Figure 6. Vertical distribution of temperature in air 
and soil (midday). 

falls with elevation. As a result of these opposing 
factors, there is a maximum in the effective outward 
radiation at elevations around 2,000 to 3,000 meters 
above sea level. The ground surface gains energy 
from the solar radiation, but the net effect of radia¬ 
tion on the atmosphere is always cooling. 

Figure 5 (from Moller) indicates the radiation bal¬ 
ance on a clear day. With clouds present, the situa¬ 
tion is markedly altered as water particles check the 
outward flow of radiation and increases the counter¬ 
radiation of the atmosphere. 

14.4 GROUND TEMPERATURES 

The black-body temperature corresponding to 
maximum energy density of the solar rays on the 
earth’s surface, 0.62 X 1.93 cal per min per sq cm 
(that is, sun directly overhead and corrections made 
for scattering), is 347 K or 74 C. The theoretic maxi¬ 
mum may exceed this value as a clear dustless sky 
may transmit more than the assumed 62%. Maxi- 


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218 


GENERAL METEOROLOGICAL PRINCIPLES 


mum ground surface temperatures have been re¬ 
ported of 71.5 C at the Desert Laboratory, Tucson, 
Arizona, and 69 C in Agra, India. 

Results of Sinclair at the Desert Laboratory in 
Tucson, Arizona, are given in Figure 6 to illustrate 
air and earth gradients with respect to the ground 
surface. 

It is observed that the temperature falls rapidly in 
the soil below the surface. In fact this rapid falling off 
makes it very difficult to measure surface tempera¬ 
ture accurately. At the surface there is a disconti¬ 
nuity between the air temperature and the surface 
temperature. At least there is a region in which no 
accurate measurements of the air gradient have been 
made, and from the very nature of the problems the 
convection air currents must be such as to render the 
temperature indefinite. 

The surface temperature is obviously a function of 
the rate of transfer of heat to the air and the con¬ 
ductivity of heat down into the soil. The first of these 
depends upon the velocity of the air and its turbu¬ 
lence. The conductivity of the soil and other surface 
materials varies greatly. Values for various sub¬ 
stances are given in Table 1. 


Table 1. Heat conductivity (cal per cm sec C). 


Air 0C 

5.6 

X 

io- s 

Basalt 

5.2 

X 

10~ 3 

Clay 

2 

X 

10- 3 

Concrete 

2.2 

X 

10~ 3 

Diatomaceous earth 

0.13 

X 

10~ 3 

Brick 

1.1 

X 

10~ 3 

Granite 

8.2 

X 

10-3 

Gypsum 

3.1 

X 

10-3 

Paper 

0.3 

X 

10-3 

Peat 

0.4 

X 

10-3 

Snow 

0.1 

X 

10-3 

Soil (heavy) 

1.5 

X 

10-3 

Soil (light) 

0.7 

X 

10-3 

Water 

1.3 

X 

10-3 

Wood 

0.4 — 0.8 

X 

10-3 


Because of the low conductivity of air, types of 
ground which contain high proportions of air show 
low heat conductivity. The conductivity of grass and 
other vegetation is also low and it is noted from the 
table that the value for snow is the lowest listed. 

If two substances have the same albedo but differ 
in thermal conductivity, the substance with poor 
conductivity will be heated to a higher temperature 
by the solar radiation in the day time and will be 
cooled to a greater degree by the thermal radiation 
at night. Thus the diurnal variation in temperature 
will increase in the following order: granite, concrete, 
clay, heavy soil, light soil. 


The variation will be greater over grass than over 
bare soil. Snow forms a highly insulating blanket, but 
at night the surface temperature of the snow will fall 
more rapidly than ordinary ground. In the daytime, 
snow reflects such a high fraction of the sun’s radia¬ 
tion that it does not show an abnormal heating. The 
effect of the low conductivity of wood is noticeable 
on frosty mornings when the coating of frost will be 
much heavier on a board walk than on a concrete 
walk. 

The presence of moisture on the surface greatly 
reduces the diurnal temperature variations. If the 
soil is moist, part of the energy which would other¬ 
wise heat the soil will be expended in vaporizing the 
water. This effect increases with the porosity or water 
content of the surface material. Thus, for granite the 
effect is slight, for moist sand, half of the radiant 
energy may be so expended, and for peat as high as 
80% of the energy may be used up in this way. The 
process of vaporization essentially transfers the 
energy to the atmosphere as the subsequent con¬ 
densation of the water vapor will again release the 
equivalent energy. 

The effect upon night radiation cooling is not so 
direct, since a moist surface may be an effective 
black-body radiator. However, if the atmosphere is 
near saturation, the cooling of the surface results in 
the formation of dew or frost and the heat liberated 
on condensation will increase the surface tem¬ 
perature. 

Diurnal temperature variations of the ocean’s sur¬ 
face are small, about 1 degree C being the maximum 
change between day and night. The solar radiation is 
not absorbed on the surface as in the soil, but pene¬ 
trates to a considerable depth before the absorption 
is complete. Thus the heat is distributed over a large 
volume of water with a correspondingly small rise in 
temperature. However, in very shallow pools, the 
sand on the bottom will absorb the radiation and 
transmit it to the water so that in this case appreci¬ 
able temperature rise may result. 

At night, the surface radiates its corresponding 
temperature radiation but as the temperature of the 
surface decreases, the increase in density causes the 
surface water to sink, and thus again, the total heat 
change is distributed over a large column. 

14.4.1 Albedo Effect 

An average value for the solar radiation reflected 
and scattered by the earth’s surface has been given 


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CONVECTION, TURBULENCE, AND GUSTINESS 


219 


as 38%. The specific effect for various types of 
substances is obviously an important factor in de¬ 
termining the surface temperatures and accounting 
for thermal differences which exist along the hori¬ 
zontal. The albedo (ratio of reflected to incident radi¬ 
ation) for a number of substances is given in Table 2. 


Table 2. Albedo values for various materials. 


Material 

Dry 

Wet 

Black soil 

0.14 

0.08 

Granite 

0.14 


Sand 

0.18 

0.09 

Short grass 

0.25 


Tall grass 

0.32 

0.22 

Old snow 

0.70 


New snow 

0.81 



14.5 CONVECTION, TURBULENCE, AND 
GUSTINESS 


Turbulence and convection are more important in 
the transfer of heat in the atmosphere than is radia¬ 
tion. Petterssen estimates that, under normal condi¬ 
tions, eddy transfer of heat is about 100 times as 
large as the radiative transfer. Most of this eddy 
transfer occurs in the daytime under high lapse con¬ 
ditions. 

The vertical movement of unstable air is called 
convection. Whenever the temperature gradient ex¬ 
ceeds the dry adiabatic lapse rate, the air is unstable 
and should rise, but actually no overturning occurs 
unless a considerable impulse is applied. Thus, very 
near the ground, the lapse rate may be 800 to 900 
times the adiabatic. 

Geiger gives the following calculation of the ac¬ 
celeration of a parcel of air which has a temperature 
gradient of 0.84 degree between the heights 5 and 
10 cm. Expressing g, the acceleration of gravity in 
meters per square second and t, the time in seconds, 
the acceleration in meters per square second is: 


<Pz 
dt 2 



(13) 


If the particle is lifted from the 5-cm level to the 
10-cm level and T is 300 K, 

d 2 z 0.84 

— = 980 —— = 2.8 cm per sec 2 . (14) 

dt 2 300 


The particle, displaced only 5 cm from its original 
position, would move 1.4 cm in the first second and 
after 4 seconds would be 0.25 m above its original 
position. The acceleration would increase so that 


these values are too small. At these velocities an ad¬ 
justment to the temperature of the surroundings is 
not probable with parcels of any considerable vol¬ 
ume. However, the very existence of superadiabatic 
lapse rates argues that an initial impulse must be 
given to start the upward movement. 

The initial impulses may be regarded as due to 
(1) unequal heating, and (2) wind. Natural surfaces 
are neither smooth nor homogeneous in material. 
Differences in reflectivity, radiation, blackness, and 
heat conductivity, as well as sunny and shady sides 
of surfaces, will give rise to temperature differences, 
and gravity differences in the horizontal will be con¬ 
verted into up and down movement. These differ¬ 
ences in density may be observed visually over 
heated ground in the middle of the day as the 
familiar shimmering of the air. 

Air is seldom at rest and the friction and roughness 
of the earth’s surface tend to convert any horizontal 
motion along the surface into turbulent motion. 
Under lapse conditions, these impulses provide the 
initial displacements necessary to set up convection 
currents, and thus break down the high superadia¬ 
batic lapse rates. At high wind speeds on a clear after¬ 
noon the lapse rate will tend to approach the adia¬ 
batic rate. Under inversion conditions the stability 
of the air tends to damp out vertical displacements, 
but if the wind is high much irregular movement will 
be present. This is frequently referred to as turbulent 
motion. The effect of turbulence is to carry the 
slower moving air upward and to replace it by faster 
moving air from above. In this way the ground speed 
is maintained. As indicated, turbulence is at a mini¬ 
mum with low wind velocity under inversion condi¬ 
tions. 

Taylor sought to express the power of eddies for 
the diffusion of heat as a constant K, the eddy dif- 
fusivity which is roughly proportional to 0 .5wd, 
where w is the vertical component of velocity in the 
eddy and d the mean diameter of the eddy. K varies 
from 10 3 to 10 5 cgs units, depending upon the nature 
of the surface and the atmospheric stability. 

Schmidt introduced the idea of the Austausch co¬ 
efficient, A, to represent the behavior of groups of 
turbulence bodies. From a consideration of the tur¬ 
bulent convection of heat, the coefficient is seen to be 
analogous to k/a, the ratio of the heat conductivity 
to the specific heat. Its magnitude may be evaluated 
from the change of temperature with height. 

7 rp ln(z 2 — Xi ) 2 
T In 8 i — In 82 


A = 


(15) 


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220 


GENERAL METEOROLOGICAL PRINCIPLES 


where x is height, 5 temperature, and p density. 
Geiger gave the following values for A from observa¬ 
tions at Schleissheim in the middle of the day. 


Height (cm) A 

140 0.015 

100 0.010 

50 0.0028 

20 0.0005 

10 0.0002 

0 0.000 


For pure heat conductivity 


k 

a 


0.000048 

0.238 


= 0.0002 • 


(16) 


Thus, at the ground, A is zero because there is no 
vertical turbulence. Just above the surface it is the 
same magnitude as k/a and it increases with height. 

Components of gustiness are defined in a Cartesian 
coordinate system as 


G 3 


i u' • 


G v = 


I v' 


G z = 


i w' i 


w 


(17) 


where ii is the average x component of the wind 
velocity, the direction of x being the mean wind 
direction, and u', v ', and w' are the differences be¬ 
tween the instantaneous and average values of the 
x, y, and z components of the velocity, respectively. 

The vertical component of gustiness is obviously 
significant in the transfer of momentum, or heat, or 
dust and smoke particles from the lower to the higher 
altitudes; experimental observations confirm this 
correlation. However, the measurement of these com¬ 
ponents involves peculiar difficulties. A bilateral vane 
described by Best gives a fair approximation to the 
relative values of the horizontal and vertical com¬ 
ponents. 

Best has discussed the effect of stability and wind 
speed upon gustiness. For low wind speeds (0.5 to 1.0 
m per sec) gustiness is much less during inversions 
than during heavy lapses, and the same is true for 
speeds between 1.0 and 1.5 m per sec. For speeds be¬ 
tween 1.5 and 4 m per sec the effect is much smaller, 
and for higher speeds there appears to be no variation 
with changing temperature gradient. For lapses less 
than 0.9 degree F and for inversion, the gustiness in 
both lateral and vertical directions increases with wind 


speed. The small gustiness is maintained for higher 
speeds in the greater inversions. The ratio G v /G, ap¬ 
pears to be independent of temperature gradient but 
decreases slightly with increasing speeds. Best gave 
a value of 1.81 as an average for this ratio. Addi¬ 
tional data on the correlation of gustiness with wind 
and temperature gradients are given in Table 3. 


14.6 WIND FLUCTUATIONS 

A fluctuation or eddy velocity may be defined by 
the equation 

u' = u — u, (18) 

where u is the instantaneous velocity and u the 
average velocity. Best has studied the mean value 
of the fluctuation ratio 

i u' l 

g = 100 — , (19) 

u 

which is the ratio of mean eddy velocity to mean 
velocity, expressed on a percentage basis. His data 
indicate that g decreases as the temperature gradient 
changes from lapse to inversion and the effect is more 
marked at low velocities than at high velocities. 

14.6.1 Wind 

Gradient wind is defined as the speed of the air at 
which the deflective force, due to the rotation of the 
earth, and the centrifugal force jointly balance the 
horizontal pressure gradient. The direction of the 
gradient wind is along the isobars and, at heights 
sufficiently great to be unaffected by surface friction 
(2,000 ft), its value may be calculated with con¬ 
siderable accuracy from the pressure gradient and 
the latitude of the station. For a general equation, 
see any standard text on meteorology. 

Closer to the ground, frictional forces cause the 
surface wind to blow between 20 and 30 degrees 
across the isobars toward the low pressure center. 
The speed at 30 ft will be about half the gradient 
wind, depending upon the stability of the air, rough¬ 
ness of the surface, and local topography. 

At heights between 10 and 400 m, the variation of 
wind speed with height is given fairly accurately by 
the equation of Chapman 

u = a log h + b, (20) 

where a and b are constants dependent upon a given 
time and place. 

For speeds near the ground, Sutton derived the 
expression 

u /h \ n/ (2 ~ n) 

- = [r) , (2D 

Ui \hi/ 

in which n is a constant varying from 0 to 1 with an 
average value about 0.25. The value of n depends 
upon the stability of the atmosphere and the rough¬ 
ness of the surface. Best states that a power law can 
be used provided only a shallow layer is considered, 


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WIND FLUCTUATIONS 


221 


Table 3. Correlation of temperature gradient, velocity gradient, and gustiness components over long grass in 
Sacramento Valley. 


U-> m 

mph 

Uo m 

U\m 

linn 

Uim 

2m-lm 

AT,F 

6m-3.5m 

G y 

G z 

Time 

4.5 

1.12 

1.29 

-0.4 

-0.2 

0.67 

0.43 

7:18 p.m. 

5.5 

1.13 

1.43 

-0.4 


0.57 

0.38 

7:44 a.m. 

5.6 

1.16 

1.44 

-0.3 

-0.2 

0.70 

0.46 

7:19 a.m. 

6.7 

1.17 

1.37 

-0.4 

-0.2 

0.90 

0.45 

3:00 p.m. 

5.2 

1.17 

1.42 

-0.8 

-0.6 

0.52 

0.42 

3:40 p.m. 

5.9 

1.19 

1.33 

-0.4 

-0.4 

0.66 

0.43 

7:49 a.m. 

5.6 

1.23 

1.23 

0.0 

0.0 

0.58 

0.43 

6:53 a.m. 

6.2 

1.24 

1.55 

0.5 

0.3 

0.70 

0.52 

8:45 p.m. 

9.3 

1.25 

1.54 

0.3 

0.2 

0.63 

0.48 

8:45 p.m. 

4.3 

1.25 

1.53 

0.6 

0.3 

0.58 

0.36 

10:23 p.m. 

5.3 

1.25 

1.59 

0.4 

0.3 

0.60 

0.44 

8:18 p.m. 

5.9 

1.29 

1.63 

0.6 

0.5 

0.58 

0.40 

8:48 p.m. 

4.3 

1.31 

1.74 

0.5 

0.6 

0.50 

0.40 

9:43 p.m. 

3.5 

1.35 

1.91 

0.5 

0.8 

0.41 

0.27 

5:48 a.m. 

3.5 

1.39 

1.73 

1.0 

0.6 

0.59 

0.24 

11:04 p.m. 

3.4 

1.43 

1.98 

1.0 

1.1 

0.32 

0.23 

10:00 p.m. 

4.0 

1.45 


0.9 

2.6 

0.28 

0.16 

10:45 p.m. 

3.2 

1.50 

2.08 

0.9 

0.7 

0.32 

0.23 

9:46 p.m. 

3.0 

1.53 

2.32 

1.6 

2.3 

0.32 

0.22 

9:20 p.m. 

3.2 

1.66 

2.78 

1.8 

2.7 

0.21 

0.15 

9:56 p.m. 

3.0 

1.68 

2.54 

1.8 

2.0 

0.18 

0.08 

10:24 p.m. 

3.5 

>1.8 


>5.0 

1.5 

0.08 

0.0 

9:58 p.m. 

1.9 

1.95 

3.61 

1.0 

1.5 

0.25 

0.17 

11:14 p.m. 

4.0 

2.2 

4.6 



0.07 

0.06 

9:26 p.m. 


and that the index for zero temperature gradient 
may vary from about 0.43 in the lowest layers to 0.13 
at greater heights. This index can increase considera¬ 
bly during light winds and big inversions. 

If the wind at two levels is different, a frictional 
stress, r, which is a function of the velocity gradient, 
is set up. 


where v is the eddy viscosity of the air. For neutral 
conditions Rossby defines v by the equation 

^ = 0.02 0 + so), (23) 

where z 0 is the roughness coefficient, approximately 
one-thirtieth of the height of the roughness elements 
of the ground. The value of v also varies with atmos¬ 
pheric stability and becomes smaller with inversion 
conditions. 

Extensive investigations have been made of the 
dependence of the velocity gradient upon atmospheric 
stability. In many of these measurements the wind 
speeds have been determined at heights of two and 
one meters and the ratio determines the so-called 
R value , 

R = - • (24) 

Ui 


The effects of temperature gradient upon the R value 
over short grass at Leifield were summarized by Best. 

1. For light winds (less than 1.5 m per sec), R is 
about 1.06 for lapses of 1 degree C per m or greater; 
R is about 1.35 for inversions of 1 degree C per m, and 
R varies linearly for lapse rates between — 1 degree C 
per m and +1 degree C per m. 

2. For moderate winds (1.5 m per sec to 4.0 m per 
sec) R varies from about 1.08 to 1.16 from lapse to 
inversion conditions. 

3. For strong winds (4.0 to 8.0 m per sec) R is ap¬ 
proximately constant at about 1.11. 

It should be emphasized that this summary applies 
to short grass and level surfaces. The R values in¬ 
crease with the roughness of the surface and will in¬ 
crease by some 0.05 unit as the grass length changes 
from 2.0 to 4.5 cm. 

An extensive study of R values, temperature co¬ 
efficients, and gustiness was made 11 in the Sacra¬ 
mento Valley. The surface was flat and covered with 
high dry grass which was bent over. The data are 
summarized in Table 3. The following points will be 
noted. High values for R occur with high inversion. 
High inversion existed only at wind speeds of 4 mph 
or under. Both G y and G z decrease with inversion 
conditions. The correlation of R values and tem¬ 
perature gradients is shown graphically in Figure 7. 


SECRET 









222 


GENERAL METEOROLOGICAL PRINCIPLES 


Table 4. Wind speed at various heights over flat open country of different surface roughness. (In all cases wind speed 
is 1.00 in arbitrary units at 30 ft.) 


Surface roughness 

low 

High lapse 
or moderate 

wind 

Neutral or 
very high wind 

High inversion 
low wind 

Height in ft 

20 

10 

6 

3 

20 

10 

6 

3 

20 

10 

6 

3 

Smooth snow field 





0.99 

0.94 

0.89 

0.81 

0.97 

0.87 

0.81 

0.69 

Close cropped grass 

0.97 

0.90 

0.86 

0.80 

0.95 

0.84 

0.77 

0.68 

0.88 

0.68 

0.53 

0.44 

Grass 12 to 24 in. high 

0.93 

0.79 

0.68 

0.50 

0.92 

0.75 

0.65 

0.48 

0.86 

0.63 

0.50 

0.32 

Desert brush 2£ ft high and 4 ft diameter 













covers 10 — 20 % of ground 





0.90 

0.71 

0.60 

0.43 






Best found that, for low lapse and inversion, R in¬ 
creased with decreasing wind speeds, but for lapses 
greater than 0.9 degree F per m the velocity gradient 
increased with increasing velocity. He concluded, 
“The chief factor which tends to minimize velocity 
gradients is mixing due to turbulence and it appears 
that mixing accompanying high lapse rate is greatest 
when there is little or no wind.” 



Figure 7. Wind velocity ratio versus temperature 
gradient. 


Dickinson, Gilman, and Johnston have given a 
table 6 of factors by which the wind speed at heights 
of 20, 10, 6, and 3 ft over various surfaces and under 
lapse, neutral, and inversion conditions may be pre¬ 
dicted from the value at 30 ft. This table is useful 
since the speed at 30 ft is normally given by the Air 
Corps forecast. The influence of the various factors 
are in agreement with principles already discussed. 


14.6.2 Gravity Winds 

Under inversion conditions, the surface layer of air 
on a slope is colder and heavier than the air on the 
same level away from the surface. The surface air 
then tends to flow down the slope under a force, 

f = gw sin 0, (25) 

where g is the acceleration of gravity, 0 the angle of 
slope, and w a factor that depends upon the differ¬ 
ence in density between the air in the surface layer 
and that of the free atmosphere at the same level. A 
steady state is usually reached in which 

gw sin 0 = kv n , (26) 

in which k is the coefficient of friction as the surface 
air moves with the velocity v f and n is a numerical 
exponent. This gravity flow is also known as moun¬ 
tain wind, canyon wind, or katabatic wind. These 
winds show their greatest development over high 
snow-covered mountains or gently sloping plateaus 
such as exist in Greenland or the Antarctic Con¬ 
tinent. In these regions katabatic wind speeds of 
100 to 200 mph occur. However, on most slopes these 


Table 5. Temperature gradient and wind speed at base 
of Mt. Shasta 11:27 p.iri., August 27, 1943. 


Temperature gradient 

Wind speed at various heights 
Height, m. Miles per hour 

T 2 m — Tim =1.5 (inversion) 

1 


1.69 

T 3 . 5 HJ — T 2 m = 1.3 

2 


1.55 

Te,m — TYsm = 1.9 

4 


1.32 

§ 

1 

*3 

I 

II 

0 

<1 

8 


1.08 



fhm / 1 m 

= 0.92 


flows are normally only a few miles per hour and the 
air currents quite shallow. Latimer, Ruben, Gwinn, 
and Norris studied the katabatic currents which 
exist on clear nights on the slope of Mt. Shasta at a 
distance about ten miles from the summit. The slope 
at the site was approximately 2%. The data in Ta¬ 
ble 5 illustrate the type of velocity and temperature 
gradients which normally existed. 


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WIND FLUCTUATIONS 


223 


It will be observed that the air next to the ground 
is moving more rapidly than at higher levels and that 
the R value is less than unity. This occurred in spite 
of the inversion present, so it is obvious that R can¬ 
not be used as a measure of stability under these 
conditions. 

Light gravity winds may occur on the shaded side 
of a mountain in the afternoon. In general, it may be 
stated that gravity flow of air under inversion con¬ 
ditions tends to follow the natural water flow from 
the area. Both the depth and speed of the stream 
will be greater down ravines, canyons, and river beds. 
An example of aerial drainage down a narrow canyon 
is the fierce wind which sometimes develops in Santa 
Ana Canyon in Southern California during a high- 
pressure area over the mountains. At night, level 
valleys surrounded by high mountains tend to fill 
with cold air, often up to well-defined levels which 
are known as thermal belts. 

In the daytime, high lapse conditions on mountain 
slopes give rise to upward surface convection currents 
or anabatic winds. The following effects were de¬ 
scribed by Jelinek from experiments with theodolite 
balloons on the slope winds of a mountain 1,100 m 
high near Innsbruck, Germany. 

1. Upslope winds developed from 15 to 45 min 
after sunrise. 

2. Speeds were greatest (max 3.7 m per sec) and 
depth of upslope wind layer highest (max 280 m) on 
the south slope. The north slope also showed the 
least development both in speed (max 1.6 m per sec) 
and depth of layer (max 170 m). 

3. Tbe speed and depth of layer of the upslope 
winds increased steadily during the morning to a 
maximum before noon, decreased toward noon with 
the development of cumulus clouds on the top of 
the mountain, increased in the afternoon when the 
clouds drifted away and decreased to zero near sun¬ 
set. 

4. Both uphill and downhill winds are best defined 
when the pressure gradient over the area is small. 

Wexler has given the following examples of valley 
winds in the region around Dugway Proving Ground. 

1. Dugway Proving Ground has a general drainage 
from the mountains to the east and southeast. During 
the early morning the winds are prevailingly from the 
southeast. During the afternoon the winds are from 
the northwest direction up the area toward the 
mountains. A tendency has been observed for the 
direction of the wind to follow the sun in the morn¬ 
ing. This can be explained by the fact that the slopes 


facing the sun receive more heat than other slopes, 
causing a rising air from the slopes and a thrust of 
air from the valley toward these slopes. The south¬ 
east winds in the morning are light, averaging less 
than 5 mph. 

2. During the afternoon, the northwest winds are 
slightly stronger, averaging about 8 mph during the 
summer months/ With cloudiness during the morn¬ 
ing, the shift from southeast to northwest may be 
delayed. Strong pressure gradient or storms in the 
vicinity will overcome the diurnal cycle of winds. The 
depth of these local winds are in the vicinity of 
2,000 ft. 

14 . 6.3 Land and Sea Breezes 

As a result of the comparative constancy of the 
ocean temperature, it can happen that during the 
day the air over the land heats above the temperature 
of the air over the ocean, and during the night cools 
below it. In daytime the hot air over the land may 
rise and be replaced by air flowing in from the sea. 
Such a wind blowing from the sea is called a sea 
breeze; the wind that blows similarly from the land 
at night is called a land breeze. 

Both land and sea breezes are shallow and do not 
extend many miles from the shore. The sea breeze is 
likely to be rather stronger than the land breeze. The 
former generally reaches 10 to 25 miles inland but the 
latter seldom extends more than 5 to 6 miles to sea. 
If hills come near the shore line, the land and sea 
breeze effect can combine with the mountain and 
valley effect. Land and sea breezes are most promi¬ 
nent when strong radiation effects occur along with 
weak general winds; they are often important in the 
tropics. 

The thermal stability of the air near a coast line 
needs special consideration. The ocean surface is 
much more constant in temperature than the land 
surface. When air flows landward or seaward it may 
flow from a region where one stability condition pre¬ 
vails to a region where there is a different stability 
condition. For example, if approximately neutral air 
from the ocean moves inland over a sunny beach, a 
short travel (for instance, 50 ft) may suffice for the 
development of a distinct lapse in the lowest foot 
or two of the air. If a very small flat island is being 
considered, air may move entirely across the island, 
retaining its neutral structure in all but the lowest 
levels. Even if the air is moving in over a large land 
surface, an examination of the temperature gradient 


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GENERAL METEOROLOGICAL PRINCIPLES 


in the lowest levels alone will give misleading in¬ 
formation concerning the thermal stability unless the 
air has moved a sufficient distance over land to 
modify all the levels of interest. Similar remarks 
apply to air moving out from land over water. 

A small island can modify the turbulence and the 
thermal stability of the lowest layers of air; but the 
land and sea breeze effect may be unimportant even 
on larger islands. On a wooded tropical island 5x7 
miles, the land and sea breeze effect was difficult to 
detect; and this was in the region of the doldrums. 
The size that an island must have in order to show 
land and sea breeze effects evidently depends on the 
magnitude of the general wind and on radiation 
conditions as well as on the mountainous or flat char¬ 
acter of the topography. 

14.7 THE EFFECT OF AIR MASS 
CHARACTERISTICS 

An air mass which has moved from a cold area to 
a warmer area will be heated from below and thus 
become unstable. This instability will be a maximum 



Figure 8. Types of temperature-height curves in trav¬ 
eling air masses. A, initial curve; B, after travel over 
warmer ocean; C, after travel over warmer continent; 

X, condensation level; D, after travel over a colder sur¬ 
face, slight wind velocity (slight turbulence); E, after 
travel over a colder surface, high wind velocity (strong 
turbulence). 

in the afternoon and a minimum at night, when a 
radiation inversion may be set up if the area is land. 
Over ocean the diurnal effects will be slight. 

Conversely, an air mass which travels toward a 
colder area will be cooled from below and develop 
stability in the surface layers. Since turbulence will 


be a minimum, convection will be small and the 
effects of cooling will be confined to the lower 
levels. 

Petterssen, 12 in discussing Figure 8, notes that “the 
development from A to B results in numerous con¬ 
vective clouds and a low condensation level, whereas 
the development from A to C results in a smaller 
number of convective clouds at a considerably higher 
level. The development from A to D usually results 
in formation of fog, whereas the development A to E 
results in formation of stratus or strato-cumulus be¬ 
low the base of the inversion.” It should also be noted 
that case E is important in smoke screening as the 
smoke will tend to rise and level off at the base of the 
inversion. 



Figure 9. The diurnal variation in stability over 
oceans: A, night; B, day. 


Subsidence in high pressure areas may produce in¬ 
versions and intensify existing inversions. These ef¬ 
fects are often difficult to recognize from temperature 
measurements alone but are disclosed by the vertical 
distribution of humidity. Petterssen has given the 
data in Figure 10. 

The relative humidity in the inversion layer near 
the ground is always high. If the inversion is pro¬ 
duced by surface radiation alone, there is no rapid 
decrease in the humidity above the inversion layer. 


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225 



Figure 10. Types of inversions. A, Kjeller, 21 Feb. 1938, inversion produced by cooling from below; B, Fargo, 27 July 
1938, inversion produced by subsidence aloft and cooling from below; C, Mildenhall, 17 Dec. 1938, inversion produced 
mainly by cooling and turbulent mixing; D, San Diego, 6 Oct. 1938, inversion produced by subsidence aloft and heating 
and turbulent mixing below. 


In the case where subsidence is a factor the descend¬ 
ing cold air is dry and the humidity will fall rapidly 
with increasing altitude. 

Since the wind normally increases with elevation, 
advection of air aloft may alter the stability of the 
atmosphere over an area. However, conditions are 
rarely favorable for potentially colder air to overrun 
potentially warmer air, but, if the air temperature 
decreases in the direction opposite to that of the wind, 
this type of instability may be produced. In cold 


fronts, cold air may overrun warmer air largely owing 
to the friction of the ground layer. Such conditions 
result in great instability and high turbulent winds. 

14.8 CORRELATION OF CONTINUOUS 
MICROMETEOROLOGICAL OBSERVATIONS 

Probably the most complete micrometeorological 
measurements in America have been made by Dr. 
M. D. Thomas of Salt Lake City, Utah, in connection 


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GENERAL METEOROLOGICAL PRINCIPLES 



Figure 11 . Typical daily recordings of meteorological data. 


with smoke problems in that region. 19 The work was 
undertaken by the American Smelting and Refining 
Company and was supported in part by Division 10, 
NDRC. A discussion of these measurements will be 
given as an illustration of the principles presented in 
this chapter. Some of the conclusions are based upon 
a study of the Thomas data. 20 

The data consist of the following elements. 

1. Continuous temperature records (10 ft above 
ground). 

2. Temperature differences for the intervals: 110 
to 10 ft, 220 to 10 ft, 330 to 10 ft, 440 to 10 ft. (After 
August 1943 the intervals were for the heights: 15, 
125, 255, and 385 ft.) 

3. Wind direction. 

4. Wind speeds at 7 m, 2 m, and 1 m. 

5. Pyroheliometer traces. 

6. Degree of turbulence. 

The above measurements are automatically re¬ 
corded throughout the 24 hr of the day. Observations 
are also made on the density of smoke in the valley. 
From the data, continuous plots have been made 
of the various elements. Figure 11 is given as an 


example of this record. The items included on this 
chart are: 

1. Temperature at 10 ft (top curve). 

2. Intake of solar radiation in cal per min per sq 
cm (inserted curves). 

3. Temperature differences for the height intervals 
385 to 15 ft and 125 to 15 ft (second and third 
curves). 

4. R' values. The ratio of the wind speed at 7 m 
to that at 1 m. R (2 m to 1 m) given in some instances 
(fourth curve). 

5. Index of turbulence of the wind. Defined as the 
logarithm of the number of degrees per hour through 
which the wind vane rotates in one direction (fifth 
curve). 

6. Wind speed (mph) at 7 m (sixth curve). 

7. Smoke observations (noted on line below solar 
radiation). 

A study of Figure 11 discloses the diurnal varia¬ 
tions in temperature, temperature gradient, and wind 
gradient previously discussed in this chapter. In 
general AT and R' are high at night, due to the sta¬ 
bility set up by radiation cooling, and are low in the 


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227 


_ TIME 4 

TIME o x 

TIME 

TIME x q 

TIME q x _ 

0030 / 

0630 / / 

12 30 \\ 

1830 \ \ 

2400 \ | 

/ 

t / 
/ / 


M 

\ 

J 

t /- 

/ /- 
* y - 

y 

JUNE 7 * _x- 

_x CLEAR, LOW WINDS 

TEMPERATURE SCALE F 

JUNE II o_o- 

_o CLOUDY, LOW WINDS 

! '- 1 -f -- 

-3 -2 -1 

i i r 

0 +1 +2+3 


Figure 12. Temperature profiles for days in June. 



Figure 13. Temperature profiles for May and June, all weather. 


daytime under the convection currents of high lapse 
conditions. The curves at A7 7 and R' are roughly 
similar but there are certain interesting divergencies. 
Thus about 8 p.m. there is a sudden drop in R' with¬ 
out a corresponding large drop in AT. This appears 
to be due to a very shallow katabatic wind flowing 
down from the mountains and occurs with a change 
of the wind direction from northwest to southeast. 
In general, there is a close correlation between the 
wind speed and the index of turbulence; high turbu¬ 
lence is associated with high wind speed. A remark¬ 
able drop in the values of the index of turbulence is 
also associated with the shallow katabat, but as the 
katabat deepens and develops into a valley wind, the 
values of both the index of turbulence and R' again 
rise. An inverse relationship exists between R' and 
the index of turbulence but it is often masked by the 
effect of the wind speed upon both of these quantities. 

The effect of clouds upon the temperature profile 
is illustrated in Figure 12. It will be observed that 
both the night inversion and the day lapse were 


greater on a clear day (June 7) than on a cloudy day 
(June 11). On foggy days AT is mainly lapse. 

Figure 13 summarizes the average temperature 
profiles for the months of May and June 1943. May 
inversions terminated rather sharply at the 330-ft 
level, and the June inversions were stronger in gen¬ 
eral than those of May. On the other hand, the in¬ 
tensity of the lapse was greater in May than in June, 
which is not to be expected, but these data include 
all weather and the normal trends will be influenced 
by the wind velocity and number of cloudy days. 

In Figure 14, the difference in the maximum tem¬ 
perature on the preceding afternoon and the mini¬ 
mum temperature before sunrise is plotted against 
the maximum inversion. It will be observed that the 
two quantities are roughly proportional; this is to be 
interpreted as the effect of temperature on the net 
nocturnal radiation loss. Thus, when the ground sur¬ 
face is hot, the radiation loss will be proportionally 
larger and the resulting inversion greater. The rate 
of cooling is probably the most important factor in 


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GENERAL METEOROLOGICAL PRINCIPLES 



Figure 14. Plot of difference in maximum and minimum temperature against maximum inversion. 



TIME ( MWT ) 

Figure 15. Diurnal temperature variations. 


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229 




0030 0230 0430 0630 0830 1030 1230 1430 1630 1830 2030 2230 

TIME (MWT) 


Figure 16. Wind velocity at A T on clear days. 


determining the extent of inversion. The time of 
maximum inversion for small heights is generally 
after the period of most rapid cooling but for gradi¬ 
ents over several hundred feet inversion may occur 
after the time of minimum temperature. The time of 
maximum lapse generally follows the time of maxi¬ 
mum temperature closely. Figure 15 gives a com¬ 
parison for T and AT curves for June. 

Figure 16 is a plot of monthly average values of AT 
for hourly recording throughout the day and, for 
comparison, a plot of the corresponding hourly 
averages of the wind velocity. Figure 17 gives similar 
plots of R' and velocity. The conclusion might 
be drawn that inversion produces low winds and 
lapse high winds. While of course there are effects 
in these directions, it must be kept in mind that high 
winds tend to break down both inversion and lapse 
conditions to neutral. If the higher wind velocities 
had not existed during the day, the lapse values 
would have been considerably larger. The effect of 


wind speed upon stability is so great that it is fre¬ 
quently difficult to differentiate between the wind 
factor and radiation factor. This is illustrated in 
Figure 18, which gives R ' values for a clear day with 
low winds in each of the months of April, May, and 
June. The inversions at night intensify as the days 
get hotter and the humidity of the desert region de¬ 
creases. However, for the days chosen, the R' values 
under lapse conditions do not show the expected order. 

The region around Salt Lake is so mountainous 
that orographic factors are usually more important 
than frontal activity or cyclonic convergencies. How¬ 
ever, the air mass characteristics play an important 
role in determining the ground conditions. In the 
wintertime, high-pressure areas of stable marine 
polar air, or even continental polar air, prevail over 
Utah; subsidence occurs, wind velocities are low and 
smoke tends to accumulate in the valley in spite of 
the fact that nocturnal inversions are not so great as 
in the summer months. 


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14.9 MICROMETEOROLOGY IN WOODED 
AREAS 

14 . 9.1 General Considerations 

For the sake of simplicity, wooded areas are 
treated here as distinct from open country. Actually 
there is no sharp demarcation between open and 
wooded terrain. There is, in reality, a continuous 
gradation in vegetation from close-cut grass to dense 
jungle. And there is also a continuous gradation in 
the complexity of meteorological factors. The same 
general principles apply to the air over and in a forest 
as do in the open. In the forest, however, emphasis 
has to be placed on the character of the vegetation 
and the effects it imparts. 

The types and characteristics of wooded areas and 
their relation to climatic conditions will not be dis¬ 
cussed in this report. In this section, the role played 
by meteorology is treated in relation to wooded areas 
in general. It must be left to the individual to apply 
the principles stated in the following text to the 


particular type of forest where operations are planned. 
Furthermore, the following sections dealing with 
wind, turbulence, and temperature are intended to 
apply to forests on level terrain. Important effects of 
topography have been treated elsewhere. 

A great variety of vegetative covers can occur. For 
definiteness, remarks will be made with a particular 
type in mind; the effect of departures from this type 
can then be discussed. Consider a fairly dense jungle 
with a canopy of irregular height; the tops of the 
trees may be mostly at, for example, 30 to 50 ft. 
Suppose that there is a moderate amount of under¬ 
growth and that little direct sun reaches the forest 
floor even at midday. 

14 . 9.2 Wind Speed 

Wind Above and in Canopy 

The wind in the free air above a forest canopy has 
a somewhat reduced velocity because of the drag 


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231 



effect of the comparatively rough surface offered by 
the canopy. On passing from the free air down into 
the tops of the tree-crowns, there is a large and 
sudden decrease in wind velocity. The heavier the 
forest growth, the greater is the magnitude of this 
decrease. Some typical wind profiles in a forest are 
shown in Figure 19. 

Wind Under the Canopy 

The winds below the tree-crowns are usually in¬ 
duced by the overhead wind. Under given thermal 
conditions the relation between the forest wind speed 
and that of the overhead wind is controlled by the 
thickness of the canopy and the development of the 
undergrowth. Speeds of greater than 2 mph below a 
moderate to heavy forest-cover are relatively in¬ 
frequent. In fact, it is not uncommon to encounter 
speeds below mph, particularly at night time. 

Relation Between Winds Above and Below A 
Forest Canopy 

The wind near the floor of a forest (say at 2 m 
above the ground) is generally caused by the motion 
of the air above the trees. As the horizontal motion is 


WIND SPEED MPH HEIGHT ABOVE WIND SPEED MPH 

DAY GROUND-FT NIGHT 



Figure 19. Wind speed at various heights in forest. 


transported downward through turbulence, most of 
the energy of the wind is dissipated by the stationary 
obstacles in its path so that the speed near the 
ground is much less than that above. The thicker the 
foliage, the greater will be the difference in speeds. 


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TIME (LST) 

Figure 20. Wind profile record. 


In addition, this downward transfer of motion from 
above is affected by the thermal structure of the air 
in and over the trees. The question of air stability in 
a forest will be taken up later. It is sufficient to say 
that when the air is stable, the transfer of motion is 
curtailed. For a given overhead wind, the wind speed 
at 2 m will be less under stable conditions than under 
unstable conditions. When the air is unstable, verti¬ 
cal mixing is enhanced; hence, there is less tendency 
for the existence of a large vertical velocity gradient. 
Thus, if the wind overhead is constant day and night, 
it is to be expected that the winds in the woods will 
be generally lower at night than during the day¬ 
time. 

Under given stability conditions the wind speed in 
a moderately heavy jungle is nearly independent of 
the wind speed over the canopy if the latter is not 
over 5 mph. With higher wind speeds overhead, those 
in the woods increase and become more nearly pro¬ 
portional to those overhead. The jungle speeds are 
then roughly one-eighth of those overhead. 

The wind profile of a typical day in the San Jose 
Forest is illustrated in Figure 20. The heights are 2 m 
in the jungle, 16.5 m at the top of the canopy, and 
24 m above the canopy. Throughout the day the 
speed at 16.5 m closely follows the speed at 24 m. 
The speed at 2 m hardly follows even the peaks and 


troughs. Worth noting is the fact that while the wind 
speed above the jungle is greater than 10 mph, the 
speed in the jungle is only about 1 mph. In contrast, 
while the speed above the jungle is about 0.5 mph 
near midnight, the speed in the jungle is also 0.5 
mph. 

Figure 21 is a plot of the ratio: wind speed at 24 m 
divided by wind speed at 2 m vs the wind speed at 
24 m. It is apparent that the ratios measured with 
inversion conditions are well enough separated from 
those measured under lapse so that separate curves 
for average values may be drawn. The implication 
here is that the speed in the jungle is more dependent 
on the speed above the jungle under lapse conditions 
than under inversion conditions. Since there is more 
downward transfer of momentum under lapse, greater 
turbulence will also result under these conditions. 

14.9.3 Wind Direction 

The wind direction above a wooded area is gen¬ 
erally the same as in open terrain. 

Insofar as the wind below the canopy is caused by 
the overhead wind, the average wind direction inside 
a forest coincides with that above. The air move¬ 
ment, however, as a rule is much more irregular than 
that above. Hence, at any given instant the direction 


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233 



Figure 21. Effect of wind speed on R' for lapse and inversion. 


near the ground may be considerably different from 
the average. It is not uncommon for the slowly mov¬ 
ing air in a wooded area to execute two complete 360- 
degree changes in direction in the space of one 
minute. Moreover, at any moment the direction of 
winds at two points at the same level in a forest 
usually differ considerably. 

On clear days or on cloudy days with moderate to 
high overhead wind speeds, the wind directions in a 
forest fluctuate rapidly over a wide range because of 
the turbulent condition of the air. When there is a 
heavy overcast and low winds during the daytime, 
the fluctuations are more subdued. At night, espe¬ 
cially with clear skies and a low overhead wind, 
turbulence is at a minimum, and the direction ob¬ 
served at one point in the woods usually exhibits 
slow and random changes. 

This last mentioned situation seems to result from 
the wind in the woods being relatively independent 
of the wind above. It is presumed that the stability 
of the air under these conditions makes this possible. 
Apparently the air movement below the canopy is 
caused not so much by the transfer of motion from 


above as by effects such as the settling of cold air and 
uneven radiational cooling whose origins are purely 
local. There results, therefore, a low local wind which 
does not fluctuate rapidly and which is not necessarily 
in the same direction as the wind above the trees, but 
which gradually shifts as one local effect becomes 
more predominant than another. 

These effects are further indicated by Figure 22, 
which compares the frequency of the wind direction 
at 24 m (above the canopy) to that observed in the 
jungle. The fact that the daytime data show larger 
deviations in the directions than do the night data 
is consistent with the greater turbulence under lapse 
conditions. 

A comparison of the low- and high-wind speed 
traces from a hot wire anemometer is given in Figure 
23. Again, greater turbulence is to be noted for lapse 
conditions. 

An important exception to the above remarks 
about wind directions in woods at night is found in 
the remarkably steady winds on slopes. These 
katabatic winds have been discussed in preceding 
text in some detail. 


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GENERAL METEOROLOGICAL PRINCIPLES 



14.9.4 Forest Temperatures 

Temperatures in and Above the Canopy 

In the free air above the tree tops, conditions are 
much the same as over open ground with the tree tops 
taking the place of the ground surface for radiation 
purposes. The surface temperatures of living leaves 
in the sun are often 10 degrees F, or hotter than the 
surrounding air; and dried leaves can give larger dif¬ 
ferences. Accordingly, the canopy and the air above 
it undergo a diurnal variation with a maximum in the 
afternoon and a minimum before sunrise. Further¬ 
more, above the canopy, lapse conditions develop in 
the sunshine, and inversion conditions develop on 
clear nights just as they do over open ground. Some 


difference arises from the fact that the canopy does 
not show nearly so well defined a surface as the open 
ground ; the temperature gradients are consequently 
not so large in the air over the tree tops as over an 
open field. Again, the ground of an open field presents 
a solid obstruction while the canopy of a forest does 
not; air, cooled by open ground during an inversion, 
pools on the ground but when cooled by the cold 
leaves of a canopy it sinks down through the canopy. 

Temperatures Below the Canopy 
If the surface of the ground or of some low vegeta¬ 
tion lies under a heavy forest canopy and has little 
or no direct exposure to the sun or sky, then the sur¬ 
face temperature undergoes a smaller diurnal varia- 


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235 


DATE 

TIME 

AVERAGE 
WIND SPEED 
(2 METERS} 

GUSTINESS 

CHARACTERISTIC 

TEMPERATURE DIFFERENCE . °C 

"^24 M “ T I2M 
(ABOVE CANOPY) 

" r i2M “ T I.0M * 
(BELOW CANOPY) 

8-24-44 

1000 

0.5 M PH 

HIGH 

-0.9° (LAPSE) 

1.2° (INVERSION) 

8-25-44 

0100 

0.5 M PH 

LOW 

2.1° (INVERSION) 

-0.4° (LAPSE) 



Figure 23. Low and high gustiness wind-speed traces. 


tion than it would if the surface were exposed. In 
woods in Florida during May and June, the average 
daily range in ground surface temperature on clear 
days was only 16 degrees F while that of the grass in 
a nearly open area was 40 degrees F. A range of 
only 5 degrees F has been found in the jungle on a 
tropical island. 

Also, the temperature of a well-shaded surface does 
not depart greatly from that of the nearby air. For 
the Florida woods, the air was usually cooler than the 
ground surface at night and warmer in the middle of 
the day; but the difference was usually less than 
2 degrees F. 

Lapses and Inversions Under the Canopy 

In the open, inversions usually develop at night 
and lapses occur in the day. Under a fairly heavy 
canopy the reverse occurs; lapses develop at night 
and inversions occur in the day. This is illustrated by 
Figure 24 drawn from observations in a jungle on a 
small tropical island. For various times of the day 
and night there are shown two temperature differ¬ 
ences: one, Tmtt — Ttott, is the temperature of the 
free air well above the crown minus that of the air in 
the crown; the other, T 40 ft— Tift, is that in the 



Figure 24. Temperature differences in jungle between 
air above and in canopy; and between air in canopy and 
near ground. 


crown minus that of the air near the ground. Positive 
differences indicate inversions. 

Rapid changes in the temperature profile occur 
rather frequently under the jungle canopy. These are 
illustrated 23 in Figures 25 and 26. Thus, in Figure 25, 
a change from inversion to lapse occurs between 10 
and 13 m in a few minutes. These rapid changes are 
indicative of the vertical and horizontal motions of 
the air due to heating and cooling of the vegetation 
and it may be concluded that any single measurement 
of the temperature profile during the day may not be 
representative of the average condition. 


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GENERAL METEOROLOGICAL PRINCIPLES 



TEMPERATURE C 


Figure 25. Variation of jungle temperature profiles 

under uniform cloud cover. 

Thermal Instability in the Forest 

Although the inversions under a heavy canopy 
occur in the daytime, it is not to be concluded from 
this that day is the time of air stability in the woods; 
for at any one height in the crown, horizontal tem¬ 
perature differences with consequent circulation 
doubtlessly exist. 

To understand this daytime inversion, consider 
that when the sun strikes a forest canopy many 
leaves at the tree tops receive direct sunshine and are 
heated to temperatures distinctly greater than of the 
surrounding air. The leaves then warm this air. Be¬ 
low the tree tops, fewer leaves are exposed to the sun; 
if the canopy is fairly heavy, very few spots receive 
direct sunlight at the lowest levels. From the ground 
on upward into the canopy there is, then, an in¬ 
creasing number of hot spots with the result that the 
average air temperature increases from the ground 
well into the canopy. Although this is an average 
temperature distribution corresponding to an in¬ 
version, its manner of production by hot spots re¬ 
sults in convective turbulence. 

Similarly, on clear nights many leaves at the top 
are exposed to the sky; they radiate freely and be¬ 
come cooler than the surrounding air which is then 
cooled by the leaves. At lower levels, fewer leaves are 
exposed so that, on the whole, the air is cooler in the 
canopy than somewhat below it, that is, the tem¬ 
perature distribution here is that of a lapse. 

This simple picture requires modification in a less 
dense forest. If considerable sun is able to reach the 
forest floor at midday but not in the morning or after¬ 
noon, it can happen that there is a lapse near the 
groundat midday but an inversion morning and after¬ 
noon. If the forest is very thin, lapses by day and 
inversions by night may be expected somewhat as in 



Figure 26. Modification of jungle temperature profile 
by passing small clouds. 


the open. Evidently, within the woods, the knowledge 
that a lapse or inversion exists is of no value alone. 

14.9.5 Turbulence in the Forest 

From what has been said it is clear that thermal 
stability and turbulence in the woods cannot be 
estimated simply from average temperature gradi¬ 
ents. However, a good idea of the turbulence in the 
woods can be formed from a knowledge of the wind 
speed and temperature gradient above the canopy. 

If lapse conditions exist above the canopy, a tur¬ 
bulence of convective origin is present in addition to 
that due to canopy roughness. But, if an inversion 
exists above the canopy, even the turbulence of me¬ 
chanical origin tends to be damped out. Accordingly, 
with a lapse over the canopy, much turbulence is 
present which can, to a greater or lesser extent, be 
communicated through the canopy to the air below. 
With an inversion over the canopy there is relatively 
little turbulence present for communication to lower 
levels. 

The turbulence in the forest also depends on the 
speed of the wind. With a given size of lapse or in¬ 
version over the canopy, the turbulence below is 
least when the magnitude of the wind speed over the 
canopy is least. 

These relations are illustrated by Figure 27, which 
shows qualitatively the amount of turbulence (low, 
medium, or high) in the jungle of a tropical island 
under various conditions over the canopy. The 
turbulence was estimated from the fluctuations of a 
hot wire anemometer 6 ft from the ground. 

The figure shows that low turbulence in the woods 
is favored by low winds aloft (5 mph or less) and an 
inversion above the canopy. These conditions are 


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MICROMETEOROLOGY IN WOODED AREAS 


237 



0 2 4 6 8 10 

SPEED 30FT ABOVE CANOPY—MPH 

Figure 27. Turbulence under canopy. 


most apt to be found in the very late afternoon, night, 
or early morning. 

In addition to suppressing turbulence in the woods, 
an inversion over the canopy tends to seal gas or 
smoke in the woods, since by the inversion, an agent 
reaching the canopy is prevented from going further. 
However, with a lapse, any agent reaching the canopy 
is carried away in the upper air and lost to the opera¬ 
tion. 

If it is not possible to estimate the temperature 
gradient and wind velocity over the canop3q the same 
quantities estimated for a near-by open field may be 
used with some success. 

14.9.6 Low Canopy Jungle or Heavy Brush 

The San Jose project investigated the condition 
inside a heavy, low-canopy jungle. Measurements 
were made of wind speed at heights of 5 m (above the 
canopy) and 2 m (jnside the canopy). The following 
text is quoted from their results. 

The relationship between the winds at the 5- and 
2-m levels and the temperature profiles showed that 
the same general effects occur in a low- as in a high- 
canopy jungle, except that the effects are concen¬ 
trated over a much smaller height interval. In fact, 
the effects are intensified by the extremely heavy 
cover which at times produces effectively a second 
ground surface at the top of the jungle in typical 
areas. For example, between the free air and the 
jungle floor (a height interval of roughly 20 m in 
high-canopy terrain) a ratio of 8/1 is common for the 
wind speeds when the overhead wind is 6 mph. In a 
heavy, low-canopy jungle this ratio would be 12/1 or 
15/1 and the height interval would be only 3 to 5 m. 
Whereas a lapse or inversion of 1 degree C might be 
found in a layer 10 m deep over a high canopy, the 



WIND SPEED AT 5 METERS 'MPH 

Figure 28. Low canopy jungle. 

same temperature difference is possible in only 1 m 
over a low canopy because of the compactness which 
makes the top akin to a ground surface. 

As in the high-canopy jungle, it was found that the 
ratio of the wind speeds above and down in the low- 
canopy jungle depended on the overhead wind. 
Figure 28 illustrates this dependence. The ratios ob¬ 
tained with the higher overhead winds were inde¬ 
pendent of the time of day. All the low-wind ratios 
were obtained at night or in the early morning. In 
the daytime the ratios were generally so large that, 
unless the overhead wind were greater than 5 mph, 
the wind below the canopy was too light to be meas¬ 
ured with a cup anemometer (a wind with speed less 
than 0.5 mph). The shaded portion of Figure 28 
represents the region in which no definite speed could 
be assigned to the lower wind and hence no ratio 
determined. 

A further similarity between the high- and low- 
canopy jungles was found in the comparable situa¬ 
tions which exist in each at night with low overhead 
wind. This is the condition most favorable for the 


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GENERAL METEOROLOGICAL PRINCIPLES 


formation of inversions (provided it is not too cloudy). 
On a calm night, it is found that the air underneath 
the canopy is relatively independent of the air above. 
Its movement is not caused so much by the down¬ 
ward transfer of momentum from the air above the 
jungle as by the existence of drainage or gravity wind 
currents inside the jungle. Under such conditions, the 


ratio of the wind speeds can fall below unity. This 
effect was undoubtedly enhanced by the location of 
the low jungle station on a slope, where drainage 
winds are most likely to occur. On a flat region, it 
would be expected that, with a strong inversion 
above the canopy, the air underneath a low canopy 
would be stagnant. 




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Chapter 15 

MICROMETEOROLOGICAL INSTRUMENTS 

By Wendell M. Latimer 

INTRODUCTION 


15.1 

T he various micrometeorological instruments 
employed on Division 10 and CWS field projects 
are described in this chapter. While, in general, they 
proved adequate for the acquisition of the desired 
data, it is realized that many of them were developed 
rapidly under the stress of an emergency and can be 
further improved. In some cases it would have been 
desirable to make the instruments self-recording. 
This may be accomplished readily for permanent 
locations but is difficult for portable field equipment. 
The following instruments are described in this 
chapter. 

1. Anemometers. 

a. Magnetic cup anemometer, 

b. Mercury cup anemometer, 

c. British anemometer, 

d. Hot wire anemometer. 

2. Wind direction recorder, 

a. CIT-type vane, 

b. Commercial eight-point vane. 

3. Temperature apparatus. 

a. Aspirated thermocouple system, 

b. Aspirated resistance thermometer system, 

c. Surface thermometer system. 

4. Vanes for gustiness. 

5. Miscellaneous, 
a. Smoke puffer. 

. b. Photocell illumination recorder. 

c. Humidity measurement. 

6. Dugway portable recording system. 

15.2 ANEMOMETERS 

15.2.1 Magnetic Cup Anemometer a 

The anemometer is of the cup type with three cups 
rotating about a vertical axis (see Figure 1). The rate 
of rotation of the cups depends on the wind speed 

a This anemometer was developed by the Lane-Wells Com¬ 
pany of Los Angeles in accordance with requirements set forth 
by Contract OEMsr-861. Since it was the anemometer most 
widely used in the field experiments, it will be described in 
some detail. 



Figure 1. Anemometer and box ready for use. The 
cable from the anemometer is attached to the box 
through a weatherproof fitting. 



Figure 2. Diagram of wiring of anemometer, relay, 
and counter. 


but is independent of direction for horizontal winds. 
For each rotation of the cup system, a set of small 
electric contacts close and open a circuit once (see 
Figure 2). Through a relay, one count is registered 
on a counter for each rotation of the cup assembly. 


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240 


MICROMETEOROLOGICAL INSTRUMENTS 



SPRING BUSHING 

Figure 3. Cup and hub sub-assembly. 


By observing the number of counts recorded in a 
calibrated instrument in a measured lapse of time, 
the average wind speed over a given time interval is 
obtained.The instrument will operate at wind speeds 


varying from a little less than 0.5 mph to perhaps 
30 mph. The instrument has been left in the rain for 
days without having water reach the internal working 
parts. 


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ANEMOMETERS 


241 


The cup assembly rides on a jeweled bearing at the 
bottom and is guided by a circular Phosphor-bronze 
bearing near the top. The coupling between the rotor 
and the electric contacts is magnetic. The rotor shaft 
carries a horizontal semicircular segment of iron 
which moves under one pole of a permanent U-shaped 
magnet once for each rotation. In the field of the 
magnet is an armature supported in jeweled bear¬ 
ings. The armature carries one of the electric con¬ 
tacts and is moved a small amount on each approach 
of the iron semicircular segment. The armature is 
restored by a hairspring. 

If it is desired to record the indications of the 
anemometer, an appropriate chronograph pen may 
be connected in place of the counter. 

Since the cup assembly gives about 20 rotations 
per min per mph of wind (fewer at low speeds), direct 
counting by a chronograph pen may often be incon¬ 
venient. An auxiliary contact built into the counter 
makes it possible to record every hundred rotations 
instead of single rotations. 

Details of the Anemometer 

Cup System. The cup system is held on the rotor 
shaft by a spring bushing and is simply lifted off when 
the instrument is to be packed away. The cups are 
matched by weighing before assembling so that the 
rotor is carefully balanced. From one instrument to 
another the rotor dimensions are held closely similar; 
except at the lowest wind speeds, the calibration 
curves should be substantially the same for all 
instruments. 

The cups (Figure 3) are somewhat deeper than 
those of the British anemometer Meteor No. 4 but 
are otherwise the same and will interchange with the 
cup system of the British instrument. 

Rotor. Figure 4 shows the semicircular iron piece 
which is carried by the vertical rotor shaft. This 
drawing also shows the pivot point of the bearing on 
which the rotor stands. 

Upper Bearing. The shaft housing carries a circu¬ 
lar Phosphor-bronze bearing near the top. If this 
bearing is made too tight, the low-speed sensitivity of 
the anemometer is seriously impaired. The design of 
the instrument is such that dirt should not collect in 
this bearing too readily; but experience on this point 
is not extensive. The bearing is readily removable 
for cleaning; the bearing retainer at the top may be 
unscrewed and the bearing shaken out. 

Inner Case. This is a small housing which carries 
the shaft housing. The inner case is cut away on one 


side to permit interaction of the soft iron segment 
with the armature, and on the other side to permit 
the introduction of a compensating magnet. A rubber 
packing ring is placed on the beveled top of this 
housing for waterproofing purposes. 

Compensating Magnet. There is, naturally, a force 
between the U-shaped magnet and the semicircular 
iron piece which is carried by the rotor. This force 
might be expected to have some influence on the 
starting wind speed. With the idea of compensating it, 
a bar magnet has been mounted on a post on the 
opposite side of the rotor from the U-shaped magnet. 
Care must be exercised in selecting and placing this 
bar magnet; if the field from it is too strong, it can 
easily do more harm than good. 

Electric Contacts Subassembly. This assembly is 
shown in Figure 5. The base (1) carries the sub- 
assembly and is fastened by two screws to the outer 
case bottom. The upright piece (3) is screwed to the 
base (1) and carries the moving parts of the sub- 
assembly. The permanent U-shaped magnet is (4). 
The armature (11) is mounted on an axis (7) and 
rocks slightly when the soft iron swings under it. This 
axis moves in jeweled bearings; one of these bearings 
is rigid in the upright (3) and the other bearing (12) 
is adjustable. A restoring force is exerted on the 
armature by a hairspring (13); tension on this spring 
may easily be altered somewhat by rotating (8) about 
the axis. The purpose of all this is to move an electric 
contact; this is carried by the right-angled piece (10) 
which is rigidly attached to the armature axis. The 
stationary contact is carried on the upright (5) which 
is electrically insulated from the base by the bakelite 
piece (2). The upright (5) carries two screws which 
limit the motion of the contact carried by (10). One 
of these two screws is tipped with a platinum con¬ 
tact; the other screw is insulated from the upright 
and is simply a stop. (In later instruments these two 
screws have been interchanged from the positions 
shown in the working drawing. In these instruments 
the hairspring closes the circuit and the magnetic 
effect opens it.) 

External Electrical Connection. Within the instru¬ 
ment the electric circuit, when made, passes through 
the base, the hairspring, the contact, the upright (5), 
and a wire from (5). The circuit is brought to the out¬ 
side of the outer case through an Amphenol part No. 
CL-PCLM. This can be connected to the cable by an 
Amphenol part No. MC1F on the end of the cable. 
The other end of the cable attaches to a receptacle in 
the carrying case. 


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035 


242 


MICROMETEOROLOGICAL INSTRUMENTS 



DURAL EXCEPT WHERE INDICATED DIFFERENTLY 

Figure 4. Shaft and rotor sub-assembl. 


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ANEMOMETERS 


243 



NOTE: TO FASTEN 5 ON TO 2 USE I #1-72 Xr FH BRASS SCREW 
TO FASTEN 2 ON TO I USE 2 #1-72 x£' RH BRASS SCREWS 
TO FASTEN 3 ON TO I USE 2# 2-56X 1 i“F H BRASS SCREWS 

Figure 5. Contact sub-assembly. 


Accessories 

A wiring diagram showing the connections of the 
anemometer to relay, batteries, and counter is shown 
in Figure 2. 

The anemometer is connected through a small 3-v 
dry battery to the coil of a 2,000-ohm relay. Under 
these operating conditions the relay is extremely 
critical in its behavior toward adjustment; a small 
fraction of a turn of the screw controlling the relay 
hairspring makes the difference between operating 
satisfactorily and not operating at all. 

Across the coil of the relay is placed a 10-juf electro¬ 
lytic condenser. Without a large condenser, the con¬ 
tacts of the anemometer are very apt to stick and 
thus cause the instrument to cease indicating. 

The counter is one made by the Cyclotron Special¬ 
ties Co. It has a resistance of about 7,500 ohms and is 


actuated by a 45-v B battery. Although not impera¬ 
tive, a small condenser (0.1 juf) has been connected 
across the relay contacts through a 500-ohm resist¬ 
ance to reduce sparking. The carrying box is built 
to receive a standard-size B battery but not a heavy- 
duty battery. One end of the counter coil has been 
connected to the counter case and to the binding 
post marked BG. 

An auxiliary contact has been built into the 
counter which allows a second independent circuit to 
be closed every 100 counts. The terminals for this 
circuit are the posts marked 100 and BG. Any ap¬ 
paratus employing this feature is additional to that 
shown in the photographs. 

The box, which has been designed as a carrying 
case, in addition to holding the anemometer, relay, 
and counter, has compartments for the batteries, a 


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244 


MICROMETEOROLOGICAL INSTRUMENTS 




Figure 6. Diagram of alternative wiring arrangements. 


cable, and calibrations. The outer dimensions of the 
box exclusive of handle and clasps are 12^ x 10% 
x 8% in. The weight of the complete outfit includ¬ 
ing batteries is about 25 lb. 

Wiring Arrangements for Recording 

In the wiring diagram of Figure 2, the apparatus is 
arranged to give one count on the counter for each 
rotation of the cup system (case A of Figure 6). If it 
is desired to record by using a chronograph pen on a 
moving paper the connections may be made in any 
of the several ways shown in Figure 6. In these dia¬ 
grams the anemometer circuit is like that of Figure 2 
and has been omitted. The points labeled B, 1, 100, 
and BG are the similarly labeled binding posts. The 
necessary connections may all be made at the binding 
posts or at the wires connected to them without re¬ 
moving the panel on which the counter is mounted. 

In case B the chronograph pen is arranged to be 
actuated by the B battery of the anemometer and 
receives one impulse per rotation of the rotor. The 
counter is shown disconnected. The chronograph 
pen of some Esterline-Angus milliammeters can be 
actuated by 45 v; but this power supply may not 
be appropriate in all cases. 

In case C the B battery is again used for the 
chronograph but the chronograph receives only one 
impulse for each 100 rotations of the rotor. The 
counter is actuated once per rotation. If a chrono¬ 
graph is used with any except very low winds this 
arrangement or case E is desirable. 

Case D is similar to B except that an external power 
supply is used for the chronograph. 

Case E is similar to C but has an external power 
supply. 



Figure 7. Anemometer calibration for higher speeds. 
Calibration Curves 

Calibration curves which are typical of all instru¬ 
ments are shown in Figures 7 and 8. 

15.2.2 Mercury Cup Anemometer 

Another anemometer which is capable of measuring 
wind speed as low as 0.5 mph is the mercury cup 
instrument. 15 This principle is quite simple. With 
each revolution, two small curved stainless steel 
knife edges attached to the cup arms make contact 
with two mercury surfaces contained in small iron 

b This anemometer was designed and constructed on 
NDRC Contract 126, University of California. 


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ANEMOMETERS 


245 



rotations per MINUTE 

Figure 8. Anemometer calibration for low speeds. 

cups attached to, but insulated from, the shaft. The 
current from a 45-v dry battery actuates the me¬ 
chanical register. A schematic diagram is shown in 
Figure 9. The mercury contacts offer no detectable 
resistance to the rotation of the cups. This method 
was employed to replace a photoelectric counter and 
had the advantages of (1) simplicity, (2) no required 
vacuum tubes or amplifiers, (3) low voltage and cur¬ 
rent consumption, thereby making it independent 
of 110-v power supply. 

15.2.3 British Anemometer 

This instrument is the 3-cup type, the cups being 
5.4 cm in diameter and the centers of the cups being 
at a distance of 7.0 cm from the axis of rotation. In 
early models the counting mechanism consists of a 
high-grade stop watch, the lever escapement of which 
is operated indirectly by the rotation of the ane¬ 
mometer spindle. The train of wheels is driven by the 
spring of the watch and thus imposes no frictional 
load upon the anemometer. As a result, this ane¬ 
mometer will function accurately to wind velocities 
as low as 1 mph. The provision of a beaded edge to 
the cups ensures a nearly constant factor for the 
instrument. 0 In later models the stop watch mech¬ 
anism has been replaced by the more orthodox 

0 The design of this anemometer is due to P. A. Sheppard. 



Figure 9. Schematic diagram of mercury cup ane¬ 
mometer. 



Figure 10. Comparison of magnetic, mercury (Berke¬ 
ley), and British anemometer. 


direct drive to a train of gears, but careful design of 
the bearings has resulted in this instrument being 
practically as sensitive at low wind speeds as the 
earlier model. 

A comparison of the three anemometers was made d 
and is shown in Figure 10. The starting velocities of 
all three ranges between 30 and 40 fpm and the run- 
over or coasting rates are also comparable. 

d Contract NDCrc-137. 


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246 


MICROMETEOROLOGICAL INSTRUMENTS 


PANEL METER 



Figure 11 . Diagram of recording-type hot wire ane¬ 
mometer. 


15.2.4 The Hot Wire Anemometer 

The hot wire anemometer, because its sensitivity 
is greatest at very low wind speeds, was found to be 
the most useful instrument in the jungle where winds 
of less than 0.5 mph (the starting velocity for the 
cup anemometers) are common. 

The electrical circuit of the anemometer consists 
of a Wheatstone bridge, one arm of which is a short, 
fine wire (usually 50 in. of 0.003-in. Pt wire in the 
form of a bird cage) which is exposed to the wind. 
Through this wire is passed a given current, supplied 
by a storage battery, which causes the wire to heat. 
The wire will assume a certain temperature (and 
hence a certain resistance) when wind of a given 
speed blows by. The bridge is balanced with the 
anemometer covered; when the cover is removed, 
the resistance of the platinum wire will change by an 
amount corresponding to the wind speed. This 
causes the bridge circuit to be out of balance. The 
amount of this unbalance is measured bj r observing 
the reading of a milliammeter or by a suitable record¬ 
ing meter. A General Electric recording millivoltmeter 
was used for this purpose. A diagram of the circuit 
used in the San Jose work is given in Figure 11. 



ing. 

15.3 WIND DIRECTION RECORDERS 
15.3.1 The CIT-Type Vane 

This vane was designed and built at the California 
Institute of Technology [CIT] for the specific pur¬ 
pose of enabling the recording of wind directions at 
speeds of a few tenths of a mile per hour. This high 
sensitivity was made possible by the use of (1) light¬ 
weight materials, (2) circular knife edge and jeweled 
bearings, and (3) mercury contacts for the electric 
circuit. A diagram of the working parts of the vane 
is given in Figure 12. Omitted from the figure are the 
brass cover and collar which slip over the electrical 
part and protect it from the weather. A schematic 
circuit diagram is given in Figure 13. 

The electrical circuit of the vane is essentially that 
of a potentiometer. By means of a B battery, a 
potential difference is applied across the 10,000-ohm 
coil in the vane. A certain fraction of this difference, 
which depends on the orientation of the vane, is 
tapped off by a small drop of mercury which touches 
the coil, and which in turn is connected with the 
recording meter. The current passing through the 
meter, then, is a function of the direction in which the 


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TEMPERATURE APPARATUS 


247 


10,000-OHM COIL 



Figure 13. Diagram of electrical circuit of continuous 
recording vane. 


vane is pointing. By having a high resistance in 
series with the meter, the current is made practically 
linear with the direction. Thus, if south is selected as 
zero, then east will read 0.2, north 0.4, and west 
0.6 ma. The variable 7,500-ohm resistor in the circuit 
is used to adjust the proper maximum current which 
can flow through the meter. Since there is of neces¬ 
sity a gap of 15 to 20° in the vicinity of the switch¬ 
over direction (that direction corresponding to zero 
or the maximum current) the vane is set up so that 
the switch-over occurs at the direction, if any, which 
is least likely to be recorded. This keeps the record 
obtained from being confused and readings are kept 
away from that part of the scale which is least linear. 

This type of recording vane was used in the winds 
normally encountered in the open, with just as satis¬ 
factory results as in the light jungle winds. A smaller 
tail was generally installed when higher wind speeds 
were encountered. 

15.3.2 The Eight-Point Commercial Vane 

At more or less permanent installations, the wind 
directions at the 2-m height were recorded by means 
of two eight-point vanes. As originally constructed, 
the vanes were designed merely to indicate direction 
by causing lights to go on inside a panel. They were 
not at all sensitive to low winds because of the 
heaviness and poor balance of the vane assembly. 
However, by devising a lighter assembly quite similar 
in its dimensions and construction to the CIT-type 
vane (the CIT tails were used), it was found that 
these vanes could be made adequately sensitive to 
winds as low as 3^ mph. Instead of indicating direc¬ 
tions on a lighted panel, the nine leads from each 
vane (see diagram) were wired to eight coils of a 



TRANSFORMER BUILT 
INTO 20-PEN RECORDER 


Figure 14. Diagram of eight-point vane. 

twenty-pen recorder. A diagram of the electrical 
circuit is presented in Figure 14. These vanes were in 
operation for over two months without requiring any 
attention; the performance has been most satis¬ 
factory. 

15.4 TEMPERATURE APPARATUS 

15.4.1 Aspirated Thermocouple Systems 

The apparatus consists essentially of a hollow mast 
carrying the radiation shields, aspiration occurring 
through the mast itself. With it, temperature differ¬ 
ences between various thermoelements are read on a 
sensitive portable galvanometer. The apparatus is 
not recording but could be so modified. It was not 
designed for quantity production (only four have 
been made) nor for rough handling, although it is 
reasonably sturdy. It is, however, believed to give 
reliable results when properly used. 

Radiation Shields 

The radiation shields are the right-angled pieces 
attached to the mast as shown in Figure 15. They 
consist simply of the elbow (see Figure 16) of thin- 
walled tubing of 1-in. OD with an inner tube 

of the same material held in the vertical part of the 


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MICROMETEOROLOGICAL INSTRUMENTS 



SHELBY TUBING CHROME PLATED 
RADIATION SHIELD 



Figure 16. Diagram of radiation shield, 
elbow by small pieces of rubber. The exposed thermo¬ 
element is placed just inside the outer opening of this 
inner tube and is held in the center by light pieces of 
wood. These various pieces of rubber and wood must 
not be so large as to impede aspiration. 

The shields fit tightly into hardwood adapters 
which, in turn, slip over short open tubes protruding 
from the mast at appropriate levels. These adapters 


would be better if made of plastic. 

The wires from the thermoelement continue 
through the length of the shield into the adapter and 
emerge from a hole in its side. 

The type of shield shown here is a simplification of 
that used by A. C. Best. 1 The principal disadvantage 
compared with that of Best is the slight uncertainty 
as to the exact level at which air is being taken in ; 
experiments with smoke suggest that the uncertainty 
is not more than 2 or 3 cm. In addition to simplicity, 
the present shield has the advantage that the air 
examined strikes the thermoelement before striking 
any part of the shield. 

The Mast 

The free opening of the highest radiation shield is 
5 m from the ground. (Higher masts with the same 
construction could doubtlessly be used.) The mast is 
made of 3-in. No. 18 Shelby steel tubing (cadmium 
plated). To give portability, it is made in five sec¬ 
tions (see Figure 17); these fit together with the aid 
of end sleeves of 3-in. ID. The top section is closed at 
the top. The top section and the middle section are 
each provided with a loose ring carrying three eyes 


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TEMPERATURE APPARATUS 


249 



Figure 17. Diagram of 5-meter mast sections. 


for light guy ropes. The various sections are pro¬ 
vided with short side tubes to receive the radiation 
shield adapters. The heights provided by the mast 
are 5, 4, 3, 2, 1, 0.3, and 0.1 m; however, the side 
tube for a 4-m shield has never been used and might 
well be omitted. The bottom section of the mast fits 
into an L joint mounted on a base plate (Figure 18). 
The base plate is designed to assist in erecting the 
mast. The L joint receives a horizontal stretch of 
Shelby tubing leading to the aspirator. This hori¬ 
zontal member consists of two plain 1-m sections 
(not shown in the drawings); it is necessary that the 
aspirator be somewhat removed from any of the 
shields so as not to disturb the air around them. 

The base plate carries a hinged flap with two %-in. 
holes, shown at the top of Figure 18. Before the mast 
is erected, this flap is pinned to the ground through 
these two holes. After the entire mast with shields is 
assembled on the ground, it is erected by rotation 
about the horizontal axis of the hinge; a third pin is 
then placed in the ground through the base plate and 
the mast is guyed. 

Without moving the guys or base plate, the mast 
and the horizontal section leading to the aspirator 
may be rotated about the vertical axis of the mast. 


This is necessary so that the radiation shields may 
be kept up-wind of the mast, auxiliary apparatus, 
and observer in case the wind shifts. 

The Aspirator 

An ordinary aluminum household vacuum-cleaner 
blower has been found satisfactory for aspiration. To 
drive it, a 6-volt model locomotive motor No. 117-4 
was used, made by Kendrick and Davis Co. of 
Lebanon, New Hampshire. A blower with its motor 
is indicated in Figure 15 at the left end of the 
horizontal 3-in. tube. The motor was operated from 
a storage battery, but alternating current may be 
used if available. 

With the arrangement described, the radiation 
shields are found to be adequately and substantially 
equally aspirated. The air flow past the thermoele¬ 
ment is 1,200 fpm or more. The shields and their 
aspiration have been considered adequate if no 
significant temperature difference developed when 
two shields were placed side by side in the sun and 
a shadow was thrown on one shield. 

A squirrel-cage blower, No. 3, made by the L-R 
Manufacturing Co. of Torrington, Connecticut, can 


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MICROMETEOROLOGICAL INSTRUMENTS 



Figure 18. Diagram of base plate and L joint. 


easily be mounted so as to be used instead of the 
vacuum-cleaner blower. Although the squirrel cage 
blower would appear to be satisfactory, field trials 
have not been made with one. 

If it is desired to measure profiles through heights 
of more than 5 to 10 m, such as is the case if a profile 
is desired from the ground up through the tree 
crowns in a forest, it may be more convenient to dis¬ 
pense with aspiration through a mast and provide 
each junction with an aspirator at its own level. 

The Electrical System 

Single-junction copper Advance thermoelements 
were used. Number 20 wire was employed; and, at 
the junction, several turns of one wire were wound 
closely around the other and the whole soldered. This 
gave a junction of moderate heat capacity, which was 
desired since it was not the intention to follow mo¬ 
mentary temperature fluctuations. The arrangement 
of the various junctions is shown in Figure 19. Thus, 



Figure 19v Diagram of thermocouple system. 


there was one junction in the top radiation shield and 
two junctions in each of the other shields, so that 
temperature differences between adjacent levels were 
measurable. 

In order to obtain temperatures as well as differ¬ 
ences, one thermocouple had one junction in an aspi¬ 
rated shield (that at 0.1 m) and the other in a pointed 
copper piece inserted about 2 in. into the ground. In 
the copper piece was also placed a mercury ther¬ 
mometer graduated to 0.1 C and with its bulb in good 
thermal contact with the thermoelement. The soil 
temperature as given by this mercury thermometer 
was relatively steady. Aside from its own interest it 
afforded the basis of determination of the air tem¬ 
peratures. 

In the soil thermometer there was also one junction 
of a couple, the other junction of which was in a 
device to measure surface temperatures. This was a 
piece of heavy felt with a fine wire junction in its 
surface. The felt was mounted in a convenient handle. 
In use, the junction is pressed against the ground for 
a second or two and then moved to a new spot pre¬ 
sumed to be similar to the first. This is repeated as 
many times as may be necessary to obtain a constant 
reading. This procedure appears to give intelligible 
results in case the ground presents a reasonably well- 
defined surface on which to make measurements. 

Although not imperative, it is highly convenient to 


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TEMPERATURE APPARATUS 


251 


have all thermocouples built with the same resistance 
so that deflections on a galvanometer may be con¬ 
verted to temperature differences, using the same 
calibration for each couple. It was found convenient 
to build all thermocouples into a single waterproof 
rubber-covered cable with appropriate tapsdeading 
to each shield. (Thus, the top section of cable be¬ 
tween 3 and 5 nr contains only two wires, one copper 
and one Advance, with increasing numbers of wires at 
lower levels. The wires in the part of the cable leading 
to the galvanometer are all copper.) 

The electromotive force given by a copper Advance 
thermocouple is only 40 X 10~ 6 v per centigrade de¬ 
gree of temperature difference. Consequently, care 
must be exercised with the insulation to avoid the 
introduction of extraneous electromotive forces; and 
precautions must be taken to eliminate thermoelec¬ 
tromotive forces other than those due to the couples. 

The thermocouple cable leads to a set of switches; 
these are contained in the upright box at the left 
of Figure 15. (This box serves as a carrying case 
for all parts except the mast, which packs in the 
horizontal box.) Ordinary copper knife switches are 
used; attempts to replace these by a compact multi¬ 
selector switch have been unsuccessful because of the 
introduction of spurious electromotive forces pre¬ 
sumably originating at the silvered switch contacts. 
With the aid of double-pole single-throw switches any 
desired couple may be connected to the galvanometer. 

The galvanometer should be a low-resistance in¬ 
strument with as high sensitivity as is compatible 
with ready portability. A Leeds and Northrup gal¬ 
vanometer No. 2420B with enclosed lamp and scale 
has been found convenient. A galvanometer chosen 
to have adequate sensitivity for small temperature 
differences may give too large deflections with large 
temperature differences. Therefore, it is convenient 
to provide one or two shunts which may be quickly 
thrown in if desired; these may be chosen so that 
the factor for converting deflections into temperature 
differences is made a small integer and thus the ap¬ 
paratus is made substantially direct reading. 

Observational Procedure 

With the apparatus set up in the desired location, 
and with the radiation shields up-wind from the mast 
and the rest of the apparatus, the blower is started 
2 or 3 minutes before observations are to start. 
The zero position of the galvanometer is read with the 


instrument shorted through a resistor; this observa¬ 
tion is repeated frequently. A series of deflections is 
then read, starting with the 5- and 3-m junctions and 
proceeding down the mast, ending with the 0.1-m soil 
thermocouple. Because of fluctuations in the indi¬ 
vidual temperatures, the 'series is immediately re¬ 
peated. About 5 min are required to make four series 
of readings; thu$ any one temperature difference is 
measured four times at intervals of a little over one 
minute and the results averaged. Along with this 
group of observations, the mercury soil thermometer 
is read and, if desired, the soil-surface difference. 

15.4.2 Recording Resistance Thermometers 

A convenient method of measuring and recording 
a series of temperatures in order to establish the 
gradient in the atmosphere is by means of resistance 
thermometers. The temperature difference between 
two thermometers at different levels may be meas¬ 
ured by placing the resistance coils in the arms of a 
Wheatstone bridge. The unbalanced bridge circuit 
may be employed to operate a Leeds and Northrup 
Micromax, or the unbalanced potential may be regis¬ 
tered directly on a recording General Electric milli- 
voltmeter. The following is a description of the 
system employed on the San Jose program. Figure 20 
is a diagram of the circuit. There are ten pairs of 
arms, any two pairs of which can be connected by 
means of automatic rotor and base selector switches 
to form a bridge. T\ through T 9 are the arms whose 
resistance indicates the desired temperatures. They 
are coils of fine copper wire inserted in the aspirated 
shields at various levels from 0.3 to 24 m on the tower. 
When two of these arms form part of a bridge, a 
temperature difference between them will cause the 
bridge to be out of balance, and a potential difference 
proportional to the unbalance will be set up across 
the meter and recorded. T 10 is a coil of Manganin 
wire. Because of the low temperature coefficient of 
resistance of Manganin, a bridge formed with this 
arm and the one selected for the reference tempera¬ 
ture will be out of balance by an amount indicative 
of the actual temperature of the base thermometer. 
Either of the bottom two thermometers is used for 
the reference because the short period temperature 
fluctuations are smallest at these points. 

When in operation, the rotor switch is actuated by 
a synchronous motor in such a way that the bridge 


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252 


MICROMETEOROLOGICAL INSTRUMENTS 



circuit is changed every minute. A complete cycle, 
then, is made every 10 min. Each time a new circuit 
is made, the synchronous motor also causes the meter 
to make a mark on the record roll, thus permitting 
the separate temperature differences to be distin¬ 
guished readily. A sample record is given in Figure 21. 
A typical cycle with Ti as the reference thermome¬ 
ter will have the following sequences. First, when T i 
is in the circuit, the meter records the zero reading, 
because there is no potential difference across the 
meter. Then, with T 2 through T 9 succeeding one an¬ 
other, the temperature differences between each 
thermometer and Ti are recorded. Readings to the 
right of the zero indicate that that thermometer is 
warmer than T x \ to the left, cooler. Finally, when T X9 
is in the circuit, the actual temperature of Ti is 
recorded. After an open circuit, the cycle repeats 
itself. 

Certain of the important details of the electrical 
circuit will be mentioned below. Reference is made 
to Figure 20. The thermometers 7\ through T 9 are 
wound with No. 38 copper wire and have a resistance 
of exactly 5 ohms. Since the nine arms containing 


these thermometers must all have the same re¬ 
sistance, the leads to them are all of the same length. 
(At the tower station 40-m lengths were used.) 

The Tio is a 3-ohm Manganin coil. The ten resistors 
Ri are Manganin coils each with a resistance equal 
to the total resistance of its opposite arm. R 2 and R s 
are fixed and variable 500-ohm resistors, respectively. 
The resistances of the 10 arms on the left-hand side 
of Figure 20 are adjusted by means of the variable 
resistors to be exactly equal to one another and as 
close to 5 ohms as possible. The variable resistor R v is 
used to adjust the voltage applied across the bridge 
and the sensitivity of the scale. 

15.4.3 Surface Thermometers 

In general, the moving felt pad method of measur¬ 
ing surface temperatures was employed with either a 
thermometer or a thermocouple junction in the pad. 

A description of the San Jos6 project thermocouple 
system follows. 

An Advance copper couple of No. 32 wire was used. 
One junction was fixed on the bottom of a rubber 


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VANES FOR GUSTINESS 


253 



Figure 21. Diagram of a thermometer profile record¬ 
ing. 


disk which was attached to a wooden handle 4 ft long. 
The other junction was set in the handle of a ther¬ 
mometer which gave its temperature. A Leeds and 
Northrup low-resistance (25-ohm), high-sensitivity 
galvanometer was mounted on a portable stand and 
connected to the circuit at the end of 20-ft leads. 
Thus, while one operator recorded the galvanometer 
reading, another would apply the junction to various 
surfaces, reading the reference temperature occasion¬ 
ally. A schematic diagram of the assembly is given in 
Figure 22. 

15.5 VANES FOR GUSTINESS 

The British bidirectional vane is probably the most 
satisfactory instrument used to obtain gustiness 
factors. However, two other instruments were de¬ 
veloped and employed to a limited extent. One, de¬ 
signed at Berkeley, was a vane which consisted of a 
single lightweight weathervane with a single turn 
of No. 40 Chromel wire mounted on the rim of a 
bakelite disk attached to the stationary shaft. A 
brush is attached to and rotates with the vane. A 
suitable potential difference (depending on the de¬ 
sired sensitivity) is applied along the full length of the 
Chromel wire and as the brush rotates with the vane, 
the difference in voltage between the brush and one 



Figure 22. Diagram of a surface temperature measur¬ 
ing device. 


end of the Chromel wire is recorded on the moving 
chart of an Esterline-Angus recording milliammeter. 

The other, developed at CIT, is a bidirectional vane 
whose movements are registered by Cenco electric 
impulse counters. The shaft of the vane is mounted 
in brass gimbals, and on each of the two axes of the 
gimbals, brass wheels are mounted which turn with 
the axes. These contact wheels are slotted around the 
periphery, and the slots are filled with an insulating 
material. As the wheel turns, a sliding contact alter¬ 
nately makes and breaks an electric circuit and re¬ 
cords on the counters the magnitude of movement of 
the wheel, and, hence, of the vane itself. One wheel 
registers lateral movements of the vane and the other 
vertical movements. Each is slotted over one-half its 
circumference to make contacts so spaced that the 
attached counter registers once for each 3° movement 
of the wheel. A single slot is cut in the center of the 
unslotted portion of each wheel, and the orientation 
of the wheel and sliding contact is made in such a 
way that this slot breaks the contact whenever the 
vane is in a mean position. 


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254 


MICROMETEOROLOGICAL INSTRUMENTS 



Two sliding contacts are mounted 180° apart on 
each wheel, and each registers on a separate counter. 
One measures the total amount of deflection which 
the vane experiences and the other records the num¬ 
ber of times that the mean position is crossed. The 
four counters required are mounted in a conveniently 
transportable box. The gimbals are mounted on a 
brass tube which can be supported by a surveyor’s 
tripod, and from the tube a cable connects the con¬ 
tact points in the gimbals with the counter box. 

The British bidirectional vane was constructed 
after the design by Best. In his original paper Best 
gives the following discussion. 

The bidirectional vanes were constructed for this 
particular investigation and in their construction, 
special attention was paid to the following points: 

1. The vanes should be as sensitive as possible to 
light winds. 

2. The sensitivities in horizontal and vertical direc¬ 
tions should be as nearly equal as possible. 


3. The supports and chart holders should be ar¬ 
ranged to cause the least possible interference with 
the vane. 

4. The two vanes should possess similar charac¬ 
teristics. 

5. The vanes should be fairly robust in order to 
prevent accidental damage. 

The first two points were satisfied by making the 
vanes light, reducing the friction at the bearings to a 
minimum, making the moment of the pressure due 
to the wind about the axis as large as possible, and 
making the vanes symmetrical about their axes. Al¬ 
lowance was made for the third point by ensuring 
that the center of the vane should be at least five 
times the height of the chart holder above the base 
of the chart holder. 

A photograph of one of the vanes is shown in 
Figure 23. As may be seen, the actual vane was con¬ 
structed of stiff wire and balsa with a brass balance 
weight at the nose. The bearings were all point bear¬ 
ings, and stops were provided to prevent the vanes 
from being deflected too far in either direction. 
Suspended from the framework of the vane was a 
wire pen arm to the end of which was attached a 
small glass pen. Every movement of the point of 
suspension of the pen on the vane arm was repro¬ 
duced, to a close approximation on the same scale, 
on a chart which formed part of a cylinder having the 
same vertical axis as the vane. The glass pen was 
made by drawing out a piece of glass tubing and 
bending the fine end suitably. 

15.6 MISCELLANEOUS 

15.6.1 Smoke Puffer 

A simple and practical means for estimating wind 
speed and direction in the jungle without the use of 
elaborate recording instruments is by observing the 
travel of a small smoke cloud. The smoke from an 
H-C mixture is fairly satisfactory, but because of its 
heat, this smoke tends to tower in low winds. On 
mixing with moist air, titanium tetrachloride 
(TiCL) forms a cool white smoke. Figure 24 gives 
the essential features of a simple device which em¬ 
ploys this material to produce puffs of smoke which 
can be followed with ease for distances of 10 to 20 
ft through the jungle. A rubber tube of suitable 
length permits the operator to generate the smoke by 
“remote control.” 


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DUGWAY RECORDING INSTRUMENTS 


255 



Figure 24. Diagram of a smoke puffer bottle. 


15.6.2 Photocell Illumination Recorder 

The primary factors influencing the magnitude of 
the daytime lapse in a given area are: (1) the altitude 
of the sun, (2) the wind speed, and (3) the amount of 
cloud cover. The first two factors can be ascertained 
readily by direct measurement and from knowledge 
of the time of day, time of year, and the approximate 
latitude of the area under consideration. The amount 
of cloud cover, however, is a different quantity to 
handle, especially in a jungle, and when more or less 
continuous observations are necessary. An instru¬ 
ment which records a quantity related to the in¬ 
tensity of the solar radiation should yield data vary¬ 
ing with cloud cover. Such an instrument was de¬ 
signed and constructed at San Jose and installed at 
the tower station. It was essentially an electronic 
circuit which amplified the current of a photocell. 

The cell with vacuum tube and batteries was 
mounted in a waterproof box at the top of the tower, 
one side of the box being made of Plexiglas, a trans¬ 
parent plastic. A sheet of white celluloid, fixed in the 
horizontal plane, reflected the light from the sun, 
sky, and clouds through the window to the photocell. 
The current induced in the cell was amplified by the 
vacuum tube and then passed through long leads to 
a recording milliammeter at the instrument shack. 

15.6.3 Humidity Measurements 

Sling psj^chrometers were generally used to meas¬ 
ure relative humidity. A hygrograph may frequently 
be employed to follow general diurnal trends in the 
forest, although it is not accurate in detail because of 
shifting of the zero point. The dry bulb of the sling 
psy chrome ter was used regularly in some projects as 
a check against the temperature profile apparatus. 


15.7 DUGWAY RECORDING INSTRUMENTS 

15.7.1 The Selection and Plan of Operation 
of Field Micrometeorological 
Instruments 

\ 

The most usual practice in the testing of chemical 
warfare munitions from which a gas cloud is pro¬ 
duced is to function the munition in a selected area 
over which samplers are distributed in a known pat¬ 
tern. These samplers produce a record at each 
sampling point of the total Ct , the Ct produced within 
a given time interval, or of the time-concentration 
curve. 

These chemical sampling results are dependent on 
the characteristics of the munition, the influence of 
the agent on the natural air-flow pattern (for ex¬ 
ample, the gravity effect), and the air-flow pattern 
itself. The effect of the latter may be stated most 
simply in terms of a wind speed representative of the 
area, a wind direction representative of the area, and 
a temperature gradient representative of the area. 
The time interval involved is the same as that used 
in the chemical sampling. 

For preparing munition requirement tables as well 
as for the intercomparison of different munitions, it 
is evident that the accuracy requirements of the 
micrometeorological assessment are fixed by the ac¬ 
curacy requirements laid down for the chemical 
sampling; if it is desired that the chemical results be 
known to ±20%, then, for example, the tolerance of 
the wind velocity measurement should be selected so 
that it is found from a consideration of gas cloud be¬ 
havior that this amount of change in the wind veloc¬ 
ity will affect the Ct by not more than ±20%. 

The instrumental accuracy of the anemometers will 
ordinarily be much better than this, but because of 
the natural variations in wind speed over the target 
area, several anemometer locations may be required 
in order to fix the representative wind velocity within 
these limits, particularly if the sampling time is short. 
For the sake of increased accuracy, the instruments 
will frequently be located within the area considered 
dangerous to personnel; hence the instruments should 
be self-recording or remote-indicating. 

Similar considerations apply to measurements of 
temperature gradient, except that ordinarily this 
quantity is steadier and more nearly uniform over 
the target area than is wind velocity. For a desired 
accuracy of ±20% as reflected in the chemical 
sampling, the required accuracy in the measurement 


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256 


8i 


MICROMETEOROLOGICAL INSTRUMENTS 


of temperature gradient between 2 and 0.3 m turns 
out to be on the order of ± 0.05 degree C, for open 
terrain. 

Another variable micrometeorological factor, usu¬ 
ally observed if present, but not measured, is the 
presence of updrafts and downdrafts over the target 
area. Ordinarily the value of the micrometeorological 
data will be much enhanced by photographic and 
visual notes; an overall estimate of the weight, which 
should be given to the results of a particular field 
trial, can be given only after a review of all the ob¬ 
servations taken, preferably as soon as possible after 
the operation. 

Another closely allied objective of chemical war¬ 
fare meteorology is to enable the prediction of gas- 
cloud behavior at a given time and location, both for 
offensive and defensive purposes as well as for select¬ 
ing the optimum time at which to run field experi¬ 
ments. In this case the accuracy requirements are 
less strict than for most proving ground work, but 
it is desirable to collect long-period records from un¬ 
attended instruments, and to have them in such form 
that they may be quickly scanned without further 
treatment. 

15.7.2 A Representative Selection of 

Recording Instruments for Field Use 

The most satisfactory instruments covering the 
optimum ranges and fulfilling the above require¬ 
ments, as indicated by NDRC experience at Dug- 
way, consist of the following: 

1. For wind speeds from 1 to 15 or 20 mph: A light, 
contacting, 3-cup anemometer such as the Lane- 
Wells or Friez 339-L used with a relay-type frequency 
meter and an Esterline-Angus recording milliam- 
meter. 

2. For wind direction (down to about 0.3 mph): A 
wind vane with a potentiometer-type head, in con¬ 
junction with another Esterline-Angus recorder. 

3. For temperature gradient: Thermocouples 
mounted between the two selected levels (now usually 
0.3 and 2 m), aspirated (or if unaspirated, then 
proven by experiment to fulfill the desired accuracy 
requirements) and connected to a photocell galva¬ 
nometer-amplifier the output of which is recorded on 
a third Esterline-Angus recorder. 

4. For wind speed from 0 to 2.5 mph: A hot wire 
anemometer, the output of which is recorded by a 
less sensitive photocell galvanometer-amplifier with 
Esterline-Angus meter. 


The above instruments (with the exception of the 
hot-wire anemometer, for which a satisfactory design 
has already been described) have all been made bat¬ 
tery-operated and self-contained in weatherproof 
cases capable of being transported by vehicle over 
rough roads, of being handled and set up in the field 
by one operator, and of operating for several hundred 
hours without attention or significant change in 
calibration. 

Although the above instruments have been thor¬ 
oughly tested by actual use over a period of a year, 
and although they can be operated and maintained 
by selected enlisted men, and have in their operation 
entailed a tremendous saving in manpower where ex¬ 
tensive records were to be taken, in many cases the 
simpler hand-read devices will suffice, particularly 
for measurements of temperature gradient, surface 
temperature, and long-time averages of wind velocity. 

The wind speed recorder, 1 to 15 or 20 mph, has in 
particular shown itself to be a far more useful instru¬ 
ment than was first anticipated by properly evaluat¬ 
ing in the simplest manner the representative wind 
speed over an area. 

15.7.3 The Relay-Type Frequency Meter 
« 

The most satisfactory means found for recording 
wind velocity from a rotating anemometer consists of 
an Esterline-Angus milliammeter used with a relay- 
type frequency meter. This system presents the ad¬ 
vantages that (1) the record is immediately available 
without further treatment, (2) the record is not far 
from linear in calibration, (3) there is a choice of 
paper speeds ranging from % in. per hr to 3 in. per 
min depending on the purpose for which the record 
is required, and (4) that the records may be preserved 
in compact form in such a way that although any 
portion may be intensively studied, there is no 
further measuring or computation to be done. 

This type of circuit, shown in Figure 25, is re¬ 
ferred to 14 as a condenser discharge anemometer. It 
operates as follows: 

When the anemometer contacts are closed, the re¬ 
lay (see Figure 25) is energized and C\ is charged 
through the lower relay contact to essentially the full 
voltage of battery B. When the anemometer con¬ 
tacts are opened, condenser C\ discharges almost 
completely into the smoothing condenser C 2 (much 
larger than C i) and eventually the charge passes 
through the milliammeter. This process is repeated 
for every make and break of the anemometer con- 


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DUGWAY RECORDING INSTRUMENTS 


257 



Figure 25. Circuit diagram of a relay-type frequency 
meter. 


Figure 26. Circuit diagram of a keep-alive relay oscil¬ 
lator. 


tacts, the quantity of electricity transferred each 
time being equal to the V b X C h where V b is the 
battery voltage and C i is in farads. The current 
through the milliammeter is then equal to F X V b 
X Ci, where F is the number of anemometer contacts 
per second. 

Since the resistance of the milliammeter is fairly 
high, the voltage drop across the terminals T is an 
appreciable fraction of V b , and Ci will not be com¬ 
pletely discharged when the milliammeter shows a 
deflection. The exact formula relating I m , the current 
in milliamperes passing through the recording meter, 
to F is given below: 

1,000 Ci FV b 

m ~ 1 + C x F R m 

where R m is the meter resistance. 

The number of contacts per second corresponding 
to each successive mile per hour of wind speed can be 
obtained from the anemometer calibration curve; 
V b and Ci can then be so chosen that the resultant 
calibration curve (milliamperes against wind speed) 
is nearly linear and corresponds in some way to the 
lines on the chart paper. Since the anemometer will 
not turn at all below a threshold of to 1 mph, the 
zero of the milliammeter may be intentionally set a 
little to the right of the first chart line and then the 
uniformly spaced chart divisions will correspond 
quite well over the whole range to uniform steps of 
miles per hour. 

The smoothing condenser C 2 is chosen to be large 
enough so that each individual pulse from Ci will 
cause, even at the lowest wind speeds, only a tolerable 
wavering of the recording pen. A larger value of C 2 
will unnecessarily reduce the speed of response of the 
system, tending to give a weighted time average of 
the wind velocity over the past period of time. The 


overall speed of response of the system then depends 
on the response time of the milliammeter, the intro¬ 
duced time delay, and hence the number of contacts 
per revolution of the anemometer, and the relation 
between the moment of inertia of the anemometer 
cups and their effective area which is exposed to the 
force of the wind. 

Both the CIT model of the Lane-Wells anemometer 
and the Friez 339-L anemometer (preferably modified 
so that it gives two contacts per revolution) have 
proven satisfactory; the use of photocells with a 
faster-acting similar type of vacuum-tube frequency 
meter has also been used with the Biram anemometer 
with good field results and a somewhat faster speed 
of response. In practice, the Lane-Wells anemometer 
with its recording circuit will in a few seconds (de¬ 
pending on the wind speed) give a 50% response to 
an abrupt change in wind speed. 

15.7.4 The Keep-Alive Circuit 

Experience with the Esterline-Angus meters in the 
field has indicated that far more satisfactory records 
are obtained with them if, in addition to the meas¬ 
uring current, a small low-frequency alternating cur¬ 
rent is passed through the moving coil. This ‘‘keep¬ 
alive’’ current, just enough to cause the pen to 
tremble visibly, serves to make the pen continually 
assume its true equilibrium position; if it is not 
present the pen will not follow rapid fluctuations in 
the measuring current with a high degree of accuracy, 
and particularly at low paper speeds the pen will tend 
to move in jumps. 

The most economical way of obtaining this small 
alternating current, of a frequency of about 10 c, is 
by the use of a relay oscillator together with a small 
transformer, condenser system, or pair of batteries 


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258 


MICROMETEOROLOGICAL INSTRUMENTS 



Parts List for Recording Wind Vane Circuit 


12 Volt Model: 


Ri to Rs 


R9 to R24 


R 26 

B 


T 


75 ohm 1 watt carbon resistors (selected for uniform 
resistance). 

1000 ohm X A watt carbon resistors (selected for uni¬ 
form resistance). 

200 ohm 4 watt rheostat. 

Two 6 volt dry batteries in series (Burgess Uniplex 
No. 4F4H). 

Terminals to Esterline-Angus recording milliam- 
meter connected in series with 12,000 ohms or more. 


2 Volt Model: 


Ri to Rs 5 ohms each (see above). 

R9 to R 24 200 ohms each. 

R 25 15 ohm rheostat. 

B 2 volt charge-retaining storage battery. 

T Terminals to E-A meter connected in series with 800 

ohm wire wound resistor. 


Figure 27. Diagram of a resistor assembly with Friez 
363-C wind vane. 


controlled by the relay contacts. A simplified diagram 
of the shunt-type relay oscillator with transformer is 
given in Figure 26, and the explanation is as follows. 

When the battery B is first connected, condenser C 
is charged through resistance Ri and as soon as the 
voltage across C becomes high enough, the relay 
armature is pulled down and a pulse of current is 
sent through the transformer. When the connection 
at the upper contact is broken, however, the relay 
armature is not released immediately because the 


WIND VANE RESISTANCE 
ASSEMBLY (SCHEMATIC) 



Parts List for 12-Volt Wind Direction and Velocity Recorder. 

B1.B2 Burgess Uniplex No. 4F4H dry batteries. 

C 150 mfd 50 volt electrolytic condenser. 

Relay Advance No. 500 DPDT 6 volt, 1000 ohm coil. 

Ri 200 ohm rheostat. 

R 2 450 ohm 1 watt carbon resistor. 

R 3 R 4 10 ohm 1 watt carbon resistor. 

Rs 5000 ohm 1 watt carbon resistor. 

R« 1500 ohm 1 watt carbon resistor. 

R- 13,500 ohms total, wire wound. 

SWi SPDT toggle switch (ordinarily in position 1; for adjust¬ 
ing Ri to give standard deflection of wind direction 
meter, switch to position 2). 

SW 2 DPST toggle switch. 

SW3 Push-button type microswitch [for simultaneous actua¬ 

tion of chronograph pens (TP)]. 

Ti,T 2 Doorbell transformers, 110 volt to 10 volt, 60 c. 

Figure 28. Diagram of a circuit for 12-volt wind direc¬ 
tion and velocity recorder. 

current stored in C continues to flow through the 
relay coil. Since the air gap in the magnetic circuit 
is reduced when the armature is held down, the 
armature can be held down by a current considerably 
smaller than that required to pull it down initially. 
Finally the condenser current through the relay coil 


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DUGWAY RECORDING INSTRUMENTS 


259 


decreases sufficiently to allow the spring tension to 
release the armature, and the cycle can then be 
repeated. 

In practice it has been found that considerable 
experimentation is required to get a given type of 
relay to function dependably over long periods of 
time; the exact analysis of the action is complicated 
and there are numerous possible variations of the 
circuit. The time the relay remains in the open and 
closed positions depends on the capacity of C, the 
battery voltage, the relay resistance, and the adjust¬ 
ment of the spring and relay contacts. The inertia of 
the armature and the resonant frequency of the con¬ 
denser-resistance-inductance combination appear to 
have quite an effect on the stability of operation. 
When properly designed, however, the circuit ap¬ 
pears capable of giving year-long uninterrupted 
service from a dry cell. 

15.7.5 The Recording of Wind Direction 

Figure 27 shows a means of obtaining an indication 
of wind direction by a resistor assembly attached to 
a standard Friez 363-C wind vane. The eight con¬ 
tacts of the vane are made to indicate 16 steps of 
direction, 15 of them as successive steps in the 
milliammeter, and one as a single position about 
midway in the deflection. It has been found in prac¬ 
tice that the latter indication, although nearly the 
same as one of the other steps, causes no confusion 
in interpretation because the vane will not ordinarily 
turn abruptly through an angle of 180° without leav¬ 
ing an indication of the intervening directions, and 
this anomalous position can in any case be oriented 
away from the prevailing directions. 

Since the circuit is a modified potentiometric cir¬ 
cuit, the resistance of the contacts is unimportant, 
and a completely open contact will show zero voltage 
on the milliammeter; this indication is different from 
that of any wind direction. The use of a specially 


designed wind vane would reduce the bulk and weight 
of the apparatus, and light-friction units are now 
commercially available for changing a circular indi¬ 
cation into linear meter indication, with a negligible 
transition interval from low-scale to high-scale read¬ 
ings. \ 

15.7.6 Examples of Complete Circuits as 
Used in the Field 

Figures 28 and 29 show the complete diagrams with 
circuit constants of two field sets for recording wind 
direction and velocity. The 12-v model, containing 
two recording meters in one case, is too heavy for 
convenient transportation away from a vehicle, but 
has the advantage of being self-contained. It will 
record for a week without attention to the meters, 
and the self-contained batteries will give about 1,500 
hr of service before it is necessary to replace them. 


R-l 



Figure 29. Diagram of a frequency meter circuit for 
12-volt recorder. 


The 2-v model, using a charge-retaining lead-acid 
storage battery, will withstand temperatures far be¬ 
low 20 F, where dry cells would freeze and become 
unreliable, and contains only the recording meter for 
wind velocity; the wind-direction recording milliam¬ 
meter can be easily carried separately and attached. 
In all cases the milliammeters must be properly 
shock-mounted to withstand transportation. 


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Chapter 16 


BEHAVIOR OF GAS CLOUDS 


By Wendell M. Latimer 


6l.l INTRODUCTION 


T he normal objective in the use of clouds of non- 
persistent toxic agents is to produce casualties 
among personnel on or near the ground level. For 
that reason the greatest efficiency is obtained when 
the cloud remains close to the earth’s surface and the 
importance of the factors influencing atmospheric 
stability, discussed in Chapter 14, are obvious. In 
general, under inversion conditions, the cloud will 
travel along the ground with a minimum of vertical 
displacement, and casualty-producing dosages may 
be expected at great distances from the source; while 
under lapse conditions the large convection currents 
arising from the instability of the air near the ground 
will tend to lift the cloud and the efficiency will fall 
off rapidly with the distance from the source. 

The Chemical Warfare Service [CWS] is inter¬ 
ested in munition requirements for certain specific 
tactical objectives. In determining such requirements, 
it is generally necessary to know the dosages of toxic 
material which are set up by a given munition. The 
quantity of toxic gas which a man may breathe is 
proportional to the average concentration C of the 
gas and the length of breathing time t, or more 
exactly, 


Dosage 


f 


Cdt 


( 1 ) 


The value of this integral is generally referred to as 
the Ct value. The actual quantity of toxic material 
breathed also depends upon the rate of breathing 
which may vary from 15 to 50 1pm. This fact is taken 
into account in assigning lethal dosages, but the 
overall Ct value is the significant quantity used in 
assessing the munition efficiency. One unit often em¬ 
ployed for nonpersistent gases is milligram minutes 
per liter. This unit is 1,000 times as large as milligram 
minutes per cubic meter, the unit generally used. 

For a definite set of field conditions the efficiency 
of the munition is also governed by the area covered 
by a stated minimum Ct. Thus, for example, a bomb 
may give Ct values of at least 20 mg min per 1 over 
1,600 sq yd, and Ct values at least 3 mg min per 1 over 
10,000 sq yd. This is generally stated as Ct = 20 area 
of 1,600 sq yd (0.16 artillery square) and Ct = 3 area 
of 10,000 sq yd (1 artillery square). 


In some reports the integral of Ct over all areas is 
given and referred to as CtA. This quantity is of 
value in the comparison of relative bomb efficiencies, 
and also in calculating the overlapping of clouds in 
multiple bomb shoots. However, it has no particular 
military or tactical significance in itself. 

As indicated above, the atmospheric stability is a 
highly important factor in the efficiency of a gas 
cloud. However, the most important single factor af¬ 
fecting the dosage or Ct value is the wind speed. With 
a source of finite time which produces a cloud of a 
given diameter, the time of passage of the cloud over 
a point, and, therefore, the dosage at the point, is 
inversely proportional to the wind speed. With a 
source of infinite output time and definite rate of 
output, the dosage in a given time for a given weight 
of material is also inversely proportional to the wind 
speed, since the volume of air into which the material 
is injected is proportional to the wind speed, and 
hence the concentration of the material is inversely 
proportional to the speed. For clouds of finite size 
the effect of wind velocity upon the area of a given Ct 
value is more complicated, but for high winds the 
area is inversely proportional to the square or cube 
of the velocity. 

Other factors that affect the efficiency of gas 
clouds, in addition to atmospheric stability and wind, 
are gravity flow, turbulence and large eddies, and 
the nature of the ground surface, including roughness 
and vegetation. In this chapter the behavior of gas 
clouds with respect to these various effects is con¬ 
sidered. 

16.2 LINE SOURCES 

16.2.1 Open Terrain 

In the early use of gas in World War I the line 
source was frequently employed. The gas was re¬ 
leased from cylinders on a line from 1 to 5 miles in 
length and the time of emission was from 2 to 5 min. 
A steady, moderately high wind blowing toward the 
enemy positions was required. The moderately high 
wind reduced efficiency by the dilution effect, in¬ 
creased the turbulence, and was unfavorable for the 
existence of high inversion conditions. Thus the loss 
of gas in traversing the territory between the lines 


260 


SECRET 


LINE SOURCES 


261 



Figure 1. Concentration at 1-foot height 150 yards 
from source versus temperature gradient between 1 and 
6 meters. 


was very great and the method was replaced by muni¬ 
tions such as the Livens projector and chemical 
mortar which placed the gas directly on the enemy 
positions. However, considerable theoretical and ex¬ 
perimental work has been done on the travel of gas 
clouds from line sources. The well-defined character 
of the source has many advantages in controlling ex¬ 
perimental conditions, and in most cases, area sources 
may be treated as line sources; therefore knowledge 
of the travel of gas clouds generated at a line may be 
applied to many problems. For this reason the line 
source is considered in some detail. 

An extensive investigation was carried out in the 
Sacramento Valley of California on the concentra¬ 
tion of butane from a line source. Because of the very 
high inversion prevalent in this region, this study in¬ 
cluded the effect of atmospheric stability over a wide 
range of conditions. 



WIND SPEED RATIO (R) (2 TO I METERS) 

Figure 2. Concentrations at 1-foot height 150 yards 
from source versus wind velocity ratio between 1 and 2 
meters. 

The correlation of the concentration at the 1-ft 
level, 150 yd from the source (0.5 lb per min per yd) 
with the temperature gradient is given in Figure 1, 
and a similar correlation with the R values is given 
in Figure 2. The general dependence upon atmos¬ 
pheric stability is apparent and the conclusion may 
be drawn that both the temperature gradient and the 
wind gradient are satisfactory measures of the sta¬ 
bility. However, the correlation is slightly better with 
the R values. Although the wind velocities were 
mostly in the general range of 3 to 5 mph, a better 
correlation might be expected if the product of the 
concentration and the wind velocity were plotted. 
Such a plot against R is given in Figure 3. The points 
fall fairly well on the curve and the deviations may be 
ascribed to experimental errors arising from fluctua¬ 
tions in the wind. These fluctuations include both 
speed and direction, the latter being the more an¬ 
noying in line source experiments as the conclusion 
assumes that the wind direction remains constantly 
at right angles to the source. 


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262 


BEHAVIOR OF GAS CLOUDS 



Figure 3. Concentration times wind velocity against 
R. 


The surface of the ground was covered with grass 
2 ft high and partly bent over. As a result of this 
roughness the R values are higher by about 0.10 unit 
than the corresponding values over smooth ground. 
The value for neutral conditions (zero temperature 
gradient) is 1.23. Values of R above 1.45 are not 
generally experienced in regions of moderately high 
relative humidities. However, at this value of R the 
efficiency is some 4 or 5 times as great as that ob¬ 
tained for moderate lapse. At an R value of 1.8 the 
efficiency is 40 to 50 times the lapse value. 

In the preceding paragraph the word “efficiency’ 7 
is used to indicate the tendency of the gas to remain 
close to the ground and not to diffuse upward. It is 
to be noted, however, that if the gas settles to the 
ground in a thin layer, a person may be able to take 
steps to avoid the high dosages of the gas; for ex¬ 
ample, he may be able to stand or to hold his canister 
above the gas cloud. In this case, the efficiency (as 
used above) is not an indication of the true effective¬ 
ness against personnel. 

The temperature gradient for the gas clouds was 
determined over various heights, but the interval of 
1 to 6 m appears to give the most satisfactory corre¬ 
lation. Measurement of temperature at 0.1 m is sub¬ 
ject to larger experimental errors because of the 



Figure 4. Concentration against distance at 1-foot 
level. 


steeper gradient near the surface. In the same way, 
velocity ratios were obtained between various heights 
and there was some evidence that the ratio for 6 to 
1 m was more satisfactory than the generally em¬ 
ployed ratio of 2 to 1 m. 

Values for the horizontal and vertical gustiness 
were obtained. In general, under inversion conditions 
both components were small; there was no simple 
correlation with the gas concentration. 

The variations of concentration with distance are 
shown in Figure 4 for several R values at the 1-ft 
level. At a given wind velocity and source strength 



HEIGHT - FEET 

Figure 5. Variation of concentration with height. 


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LINE SOURCES 


263 


the concentration depends upon some inverse power 
of the distance, and this power is a function of R. 


C = 


k 


( 2 ) 


The theoretical treatment of the problem is dis¬ 
cussed later. 

Figure 5 shows the variation in concentration with 
height. Under high inversion most of the gas lies close 
to the ground. In fact, in the highest inversions 
studied in the Sacramento Valley, the stability was 
such that streamline flow was approached with 
almost no diffusion into higher levels. Under lapse, 
even at 50 yd from the source, the diffusion and tur¬ 
bulence are so great that the concentration gradient 
is small within the first 6 ft. 

The suggestion has been made that the travel of 
gas clouds should be related to the Richardson 
number 


Ri = 



( 3 ) 


o 

2 


< 

ce 

H 

2 

UJ 

o 


16 


12 


6 


4 


0 



0.050 0.100 0.150 

RICHARDSON'S NUMBER 


Figure 6. Concentration at 1-foot height 150 yards 
from source versus Richardson’s number. 


where g is the gravity constant; y the adiabatic lapse 
rate; T the absolute temperature; and u the mean 
wind velocity. A plot of concentration against the 
Richardson number, shown in Figure 6, gives no in¬ 
dication of any simple correlation. 

16.2.2 Forested Areas 

Each forested area is a problem in itself, depending 
upon the height of the vegetation and its density at 
various levels. A pine forest with a heavy canopy of 
interlacing branches and open (brush free) space 
below is quite different from a tropical jungle with 
tall trees intertwined with vines and thick ferns 
covering the ground. 

There are practically no data for line sources in the 
tropical jungle. Data for a typical pine forest were 
obtained but the problem was complicated by the 
existence of strong katabatic winds at night. The 
following experiments illustrate the cloud travel 
observed. 


Experiment 1 


Type, source, and strength 

Line 0.25 lb/min yd 

Wind velocity 1.70 mph 

1 2 

R 

0.99 

Temperature difference 

Tim — To-im Tom — Tim 

-1.8 to -2.4 -0.4 to -0.7 

(lapse) (lapse) 

Gas concentration, mg/1 
Distance 

100 yd 

Height 

1 ft 6 ft 10 ft 

0.02 0.02 0.03 


Experiment 2 


Type, source, and strength 

Line 0.25 lb/min yd 

Wind velocity, 1.10 mph 

1 


2 

R 

0.76 



Temperature difference 

Tim — To 

•im T<zm 

— Tim 


0.15 (inversion) 0.75 (i: 

n version) 

Gas concentration, mg/1 




Distance 


Height 



1 ft 

6 ft 

10 ft 

70 yd 

2.2 

1.5 

0.35 

100 yd 

1.7 

0.82 

0.16 

125 yd 

1.5 

0.52 


150 yd 

1.3 

0.65 

0.26 


The large difference between lapse and inversion conditions is due in 
part to “chimney effects” set up under lapse around openings in the can¬ 
opy. In the heavy brush type of forest in Florida and in typical tropical 
jungle the night and day values probably do not differ by more than a 
factor of 3 or 4. The inversion values given in experimental data are 
comparable t o the behavior with R = 1.35 in the open. 


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264 


BEHAVIOR OF GAS CLOUDS 


16.2.3 Beach Areas 

The behavior of gas on a beach area with a land 
breeze corresponds to that of a gas on any other land 
area with a similar wind. With a sea breeze, the be¬ 
havior for several hundred yards inland is modified 
by the character of the wind. In general, since no 
marked lapse or inversion conditions exist over the 
ocean, the behavior tends toward neutral conditions; 
however, considerable variation may be expected, 
depending upon the air-mass stability. On the Cali¬ 
fornia coast the sea breeze consists of warm air from 
the Japanese current which has traveled over the 
cold coast current. It has been thus cooled near the 
surface and has great stability and low turbulence. 
Rather fragmentary data obtained in this region 
indicate that under afternoon lapse conditions, gas 
cloud travel in the sea breeze is somewhat more 
efficient than under neutral conditions with a land 
breeze. 

16.3 BRITISH THEORY OF CLOUD 

TRAVEL FROM LINE AND 
POINT SOURCES 

The theory of cloud travel developed at Porton 
describes the travel of gas clouds from point and line 
sources with considerable accuracy. It is based upon 
sound theoretical reasoning and was supported by a 
fair amount of experimental data, especially under 
neutral atmospheric conditions. 

The basis of the theory is the assumption that the 
vertical eddy velocity w [, associated with a mass of 
fluid at time t, is correlated with the subsequent 
velocity w t '+ $ of the same mass at time t + £, by a 
correlation coefficient R This coefficient is defined as 

X 


R* 


M_y 

Vx + w'V 


(4) 


where X is a quantity independent of time and identi¬ 
fied with the kinematic viscosity of the medium and 
n is a dimensionless parameter given by the velocity 
gradient expression 




/ (2 - n) 


(5) 


where u is the mean velocity at height z. The param¬ 
eter n varies between 0 and 1. It has been shown that 
the scatter of a group of particles in a diffusing me¬ 
dium is given by 

T 


X 2 = 2 u' 2 


II 


Rtdi-dt , 


( 6 ) 


where X is the distance traveled by a particle in 
time T, and R$ is the same as defined in equation (4). 

Define the component velocities u, v, w, and mean 
velocities ii, v, w, and u = ii + u', v = v + v', 
w = w + w', and consider the instantaneous genera¬ 
tion of matter at a point in space by taking axes 
moving with the mean wind velocity u. The scatter¬ 
ing due to disturbances of mean energy u ' 2 , v' 2 , and 
w ' 2 along the three axes after time T is 

X 2 = 4= 2 V 2 f T f l R m dm , (7) 

Jo Jo 

and similar equations for Y 2 and Z 2 . Then, 

R((l) = (\+w) _ (8) 

and similar equations for R# V ) and v' 2 , and R& Z ) 
and w' 2 . One then obtains 

4 = i C 2 X (u T) 2 ~ n 


(9) 


r 2 - 1 

•y 


= hCl(V T) 2 ~ n 


4 = i C 2 Z tw T)‘ 


with 


Cl = 


4X n 


(u?y 

n \u 2 / 


( 10 ) 


(1 — n) (2 — n)u 

and similar equations for C 2 y and Cf. 

These are the basic formulas in the simplest form. 
To apply, assume C z independent of height. This is 
equivalent to regarding the lower atmosphere as one 
in which the mean wind velocity and gustiness com¬ 
ponents may be regarded as independent of height as 
far as such variations affect actual diffusion, but the 
variation of wind with height is actually used to 
determine the value of n. In other words, the slow 
variation of wind with height on this approximate 
theory is looked upon merely as an indicator of the 
degree of turbulence present. The method adopted is 
then to seek expressions for the density distribution 
which satisfy equation (9) and the equation of con¬ 
tinuity. 

The general solutions obtained are: 

For continuous point source, Q g per sec; X at 
(x,y,z ); x, downwind; y, across wind; z, vertical. 

Q 

exp 


X = 


T CyC z UX m 


[?(&©)] 


( 11 ) 


For continuous infinite line source, Q g per sec m. 

Q 


x = 


exp 


mm 


( 12 ) 


7 YC z ux r 

In all cases m = 2 — n. If the source is at ground 
level, all concentrations must be doubled to allow for 
ground reflection. 


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CLOUD TRAVEL FROM LINE AND POINT SOURCES 


265 



1000 2000 3000 

DISTANCE DOWNWIND (YARDS) 


Figure 7. Concentration from a continuous point 
source. British theory. 

It has been the practice of the British to measure u 
at 2 m, and to evaluate m from R values; that is, the 
ratio of u 2 meters/th meter- a Also since the components 
of gustiness vary roughly with R and u , average val¬ 
ues for these quantities are employed. The following 
tables give these values. 8 


Table 1. Continuous point source 1 lb per min ap¬ 
proximate concentration in mg per cu m on axis of cloud 
at ground level. 


Conditions for use of gas Unfavorable 

Moderate 

Favorable 

Value of R 

1.05 

1.13 

1.25 

Index of X 

1.85 

1.74 

1.60 

Wind velocity, mph 

10 

10 

5 

Distance downwind, yd 

Gas concentration 

100 

2.2 

14.0 

150.0 

200 

0.6 

4.0 

48.0 

500 

0.12 

0.85 

11.0 

1,000 

0.03 

0.26 

3.5 



Figure 8. Concentration from a continuous line 
source. British theory. 


Table 2. Continuous line source 1 lb per min yd 
concentration in mg per cu m at ground level. 


Conditions for use of gas 
Value of R 

Index of X 

Wind velocity, mph 

Unfavorable 

1.05 

0.93 

10 

Moderate 

1.13 

0.87 

10 

Favorable 

1.25 

0.80 

5 

Distance downwind, yd 

Gas concentration 

100 

130 

320 

1400 

200 

65 

170 

800 

500 

28 

76 

380 

1,000 

14 

41 

210 


grass about 1 in. long. To find the correction factor 
for any given site (allow 50 yd of representative ter¬ 
rain upwind), reading should be on a completely 
overcast day or night in a steady wind, preferably of 
about 10 fps (about 6 mph). The value over the 
standard surface should then be 1.15. If the observed 
value due to roughness is greater, for example 1.24, 
the correction factor may be found from Table 3. 


For other values of Q, u, and x , the concentration 
is: 

1. Directly proportional to Q. 

2. Inversely proportional to u. 

3. Inversely proportional to x raised to the index 
ofX. Graphical presentation of data for various values 
of R and u are given in Figures 7 and 8. 

Since R is also dependent upon roughness, ob¬ 
served values must be corrected to a standard condi¬ 
tion. This is taken as a close-cut grass surface, having 


Table 3. Correction factors in R for roughness. 


R (observed) 

Correction 

1.15 

0 

1.16 

0.01 

1.17 

0.03 

1.18 

0.04 

1.19 

0.06 

1.20 

0.07 

1.21 

0.08 

1.22 

0.10 

1.24 

0.13 

1.26 

0.15 


a The recent trend has been to evaluate the parameter R 
from other meteorological factors without reference to wind 
speed ratios. 


From this table the correction here is 0.13 and the 
value to be used is 1.11. The correction is composed 
of two parts: (1), a correction for additional drag, in 


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266 


BEHAVIOR OF GAS CLOUDS 


Table 4. Finite line source. Axial concentrations at 
distance x from a continuous source of width L expressed 
as percentage of concentration from infinite line source. 




R = 

1.07 


R = l.U 

1 

L yd 

50 

100 

500 

1,000 

50 

100 

500 

x yd 







100 

50 

93 

100 

100 

100 

100 

100 

100 

74 

94 

100 

100 

98 

100 

100 

500 

2*> 

44 

96 

100 

55 

82 

100 

1,000 

14 

26 

81 

97 

33 

59 

100 

5,000 

3 

6 

29 

51 

9 

18 

68 


R = 1.20 

R = 

1.25 

R = 

1.35 

L yd 

50 

100 

200 

50 

100 

50 

100 

x yd 








50 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

100 

500 

77 

97 

100 

95 

100 

100 

100 

1,000 

53 

87 

98 

76 

97 

95 

100 

5,000 

16 

30 

55 

27 

49 

44 

75 


this example 0.09; and (2) a correction for increased 
turbulence, in this case 0.04. 

The equations give concentrations for infinite time 
of emission and for infinite width of line sources. To 
correct for finite time and length of line sources, the 
following procedure is employed. 

1. To find the concentration from a line source 
continuous in time, but finite in length, multiply the 
value from the equation by the factor in Table 4 for 
the appropriate value of R, x, and L. Divide by 100. 

2. To find the concentration from a source which 
emits at a uniform rate for a finite time: (a) find the 
initial length (yards) z, by multiplying the wind 
velocity by the time of emission; (b) multiply the 
value from the equation by the factor in Table 5 for 
the appropriate values of R, x, and z. Multiply by 
100. This rule applies only if x is greater than z. 

3. For both finite length and time apply both cor¬ 
rections. 

Table 5. Finite time source. Mean (axial) concentra¬ 
tion over central portion of the cloud at a distance x 
from a source emitting for a finite time t, expressed as a 
percentage of the axial concentration from a correspond¬ 
ing continuous source. 




R = 

= 1.07 

R 

: = 1.14 

R 

= 1.20 

R 

= 1.25 

z* yd 20 

50 

100 

200 

20 

100 

200 

20 

50 

100 

20 

50 

100 

x yd 
50 

69 

88 

100 

100 

88 

100 

100 

94 

97 

100 

96 

99 

100 

100 

48 

71 

88 

100 

79 

96 

100 

89 

96 

97 

93 

97 

99 

500 

13 

30 

53 

75 

34 

84 

92 

62 

85 

93 

77 

91 

95 

1,000 

3 

17 

33 

56 

22 

71 

85 

43 

73 

87 

62 

85 

92 

5,000 

1 

4 

8 

15 

2 

28 

49 

13 

32 

55 

24 

50 

74 


* z = distance traveled by gas during time of emission = wind velocity 
yd per sec multiplied by time of emission (sec). 


16.3.1 The Gas Concentration Slide 

Rule 

In order to permit the rapid calculation of con¬ 
centration from given source strengths under various 
conditions and at various distances from equations 
(11) and (12), the British developed a special slide 
rule. 

The gas slide rule resembles an ordinary slide rule 
in that it consists of three parts, the stock, a slide, and 
a cursor. The graduations or scales are its special 
feature. 

The stock carries two scales, marked Scale A and 
Scale D. Scale A at the top gives concentrations in 
milligrams per cubic meter. Scale D at the bottom 
shows rates of emission of gas, either in pounds per 
minute (point source) or pounds per minute per yard 
(line source). The mixed metric and British units are 
adopted in order to agree with the units in general 
use for chemical warfare purposes. 

The center slide, which is rather wide, also carries 
two scales on its face. Scale B is toward the right and 
indicates distance downwind from the point of emis¬ 
sion (beam discharge). Scale C is towards the left and 
is the wind velocity at a height of 2 m. These two 
scales extend across the whole width of the center 
slide, being in the form of curved lines for Scale B and 
almost straight lines for Scale C. The reverse side of 
the slide carries a further two scales, Bi and Ci, which 
are the corresponding scales for a line source (that is, 
trench discharge). 

A seventh scale is engraved vertically on the cursor 
and refers to R, the ratio of the wind velocity at a 
height of 2 m to that at a height of 1 m. This scale 
reads from 1.05 at the bottom to 1.35 at the top. 

For detailed description of the operation of the 
slide rule and its application to various types of 
problems, reference should be made to the British 
manuals. 

16.3.2 Application of British Theory 

to Bombs 

Table 6 gives values of the concentrations which 
were calculated from the British theory for a single 
250-lb tail-ejection bomb for neutral (15-mph wind) 
and inversion (5-mph wind). The general method of 
treating the problem is indicated in the discussion 
following the table. 

Concentrations are at ground level. For a burster- 
type bomb, concentrations would vary from 1/20 to 


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CLOUD TRAVEL FROM LINE AND POINT SOURCES 


267 


Table 6. Gas concentration from a single tail-ejection 
250-lb LC bomb charged CG. 


Mean ground 


Distance 

axial cone 

Mean ground Width 

Time 

from 

Peak 

during 

cone over 

of 

of 

burst 

cone 

passage 

entire cloud 

cloud 

passage 

yd 

mg/cu m 

mg/cu m 

mg/cu m 

yd 

sec 


For R = 1.15; 

; 15 mph wind 



75 

* 

* 

20,000f 

25 

29 

50 

* 

* 

10,000f 

30 

30 

100 

5,800 

4,800 

3,800 

37 

31 

200 

2,200 

1,700 

1,200 

50 

34 

500 

500 

330 

230 

90 

42 

1,000 

150 

95 

60 

145 

53 

2,000 

30 

20 

12 

250 

74 


For 

R = 1.25; 

5.5 mph wind 



75 

* 

* 

62,000f 

22 

36 

50 

* 

* 

35,000f 

24 

37 

100 

26,000 

20,000 

18,000 

27 

38 

200 

13,000 

10,000 

8,900 

33 

40 

500 

8,500 

6,300 

3,300 

46 

45 

1,000 

1,500 

950 

670 

66 

52 

2,000 

450 

270 

180 

100 

65 


* Not estimated at short ranges, 
t Very approximate. 


1/4 of those given, depending on range. Figures given 
are for open-type country. The time of emission is 
taken as 20 sec. It is assumed that 130 lb of CG is 
rained down onto an area 40 yd downwind by 20 yd 
crosswind, from which it evaporates in 20 sec. The 
area source is treated as a line source across the 
center, emitting at the rate of 20 lb per min yd. Cal¬ 
culations are made by use of the concentration slide 
rule. 

To determine mean axial concentration at given 
distance from source, such as a bomb or shell which 
has a short time of emission: 

1. If Q is source strength per unit time, that is, gas 
content divided by the time of emission t, and T the 
time of passage of the cloud, 

mean axial concentration = 

Concentration from continuous point source of strength Q 
T 

The time T of passage of a cloud may be calculated 
by finding the width of the point source cloud at the 
given distance, dividing by the wind velocity, and 
adding t the time of emission. 

The assumed time of emission t for a Livens drum 
and for a 250-lb LC bomb is 30 sec, for a volatile 
nonpersistent gas. 

2. If the dimensions of the puff of gas from a single 
weapon are known, the concentration can be deter¬ 
mined by assuming that the cloud is identical with 


that part of the cloud from a continuous point source 
at a distance from its origin where the width is equal 
to the width of the puff. The concentration then de¬ 
creases with the distance in accordance with the 
usual curves for a continuous point source. 

3. Approximately, the yddth of a puff is one-half 
that of a cloud from a continuous point source, and 
its length equal to its width. The length of a cloud 
from a finite point source is obtained by taking the 
width (or length) of a puff and adding the initial 
dimension, that is, the product of wind velocity and 
duration of emission. From this value the time of 
passage of the cloud can also be found. 

Dugway Proving Ground gave the following com¬ 
parison of observed bomb data with the British 
theory. 

Dugway: 1,000-lb CG; lapse; R < 1.1; Wind < 1 ft per sec 
Distance, yd Ct observed Ct calculated 
40 2,380 2,200 

80 1,180 1,300 

120 304 810 

Targhee Forest; 1,000-lb CG; inversion; wind, 2.25 ft sec 
Distance, yd Ct observed Ct calculated 
50 9,800 1,200 

100 3,710 700 

150 499 500 

200 297 400 

While the agreement is very good in the open under 
lapse conditions, quite the reverse is true for inversion 
conditions in a forest. 

16.3.3 Discussion of British Theory 

The agreement between calculated and observed 
concentrations is excellent for moderate source 
strengths, especially under neutral and small inver¬ 
sion conditions. Because of the assumption that the 
velocity gradient is negligible in the diffusion process 
itself, there is considerable divergence between calcu¬ 
lated and observed values when R is above 1.45, but 
this is not serious since these conditions are seldom 
encountered. However, the application of the theory 
to clouds produced by large aerial bombs introduced 
serious difficulties. These arose because the theory 
neglected gravity effects and in the case of large 
aerial bombs the heavy clouds tended to flatten or 
“pancake” to a very pronounced extent. The weight 
of the clouds was due in part to the fact that the 
molecular weight of most of the agents was greater 
than the average molecular weight of air, and in part 
to the greater density arising from the cooling pro- 


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268 


BEHAVIOR OF GAS CLOUDS 


duced by the rapid evaporation of a large quantity of 
liquid. This effect also greatly enhanced the stability 
of the ground layer. It could be said that the large 
gas bomb tended to create its own meteorological 
conditions, and these predominated over the first 
hundred yards or more of the cloud travel. 

In addition to the unsatisfactory handling of the 
large bomb problem, the original British approach had 
certain practical difficulties. For example, the exact 
measurement of the wind velocity gradient is diffi¬ 
cult, especially at velocities below 1 mph, since in this 
range none of the common cup-type anemometers 
are accurate. In addition, with katabatic or gravity 
winds, which generally occur at night on hillsides, the 
ground air velocity may be even larger than the 
velocity at higher levels, thereby giving R values less 
than unity, which are difficult to correlate. Also the 
corrections for the roughness of the surface, that is 
vegetation, are large and are often impossible to make 
accurately. Inside a forest or jungle both the tem¬ 
perature gradient and the velocity gradient are gener¬ 
ally small, and show little variation with lapse and 
inversion, although there may be considerable varia¬ 
tion in cloud travel under the two conditions. Finally, 
the efficient use of the relatively complicated British 
manual requires an extensive training program. In 
the rapid development of an army from civilian per¬ 
sonnel, which occurred in the American Army in 
World War II, such a training program would have 
been very difficult. 

16.4 CLOUDS FROM CW BOMBS 
16.4.1 Gravity Effects 

Upon impact, the explosive force of the burster 
causes the liquid filling of a nonpersistent agent to be 
dispersed as small droplets. Most of these vaporize in 
the air, but a small amount of the liquid reaches the 
ground and under temperate conditions vaporizes 
immediately. The normal crater loss is very small 
with CG or CK but, in the case of AC, an appreciable 
amount of liquid remains in and around the crater. 

The concentration of gas in the initial cloud varies 
from 15 to 50 mg per 1 or higher, depending upon the 
size of the bomb, the weight of burster, and the thick¬ 
ness of the bomb case. If the weight of agent, CG for 
example, is 20 mg per 1, the increase in density of the 
air is about 14 mg per 1, taking into account the rela¬ 
tive molecular weights of phosgene, 98, and air, 28.8. 
The heat of vaporization of CG is 60 cal per g, or 1.2 


cal for 20 mg. The specific heat of air is 0.3 cal per 1. 
Hence the vaporization of 20 mg per 1 would produce 
a cooling of about 4 C. If the initial temperature were 
20 C where air has a density of 1.2046 g per 1, the 
final temperature would be 16 C, with a density of 
the air of 1.2213 g per 1. This represents a gain of 
about 17 mg per 1 in weight, neglecting the heat 
liberated by the explosion of the bomb. 

Thus, the air in the gas cloud is heavier by 14 mg 
per 1 because of the greater molecular weight of the 
phosgene and by 17 mg per 1 because of the cooling 
effect. In other words, the two effects are approxi¬ 
mately the same for CG. For CK the two effects are 
also of the same order of magnitude, but for AC the 
molecular weight is about equal to that of air and the 
increased weight of the cloud is due to the cooling 
effect alone. 

The heavier gas cloud tends to fall or pancake 
under the force of gravity and the rate of fall is pro¬ 
portional to the square root of the difference in den¬ 
sity and to the square root of the initial height of the 
cloud. 



Figure 9. Cloud diameters against time after burst. 

Figure 9 7 illustrates the increase in diameter of the 
cloud in the first 60 sec after the burst due to the pan¬ 
cake effect. Figure 10, from the same report, gives a 
comparison of the concentration of gas and tempera¬ 
ture of the cloud. 

The initial height of the cloud depends to some 
extent upon the hardness of the ground; with very 
soft ground the bomb tends to bury itself and the 


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DATA ON CLOUDS FROM SINGLE BOMBS 


269 



+3 


TIME FROM BURST IN MINUTES 

Figure 10. Comparison of temperature and CG concentration in the gas cloud. 


gas cloud is shot upward to a greater height. In the 
open, the final height of the cloud is usually around 
10 ft, but with low wind velocity and high inversion 
it may drop to as low as 2 ft. 

The gravity effect in heavy jungle was studied by 
the San Jose Project on the 1,000-lb M79 bomb. 14 The 
following conclusions can be drawn. 

1. The burst cloud radius, with either CG or CK 
and static burst, is between 35 and 55 ft (average 
about 50 ft). 

2. The pancake cloud radius of the bomb is be¬ 
tween 80 and 100 ft. The time required for the gas to 
reach this distance is approximately 30 sec. 

3. Sixty seconds after the burst at a radius of 90 
ft, most (80%) of the cloud was below the 18-in. 
level. 

On the basis of mathematical theory 24 the gravity 
spread of heavy gas clouds has been discussed. 

The equation of motion of the cloud along the 
ground in the initial stages where friction may be 
neglected is 


f-m 

dt 


f; 


b 

+ -x 
a 


4 , . 
' 2a? X 


(13) 


where b is the initial radius; (3 the radius at time t; 
x = (3/b; a the initial height; and B is given by an 
expression involving the density of the cloud and the 
surrounding air pi and p 2 , respectively, and of the 
acceleration of gravity g, 


B = 


t 


15 0 (pi ~ P 2 ) . 
16 pi a 


(14) 


Neglecting friction, the terminal velocity would be 


dp 

dt 



For the slowing-down process, it is assumed that 
the frictional conversion of kinetic energy into heat is 
approximated by the case of flow between two par¬ 
allel plates, 

t ^ = V2aBe-“ m <- bM ’ 3 (16) 

dt 

where / is the dimensionless friction factor. From 
these equations calculations have been made giving 
the gravity spread which are in reasonable agreement 
with experimental observations. 

Under inversion conditions and at low wind veloc¬ 
ities the effect of gravity flow is very pronounced in 
large clouds even after the initial pancake effect. 
This is especially true in heavy forests. This point is 
discussed 17 and on the basis of data obtained on the 
San Jose Project, the conclusion was drawn that “a 
slope of 6 degrees is sufficiently steep to cause the 
gravitational force of the relatively dense cloud re¬ 
leased from a single 1,000-lb M79 bomb of CK or 
CG to predominate over a 0.5-to 0.7-mph wind in 
determining the movement of the cloud during its 
early stages in this jungle.” As a consequence clouds 
under these conditions tend to follow the natural 
course of the watershed and dosages are extremely 
high along stream beds. 

16.5 DATA ON CLOUDS FROM 
SINGLE BOMBS 

16.5.1 Open Terrain 

Dugway has studied the behavior of the 1,000-lb 
M79 T2 bomb in a large number of single shoots. 
Unfortunately the experiments were not planned to 
cover all ranges of wind speed and stability and in 


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270 


BEHAVIOR OF GAS CLOUDS 


some cases the sampling data were erratic. However, 
approximate values can be given for the behavior of 
clouds from these bombs and these data are sum¬ 
marized in Table 7. At a wind speed of 1 mph the 


Table 7. Data on 1,000-lb bombs charged approxi¬ 
mately 410 lb CG.* 


Area, Ct = 

1, in artillery squares per bomb 


Wind speed, mph 

1 

2 

4 

8 

Strong inversion 

21 

10 

4.5 


Moderate inversion 

16 

7 

3 

1.4 

Neutral 

11 

5 

2 

0.9 

Lapse 

3 

1.8 

1.5 

0.9 

Area, Ct = 

3, in artillery squares per bomb 


Wind speed, mph 

1 

2 

4 

8 

Strong inversion 

14 

6 

2.9 


Moderate inversion 

10 

4.5 

2.0 

1 

Neutral 

6 

3 

1.5 

0.7 

Lapse 

2 

1.5 

1.0 

0.6 

Area, Ct = 

30, in artillery squares per bomb 


Wind speed, mph 

1 

2 

4 


Strong inversion 

1.5 

0.8 

0.3 


Moderate inversion 

1.0 

0.4 



Neutral 

0.5 

0.2 



Lapse 

0.3 

0.1 



Maximum Ct on axis of cloud 



Wind speed, mph 

1 

2 

4 

8 

Strong inversion 

120 

60 

30 


Moderate inversion 

100 

50 

25 

8 

Neutral 

70 

32 

12 

5 

Lapse 

60 

30 

10 

3 


* Values for 18-in. height. 


area covered by (Ct = 3) varies from about 16 artil¬ 
lery squares (16 X 10 4 sq yd) for high inversion to 2 
artillery squares for lapse. At low wind speeds the 
area under inversion conditions decreases inversely 
proportionally to the speed to the first power but at 
higher velocities the decrease corresponds to a power 
between 1 and 2. The length of the (Ct = 3) area 
under inversion conditions may be 500 to 600 yd. At 
a distance 100 yd from the source, the width is about 
100 yd at low wind speeds, and increases to about 
200 to 300 yd downwind to give an egg-shaped area. 
With high winds the width is somewhat less. Under 
lapse with low wind the cloud tends to rise with very 
little spread. Higher wind speeds break down the 
lapse conditions and this operates to hold the cloud 
down to the ground and increase the dosage area, and 
thus counteracts the effect of the shorter time of 
passage. For this reason the area covered by (Ct = 3) 
does not change so much with wind speed under lapse 
as it does under inversion. These effects are illus¬ 
trated in Figure 11. 




HIGH INVERSION WIND 4 MPH 


1 


100 YDS 


LAPSE 



a 


LAPSE WIND 4 MPH 


Figure 11. Areas for single 1,000-lb bombs charged CG. 


For low wind speeds the areas covered by various 
Ct values are roughly proportional to the square root 
of the Ct values: This relationship obviously breaks 
down for greater wind speeds, as the time factor be¬ 
comes so small that the product Ct never attains the 
higher values. 

The concentration of gas in the initial cloud is in¬ 
dependent of meteorological conditions, so that at 
winds of 1 mph it might be expected that the Ct of the 
impact area would be constant for lapse and inver¬ 
sion. However, under inversion the cloud sinks to a 
lower level and the actual concentration is probably 
about twice that obtained under lapse condition. 

Experiments on other fillings besides CG include 
CK and AC. In general the Ct values are propor¬ 
tional to the weight of agents per bomb. For CK the 
results are about equivalent to CG. For most of the 
shoots the weight of CK was 360 lb per bomb as 
compared to 406 to 430 lb for the CG; this difference 
in weight was not reflected in the Ct areas obtained. 
For AC the filling was 215 to 240 lb per bomb, and the 
area for (Ct = 3) was about half that obtained with 
the same bomb charged CG under similar conditions. 


16.5.2 Results on 500-Lb Bombs 

The data on 500-lb bombs are not very complete 
since the rather brief field experiments have been 
carried out on various bomb types with widely vary¬ 
ing weights of charge. The results seem to indicate 
that, per hundred pounds of agent, the areas for low 
values of Ct are slightly greater for the smaller bombs, 
but that the areas for large values of Ct are less. 


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DATA ON CLOUDS FROM SINGLE BOMBS 


271 


16.5.3 Results on 2,000- and 4,000-Lb 
Bombs 

The experiment on one 2,000-lb T2 bomb charged 
822 lb of CG gave an area covered by (Ct = 3) of 15 
artillery squares under high inversion and wind speed 
of 2 mph. The corresponding value for a 1,000-lb 
bomb charged 410 lb of CG from Table 7 is 7 artillery 
squares. Thus the areas appear to be proportional to 
the weight of charge. The same is true for areas of 
(Ct = 3) for the 4,000-lb bomb M56 charged 2,341 lb 
of CG. Thus under neutral conditions and 4.6 mph 
the observed area was 9.4 artillery squares, which 
may be compared with the value of 1.5 from Table 7. 
However, the maximum Ct values observed were con¬ 
siderably higher than the values for 1,000-lb bombs. 
For a 2,000-lb bomb with wind speed 1.9 mph and 
neutral conditions the maximum Ct recorded was 48. 
The corresponding value for the 1,000-lb bomb is 
about 35. A 4,000-lb bomb, lapse conditions and wind 

11.4 mph, gave a maximum of 43. Under the same 
conditions a 1,000-lb bomb would probably give a 
maximum Ct of about 2. 

16.5.4 Multiple Shoots— Bombs in Line 

The Dugway reports give data on two field experi¬ 
ments with six 1,000-lb bombs charged CG. The 
bombs were placed at 100-yd intervals crosswind and 
fired statically. The following comparison gives the 
observed areas for various Ct -values and six times the 
value for a single bomb under similar conditions. The 
meteorological conditions were high inversion with 
wind speed 2.6 mph. Areas are in artillery squares. 


Ct mg min per 1 

6 bombs in line 

6 X single bomb 

1 

119 

58 

3 

96 

34 

5 

85 


10 

57 

27 

30 

2* 

4 

Maximum 

59 

50 


* Value low, probably sampling error. 


It is observed that the reinforcement given by the 
merging of the clouds tends to increase the areas of 
low Ct values by a factor of 2 or 3. Little reinforce¬ 
ment occurs over the target area and the maximum 
Ct remains approximately the value for a single bomb. 
Under lapse conditions the distance of cloud travel 
decreases and the diminished effect of the reinforce¬ 
ment tends to make the total Ct areas more nearly 
the value for six single bombs. 


16.5.5 Multiple Bombs Over Area 

Dugway carried out 6 shoots using in each 11 to 
41 of the 1,000-lb bombs on area targets. Unfortu¬ 
nately, none of the experiments was under high in¬ 
version conditions. Table/ 8 summarizes the results 
on three of these trials. 

These results indicate that for (Ct — 1) and 
(Ct = 3) the multiple shoots under lapse or neutral 
conditions gave about the same area per 100 lb of 
agent as observed for single bombs. For low inversion 
the efficiency was about 2 or 3 times that of a single 



Figure 12. Ct areas for 41-bomb shoot of M79 bombs, 
charged CG + 5 per cent NO 2 . 


bomb due to the reinforcement of the cloud from one 
bomb by adjacent clouds. In the 41-bomb shoot a 
large area was covered by (Ct = 50) which is a greater 
dosage than could have been obtained from a single 
bomb under these conditions. Figure 12 gives the Ct 
contour map obtained for this shoot. 

16.5.6 Variation of Dosage with Height 

From the previous discussion of gravity effects in 
clouds from large bombs, it follows that the pan¬ 
caking of a cloud under inversion conditions and low 
wind results in large concentration gradients. For 
good inversion, Dugway states “the dosage at 5 feet 
is only about 30-40 per cent of the dosage at 18 inches 
as determined as the average of a large number of 
measurements. Under neutral conditions this per¬ 
centage is between 50 and 75 while under lapse it is 
still higher.” Downwind dosages at 18 in. and 5 ft 
become nearly identical under all conditions. 


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272 


li 


BEHAVIOR OF GAS CLOUDS 


Table 8. Summary of Dugway results on area targets with 1,000-lb bombs. 


No. of 
bombs 

Wt of 
agent, 
lb 

Wind 

speed, 

mph 

R 

Tun— 

To-im 

Area covered by 

various dosages Ct at 18 in., 
artillery squares 

in 

Area 

of 

Average 
Ct over 
impact 
area 

1 

3 

5 

10 

30 

50 

impact 

12 

5,136 

2 

1.45 

+ 1.4°(I) 

64 

53 

43 

29 

11 

4 

12 

37 

12 

5,148 

4.8 

1.2 

— 1.0(L) 

40 

26 

20 

15 

2.3 

<1 

12 

18 

41 

17,163 

3.3 

1.4 - 1.7 

N to I 

>332 

>266* 

>216 

155 

28 

14 

16 for f 

32 bombs 

40 


* Cloud off target area, value estimated 350 artillery squares, 
t 9 bombs short distance away. 

16.5.7 Surprise Areas 

In view of the importance which has been attached 
to the use of nonpersistent gases as surprise agents, 
Dugway has discussed this subject with respect to 
two concepts: (1) a dosage of 5 mg min per 1 estab¬ 
lished in 30 sec, and (2) a dosage of 3 mg min per 1 in 
2 min. Their results are summarized in Table 9. 


Table 9. Surprise areas for large bombs. 


1. Thirty-second surprise area at low winds 
min/1 in 30 sec) 

(Ct = 5 mg 


Bomb, 

lb 

Area, artillery square 


500 


0.2 



1,000 


0.3 



2,000 


0.5 



4,000 


1.0 


2. Two-minute surprise area (Ct 

= 3 mg min/1 

in 2 min) 



Area, 

Downwind 

Cross wind 

Bomb, 

Wind, 

artillery 

distance, 

distance, 

lb 

mph 

square 

yd 

yd 

500 

<1 

0.6 

90 

90 

1,000 

<1 

1.0 

110 

110 

1,000 

3 

0.7 

125 

60 

2,000 

<1 

1.8 

150 

150 

2,000 

11.0 

1.8 

240 

100 

4,000 

<1 

4.9 

250 

250 

4,000 

11.0 

4.5 

380 

120 


Suffield reported 30-sec surprise areas (Ct = 3.2) for 
a 4,000-lb bomb (charged 2,160 lb CG) of 1.0 and 1.35 
artillery squares for wind speeds of 5 and 10 mph, 
respectively. 

16.5.8 Munition Requirements—Bombs, 
Open Terrain 

In order to state bomb requirements it is necessary 
to specify the objectives to be attained. In addition 
to the objectives of surprise given above, the follow¬ 
ing tactical uses have received general consideration. 

1. Masking [AfJ; troops forced to mask to escape 
injury (Ct = 1 mg min per 1 for CG and CK and 0.5 
for AC). In general, troops would mask at a lower 


dosage, but this dosage requires enemy personnel to 
mask to avoid disablement. 

2. Casualty producing among unprotected per¬ 
sonnel [C M ]; this depends on the lethal dosage b 
which for CG was chosen as a Ct = 3; for CK, 
Ct = 6; and for AC, Ct = 2. The area covered by this 
dosage is called the lethal area. (These dosage values 
were chosen during the early stages of the war from 
the best experimental data available at that time. It 
is to be noted that they do not agree with the values 
adopted in 1944 by the U. S.-U. K.-Canadian com¬ 
mittee: for CG, Ct = 3.2; for CK, Ct = 11; for AC, 
Ct = 5.) 

3. Casualty producing among imperfectly pro¬ 
tected troops [Ci] (considered as 10 times the lethal 
dosage); this dosage will cause casualties among 
troops with a 10% mask leakage. In combat this 
leakage may occur even with well disciplined troops 
because of the difficulty in obtaining tight-fitting 
facepieces and because of valve leakage or defects 
due to manufacture or subsequent damage. 

4. Casualty producing among protected troops 
[Cp] (Ct = 200 for CK). Canister penetration; this 
dosage will penetrate the present enemy canisters 
with CK, provided the time of required wearing of 
mask is 1 hr or more. Canister penetration is probably 
not feasible for CG. A dosage of Ct = 200 will also 
cause casualties, if not fatalities, with all gases on 
troops with a 1 to 3% mask leakage. 

The munitions required to attain these objectives, 
that is, Ct values of 1, 3, 30, and 200 for CG and CK, 
may be deduced from the experimental data pre¬ 
sented above (at least to a fair approximation) al- 


b Although the dosage necessary to produce a casualty varies 
with time, the variation of the value of the lethal Ct in a time 
greater than 1 min and less than the time of passage of a gas 
cloud in the open is not great enough to affect appreciably the 
ammunition requirements. In the woods, even though the 
time of passage of the cloud is considerably longer, the re¬ 
quirements will not be appreciably altered, since they do not 
change rapidly as the time increases. 


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DATA ON CLOUDS FROM SINGLE BOMBS 


273 


though more experiments with multiple shoots under 
inversion conditions would have been desirable. 

16.5.9 Uniform Distribution 

Dugway gave the values listed in Table 10 for the 
1,000-lb bomb requirement. 

Table 10. Ammunition expenditures uniform coverage 
for open terrain (bombs per 100 artillery squares); 
1,000-lb M79 bombs filled CG or CK.* 


Wind _ Ct = 3 Ct = 30 t 

mph Inversion Neutral Lapse Inversion Neutral Lapse 


2 

30 

50 

130 

110 

180 

600 

4 

50 

70 

150 

190 

280 

700 

8 

160 

200 

220 

550 

700 

1,100 


* For AC, multiply by 1.5. 
t For Ct = 200, multiply (Ct = 30) values by 6. 


The requirements given in Table 10 are very high 
and it is obvious that a uniform coverage of a target 
area is quite inefficient. Thus the 41-bomb shoot at 
Dugway gave a (Ct = 3) area of at least 350 artillery 
squares compared with the 30-bomb for 100 squares 
given in the table. Thus to attain the required dosage 
over the target area, large additional areas downwind 
will be covered by dosages almost as large as those 
over the target. The values in Table 10 could be cut 
in about half if two-thirds of the bombs were distrib¬ 
uted over the upwind half of the target. A uniform 
distribution is also open to the objection that in 
actual application any nonuniformity in the distri¬ 
bution, especially along the upwind edge, results in 
dosages in that area which are below the desired 
value. These statements apply in particular to non- 
persistent gas clouds and not to the persistent agents. 

For other bomb sizes the figures in Table 10 may 
be multiplied by the appropriate factor to give an 
equivalent weight of agent. 

16.5.10 Expenditures for Line and 

Upwind Distribution in the Open c 

The following is quoted from the Dugway Report 
No. 18. 7 

For the purpose of obtaining the actual values to be used, 
the results of the field experiments have been analyzed in the 
following manner. 

To estimate the number of 1,000-lb M79 bombs needed 

0 The reported results of bombing missions in World War II 
demonstrated the impossibility of putting bombs down in an 
orderly pattern on the target. For mutual protection the 


under various conditions, the areas covered by a given dosage 
at 18 inches in the field experiments were plotted on a per 
bomb basis against the wind speed in several different ways 
(chiefly as log-log plots). From the curves for inversion, neutral, 
and lapse conditions the variation of area with wind speed 
could be determined, and the areas covered per bomb under 
inversion, neutral, and lapse (Conditions for wind speeds at 
2, 4, and 8 mph could be obtained. In calculating the number 
of bombs required for an area of 100 artillery squares, the most 
weight was given to the areas observed in the larger scale tests. 

The dimensions of the experimentally measured Ct areas 
were used to determine the maximum allowable spacings for 
the bombs. The overlapping of areas of low dosage (from 
nearby bombs) to form an area of higher dosage has been 
taken into consideration. 

CtA was also employed to determine the requirements for 
the highest dosages, and wherever possible the values were 
checked by extrapolation from lower dosages. Plots of the 
variation of CtA per 100 pounds of agent with wind speed 
were made for inversion, neutral, and lapse so that the values 
of CtA corresponding to the conditions given in the table could 
be obtained. However, it is to be noted that the CtA values 
per 100 pounds of agent (or area for a given dosage) cannot 
be used directly for the present calculations, since additional 
bombs will be needed to compensate for the portion of the 
total CtA (or area) which will be lost outside the 100 artillery 
square area. For the woods, an additional number of bombs 
above that calculated by CtA will be necessary to take care 
of the fraction of CtA lost in building up dosages above 
Ct = 200. For areas larger than 100 artillery squares and 
dosages higher than 200, these corrections will become less 
important. 

The ammunition expenditures obtained in the 
manner described above are shown in Table 11. 

Comments on the Use of Table 11 

1. The requirements in Table 11 are based on the 
use of an attack area obtained by circumscribing the 
designated target with a straight-edged figure ap¬ 
proximately 50 yd larger in every direction than the 
target area. If the upwind edge of the target area is 
bounded by water or other natural obstacles which 
prevent dropping of bombs on this part of the attack 
area, it is assumed that the bombs for this area will 
be dropped along the upwind edge of the target area. 


planes flew in definite patterns; generally the bombs were re¬ 
leased upon signal from the lead plane; bombings were usually 
made from high altitudes. For all of these reasons, the pattern 
of the impacts was essentially random. This is why the Proj¬ 
ect Coordination Staff adopted for their own use the random 
distribution method developed by two members of Division 
10, NDRC. In World War II acceptance of such randomness 
of impact was a much more realistic approach than the use 
of any planned pattern on the target. However, this early 
work from Dugway is recorded here, since it may be that 
developments and changes in attack will some day permit 
placing bombs at predetermined points. In such event, these 
considerations should be of value in planning attacks. 


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274 


BEHAVIOR OF GAS CLOUDS 


Table 11. Ammunition requirements for M79 bombs filled CG and CK. Open terrain. Bombs per 100 artillery squares. 



Inversion 

Neutral 

Lapse 

Wind, mph 

2 

4 

8 

2 

4 

8 

2 

4 

8 


No. of bombs 

11 

20 

54 

20 

36 

90 

55 

60 

95 

Ct = 1 

Max crosswind spacing, yd 

150 

125 

75 

150 

125 

75 

125 

90 

60 


No. of bombs 

16 

30 

96 

27 

50 

140 

110 

120 

180 

Ct =3 

Max crosswind spacing, yd 

125 

90 

60 

125 

90 

60 

100 

75 

50 


No. of bombs 

54 

130 

440 

110 

220 

640 

600 

700 

1,100 

Ct = 30 

Max crosswind spacing, yd 

50 

40 

30 

50 

40 

30 

45 

35 

25 

Ct = 200 No. of bombs 

350 

800 

2,700 

550 

1,100 

3,200 

Prohibitive 


2. The size of the attack area is measured in artil¬ 
lery squares and the requirement for a given area is 
computed from the table by comparison with that for 
100 artillery squares. In the open, for objectives M a 
and C u , the tabular requirements (per artillery square) 
are satisfactory for areas larger than 10 artillery 
squares. For smaller targets, the requirements per 
artillery square will be approximately double the 
values given in the tables, with a minimum of 1 bomb 
per artillery square for area in the neighborhood of 
2 artillery squares. For objectives C* and C p the re¬ 
quirements for areas less than 50 artillery squares can 
be obtained by multiplying the tabular values (per 
artillery square) by a factor of 2 for areas near 10 
artillery squares, and by 1.5 for areas near 30 artillery 
squares. An alternative method for the calculation of 
requirements for small targets is by the use of the 
values for uniform coverage given in Table 10. 

3. For open terrain at wind speeds greater than 
8 mph the requirements become large, but they may 
be estimated by extrapolation from the tabular 
values. Above 10 mph the atmosphere tends toward 
neutral conditions at all times. 

4. The type of distribution is determined from the 
nature of the target and the meteorological condi¬ 
tions. For open terrain, if the wind direction is known, 
the expenditures for the following types of bomb 
distribution may be obtained from Table 11. 

a. Line distribution. For line coverage all the bombs 
are dropped in a line along the upwind edge of the 
target. As already stated, the number of bombs 
needed to cover a given area can be calculated from 
the values in the table for a 100 artillery square 
area, but if the calculated requirement is not as 
large as the number of bombs obtained by dividing 
the crosswind dimension of the area by the maxi¬ 
mum crosswind spacing, the latter value should be 
used. Under conditions similar to those used in the 


field experiments, the gas from a single line source 
cannot be depended upon to cover a target under 
inversion conditions more than 1,000 yd downwind 
for Ct = 1 to 5, and 500 yd downwind for Ct = 30. 
Under neutral conditions, the distances are 600 and 
300 yd, respectively. If an area with a considerabty 
greater distance downwind is to be covered, it is 
possible to divide the area into smaller areas with 
shorter downwind distances and to cover each of 
the smaller areas in an identical manner by a line 
of bombs on the upwind edge of each small area. 
If conditions are very favorable, the downwind 
effect of gas in the upwind areas will add to the 
effect of the lines of bombs in the areas farther 
downwind. 

b. Upwind distribution. Bombs are distributed 
over the attack area. The downwind effect is em¬ 
ployed to some extent by displacing the bombs 
toward the upwind edge of the area. d This can be 
accomplished by placing the first row of bombs on 
the upwind edge of the attack area and spacing the 
remaining bombs in rows at equal distances down¬ 
wind on the target area, with no bombs on the 
downwind edge. 

For example, in Figure 13 it is assumed that the 
requirements and distribution of bombs for a dosage 
of 3 for CG (task C u ) for the accompanying area con¬ 
sisting of open, flat terrain under inversion conditions 
and a wind speed of 4 mph are to be calculated. The 
size of attack area is (1,050/100) x (1,110/100) equals 
117 artillery squares. The requirement for 100 artil¬ 
lery squares equals 30 bombs with maximum cross- 
wind spacing of 90 yd. The requirement for 117 artil¬ 
lery squares equals 35; bombs in first row 1,050/90 
equals 12. Number of rows 35/12 equals 3. Down¬ 
wind spacing between rows 1,110/3 equals 370. 

d For objective Ct = 200, approximately 60% of the bombs 
should be dropped in the upwind half of the target area. 


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DATA ON CLOUDS FROM SINGLE BOMBS 


275 



Figure 13. Upwind distribution. 


Bombs in second row equal 12. Bombs in third row 
equal 11 (or 12 as shown). 

5. The economy of munitions usually obtained 
when the effect of wind is utilized makes desirable the 
use of upwind or line distribution wherever possible. 
For these types of coverage the wind direction must 
be reasonably well known; with upwind coverage it 
is estimated that for most targets of approximately 
100 artillery squares, 90% of the area or more will 
still be covered with a wind shift of ± 30°. It is ap¬ 
parent that a shift in wind direction will be more 
serious for line distribution than for upwind. 

6. The distribution and spacings suggested in this 
report are made chiefly on the basis of efficient use of 
the gas clouds produced, but it is expected that 
modifications will have to be made in any actual 
operational use. No increases have been made in 
tabular value to allow for operational difficulties in 
bombing. However, in the case of nonpersistent gas 
bombs, small errors in placement of bombs are not 
serious (except on upwind edge of target) since the 
gas clouds from different bombs will probably expand 
and merge together to cover the target. 

7. The tabular requirements are not intended to 
apply to gas-proofed fortifications, since many addi¬ 
tional bombs will be needed for such an attack. 


The Project Coordination Staff [PCS] of the 
Chemical Warfare Service have made a careful study 
of all available data on nonpersistent gases. From the 
integral J* A d(Ct) they have obtained the values for 
CtA given in Table 12 for a 1,000-lb bomb with 
approximately 400 lb of agent. 


Table 12. CtA values for 400-lb agent at 18-in. height. 


Wind speed 
mph 

Clear day 

Neutral 

Clear night 

2 

12 

20 

50 

4 

7 

11 

20 

8 

4 

5 

6 

10 

2 

2.5 

3 


Table 12 has been used to calculate the over¬ 
lapping in multiple bomb shoots and hence munition 
requirements. These are summarized in Table 13. 

Table 13. PCS munition requirements. Area targets Ct 
values for 18-in. height. Bombs per artillery square, as¬ 
suming statistical distribution. 


Speed (mph) Clear day Neutral Clear night 



1. M79 for Ct = 30 



(from Table 10) 


2 

2.3 

2.3 

0.9 

4 

6.4 

4.1 

2.3 

8 

11 

9 

7.5 

16 

22 

18 

15 


Comparison with Dugway report 


2 

6 

1.8 

1.1 

4 

7 

2.8 

1.9 

8 

11 

7 

5.5 

2. 

M79 for Ct = 

200 with agent CK* 


2 

21 

12 

5 

4 

35 

23 

12 

8 

62 

50 

41 

16 

124 

100 

83 

3. M79 for Ct = 11 with CK or Ct = 5 for ACf 

2 

2.5 

1.5 

0.7 

4 

3 

2.5 

1.5 

8 

5 

4 

3.5 

16 

8 

6.5 

5.5 


4. M79 for Ct = 3.2 with CGf 


2 

0.9 

0.6 

0.3 

4 

1.5 

0.8 

0.6 

9 

2 

1.5 

1.5 

16 

3 

2.5 

2 


* For M78 multiply by 2.2. 
t For M78 multiply by 1.8. 
t For M78 multiply by 1.7. 


The comparison mentioned in (1) Table 13 refers 
to the values given in Table 10 for uniform distribu¬ 
tion, and it will be observed that except for lapse and 


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276 


BEHAVIOR OF GAS CLOUDS 



low winds, the values are essentially the same. As 
noted in the discussion of that table, these require¬ 
ments give large areas downwind which have very 
high Ct values. If this region is occupied by enemy 
troops this may be looked upon as an extra premium 
obtained in the operation. However, it seems to the 
reviewer that the placement of 80% of the bombs on 
the upwind half of the target would cut the number 
of bombs required by 30% to 50%, depending upon 
the size of the target, and if such a procedure should 
ever be possible from the operational standpoint, it 
should be recommended in place of statistical distri¬ 
bution over the whole target. The same comments 
apply to all sections of Table 13. 


16.5.11 Munition Requirements for Surprise 

The following discussion 2 was given of the require¬ 
ments for surprise effects with the M79 bomb. 

To set up a lethal dosage of CG (5 mg min per 1) over 90 
per cent of an open area within 30 seconds requires a density 
of at least three M79 bombs per artillery square (dropped 
within 5 seconds): for a lethal dosage over 80 to 90 per cent 
of the area within 2 minutes (3 mg min per 1) requires at 
least one M79 bomb per artillery square. 

There is little advantage in using gas bombs under high 
wind speeds for surprise since the 30 second and 2 minute 
surprise areas are not appreciably increased by higher wind 
speeds. On the other hand, if gas bombs are used for surprise 
under conditions where gas is not dissipated rapidly, other 
objectives will be usually achieved in addition to surprise. 


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DATA ON CLOUDS FROM SINGLE BOMBS 


277 


The Project Coordination Staff give the values 
tabulated in Table 14. The 30-sec requirements apply 
to well-trained personnel and the 2-min values to men 
poorly trained, or sleeping. 


Table 14. Munition requirements for surprise casualties. 


Type of bomb 

Agent 

Ct 

Number of bombs 
per artillery square 
30 sec 2 min 

British 250 LC 

CG 

3.2 

12 

6 

British 500 LC 

CG 

3.2 

8 

4 

M78 500-lb 

CG 

3.2 

8 

4 

M78 500-lb 

CK 

3.2 

12 

6 

M78 500-lb 

AC 

5. 

12 

6 

M79 1,000-lb 

CG 

3.2 

4 

2 

M79 1,000-lb 

CK 

11. 

6 

3 

M79 1,000-lb 

AC 

5. 

6 

3 


16.5.12 Clouds from Area Sources Set 
Up by 4.2-In. Mortar Shells 

At the Dugway Proving Ground 18 shoots were 
carried out with the 4.2-in. mortars charged CG and 
at San Jose 2 shoots with the shells charged CK. 
Data on the larger Dugway trials and the two at 
San Jos6 are summarized in Table 15, and a typical 
Dugway concentration plot is given in Figure 14. 

Open Terrain 

On the basis of the Dugway trials it was concluded 
that the behavior of the gas cloud over flat open 
terrain is comparable with the behavior of a cloud 
set up by large aerial bombs, and comparisons for 
equal weights of agent indicate that the mortar and 
the bomb are about equally efficient for covering 
areas with dosages up to 30 mg min per 1. An analysis 
of the factors affecting the efficiency was made by 
Walters and Zabor and their conclusions follow. 


Effect of Wind Velocity 
The area covered at 18 in. above the ground varies 
inversely as a power of the wind velocity — a power 
which increases with increasing wind speed, with in¬ 
creasing degree of inversion, and with increasing 
dosage. For example, for a dosage of 1 mg min per 1 
under neutral conditions, the area varies inversely 
as the 1.1 power of the wind velocity between 2 and 
4 mph and inversely as the 1.5 power between 8 and 
10 mph; for Ct = 3 mg min per 1 these exponents are 
increased to 1.4 and 2.0, respectively, and for Ct = 30 
mg min per 1 the area is inversely proportional to the 
1.6 power in the range of 2 to 4 mph. For high in¬ 
version in the range of 2 to 4 mph the area varies as 
the reciprocal of the wind velocity to the 1.1 power 
for Ct = 1 mg min per 1, the 1.5 power for Ct = 3 
mg min per 1, and the 1.9 power for Ct = 30 mg min 
per 1. The rate of increase of this exponent with the 
wind velocity increases with increasing degree of in¬ 
version and decreases with increasing degree of lapse. 

Effect of Atmospheric Stability 
The temperature profile offers the best measure of 
atmospheric stability; in restricted cases only can the 
wind profile be used as a quantitative measure of the 
effective stability. An unsuccessful attempt was made 
to use the temperature difference from the surface to 
2 m above the surface. The failure of this difference 
is probably due to two factors: (1) the difficulty of 
trying to obtain a representative macro surface tem¬ 
perature and (2) the fact that the surface temperature 
is only effective inasmuch as it governs the tempera¬ 
ture profile of the air above the surface. Conse¬ 
quently, it was found to be convenient to employ the 
temperature difference from 1 to 3 m as a measure of 
the atmospheric stability; this is defined as AT and is 
expressed in degrees centigrade. 


Table 15. Data on 4.2-in. mortar shoots. 


Wind 

speed, 

mph 

AT 

R 

Target area for 
80% of shell 
yd X yd 

Weight 
of agent 
lb 

Max 

Ct] 

Area* 
Ct\ = 3 

Area* Area* 

Ct] = 10 Ct f = 100 

3.5 

3.51 

1.7 

267 X 195 

Dugway 

920 

430 

72 


2.8 

1.61 

1.7 

223 X 154 

2,100 

140 

150 

120 

2.9 

1.31 

1.8 

243 X 187 

2,110 

180 

128 


5.6 

1.01 

1.2 

275 X 216 

1,660 

27 

50 


calm 

2.7L 


240 X 193 

1,550 

42 

24 


0.5 

I 


100 X 400 

San Jose 
6,615 

780 


>46 10 

0.5 

I 


100 X 400 

6,589 

325 


>30 15 


* Areas in artillery squares, 
t Ct values for 18 in. 


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BEHAVIOR OF GAS CLOUDS 


Table 16. Ammunition requirements for the 4.2-in. chemical mortar shell charged CG over open terrain. 

Requirement (round per artillery square) at indicated wind velocities 



Objective 

Mg min/1 

2 

4 

6 

8 

10 

Time of day 

for Ct 

mph 

mph 

mph 

mph 

mph 

Inversion 

1 

45 

45 

45 

45 

50 


3* 

45 

45 

60 

105 

165 


5 (in 2 min) 

180f 

isot 

180f 

185f 

285f 


30* 

• 4 

l 

50 

170 

375 

660 

995 

Neutral 

45 

45 

45 

65 

90 


3* 

45 

55 

110 

185 

290 


5 (in 2 min) 

180f 

180f 

180f 

300f 

465f 


30* 

• 4 

l 

100 

295 

580 

925 

1,300 

Lapse 

60 

130 

210 

305 

410 

3* 

110 

265 

480 

745 

1,055 


5 (in 2 min) 

180f 

340f 

650f 

1,100| 

l,760f 


30* 

1,015 

1,600 

2,120 

2,615 



•4 


* When using shell charged CK multiply these requirements by a factor of 1.5 
t Must be fired in 30 to 45 sec or less. 

J For Ct — 200 fire 7 successive attacks using requirements for Ct = 30, at 10-min intervals. 


The area covered by a given dosage at any height 
above the ground and at a specified wind velocity 
varies approximately as (A T + 0.37)". This varia¬ 
tion is essentially independent of the dosage and the 
wind velocity. From this it is noted that the munition 
requirement for a given mission increases very 
rapidly as the lapse rate increases; for AT = — 0.36 C, 
the requirement is ten times the requirement under 
inversion when AT = +0.63 C. However, this rela¬ 
tionship should be used with caution, especially under 
lapse conditions. When AT = —0.37 C, the area indi¬ 
cated is zero, while actually the area is not zero even 
when AT = — 1 C, as it has been observed to be at 
times at Dugway. Under neutral and inversion con¬ 
ditions, the relationship is perhaps rather more valid. 
Inversions as great as +3.5 degrees have been ob¬ 
served at Dugway. 

Effect of Dosage 

At low dosages (Ct = 1 to 5 mg min per 1) the area 
varies inversely as the 0.45 power of the Ct at a wind 
velocity of 2 mph. This exponent increases to 0.8 at 
6 mph and to 1.1 at 10 mph. It also increases with 
increasing dosages; for Ct = 10 to 30 mg min per 1 it 
is about 0.8 at a wind velocity of 2 mph. Variations 
of the power of the Ct with atmospheric stability and 
height above the ground are of second order. 

The area enclosed by a specified dosage contour is 
inversely proportional to the height above the ground 
raised to a power which increases with increasing 
wind velocity, Ct, and degree of inversion. 


On the basis of this analysis of the experimental 
data Walters and Zabor recommended the munition 
requirements given in Table 16. 

From a study of the Dugway data the PCS gave 
the following munition requirements for the 4.2-in. 
mortar. 


Table 17. Munition requirements for 4.2-in. mortar. 
Open terrain. 


1. CG for Ct 

= 3.2 on 80% of target 

Wind 

Shell* per artillery square 

mph 

Neutral to moderate inversion 

2 

30 

4 

55 

8 

100 

2. CK for Ct 

= 200 on 80% of target 

Wind 

Shell* per artillery square 

mph 

Neutral Inversion 

2 

600 300 

4 

1,800 1,000 


* 6.25 lb of CG per shell. 


Because of the slow firing rate and low weight of 
agent per shell, the 4.2-in. mortar is impractical for 
attainment of surprise lethal dosages in 30 sec. How¬ 
ever, Table 16 includes a requirement to give a Ct of 
5 in 2 min. It has been argued that the fragmentation 
of the shells will cause troops to seek shelter and thus 
delay the adjustment of their masks for a period of 
about 2 minutes. 


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DATA ON CLOUDS FROM SINGLE BOMBS 


279 


Wooded Areas 

The two San Jose mortar shoots do not provide 
sufficient data to permit an experimental evaluation 
of munition requirements for wooded areas. In the 
second of these shoots 300 shells per artillery square 
on four squares gave Ct of 100 on 85% of the target, 
but the total area for Ct = 100 was some 15 artillery 
squares, mostly beyond the target. The area for 
Ct = 200 was about 4 artillery squares, but again 
much of this was beyond the target. When the cloud 
moved off the region of the target, the dosages were 
still very high, so the total area for lower dosages was 
unknown. The slow motion of clouds in forests or 
jungles would appear to make it possible to use the 
mortar to maintain low concentrations over large 
areas for long periods of time. Whether this would 
result in very high dosages per pound of agent ex¬ 
pended is at present unknown. However, the re¬ 
quirements stated in Table 17 for 2 mph may be em¬ 
ployed with the assurance that they are ample for 
average conditions inside the forest. 

Bombs in Wooded Areas 

The salient features of the micrometeorology inside 
a forest and jungle canopy, as discussed in Chapter 
14, included: (1) low wind velocities, (2) zero or small 
temperature gradients both night and day, and (3) 
fairly large vertical air mass movement even with 
good inversion over the canopy. These factors result 
in considerable deviation in the travel of gas clouds 
in wooded £reas from that observed in open terrain. 
The following comparison of Ct values for the 1,000-lb 
bomb is typical. 


Table 18. Comparison of Ct areas in artillery squares 
for 1,000-lb bomb charged CK in open terrain and in 
forest. Wind speed 1 mph, clear night, 18-in. level. 



Ct = 3 

Areas 

Ct =30 Ct = 100 

Max Ct 

Open 

10 

1 

0.05 

100 

Woods 

3 

1 

0.3 

130 


It is observed that (1) the area covered by (Ct = 3) 
is much greater in the open but (2) the maximum Ct, 
and (3) the areas covered by (Ct = 100) are much 
larger in the forest. Effect (1) is understandable be¬ 
cause of the larger vertical air movement in the for¬ 
est, and the vertical component which is constantly 
being introduced by a parcel of air in horizontal mo¬ 
tion striking a branch or leaf. Effects (2) and (3) are 
harder to understand and doubtless are not true at 


all levels since they appear to be related to the smaller 
gravity spread and lower concentration gradients in 
the forest. In the open, many drops of the liquid from 
a bomb burst will fall nearly to the ground before 
they vaporize, thus setting up an initial concentration 
gradient, while in the forest Considerable vaporization 
will occur from the surface of the foliage high above 
the ground. The,observed temperature decrease in 
the cloud is much less in the forest than in the open, 
which indicates that heat has been absorbed from 
the vegetation. This decreases the density of the 
gravity effect. The friction of the vegetation tends to 
slow down the gravity spread of the cloud and it 
comes to rest with the top of the cloud considerably 
above the height observed in the open. As a result of 
these effects the concentration gradient is considera¬ 
bly smaller in the forest, and Ct values at higher levels 
will be greater. Under inversion, with low winds in 
the open at 100 yd from the burst, most of the gas 
from the charge will lie below the 18-in. level. 

The difference between open terrain and woods 
indicated in Table 18 for the area of high Ct values is 
further accentuated by the fact that the average 
wind speed at night in a forest is around 0.5 mph and 
the average in the open certainly above 2 mph. It is 
this general occurrence of low wind speeds at night 
in forests and jungles which enhances the efficiency 
of nonpersistent agents in these areas. 

Experiments with single 1,000-lb bombs were 
carried out in the Shasta, Targhee, and Florida for¬ 
ests, and the jungle of San Jose Island. The data ob¬ 
tained are adequate to give a fairly complete picture 
of the cloud travel under wide ranges of meteorologi¬ 
cal conditions. Figure 15 gives typical Ct contour for 
a bomb charged CK at Bushnell. While it is difficult 
to summarize in a single table the behavior of the 
1,000-lb bomb for forests of varying density of foliage 
and height of canopy, it is believed that Table 19 
gives representative values for the agent CK. 

It should be emphasized that these values are for 
level ground. At the low wind speeds generally preva¬ 
lent in the forest, gravity flow may be more important 
than the wind in determining the course of the cloud, 
if the terrain is sloping. In this case extremely high 
Ct values may be observed in stream beds and in 
general along the natural water course. This effect 
has been discussed in detail. 17 

For the agent phosgene [CG] considerable reaction 
occurs with the foliage, and the fall-off of concentra¬ 
tion with distance is greater than that observed with 
the agent cyanogen chloride [CK]. CG is also 


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280 


BEHAVIOR OF GAS CLOUDS 



Table 19. Summary for 1,000-lb bomb charged CK in heavy forest. 



Wind speed 
in forest, 
mph 

Area in artillery squares covered bv given Ct value* 
Ct = 3 Ct = 30 Ct = 100 Ct = 200 

Maximum Ct , 
mg min/1 

Clear night 

1 

3 

1 

0.3 

0 

130 


0.5 

8 

2 

0.5 

0.1 

225 


0.3 

14 

3 

0.8 

0.2 

300 

Clear day 

1 

1.5 

0.5 

0.02 

0 

120 


0.5 

2.5 

1 

0.25 

0 

190 


0.3 

3.5 

1.6 

0.4 

0.05 

250 

* 18-in. height. 


hydrolyzed by water, and following a rain or in a wet 
jungle much of the agent may be lost by this process. 
Rate constants for the absorption by a definite den¬ 
sity of foliage were determined. 16 

The experimental field data for multiple bomb 
shoots in forest areas are not complete either with 
respect to the variation of meteorological conditions 


or the number of bombs per artillery square. Two 
multiple bomb CK shoots were carried out at Bush- 
nell and two at San Jose. In all cases inversion over 
the canopy and low wind velocities beneath the can¬ 
opy prevailed. Unfortunately the bombs were highly 
concentrated in a few artillery squares so that it is 
difficult to draw conclusions as to probable dosages 


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GAS CLOUDS IN URBAN AREAS 


281 


Table 20. Ct area and maximum Ct values from multiple bomb CK shoots (values for 18-in. height). 


No. 

of 

bombs 

Bombs 

per 

artillery 

square 

Wind 

mph 

Area covered by stated Ct in 
Ct — 5 Ct = 30 Ct = 100 

artillery square 

Ct = 200 Ct = 1000 

Maximum 

Ct 





Bushnell 


\ 


10 

8 

0.4 

20 

14 

11 

7.5 

1.4 

2,000 

8 

9 

0.7 

14 

9 

7.5 

6, 

0.6 

1,900 





San Jose 




18* 

4 

0.4 



> 5 

2 


470 

96 

5-9 

0.5 



>55 

38 

10 

7,500 

8 

4 

0.3 

18 


8 

4 

1 

1,185 

8 

2-6 

0.3 

20 


8 

4.5 

0.7 

1,600 


* 500-lb bombs. All others shoots 1,000-lb bombs. 


with more normal bomb distributions. The observed 
Ct areas and the maximum Ct values are summarized 
in Table 20. 

A comparison of the multiple shoots with the single 
bomb shoots indicates that the maximum Ct obtained 
is roughly the maximum for the single bomb multi¬ 
plied by the number of bombs per artillery square. 
On the other hand, the overlapping of the single bonib 
effects results in a correspondingly smaller area per 
bomb for (Ct = 5) for the multiple shoots. 

In general, the concentration gradient in the forest 
was less than that observed in the open. Over the 
target area, the concentration at 72 in. was from one- 
sixth to one-half the value at 18 in. with an average 
of about one-third. At a distance of 200 yd there was 
little difference in the values at the two heights ex¬ 
cept in stream beds where gravity flow was occurring. 

The gas CK remained in covered fox holes and 
dugouts for fairly long periods. Although the maxi¬ 
mum concentrations were generally lower than the 
outside, the Ct values were 30 to 50% greater. 

Table 21. Munition requirements in wooded areas for 
1,000-lb bombs charged CK; number of bombs per 100 
artillery squares after Walters and Zabor; wind speed 
over woods. 



Inversion 
wind, mpn 

Neutral 
wind, mph 

Lapse 
wind, mph 


4 

8 

4 

8 

4 

8 

Ct =3 

36 

45 

42 

54 

50 

64 

Ct = 30 

72 

90 

85 

100 

110 

144 

Ct = 200 

140 

230 

150 

270 

170 

320 


16.5.13 Munition Requirements in 
Wooded Areas 

By referring to the rather meager Bushnell data 
and by superimposing CtA data for single bombs, 


Walters and Zabor derived the munition require¬ 
ments given in Table 21 for the 1,000-lb bomb. It is 
estimated that the requirements for CG would be 
about double that for CK. 

The Project Coordination Staff reviewed all the 
data from Bushnell and San Jose and calculated 
f A d(Ct) for single and multiple bomb shoots. From 
their study they recommended the requirements 
given in Table 22. 


Table 22. Requirements for 1,000-lb M79 bomb. 


Wind over canopy 
in mph 

Bombs per artillery square 

Clear day 

Neutral 

Clear night 

Charged CK in wooded terrain* for Ct 

= 200 

0-10 

4.5 

1.5 

1.0 

Charged CG for Ct = 200 


0-10 

4.5 

2.5 

2.0 


* Jungle terrain, multiply by 1.4. For other bomb sizes, multiply by 
344/(lb of agent per bomb). 


16.6 GAS CLOUDS IN URBAN AREAS 

The following discussion is taken from Porton 
Memorandum No. 6. 1 

16.6.1 Air Circulation in Streets and 
Courtyards 

As a preliminary, qualitative studies have been 
made of circulation of air in London streets. The re¬ 
sults are best explained by diagrams. 

Under calm conditions the circulation is controlled 
by temperature, and is as shown in Figure 16. A wind 
of about m per sec is sufficient to mask this 
thermal circulation. When the wind blows along a 


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BEHAVIOR OF GAS CLOUDS 




Figure 16. Temperature effect on circulation.. 

street, the air in the street flows in the same direction, 
continuing down the street until it is forced to rise 
over the houses at the end. At junctions with side 
streets, stationary eddies are formed which extend 
up these streets for a distance about equal to the 
width of the street; the flow in these horizontal eddies 
is away from the main street at the downwind side of 
the junction and toward it at the upwind side. If 
houses form a barrier across the top of the main 
street, the wind must flow over these houses before 
reaching the main street so that an eddy is formed. 
This extends down the street for a distance approxi¬ 
mately equal to the height of the barrier. This tri¬ 
angular eddy maintains an upward current at the lee 
wall of the barrier, so that for a short distance down¬ 
wind of the barrier the flow of the air near the ground 
is opposite to the undisturbed wind. 

When the free wind blows across a street, the air 
descends at the downwind side of the street and rises 
at the upwind side. At street level the flow is there¬ 
fore opposite to the wind direction as shown in 
Figure 17. 

WIND ACROSS STREET 



Figure 17. Flow of wind at street level. 

For winds blowing diagonally across a street the 
circulation is a combination of the simple cases dis¬ 
cussed, and the main flow can be roughly represented 
by a helix. 

The circulation in a courtyard is the same as that 
in a street when the wind is blowing across the street. 
When the walls of the street or the courtyard are very 


high, however, the dynamical circulations extend 
only to a depth below the roofs approximately equal 
to the breadth of the street or yard. In these cases 
there is thermal circulation below the critical depth. 

To illustrate how the circulations can be super¬ 
posed for the case of the diagonal wind, observations 
taken at Porton provide an example. A site was made 
to simulate a blind alley 50 m long with no obstruc¬ 
tions at the open end so that the wind could approach 
undisturbed. A typical observed circulation is shown 
in Figure 18. 



Figure 18. Observed circulation of air in a blind alley. 

The circulation of air in drains and sewers is found 
to be independent of the direction of flow of the water, 
but is determined by the direction of the wind. When 
the wind blows along a street the direction of the 
flow of air in the sewers is opposite to that of the 
wind. 

Concentrations in a Simulated Built-Up Area 

The potential dangers due to a large aircraft bomb 
charged with phosgene have been examined in a 
simulated built-up area at Porton. The site chosen 
was a space between 2 one-story buildings whose 
height was increased to 12 m by false roofs, the 
° ‘street” being really a cul-de-sac some 50 m in length. 
Two types of bombs were examined under conditions 
of lapse, zero gradient, and inversion. The tail ejec¬ 
tion bomb, which was sunk into the ground to a depth 
equal to its own length, was an aircraft bomb, 250-lb 
LC Mk I charged 41.3 1 phosgene, and the burster- 
type of bomb was simulated by five Livens drums 
each charged 30 lb (13.6 kg) phosgene. 

It was found that high concentrations were pro¬ 
duced in the area, particularly in inversion condi¬ 
tions. The initial cloud, which filled about half the 
area, gave concentrations as high as 1 part in 50, and 
up to a height of 10 m concentrations of approxi¬ 
mately 1 part in 10,000 persisted for some minutes, 
while appreciable amounts of gas were found to per¬ 
sist for about 40 min. As a general result, it was found 
that rooms with sound windows afforded a reason- 


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GAS CLOUDS IN URBAN AREAS 


283 


able degree of protection, which was considerably 
enhanced by simple measures of gas protection. 

It is a matter of considerable difficulty to extend 
these results to the densely populated areas of a large 
city, but it is already clear that cul-de-sacs and court¬ 
yards may be very dangerous in the event of an at¬ 
tack with gas bombs. In the Porton cul-de-sac, it was 
found that the decay of concentration with time 
could be represented fairly well by the law 

C t = C 0 exp ( — kt) 


where C 0 is the maximum concentration at the point 
in question and C t the concentration after a lapse of t 
seconds. The decay coefficient k was found to vary 
with the site, meteorological conditions, and with the 
wind velocity, the ariation with the last factor being 
linear. Trials with smokdj in London courtyards 
showed that the same law applies, and brought 
out the interestmg fact that the cul-de-sac at Por¬ 
ton was much less dangerous than certain Lon¬ 
don areas, where the value of k may be as low as 
5 X 10 -3 sec -1 . 


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Chapter 17 

FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 

By Francis E. Blacet 


N onpersistent agents are those which normally 
enter the gas phase quickly after being dis¬ 
persed. Phosgene, hydrocyanic acid, and cyanogen 
chloride are examples of such gases. In contrast to 
these agents are persistent gases, those with low 
vapor pressures at normal temperatures, of which 
mustard gas is the outstanding example. In general, 
the gas concentration ranges encountered in the 
study of the two classes of agents are of a different 
order of magnitude, and hence sampling devices 
which are satisfactory for one class usually do not 
prove' good for the other. Accordingly, in studying 
the behavior and effects of toxic agents, a logical 
division of endeavor has taken place and Division 10 
of NDRC was given problems pertaining to the non- 
persistent gases. The sampling methods and equip¬ 
ment described on the following pages were developed 
for this type of agent. The merits of each instrument 
are discussed, including the possibility of its use with 
persistent gases. 

17.1 HYDROSTATIC HEAD PUMP 
SAMPLER 9 

This device, which was developed for field use by 
Division 10 at Dugway Proving Ground, makes use 
of the simple and well known fact that a liquid flow¬ 
ing by gravity from a bottle tends to produce a re¬ 
duced pressure and, therefore, can be used to draw 
air or gas through an absorption tube. 

Figure 1 is a schematic diagram of the apparatus 
as used extensively in the field. It contains two inde¬ 
pendent pumping units which can be used to collect 
two samples at the same level, or with the aid of 
rubber tubing can collect single samples at any two 
positions at reasonable heights or distances from the 
pumps. The 2 3^-1 acid bottles used in the pumps are 
graduated in 100-ml divisions. Approximately 1-mm 
capillary tubing forms the connection between the 
upper and lower bottles. The diameter of the capillary 
is selected to give approximately the flow rates 
desired. Flow rates of 3^ to 1 1 per hr prove to be 
satisfactory and hence sampling can be carried on 
over periods of from 2 to 4 hr without attention from 
an operator. The U-tubes in the bottles insure con¬ 


stant hydrostatic head during operation of the ap¬ 
paratus. The glass parts are mounted and securely 
held inside substantial wooden frames so that the 
pumps can be transported over rough terrain with 
little loss from breakage. The apparatus is completely 
symmetrical and can be used with either end up. 
Thus the same water is used over and over again for 
pumping purposes. All-glass bubbler absorption tubes 
are used for the absorbing solutions. Each bubbler 
has a 30-ml graduation mark. 



ANY DESIRED HEIGHT FOR GAS 
SAMPLING 


Figure 1 . Diagram of hydrostatic head pump sampler. 


17 . 1.1 Operation of Sampler 

When the sampler is not in use, the water is in the 
lower upright bottles. In preparation for sampling, 
the entire apparatus is inverted and the absorption 
tubes attached by means of appropriate lengths of 
rubber tubing. The heights of the tubes and the water 
levels in the two inverted bottles are recorded. The 
time of reading the water levels is also recorded. Re¬ 
gardless of the nature of the experiment, the samplers 
are allowed to operate until at least 1 liter of water 
drains from each of the upper bottles. Upon com¬ 
pletion of sampling, the final time and the water 
levels in the upper bottles are recorded, and the 
absorption tubes are detached and taken to the 
laboratory for analysis. 


284 


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HYDROSTATIC HEAD PUMP SAMPLER 


285 


17 . 1.2 Preparation and Analysis of Solutions 

The sampler has been used extensively in the study 
of CG, CK, and AC. For all three agents conducti- 
metric analyses are employed. 

Phosgene 

The absorbing solution for this gas is made by 
mixing equal volumes of 95% ethyl alcohol and a 
good grade distilled water, and then adding sufficient 
HC1 to bring the blank within the range of the 
conductance meter. 

Twenty-five ml of this solution are placed in each 
absorption tube. After the gas is absorbed the tubes 
are brought back to the laboratory and more solution 
added to bring the total volume in each to exactly 
30 ml. The solutions are allowed to stand for at least 
8 hr to insure complete hydrolysis of the phosgene. 
Thereafter, they are passed in rapid succession 
through the cell, and the conductance readings and 
temperature are recorded. 

From the conductance values and previously pre¬ 
pared concentration (mg per 30 ml) vs specific con¬ 
ductance curves the concentration of each solution is 
obtained. These data combined with the gas volumes 
and times recorded in the field make possible the 
calculation of the total gas dosage Ct attained at 
each sampling point. 

^ mg of agent _ mg min 

flow rate, 1 per min 1 

Cyanogen Chloride 

The absorbing solution for this gas is made by 
mixing the following substances in the proportions 
given: ethyl alcohol, 250 ml; distilled water, 775 ml; 
formaldehyde (37%), 10 ml; and hexamethylenetet¬ 
ramine, 10 g. The sampling and analytical methods 
used for this gas are essentially the same as those used 
for phosgene. 

Hydrogen Cyanide 

This gas is absorbed in a 0.5% solution of mercuric 
chloride in distilled water. The sampling and analysis 
are the same as for phosgene, except that it is not 
necessary to allow a minimum time to elapse between 
gas absorption and the conductance measurements. 

17 . 1.3 Notes 

1. With this apparatus Ct values from 0 to at least 
10,000 mg min per 1 can be obtained without diffi¬ 


culty. Over the majority of this range results may be 
expected to average an accuracy within about 10%. 

2. This sampler is simple and cheap to construct, 
and proved to be very reliable in the field. The only 
replacement problem was due to breakage from bomb 
fragments and the loss from this cause was light. 

3. Because of the simplicity of this sampler, per¬ 
sonnel with little education and no background in 
science could be trained to do the field work. That 
proved to be a very important factor in trials in which 
a large area of rugged terrain had to be covered in a 
short time. 

4. In the laboratory two men with one conductance 
meter could handle about 100 samples an hour. The 
biggest laboratory problem was the rinsing and 
filling of the absorption tubes. This work could be 
done by unskilled labor. 

5. This method will work with other gases. For 
example, ammonia and sulfur dioxide can be ab¬ 
sorbed in distilled water and analyzed by conduc¬ 
tivity. Other analytical methods can be used if 
necessary. 

6. Because of the small total volume of sample 
which it can take, no way has been devised so far to 
use this sampler for persistent agents. 

7. The apparatus, constructed and used as de¬ 
scribed above, gives only the total dosage Ct attained 
at the sampling point. However, in certain limited 
experiments in which the operator can stay at the 
location of the sampler, it is possible to get a series 
of samples from which can be obtained points for a 
concentration vs time curve. This was done in early 
field and indoor experiments with ammonia, sulfur 
dioxide, and phosgene. The apparatus was modified 
by replacing the capillary connecting the two bottles 
by a rubber tube and pinch clamp, the quantity of 
water was adjusted so that just 1 1 would flow from 
one bottle to the other. By means of the clamp the 
flow rate was made approximately 1 1pm. The oper¬ 
ator had a rack full of bubbler tubes and during an 
experiment used them at recorded times. Because of 
the rapid flow rates involved it was necessary to use 
absorbents which could not be analyzed by con¬ 
ductivity means. Ammonia was absorbed in 1.5% 
boric acid and titrated with HC1. Sulfur dioxide was 
absorbed in 10% NaOH to which had been added a 
trace of stannous chloride. The excess of NaOH was 
neutralized by 6 A acetic acid and the sulfurous acid 
titrated with iodine. Phosgene was absorbed in 1 A 
NaOH in 50% methyl alcohol and the chloride de¬ 
termined potentiometrically. 


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286 


FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 


17.2 DIAPHRAGM PUMP SAMPLER 


This sampler was developed by Division 10 at 
Dugway Proving Ground and Northwestern Uni¬ 
versity. It makes use of the fact that an electrically 
operated vibrating diaphragm, operated in conjunc¬ 
tion with two simple check valves, may be caused to 
circulate a gas against a small hydrostatic head. 


6-V "HOT SHOT" 
ORY BATTERY 


SWITCH 




CONTROL RELAY 



I 



Figure 2. Diagram of diaphragm pump and electric 
circuits. 


Figure 2 contains a diagram of the pump and elec¬ 
trical circuits. The entire pump, including battery 
and flowmeters, is enclosed in a rainproof box of 
dimensions 9x9x10 in. equipped with handle for 
carrying. The capacity of the pump is between 600 
and 800 ml per min when operated against a 2-in. 
water head. Since half of this flow rate is sufficient for 
sampling purposes the apparatus is designed to 
operate two gas absorption tubes at the same time. 


A separate flowmeter is provided for each bubbler. 
The bubblers are 8-in. test tubes fitted with rubber 
stoppers and an inlet tube leading to the bottom. 
With the aid of rubber tubing, the bubblers can be 
placed at any desired reasonable height or distance 
from the pump. 

17.2.1 Operation 

Because of minor changes in pumping rate during 
the time the electrical circuit is reaching thermal 
equilibrium, it is found desirable to start operation of 
the sampler at least 15 min before taking the initial 
flowmeter reading. Flow rates are taken before and 
after the cloud is sampled and the average is taken 
in calculating results. 

17.2.2 Preparation and Analysis of Solutions 

Phosgene 

The solution for this agent is made by mixing 
equal volumes of 95% ethyl alcohol and aqueous 2 N 
sodium hydroxide. Twenty-five ml are used in each 
absorption tube. After the gas is absorbed the tubes 
are returned to the laboratory and titrated for chloride 
by a standard procedure. From the data thus ob¬ 
tained and the recorded flow rates, total dosages are 
calculated in the same manner as discussed in Sec¬ 
tion 17.1. 

Cyanogen Chloride 

The same solution and analytical method are used 
for this agent as previously described for phosgene. 

Hydrogen Cyanide 

This gas is absorbed in aqueous 2 N sodium hy¬ 
droxide and titrated for cyanide by a standard 
method. The calculation of dosage is the same as 
given for phosgene. 

17.2.3 Notes 

1. This type of pump will operate for a total of 
from 30 to 50 hr on a single 6-v dry battery (Burgess 
4F4H). For this reason it is especially suitable for 
distant and inaccessible places where it can be started 
well before a gas trial is scheduled, thus giving the 
operator ample time to leave the area. 

2. Because of the comparatively high capacity of 
the pumps, they will measure low dosages with con¬ 
siderable accuracy. Thus they are especially useful in 
defining the outer fringes of a gas cloud. 


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HOT WIRE ANALYZER 


287 


3. For the same reason, this apparatus has some 
promise for the sampling of persistent agents with 
low vapor pressures. 

4. The major fault which developed in this sampler 
was the gradual pitting and finally, the sticking of the 
electrodes of the vibrating relay. The contact points 
are silver. Laboratory studies indicate that points of 
platinum or tungsten would be very much better. 

5. In brief trials with mustard vapor in a moist 
tropical atmosphere there was considerable corrosion 
of the electrical parts. This served to emphasize that 
the sampler could be improved by enclosing all the 
electrical parts in a gasproof box. 

17.3 HOT WIRE ANALYZER 7 

This instrument, which was developed under a 
Division 10 contract at the University of California, 
made use of the fact that many gases are induced to 
react by oxidation or decomposition when they come 
in contact with a hot wire. The reaction in turn 
affects the temperature, and therefore the electric re¬ 
sistance, of the wire. The wire filament in the ap¬ 
paratus is incorporated in a Wheatstone bridge and 
used with a continuously recording, photoelectric 
microvoltmeter. 



Figure 3. Diagram of hot wire analyzer electric circuit. 


Figure 3 is an electrical circuit diagram of the 
analyzer in its simplest form. The photoelectric re¬ 
corder, a General Electric Model 8CE1CM57Y1, 
covers the range 0 to 1 mv. The filaments are em¬ 
bedded in a brass block as indicated in Figure 4. By 
means of a suitable pump, the gas-air mixture to be 
analyzed is drawn over one filament, and air, which 
had been purified by first passing through a canister 
filled with type ASC charcoal, is drawn over the 
other. Capillary tubes are placed between the fila¬ 
ments and the pump to provide a critical orifice and 


hence a flow of approximately 1 1pm past each 
filament. 

In order to conserve electric cable, triple unit sam¬ 
plers as diagrammed in Figure 5 usually were used 
in field experiments but the operation of these was 
essentially the same as given here for the single unit. 
If conservation of wire is no important object it is 
better to use single units, because in the triple units 
there is some coupling between the bridge circuits 
which materially reduces the sensitivity in the low 
gas concentration range. 




BLOCK DETAIL 

Figure 4. Diagram of reaction cell of hot wire analyzer. 

17.3.1 Operation 

In the field, the filament block, battery, and pump 
(No. 4F5, Gast Mfg. Co., Benton Harbor, Michigan) 
are located near the desired sampling point. Tygon 
(plastic) tubing, which does not in any way affect the* 
gases studied, is used to convey the gas-air mixture 
from the sampling point to the filament block. The 
remainder of the apparatus is located at a control 
center, which at times may be as much as 1,200 ft 
from the sampling point. 

At least 20 min before sampling is to begin, the 
pump is turned on (after that the filaments are con¬ 
nected to the 2-v battery). Care is taken never to 
heat the filaments before starting the pump, never 
to have more than 2-v battery potential, and always 


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288 


FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 



Figure 5. Diagram of triple unit sampler. 


to have the recorder disconnected during the time the 
block is coming to equilibrium temperature. 

Just before measurements are expected to start, the 
bridge circuit is balanced so that on high sensitivity 
(Circuit 1, Figure 3) the zero position is at about 0.2 
of the full recorder scale. This is done by making a 
preliminary bridge adjustment on circuit 4, switching 
.to 3 and adjusting with potentiometer G, switching to 
2 and adjusting with both G and H, then finally 
switching to circuit 1 and adjusting by means of H. 

Whenever possible the recorder is kept under con¬ 
stant observation, and when the gas concentration 
increases to the point where there is danger of the 
needle going off scale, the switch is changed to the 
medium scale (position 2) and a notation made on 
the tape to indicate that change. By shifting to 
different ranges of sensitivity in this way, a con¬ 
tinuous record may be obtained for the duration of 


the experiment. Time and rate of tape movement are 
recorded. If drifts occur which make it necessary for 
the zero position to be aj dusted during an experiment, 
the magnitude of this adjustment is noted so that 
suitable corrections can be made in the final calcula¬ 
tion of concentrations. 

17.3.2 Calibration 

Each analyzer is calibrated in its field position by 
getting meter readings in each sensitivity range for 
five or six known gas-air mixtures. The known mix¬ 
tures are prepared by allowing pure gas, contained in 
gas pipets of known volume, to flow into partially 
evacuated 20-1 carboys. After equilibrium pressure 
has been established with the atmosphere the pipets 
are removed, and the bottles are allowed to stand 
sealed until uniform concentrations are established. 
In use, each bottle is opened and gas is drawn im¬ 
mediately from near its bottom through the Tygon 
sampling tube and over the hot filament. In response 
to this the recorder needle quickly levels off and re¬ 
mains for a short time at a maximum value repre¬ 
senting the specific concentration involved. From 
such measurements, calibration curves of meter read¬ 
ings versus concentration are obtained. 

17.3.3 Calculation of Results 

The time of arrival and the duration of a gas cloud 
at the sampling point is read directly from the record. 
The concentration at any time is obtained with the 
aid of the calibration curves. The total dosage is 
obtained by integrating the area under the total 
recorder curve. 

17.3.4 Notes 

1. This type of apparatus has been used success¬ 
fully in the field with AC, CG, CK, NH 3 , N0 2 , and 
butane. Doubtless it could handle practically all other 
nonpersistent gases as well. 

2. The lower range of sensitivity of the apparatus 
varies with the gas. With butane, a concentration of 
0.05 mg per 1 can be measured with fair accuracy. 
For AC, the lowest concentration which can be de¬ 
tected is approximately 0.1 mg per 1; for CK, 0.3 mg 
per 1; and for CG, 0.3 mg per 1. The magnitude of 
these limiting values will vary with the quality of the 
instrument and with climatic conditions at the time 
of the test. Scale readings are not necessarily linear 


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FIELD CONDUCTIVITY ANALYZER 


289 


functions of concentrations. The character of the 
calibration curve varies with the gas and also from 
filament to filament. However, the average instru¬ 
ment may be expected to give reliable results up to 
concentrations of 50 mg per 1 and good approxima¬ 
tions can be obtained up to 100 mg per 1. 

3. A minimum of chemical laboratory equipment 
is required. Except for the possible necessity for a 
chemical analysis of the calibration gas, all measure¬ 
ments are physical in nature and, accordingly, all 
data are available for the calculation of results as 
soon as the gas cloud experiment is finished. 

4. No other field instrument will handle inert 
gases such as butane. Likewise, no other instrument 
will give arrival times of gas cloud fronts or instan¬ 
taneous concentrations so exactly. Because of these 
latter features the hot wire analyzer is an ideal instru¬ 
ment for studying the characteristics of clouds formed 
from single bombs. 

5. Along with the attractive features of the ap¬ 
paratus must, of course, be listed its drawbacks. The 
more important of these are as follows: 

a. For even a moderate sampling layout a large 
amount of well insulated electric wire is re¬ 
quired. For example, one triple unit located 
400 yd from the control center requires the 
equivalent of 1 y± miles of single strand wire. 
To install the necessary wire to cover ade¬ 
quately, an experimental plot is no small task. 
Because of this, in forested areas where most 
liberated gases will destroy the foliage and 
hence the worth of the area for testing in a 
very short time, it is doubtful whether this 
apparatus should be adopted for general use 
to the exclusion of all others. 

b. The large amount of exposed wire is vulner¬ 
able to bomb fragments, and it has been 
common experience to have crucial sampling 
points missing from the records, because of 
wires being cut. 

c. The filaments used in the apparatus have 
neither been so rugged nor so long lived as 
one would like. When a new one is installed 
a new calibration is required. 

d. Variations in the absolute humidity may 
seriously affect the accuracy of results in the 
low concentration range. 

e. The relatively large lower limit of sensitivity 
for most gases means that a dangerous or 
lethal dosage could be built up at a sampling 


point without being detected by this instru¬ 
ment. It is for this reason that the hot wire 
analyzer in its present design cannot be used 
for persistent gases such as mustard, which 
have low vapor pressures, 

f. In order to obtain the best results the record¬ 
ing instruments must be under observation 
at all times. In large scale aerial trials it was 
not practical to do this because of the hazard 
to personnel. 



Figure 6. Photograph of absorption unit and conduct¬ 
ance cell. 

17.4 FIELD CONDUCTIVITY 
ANALYZER 4 » 5 > 6 * 8 

This instrument, which is referred to frequently as 
the Dickinson meter, was developed at the California 
Institute of Technology. It made use of the fact that 


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290 


FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 


R-4 



Figure 7. Diagram of electronic circuit for alternating-current model (left) and battery model (right). 


the nonpersistent gases, when absorbed by an ap¬ 
propriate solvent, cause large changes in conductivity. 
The agent is absorbed continuously with fresh solvent 
and the solution so formed is then passed through a 
conductivity cell. The amplitude of an alternating 
current passing through the cell is a function of the 
concentration of dissolved gas, and with the aid of a 
rectifier, it can be recorded continuously on a record¬ 
ing milliammeter. 

Figure 6 is a photograph which shows the manner 
in which the agent is absorbed and passed through the 
conductance cell. The solvent flows by gravity, at a 
controlled rate of approximately 10 ml per min, 
through a capillary T-tube which serves to aspirate 
the gas-air mixture into the spiral where absorption 
occurs. Then it passes through the cell, and finally 
around a thermometer bulb and out of the system as 
waste. The purified air after passing through the 
spiral escapes by way of a constant-head tube to the 
space above the remaining solvent in the reservoir. 

The analyzer can be operated either with batteries 
or with 115-v alternating current. Wiring diagrams 
for both circuits are given in Figure 7. 


In the last model developed, the complete elec¬ 
tronic circuits and batteries are enclosed in a weather¬ 
proof and gastight can. The recorder, an Esterline- 
Angus Model A.W., is protected in a gastight metal 
container fashioned after the conventional bell jar. 
The recorder can be placed either near the sampler in 
the field or in a distant central shelter. 

17 . 4.1 Operation of Sampler 

Preliminary to an experiment the reservoir is filled 
with the appropriate solvent, the capillary intake is 
inspected to make sure that it is dry, the flow rate 
is tested and, if the battery system is used, this is 
turned on well ahead of time. A calibration curve is 
obtained on the record both before and after the ex¬ 
periment by means of the fixed resistors R4-R8, 
(Figure 7). The lag time of the instrument is obtained 
by noting the period elapsing between the time an 
open bottle of ammonia is held to the intake tube and 
the response of the recorder needle. 

Other necessary data taken during an experiment 
are reference times on the record, time of gas release, 
speed of meter tape, and solution temperature. 


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ROTARY DISTRIBUTOR SAMPLER 


291 


17.4.2 Solutions 

A good grade of distilled water must be used in 
making up all solutions. 

Phosgene 

This gas can be absorbed in water, but best re¬ 
sults are obtained by using 20% ethyl alcohol. Suf¬ 
ficient HC1 is added if necessary to bring the cell 
resistance down to 200,000 ohms. 

Cyanogen Chloride 

Cyanogen chloride is absorbed in 20% ethyl 
alcohol to which 14 g of hexamethylenetetramine 
per 1 have been added. 

Hydrogen Cyanide 

Hydrogen cyanide is absorbed in 20% ethyl alco¬ 
hol to which 400 mg of mercuric chloride per 1 are 
added. Sufficient HC1 is added, if necessary, to bring 
the cell resistance down to 200,000 ohms. 

17.4.3 Calibration of Results 

If battery-operated circuits are used, the records 
are corrected for scale drift at as many points as 
necessary with the aid of the calibration points 
recorded at the beginning and at the end of the ex¬ 
periment. If constant voltage alternating current is 
used, the meter readings are changed to cell conduct¬ 
ances and these converted to gas concentrations with 
the aid of the known cell constant and the tem¬ 
perature. Actually, from data obtained in laboratory 
experiments, charts and scales are constructed for 
each gas, from which the gas concentrations can be 
obtained directly from corrected meter readings. 

17.4.4 Notes 

1. This instrument was designed originally to 
operate as an independent battery-powered unit. As 
such, it has no peer among present field sampling 
devices for overall performance. It gives arrival times, 
duration, total dosage, maximum concentration, and 
other characteristics of gas clouds with sufficient ac¬ 
curacy for practically all purposes. It will perform all 
functions especially ascribed to the various samplers 
previously described, but may not perform some func¬ 
tions as well as will some of the other instruments. 
For example, the response is slower than that of the 
hot wire analyzer, and consequently, if the interval of 
time between a bomb burst and the arrival of the gas 
is extremely short this time interval can be measured 
more accurately and more easily by the hot wire 
instrument. 


2. The instrument is much easier to service when 
operated on a 115-v a-c circuit and since there is no 
drift in the calibration points the records are simpler 
to evaluate. However, the use of alternating current 
restricts the location of tfie instrument and intro¬ 
duces all the disadvantages of a wired experimenting 
area mentioned previously in discussing the hot wire 
analyzer. 

3. The lower limit of sensitivity varies somewhat 
for the different gases but, in general, concentration 
measurements below 0.3 mg per 1 will not be reliable. 
Accordingly, total dosages from low concentrations 
over a long period of time cannot be obtained satis¬ 
factorily with this sampler. 

4. In addition to the toxic gases mentioned above, 
this analyzer has been used successfully with am¬ 
monia and sulfur dioxide. Distilled water was the 
solvent in each case. 

17.5 ROTARY DISTRIBUTOR SAMPLER 9 

The first model of this apparatus was designed and 
built by a member of Division 10 at Dug way Proving 
Ground. Subsequent changes in design were made in 
cooperation with the Chemistry Section there. 

17.5.1 Operation of Sampler 

This sampler was designed to pull air at a known 
rate through a bubbler tube for a controlled interval 
of time, and then shift to another tube and so on up 
to as many as 20 samples with some models. This was 
done by use of a continuously acting pump which 
could be connected successively to different absorp¬ 
tion tubes by the intermittent movement of a rotary 
mechanism. The latest model was designed to operate 
by electrical impulses from a central control point. 
The current activated a solenoid which permitted a 
ratchet mechanism to move forward one space. A 
clock spring mounted in the instrument and attached 
to the rotary arm produced power for rotation. The 
motion was quite rapid so that there was little time 
lost between the termination of sampling through one 
bubbler and the beginning of sampling on the next. 

The absorbing solutions and methods of analysis 
were essentially the same as those described in 
Section 17.2. 

17.5.2 Notes 

1. When the instrument was used for the duration 
of the cloud, it was possible to calculate the total Ct 
at the sampling point. However, it was more than a 


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FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 


total dosage meter, for it could be used to give the 
dosage, and, hence, the average concentration over 
short periods of time up to the limit of sample tubes. 
Thus, it proved especially useful for obtaining “sur¬ 
prise” dosages from single munitions. The dosages 
for the first 30 seconds first minute, etc., could be 
obtained very well. 

2. The sampler was used with power and control 
wires emanating from central points, and, hence, was 
subject to hazards caused by wire being cut by bomb 
fragments and to other disadvantages associated with 
the wiring of an area for tests. 

3. An early model made use of an automatic starter 
and was designed to be self-contained with no neces¬ 
sary external wiring. A pair of conductivity cells was 
arranged in a bridge circuit and connected to a pump 
so that air was pulled through the cells in series. The 
presence of CG or any agent producing a conductivity 
change upset the bridge balance and tripped a relay 
in the plate circuit of a single tube amplifier. The 
relay in turn started an alarm clock equipped with 
contact on one gear which activated the rotary distri¬ 
bution solenoid. Further, by noting the time of gas 
release and the reading of the alarm clock after the 
test, the time for the gas to reach the sampler could 
be found within limits. 

17.6 THE FIELD CANISTER TESTER 

This apparatus, which is sometimes referred to as 
the mechanical goat, was developed in the Division 
10 Central Laboratory, Northwestern University. It 
was able to draw air through canisters in a manner 
designed to simulate the human breathing cycle and 
was used to evaluate the performance of canisters in 
actual gas clouds. 

Figure 8 is a schematic diagram of the field tester. 
The bellows pump C is operated by a small 120-v 
a-c motor D which is geared down internally to 
25 rpm. The connecting rod which works the bellows 
can be connected to either one of two positions on the 
crank disk which correspond to pump capacities of 
16 and 32 1pm, respectively. Air is drawn into the 
bellows through the canister and valve A and then 
forced out through valve B. 

By means of the small pump H, which maintains 
reduced pressure in chamber I, continuous sampling 
of the canister effluent stream is done at point E and 
the gas is drawn through an appropriate absorbing 
reagent in G. The capillary J keeps the flow constant 
at a known rate. By sampling with a conductivity 


meter at point F a continuous effluent concentration 
curve can be obtained. The pumps and motor are en¬ 
closed in a weatherproof case and are protected from 
the corrosive gases by a breather canister K. 

17.6.1 Operation of the Tester 

The tester is always placed in the field beside one 
of the sampling devices previously described so that 
the total dosage of exposure is obtained. The solutions 
used in G are the same as used with the diaphragm 
pump samplers. The operation of the conductivity 
meter, which is attached at point F, is described in 
the previous section. 

17.6.2 Notes 

1. This apparatus was designed and used on the 
assumption that since the lethal dosages of the 
several gases were known, it would give more data, 
and more reliable data, concerning the penetration of 
canisters in the field than could be obtained by the 
use of animals. For a known exposure, it will give the 



Figure 8. Schematic diagram of field canister testing 
apparatus. 


total effluent dosage at a known breathing rate, the 
shape of the effluent curve, and a measure of the 
amount of desorption from the charcoal. In animal 
field experiments so far devised, if the animal survives 
the gas cloud it is certain that he did not draw a 
lethal quantity of agent through the canister, but if 
he dies, it is not known (a) whether the agent came 
through the charcoal or from facepiece leakage, 
(b) whether he died exclusively as a result of the 
agent or a combination of agent and strangulation, 


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OTHER SAMPLING DEVICES 


293 


(c) whether the dosage which came through the 
canister was large or small, or (d) whether the animal 
died as the result of direct canister penetration or 
desorption from the charcoal after the gas cloud had 
passed. 

2. With canisters that broke slowly, the conductiv¬ 
ity meter gave only moderately valuable results when 
used in conjunction with this apparatus, because it 
did not measure low effluent concentration with 
sufficient accuracy. Accordingly, it was found desir¬ 
able, whenever practical to do so, to go into the field 
and change bubblers G, at known times. In this way, 
effluent Ct values could be obtained accurately and 
the shape of the effluent Ct curve could be obtained 
approximately. 

17.7 OTHER SAMPLING DEVICES 

Mention is made in this section of several sampling 
methods which were developed and used by other 
United States and Allied agencies but which were not 
used in field experiments by Division 10. Reference 
is made also to some methods which offered promise 
but which never got beyond the developmental stages. 

17 . 7.1 The Snap Sampler 

In this device an evacuated vessel is opened at a 
selected time in a gas cloud, the air enters and sub¬ 
sequently the amount of agent is determined. An 
almost instantaneous sample is obtained, but since 
gas clouds are not homogeneous especially in the 
first few minutes of their existence, the results from 
snap samplers may be misleading. If a number of 
consecutive samples are taken the discrepancies tend 
to be eliminated, and a fairly accurate total dosage 
can be obtained by plotting concentrations vs time, 
and drawing a smooth curve through the points. 

An instrument which operated on this principle was 
made under a Division 10 contract at Stanford Uni¬ 
versity, and was used extensively at Dugway Proving 
Ground by the Chemical Warfare Service. It con¬ 
tained ten evacuated tubes which were opened at 
known time intervals by means of a clock mechanism. 
Various modifications of the device were made at 
Dugway. A sampler operating on the same principle 
and known as the Berthette is used at Suffield, 
Canada. 

17 . 7.2 The Ultraviolet Photometer 1 

This instrument, which was developed at North¬ 
western University for gas sampling, will give con¬ 


centrations of gases (such as phosgene) which ab¬ 
sorb strongly at a wavelength of 2537 A. It is used 
with a continuous recorder. It is probably an ulti¬ 
mate standard in sampling for those gases for which 
it is applicable. The response is rapid and the calibra¬ 
tion can be very exact. However, as originally built, 
the instrument was not sufficiently rugged for field 
use and, since it could analyze only gases which 
absorbed the above-mentioned wavelength, it was 
not used extensively. 

17 . 7.3 The Air Injector 

At Suffield, Canada, compressed air injectors were 
used to obtain total dosage during the passage of gas 
clouds of small duration. Over short periods of time 
the injectors could aspirate the gas through an ab¬ 
sorbing tube at a very nearly constant rate. The ab¬ 
sorbing solutions were analyzed by standard methods. 

17 . 7.4 The Tape Recorder 

This sampler was developed under a Division 9, 
NDRC, contract at the University of Chicago. It 
draws a known volume of gas through a frame on a 
strip of specially impregnated filter paper. An auto¬ 
matic mechanism then moves the strip forward one 
frame and repeats the process. The gas cloud is 
sampled at 2- or 6-sec intervals. The tape, which is 
cut and perforated like a 16-mm movie film, is an¬ 
alyzed by a photoelectric measurement of the in¬ 
tensity of the color produced on the paper by the gas. 
The instrument can be set to cover a fortyfold range 
of concentration, within the anticipated range. The 
instrument is portable and completely self-contained 
in a single small box. Considerable difficulty was en¬ 
countered in developing satisfactory tapes for the 
various gases, and, as a consequence, the samplers 
were not used to an appreciable extent in the large- 
scale field experiments discussed elsewhere in this 
volume. 

17 . 7.5 Radio Control for Samplers 

The rotary distributor sampler and other samplers 
described in this chapter could be adapted to radio 
control. This would eliminate the problems associ¬ 
ated with wiring a testing area, and possibly would 
simplify many of the other problems connected with 
large-scale experiments. At Northwestern University 
experimental models of a radio transmitter and a re¬ 
ceiver were made which appeared to operate a rotary 


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294 


FIELD SAMPLING METHODS FOR NONPERSISTENT GASES 


sampler very well. However, at the time this was 
done, the need for performing field tests without 
delay was so great that the models were set aside, 
and the experiments were carried out with the equip¬ 
ment available. With the new developments which 
are being made in electronics, there is no doubt that, 
in the future, excellent remote radio controlled 
samplers can be made. 

17.8 SUMMARY AND SUGGESTIONS 

In the course of the many field experiments with 
nonpersistent gases performed or cooperated in by 
contracts of Division 10, most of the samplers de¬ 
scribed in this section have proved very useful. The 
nature of the experiment to be performed determines 
the types of sampler that should be used. Accord¬ 
ingly, an installation designed to do a large variety 
of tests should have several kinds of samplers avail¬ 
able. 

If the characteristics of clouds liberated from single 
munitions are to be determined, recording instru¬ 
ments with a rapid response are necessary. In multi¬ 
ple bomb tests made over a comparatively large area 
the relative importance of recording instruments 
diminishes, although some should be used; a large 
number of total dosage samplers, such as the hydro¬ 
static head pump and the diaphragm pump, should 
be employed. 

If a test area is in the open country, without vege¬ 
tation, where many experiments (usually of short 


duration) may be run, it is doubtlessly advantageous 
to wire the area for alternating electric current in 
order to operate samplers. However, in wooded and 
jungle areas where wiring is difficult to accomplish 
and where only a few experiments can be performed 
before the trees are defoliated as a result of the action 
of the gas, it is desirable to use independent, self- 
contained samplers as much as possible, and thus 
reduce the stringing of wires to a minimum. 

In large-scale experiments of from to 4 hr dura¬ 
tion it was found satisfactory to use a limited number 
of recording instruments at strategic locations to get 
arrival times, maximum concentrations, and cloud 
durations, and to depend on total dosage, bubbler- 
type samplers to furnish the remaining necessary 
sampling information. Hydrostatic head samplers 
were used in parts of the area where the dosages were 
expected to be high, and diaphragm pumps were 
placed at distant points where only traces of gases 
were expected. The hydrostatic head pumps operate 
only for a limited time and hence must be serviced 
shortly before the gas is liberated. Accordingly, it is 
best to have them at accessible points. Also, they are 
easy to make from nonstrategic material, and thus, 
being expendable, can be placed right up in the 
target area without danger of an irreplaceable loss. 
Because the diaphragm pumps will operate for hours, 
they are good to put in distant and inaccessible 
places since they can be serviced long before an ex¬ 
periment is scheduled to start, giving the operator 
ample time to leave the area before the cloud is 
released. 


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PART III 


AEROSOLS 


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Chapter 18 

GENERAL PROPERTIES OF AEROSOLS 

By W. H. Rodebush 


18.1 INTRODUCTION 

he term aerosol is used to designate particles dis¬ 
persed in a gaseous medium. The term particulate 
is preferred in Great Britain and more specific and 
familiar terms such as smoke , fog, and dust should be 
used whenever applicable. For example, an aerosol of 
particles of diameter less than about one micron will 
exhibit the characteristic behavior of a smoke and 
may be properly so designated. The particles of 
which the aerosol is composed may be either solid or 
liquid. If liquid the particles will be spherical, but 
solid particles will usually behave approximately as 
spheres. 

18.2 STABILITY 

Aerosols, like most colloidal forms of matter, are 
essentially unstable, and will usually disappear with 
the passage of time either by evaporation or precipi¬ 
tation. Evaporation will occur if the substance of 
which the aerosol is composed has an appreciable 
vapor pressure at room temperature. The vapor 
pressure of a small drop is larger than that from a 
large mass of substance, but this effect is not im¬ 
portant for a drop diameter greater than 0.01 micron. 1 

Precipitation may occur as a result of diffusion or 
settling. The diffusion constant varies inversely as 
the particle diameter, and the rate of diffusion to a 
wall depends upon the concentration of aerosol in 
the surface layer. Unless the surface layer is con¬ 
stantly renewed the concentration quickly falls to 
zero, and only by very violent stirring can the surface 
layer be kept moving with sufficient velocity to main¬ 
tain the diffusion process. 

These statements concern ordinary or kinetic dif¬ 
fusion. Thermal diffusion is the process by which an 
aerosol is deposited on cold surfaces. It is a much 
more effective process in the precipitation of aerosols 
but the theory of thermal diffusion is not in very good 
agreement with the observed facts. 

Settling, ordinarily, accounts for the precipitation 
of aerosols of diameter 1 micron or greater. According 
to Stokes’ law a particle falls with a steady velocity 
which is proportional to the square of the diameter. 
The instantaneous rate of precipitation is independ- 


i 

\ 

ent of the amount of stirring (within limits) because 
the layer of air,in contact with the surface remains 
stationary and the particles fall through this layer 
at constant velocitjr. 

It follows, therefore, that aerosols of large particle 
diameter disappear by settling, and those of very 
small particle diameter by diffusion. For particles in 
the range of 0.1 to 1.0 micron diameter, the diffusion 
constant is small and the Stokes’ law rate-of-fall is 
small. Smokes, which are usually composed of par¬ 
ticles in this size range, therefore, are remarkably 
stable, and remain dispersed for long periods of 
time. The foregoing statements apply to aerosols 
which do not carry electrical charges. The behavior 
of charged aerosols will be discussed later. 

18.3 COAGULATION 

When a particle of small diameter collides with a 
surface it adheres because of surface forces. Large 
dust particles may be dislodged by a strong blast of 
air so that air cleaners are often coated with a film 
of oil or sticky liquid, but small particles will adhere 
regardless of the surface. Similarly, the collision is 
inelastic and a single particle is the result when two 
particles collide. If the particles are liquid they 
coalesce to a single drop whereas solid particles form 
aggregates which often take the form of chains and 
resemble fibers on casual inspection. This coagulation 
resembles a bimolecular mechanism, and is described 
by the equation for a second order reaction. Table 1 

Table 1 . Rates of coagulation ( t 0 ) equals time required to 
reduce the number of particles to one-tenth of the initial 
number. W equals mg per 1, assuming diameter equals 
1 n, and density equals 1. 


No. per cm 3 

W mg per 1 

to sec 

10 10 

5,236 

3 

10 9 

523.6 

30 

10 8 

52.36 

300 

10 7 

5.236 

3,000 


gives the approximate times necessary to reduce the 
number of particles to one-tenth of the original num¬ 
ber [computed on the basis of equation (19), Chap¬ 
ter 19]. 



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298 


GENERAL PROPERTIES OF AEROSOLS 


As a result of this coagulation a smoke of uniform 
small particle size will become heterogeneous, and the 
larger particles will settle out. It follows, therefore, 
that a smoke with a concentration of particles greater 
than 10 7 per cubic centimeter will not be stable. 
There is no method known for preventing the coagu¬ 
lation of aerosols. The stabilizers which are effective 
for preventing the coagulation of solids or liquids dis¬ 
persed in a liquid medium are completely ineffective 
with aerosols. 

18.4 FORMATION OF AEROSOLS 

Natural-occurring fogs are of relatively large par¬ 
ticle size, 10 to 50 microns diameter, and of relatively 
low concentrations, a few droplets per cubic centi¬ 
meter. Each droplet is formed by the condensation of 
water on a nucleus, which in the neighborhood of 
cities may be a particle of dust or soot. Near the 
ocean, minute salt crystals, which are thrown into 
the air by spray, serve as nuclei, and the water col¬ 
lected always contains dissolved salt. Therefore, fogs 
are more common near the ocean, or in the neighbor¬ 
hood of large cities, or industrial areas. 

Because of the large particle size, fogs tend to fall 
out as a fine mist or rain, and this process is acceler¬ 
ated by the tendency of the small drops to evaporate; 
the vapor condensing on the larger drops. Thus, fogs 
will only persist if meteorological conditions are such 
that new drops are constantly forming to replace 
those that fall. 

The droplets of natural fogs often carry consider¬ 
able electrical charges and the accumulation of these 
charges accounts for the electrical effects that oc¬ 
cur in thunderstorms when the small drops coalesce 
rapidly to form larger drops. It may be remarked 
that the conditions which produce rapid coalescence 
and the heavy downfall of rain are not compatible 
with the conditions that produce fog, and vice versa. 

The methods of producing aerosols artificially fall 
into two categories: mechanical dispersion, and vapor 
condensation. Mechanical dispersion appears at first 
thought to offer the most promise. The work re¬ 
quired to break up a liquid into drops of 1 micron 
diameter is negligible when compared to the heat of 
vaporization. There are two difficulties. The first is 
that the only method for bringing about this break¬ 
up is that of turbulent flow through a nozzle which 
is, of course, a very inefficient process mechanically. 
An even more fundamental difficulty, however, is 
that the concentration of drops leaving the nozzle 


is so high that most of the small drops coagulate be¬ 
fore leaving the immediate vicinity of the nozzle. 
This difficulty can be avoided only by using an as¬ 
pirator nozzle, and maintaining a very high air 
velocity to scatter the drops before they can coalesce. 
One hundred and fifty cubic feet of air at 50 lb pres¬ 
sure per gallon of liquid will give only a fair disper¬ 
sion. The dispersion of solids is even more difficult. 
The solids must be ground to the required particle 
size, which is a very inefficient process mechanically, 
and then dispersed in an air jet. It has been pointed 
out earlier that the surface forces which cause par¬ 
ticles to adhere are relatively very strong so that it is 
difficult to bring a sufficient shearing force to over¬ 
come them by a blast of air. The operation of grind¬ 
ing and dispersal may be combined in one operation 
by the use of a micronizer but the process remains an 
inefficient one. 

The most satisfactory way to produce an aerosol is 
to imitate the process by which natural fogs are pro¬ 
duced. Any substance which can be vaporized with¬ 
out decomposition can be converted to an aerosol by 
blowing a jet of the vapor into cool air. When the 
degree of supersaturation is small, drops will not 
form by condensation except on nuclei which may be 
present in the form of ions, dust particles, etc. When 
the degree of supersaturation is great, as when the 



Figure 1. Electron microscope picture of magnesium 
oxide smoke particles. 

vapor of a high boiling oil escapes into the atmos¬ 
phere at high velocity, an enormous number of very 
small droplets will be formed. It is difficult to see 
what sort of nuclei can be present in such enormous 
numbers but it cannot be stated categorically that 
nuclei are not present. It may be in the case of the oil 
that the larger molecules behave as nuclei. Coagula¬ 
tion takes place very rapidly as described in Chapter 
22 but the size range remains narrow as the process 


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FILTRATION 


299 



Figure 2. Electron microscope picture of titanium 
oxide smoke particles. 


goes on, so that it is possible to control the size of 
droplets quite precisely by regulating the rate of 
vapor flow. 

A modification of the vapor condensation process 
is used when smokes are produced by combustion. 
When magnesium ribbon is burned, the ultimate par¬ 
ticles produced are nearly perfect crystals of mag¬ 
nesium oxide which are too small to be seen by the 
ordinary microscope, but are revealed by the electron 
microscope 2 as shown in Figure 1. These submicro- 
scopic crystals agglomerate into chains and clusters 
of fantastic shape and structure, which appear under 
the microscope as though they were solid particles. 
Figure 2 is an electron microscope photograph of 
titanium particles produced by thermal dispersion. 
When carbon smoke is produced by incomplete com¬ 
bustion the small crystals of graphite tend to form 
filaments that resemble a string of beads (see Figure 
3). This tendency of soot and dust particles to form 
filaments often deceives the housewife who supposes 
these “cobwebs” to be produced by spiders. 

18.5 ELECTRICAL PROPERTIES OF 
AEROSOLS 

Except for special cases, which will be discussed 
later, electrical charges are of minor importance. 
Most of the particles produced are uncharged, par- 



Figure 3. Electron microscope pictures of carbon par¬ 
ticles from camphor smoke. 

ticularly if the concentration of the aerosol is high, 
since normally there are only a few ions present per 
cubic centimeter. Even in the case where ions are 
produced by special means to serve as nuclei, the 
resulting aerosol will contain many uncharged par¬ 
ticles, since the positively and negatively charged 
particles have a tendency to neutralize each other by 
agglomeration. If it is desired to precipitate aerosols 
in a uniform field, it is necessary to charge the aerosol 
before the process will be effective. 

18.6 FILTRATION 

Neither electrical nor thermal precipitation have 
proved in the past to be practical for the rapid re¬ 
moval of aerosols. Filtration appears to be, by long 
odds, the most satisfactory method of precipitation. 
Aerosol filters consist of loosely aggregated fibers, 
and, in order to avoid excessive resistance to the flow 
of air, the mesh of the filter must be large compared to 
the size of the particle to be removed. There is there¬ 
fore no screening action; the removal of a particle 
depends entirely upon a chance collision of the par¬ 
ticle with a fiber of the filter. Once having collided, 
the particle adheres by the natural forces which are 
always operative. 

Very large particles can be precipitated by centrif¬ 
ugal action as in a cyclone separator. For smaller 
particles whose diameter is in the neighborhood of 
1 micron the centrifugal action is no longer effective 
since the inertia of the particle is not sufficient to 
overcome the resistance of the air. Thus the air flows 


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300 


GENERAL PROPERTIES OF AEROSOLS 


around the fibers of a filter in stream lines and the 
particles are carried around with the stream lines. 
There is a range of particle sizes for which a higher 
velocity will improve the operation of the filter since 
the inertial effects will carry the particles across the 
stream lines into collision with the fibers of the filter. 
For particles smaller than 1 micron diameter no 
inertial effects exist, but the kinetic diffusion becomes 
of greater importance in the smaller particle. Very 
small particles(« 0.01 micron) are precipitated very 
rapidly by diffusion. The process is analogous to 
the condensation of a vapor on a cold surface. The 
particles most difficult to remove by filtration are 
those in the range 0.1 to 1.0 micron, i.e., smokes. In 
order to obtain efficient filtration without excessive 
resistance the filter must contain fibers of small 
diameter approaching that of the particles them¬ 
selves. 

18.7 BULK DENSITY OF AEROSOLS 

It will be apparent from reference to Table 1 that 
the increase in density of the air due to the presence 
of an aerosol cannot be very great unless (1) the 
number of particles per cubic centimeter is very 
large, or (2) the particle size is very large. If the 
number of particles per cubic centimeter is large, 
however, the particle size will increase rapidly so 
that the second condition is actually the only one 
under which a considerable mass of aerosol can be 
present. If the particle size is very large, the particles 
will fall so rapidly under the force of gravity that the 
aerosol concentration cannot persist. If a high con¬ 
centration of aerosol particles of 10 microns diameter 


could be produced, a very great increase in the bulk 
density of the air would result, but there is no simple 
method of doing this. In general, therefore, the den¬ 
sity of an aerosol cloud does not differ greatly from 
that of the air itself. 

18.8 OPTICAL PROPERTIES 

Lord Rayleigh called attention to the very im¬ 
portant optical properties of finely dispersed par¬ 
ticles in his theory of the blue color of the sky. The 
theory of optical behavior is still obscure for opaque 
or reflecting particles but for transparent spheres 
such as oil drops the behavior is now well under¬ 
stood (see Chapter 21). The maximum scattering 
effects are obtained when the particle size approxi¬ 
mates the wavelength of the light being scattered. 
The greatest scattering is in the forward direction 
and the maximum polarization is at right angles to 
the incident light. It is entirely a coincidence that the 
particle size which gives the greatest stability against 
precipitation and filtration lies in the range which 
gives the maximum scattering for visible light. 

18.9 SMOKE SCREENS 

Smoke screens composed of small drops of trans¬ 
parent liquids actually have greater obscuring power 
than those of opaque particles. The reason for this is 
that the transparent drop transmits a background of 
light which makes it difficult for the observer to dis¬ 
tinguish inconspicuous objects. This effect is par¬ 
ticularly important when the observer is facing the 
sun so that the forward scattering causes a glare. 


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Chapter 19 

STABILITY OF AEROSOLS AND BEHAVIOR OF AEROSOL PARTICLES 

By David Sinclair 


19.1 DEFINITIONS 

n aerosol is an assemblage of small particles, 
solid or liquid, suspended in air. By small par¬ 
ticle is meant a particle with a radius less than about 
50 microns. The usual range of particle radii in 
aerosols is from 0.1 to 10 microns, although particles 
as small as 0.01 micron may be encountered. 

Aerosol is the generic term for dust, smoke, fog, 
and haze. Dust is commonly thought of as solid 
particles of any material blown up by the wind, 
smoke as solid particles of ash or carbon resulting 
from fires, and fog as water droplets. These defini¬ 
tions are satisfactory for natural aerosols. For arti¬ 
ficial aerosols, a smoke is defined as an aerosol of 
solid particles, and fog is defined to include droplets 
of any liquid such as water, oil or acid. 

The different types of aerosol frequently overlap. 
Carbon may produce a smoke or a dust. Tobacco 
smoke is very hygroscopic and consists chiefly of 
water droplets. When fresh, stearic acid aerosol is a 
fog of supercooled droplets, which slowly change to 
a smoke of crystal particles. Haze may be composed 
of fine particles from any source. 

19.2 RANGE OF PARTICLE SIZE 

The range of particle sizes in the various types of 
aerosol is considerable. Dust may range from fine 
particles of 0.1 micron radius or less, which produce 
haze, to sandstorms having large particles beyond 
the range considered to be aerosols. Smoke is often 
composed of extremely fine primary particles which 
have coagulated to form groups (see Figures 1 and 2 
in Chapter 18, 1 and 2 in Chapter 22). Carbon smoke 
is composed of small primaries about 0.01 micron 
radius which coagulate into long irregular filaments 
that may reach several microns in length (see Figure 
3, Chapter 18). Screening oil for droplets should be 
about 0.3 micron radius for maximum screening. 
Water fog droplets are much larger, ranging from 
4 to 40 microns in radius. 

19.3 STABILITY 

The stability of an aerosol is determined by a 
number of factors. The individual particles may move 


about under the influence of several different forces: 
(1) Brownian movement, which consists of random 
oscillations and rotations causing coagulation, ac¬ 
companied by drift which results in diffusion to any 
solid object such as the walls of a containing vessel 
or the ground; (2) settling under gravity; (3) thermal 
forces, causing movement of the particles toward any 
object colder than its surroundings; (4) electrical 
forces; (5) acoustical forces; and (6) centrifugal 
forces. 

In addition, convection currents are usually present 
which consist of motion of large or small regions of 
the aerosol relative to other regions. 

Finally, there may be evaporation, causing the 
particles to decrease in size and even disappear, and 
condensation which may cause the particles to in¬ 
crease in size until they fall out very rapidly. 

Under ordinary conditions the stability of an 
aerosol is chiefly affected by the Brownian oscilla¬ 
tions and by gravity settling. Owing to the Brownian 
oscillations the particles collide and either adhere or 
coalesce. If the particles are solid they adhere to 
form more or less loose aggregates which may be 
roughly spherical in shape as those for ZnO or al¬ 
bumin, or filamentary like carbon. If the particles are 
spherical droplets such as oil or water fog, they 
coalesce to form larger spherical droplets. As a result 
of this coagulation process, the number of particles 
per unit volume of aerosol and the number concentra¬ 
tion decreases, and the average size of the particles 
increases. 

Filtration of fine particles is largely a diffusion 
process (see Chapter 23). Otherwise, except for an 
aerosol of very fine and highly concentrated particles 
in a small containing vessel, 1 diffusion is unimportant. 

The question often arises as to the efficiency of 
collision, i.e., what proportion of the colliding par¬ 
ticles will adhere rather than rebound. It would be 
difficult to observe the process directly under the 
microscope, but indirect experiments indicate that 
the collision process is 100% efficient. In most ex¬ 
periments, the observed coagulation of solid particles 
is greater than that calculated from the simple theory, 
and not less, as it would be if the efficiency of collision 
were appreciably less than 100%. In the case of 



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301 


302 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


liquid droplets it can be safely assumed that all drop¬ 
lets will coalesce on collision. Whytlaw-Gray 2 finds 
that his experiments on coagulation justify the as¬ 
sumption of 100% efficiency. We know of no experi¬ 
ments to contradict it. 

Numerous attempts have been made to surface- 
treat solid particles, 3 or charge them electrically so 
that they would be less likely to adhere on collision, 
but no significant effect has as yet been observed. 
The only observed effect has been either to cause 
aerosol particles to disappear more rapidly, or to 
cause the particles in powder form to adhere less 
tightly, thus making them more easily dispersed in 
an air jet or by explosion. In the aerosol state, the 
forces of adhesion are always greater than any ordi¬ 
nary forces of separation. 

Under the force of gravity, aerosol particles settle 
onto any surface having a horizontal component. 
The large particles settle out faster than the small 
particles, the rate of settling being proportional to the 
cross-sectional area of the particle. As a result, both 
the number concentration and the average particle 
size decrease. 

Because of their comparatively small size, the par¬ 
ticles adhere to whatever type of surface they settle 
upon, and the efficiency is again 100% as in the case 
of coagulation. The forces of adhesion are greater 
than the ordinary forces tending to pull the particle 
away from the surface. 

Whenever aerosol particles are found adhering to 
vertical or inverted surfaces, forces other than gravity 
must be present. 

Thermal and electrical forces are more common 
than generally realized. Dust near steam pipes or 
other hot bodies is precipitated onto the neighboring 
walls or ceiling. Ink fog in printing plants or dust in 
textile mills is precipitated onto the walls or ceiling 
by static electrification from the rollers or other 
machinery. Filtration is in some cases due largely 
to static electrification. 

Acoustical forces are also fairly common. Sound 
vibrations above a certain minimum frequency, de¬ 
pending on the particle size, increase the rate of 
coagulation. Intense vibrations in factory buildings 
may cause precipitation, particularly in pipes. Thun¬ 
der claps and explosions are known to precipitate 
rain and dust. Air raid sirens and similar sound 
sources will precipitate natural and artificial water 
fog. 

Centrifugal forces large enough to cause coagula¬ 
tion or precipitation are less common. Small particle 


aerosols will travel around bends in pipes or through 
constrictions (provided they are free of sharp edges) 
without serious precipitation. For example, a particle 
of 0.1 micron radius requires a centrifugal accelera¬ 
tion of one million times gravity to precipitate it in 
a centrifugal separator. 4 Much of the coagulation of 
small particle aerosols in pipes and ducts is attributa¬ 
ble to thermal, electrical, or acoustical forces rather 
than to centrifugal forces. This is not true, however, 
for aerosols of large particles, i.e., radii above a few 
microns. 

One or the other of these factors may dominate in 
determining the stability of an aerosol. In a natural 
water fog, settling is the predominant factor, as it 
usually is in large particle aerosols. In flue gases, 
which contain very large numbers of very fine par¬ 
ticles, coagulation is very rapid at first. Later, set¬ 
tling becomes more important, usually after emission 
into the atmosphere. In the case of screening oil fogs, 
evaporation and wind are the important factors. 

Dilute aerosols of fine solid particles that neither 
coagulate nor evaporate may be so stable as to per¬ 
sist almost indefinitely. For example, volcanic dust, 
which may be expelled into the air several miles 
above sea level and which has a particle radius of 
0.3 micron, falls at the velocity of about one mile 
per year. This is the size of the droplets of a screening 
oil fog. It is the slow rate of fall of fine particles that 
makes it possible to maintain a smoke screen for long 
periods. 

19.4 SETTLING OF AIRBORNE PARTICLES 
UNDER GRAVITY 

19.4.1 Uniform Particle Size or Homo¬ 
geneous Aerosols 

In aerosols of uniform particle size, which may be 
produced in the laboratory by a method described in 
Chapter 20, two cases may be distinguished: (1) set¬ 
tling when the aerosol is completely free from convec¬ 
tion currents, called tranquil settling, and (2) settling 
when the aerosol is kept stirred so that the concen¬ 
tration throughout the containing vessel is uniform 
at all times. 

Tranquil Settling 

In tranquil settling all the particles fall with the 
same velocity. The cloud will have a well-defined flat 
top which will be observed to fall with a constant 
velocity equal to that of a single particle. This is the 
basis of a method of measurement of the particle 
radius of a uniform aerosol, described in Chapter 22. 


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SETTLING OF AIRBORNE PARTICLES UNDER GRAVITY 


303 


The velocity of fall in centimeters per second is 
given by Stokes’ law 5 of fall of small spheres in a 
continuous viscous medium. In air 

2 r 2 pq 

v = - — = 1.2 X 10V 2 , (1) 

9 T] 

where r is the particle radius in centimeters, p the 
particle density, q the coefficient of viscosity of the 
air, and g the acceleration of gravity. 

This law is correct to 5% or better for spherical 
particles between 1 and 50 microns radius. The par¬ 
ticles fall with a velocity less than that given by 
Stokes’ law when they are so large 6 that vr = n\/p h 
where pi is the density of the air. For air rj/pi = 0.15 
and when r = 50p, vr — 0.15 for particles of unit 
density. For such particles the velocity becomes so 
large that turbulence occurs, decreasing the velocity 
more than does the viscous drag alone. 

For smaller particles whose size is comparable with 
the mean free path of the air molecules, a correction 
must be applied to compensate for the tendency of 
the particles to “slip” between the air molecules, and 
thus move faster than predicted by Stokes’ law. This 
correction has been calculated from Cunningham’s 
equation 5 and it was found that the true radius is 
given quite accurately by subtracting 0.04 micron 
from the Stokes radius (in microns), for all radii be¬ 
tween 2 and 0.1 microns. 

For still smaller particles the correction is much 
larger. However, the velocity of fall of particles be¬ 
low 0.1 micron is so small that it is extremely difficult 
if not impossible to make observations of their set¬ 
tling velocity. 

Stokes’ law applies strictly only to spherical par¬ 
ticles. Millikan 7 has shown, however, that the law 
holds quite well for particles whose shape is somewhat 
different from spherical. 

Stirred Settling 

In stirred settling the motion of the particles is 
complicated by random convection currents. Ex¬ 
cept for very large particles or violent stirring there 
is little or no impingement on the walls or ceiling. 
Nearly all the particles eventually settle on the floor. 

The horizontal components of convection current 
have no effect on the velocity of fall. Since the up¬ 
ward convection currents will, on the average, ex¬ 
actly compensate for the downward convection cur¬ 
rents they also have no effect on the velocity of fall. 
The convection currents merely serve to keep the 
concentration uniform throughout the containing 


vessel. The result is that the concentration continu¬ 
ously decreases as the settling continues so that the 
amount of aerosol settling out per unit of time con¬ 
tinuously decreases. 

The number of particles dn that settle out during a 
small interval of time dt is proportional to the number 
concentration n at the time t. The fraction of particles 
having velocity of fall v that settle out of a rectangular 
box of height h in time dt is 


By integrating this equation we find that 

n = n«T’ tlh , (2) 

where n 0 is the initial concentration in the box. Thus 
the rate of settling (in terms of the number of par¬ 
ticles per second), as well as the number concentra¬ 
tion, decreases exponentially with time. 

19.4.2 Heterogeneous Aerosols 

In ordinary aerosols, composed of particles of many 
sizes, the settling process is more difficult to analyze. 
Again the two cases of tranquil and stirred settling 
will be considered separately. 

Tranquil Settling 

In tranquil settling, a differential separation ac¬ 
cording to size will occur, which may be analyzed as 
follows. Suppose at time t = 0 the concentration is 
uniform throughout the containing vessel and no 
convection currents are present. The particles of 
radius r will begin falling with the constant velocity 
v r corresponding to that radius, and will continue to 
fall with that velocity independent of larger or smaller 
particles. 

Consider a layer in the aerosol at a height x below 
the top of a containing vessel. At a time ti = x/vi 
there will be no particles in or above this layer, of 
radius greater than r x . At a greater time ^ = x/v 2 , 
there will be no particles in or above this layer of 
radius greater than r 2 , where r 2 is less than r\. Conse¬ 
quently, observation of the decrease in number con¬ 
centration at a height x, during the time interval 
t 2 — t\ will give the number of particles having veloci¬ 
ties of fall between v 2 and Vi, or radii between r 2 and r h 
given by Stokes’ law. 

This is the principle of the differential settler, 
described in Chapter 22, in which the decrease in 
number concentration is measured by the decrease 
in scattered light. 


SECRET 



304 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


Stirred Settling 


The analysis of stirred settling of heterogeneous 
aerosols is more complicated. Each group of particles 
of radius r will settle exponentially, at a rate given by 
equation (2). The following discussion is based on the 
assumption that the particles have a logarithmic 
probability distribution. 

Most natural distribution curves are found to be 
skewed from the symmetrical probability distribu¬ 
tion. The number at larger sizes decreases more 
slowly than at smaller sizes in such a way that the 
distribution curve is made symmetrical when the 
number at a given size is plotted against the logarithm 
of the size. 8 - 9 This type of distribution has been 
found approximately in the thermally generated 
smokes produced in the laboratory (see Chapter 20). 

One can characterize a given physical property of a 
heterogeneous aerosol, such as particulate volume or 
cross-sectional area, by an average diameter. For 
example, the total cross-sectional area of N spherical 
particles is ^irNdl, where 

d 2 = (nd 2 )/]Fn 

is the diameter of the sphere having the average area; 
and the total volume of these N particles is y^irNdl, 
where 

d* = ^(nd 3 )/En 


is the diameter of the sphere having the average 
volume. 

If the aerosol has a logarithmic probability distri¬ 
bution of sizes, the number of particles per cubic 
centimeter having diameter d is: 


n ex r (iogd-iQgrf,)» i 

lOgO-ffV^TT eXP L 2 log 2 Gg J 


(3) 


Here N is the total number per cubic centimeter of 
particles of all sizes, d 0 is the geometric mean diam¬ 
eter, i.e., 


log d g = 


Lfo lQ g d) 
N 


) 


which is equal to the number median diameter in 
this type of distribution and <j g is the geometric 
standard deviation, i.e., 


log <r 0 = 


i/ 


(w log d — n log d g ) 2 
N~ 


It follows that 


d\ = 


yidu j 

N 


i: 


d 2 exp 


i 

log a g \ / 27r 
T (log d - log d g ) 2 ~j § 
L 2 log 2 (Jg J 


with similar expressions for d 3 , d 4 , d m . These equations 
have been integrated 9 and it is found that, in 
general, 

TVtYl 

log d* = n log dg + 2.303 — log 2 a g . (5) 

At time t = 0, when the aerosol is formed, the 
number of particles per cubic centimeter having 
diameters between log d and log d -f- 8 log d is n d 
8 log d. Therefore the initial total cross-sectional area 
per cubic centimeter of particles is: 

Co = — f d 2 n d 8 log d = — N 0 d% . (6) 

4 Jo 4 

Similarly the initial mass concentration in grams 
per cubic centimeter is: 

/•co 

Mo = I (Pn '> s log d = ^ N 0 pdl ■ (7) 

o Jo b 

Due to stirred settling, the mass concentration and 
cross section per cubic centimeter decrease expo¬ 
nentially with time according to equation (2). There¬ 


fore, at time t : 

«=iJ 

d 2 n d exp 

0 

/ Vdt' 

\ h / 

) 5 log d , 

(8) 

and 

j * d 3 n d exp | 

f v d t\ 
K h) 

5 log d • 

(9) 


in Stokes, settling [equation (1)] the velocity v d 
in centimeters per second is 


Vd = 3.0 X 10 5 pd 2 . 


( 10 ) 


Taking the logarithm (to the base 10) of C and 
differentiating with respect to t, we obtain on substi¬ 
tuting the value of v d given by equation (10): 




1.3 X 10 5 


f 00 / v d t\ 

J d A n d exp ( — ~ J 8 log d 

J* d 2 n d exp ^ 5 log d 


(ID 


For time t, small compared to h/v, equation (11) 

becomes: f°° 

J dHi d 8 log d 


- j log C, = 1.3 X 10 5 f 
dt h 


or 


f. 


d 2 n d 8 log d 


-lkgC.-UX10.jl 


( 12 ) 


(13) 


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BROWNIAN MOTION. COAGULATION 


305 


Similarly: 

- | log it/, = 1.3 X 10 6 £ (14) 

dt lx 

Making use of equation (5), we find that equations 
(13) and (14) become: 

- jlogC, = 1.3 X W-dl , (15) 

at h 

and 

- jlogM, = 1.3 X 10 5 -£di • (16) 

at h 

It can be readily shown 10 that d 6 is the median 
weight diameter, which is equal to the geometric 
mean weight diameter in a logarithmic probability 
distribution. Consequently, when the particle density 
is known, the median weight diameter can be ob¬ 
tained by measurement of the decrease in cross sec¬ 
tion per cubic centimeter. Measurement of the de¬ 
crease of mass concentration will yield d 8 . 

By substituting the values of d 6 and d 8 into equa¬ 
tion (5), the number median diameter d g , and the 
geometric standard deviation <r g , may be calculated. 
By substituting the values of d g and a g into equation 
(3), the particle size number distribution curve may 
be calculated. 

This is the basis of a method of particle size distri¬ 
bution measurement described in Chapter 22, in 
which the geometric cross section is obtained by 
measuring the scattering cross section. 

19.5 BROWNIAN MOTION. COAGULATION 

19.5.1 Brownian Motion 

In the preceding discussion it was assumed that 
coagulation and the other effects of Brownian motion 
were negligible. Due to the random Brownian mo¬ 
tion, the top of a tranquil settling cloud of uniform 
particles will become blurred. Similarly, the upper 
boundary of the region of occurrence of particles of 
radius r in differential settling of nonuniform smoke 
will be spread vertically. This effect is unimportant 
except for very small particle sizes. 

According to Einstein’s 11 and Smoluchowski’s 
equation of Brownian movement, the average dis¬ 
placement x, in a given direction of a spherical par¬ 
ticle of radius r in air in the time t, is 

x = ]/—■ —— — 4.8 X 10 -6 [/— cm (17) 

r N ‘■iirqr V r 


at T = 293 K. For a particle of radius 0.2 micron, 
in 1 hr x = 6.4 X 10~ 2 cm, or slightly over mm. 

If this displacement is taken to be upward, then 
during the same time other particles will move an 
equal distance downward, so that after 1 hr the top 
of a cloud of uniform particles falling in still air will 
be spread vertically over a distance of about 134 mm - 
During this same time the whole cloud would have 
fallen through a distance, given by the Stokes-Cun- 
ningham equation of fall, of 2.5 cm. 

The spread of 1)4 mm i n 2.5 cm corresponds to a 
particle size spread of 2)4%. This is considerably less 
than the spread of particle size in the most uniform 
aerosols. 

19.5.2 Law of Atmosphere 

Since the particles of an aerosol are in constant 
random motion, they exert a pressure just as do the 
molecules of a gas. Due to gravity, the pressure and 
particle concentration, i.e., the density of the aerosol, 
will ultimately vary with height according to the law 
of atmosphere: 12 

n h = ne ~ mgh/KT = ne -^x2.46 X io« (18) 

when T = 293 K. Here rih is the number concentra¬ 
tion at a height h above the region where the con¬ 
centration is w, and m is the mass of a particle. 

As the aerosol particles fall under the action of 
gravity, and diffuse due to Brownian motion, the 
cloud approaches a concentration gradient given by 
equation (18). The time required to reach this con¬ 
centration gradient decreases with the size of the 
particle, according to equation (17). Due to the 
settling and adhering of the particles onto the floor, 
the magnitude of the concentration at any point will 
finally decrease to zero, although the rate of disap¬ 
pearance is retarded by the Brownian movement. 

It is seen that the concentration gradient increases 
rapidly with particle size. For example, particles of 
unit density of 0.01 micron radius will approach a 
concentration gradient of 10% per centimeter. For 
such particles the rate of diffusion is approximately 
equal to the rate of fall. For particles of 0.03 micron 
the final gradient is 90% per centimeter. 

Above this size the final gradient is so large as to be 
practically equivalent to complete settling. Such sizes 
are well below the limit of usefulness of settling 
methods. Thus the law of atmosphere has no practical 
significance in aerosols of particle size greater than 
0.05 micron in radius. 

Perrin 12 found considerable effect in hydrosols for 


SECRET 




306 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


particles of about 0.5 micron radius. Due to the 
buoyancy of the water, the concentration gradient is 
much less than in air. 

19.5.3 Coagulation in a Homogeneous 
Aerosol 

It has been found experimentally that due to 
coagulation alone the particle concentration in a 
uniform aerosol varies inversely with the time 13 
that is: 

- - — = 3C t, (19) 

n n 0 

where n 0 is the initial particle concentration, and 
JC is the coagulation constant. The differential equa¬ 
tion of this process is evidently: 


showing that the rate of coagulation is proportional 
to the square of the concentration. 

According to the theory of Smoluchowski 13 3C is 
equal to 4kT/3r) = 3.0 X 10 -10 cc per sec in air at 
T = 293 K. Thus the rate of coagulation is inde¬ 
pendent of particle size. The equation is, of course, 
true only during the initial stages of coagulation be¬ 
fore the process has introduced appreciable nonuni¬ 
formity of particle size. 

The coagulation equation has been tested experi¬ 
mentally by Whytlaw-Gray 13 who obtained good 
agreement with the theory when using approxi¬ 
mately uniform particle size aerosols. 

This equation holds only for particles that are 
large compared to the mean free path l. For smaller 
particles, the Cunningham correction must be ap¬ 
plied. Equation (20) then becomes 13 



In air at room temperature, the mean free path 
l = 10 -5 cm. Consequently, due to the Cunningham 
correction 1 micron radius particles coagulate 8% 
faster, and 0.1 micron radius particles 88% faster 
than 10 micron radius particles. 

The rate of coagulation at ordinary concentrations 
is quite low. For example, rewriting equation (20) in 
terms of the per cent coagulation per hour, gives: 

dn 

- 100— = 1.08 X 10~ 4 n. (22) 

n 

Taking n = 10 5 (the concentration of a screening oil 


fog of 133-ft visibility) it is seen that approximately 
11 % of the particles coagulate per hour. A concentra¬ 
tion of 10 5 particles per cubic centimeter is also 
frequently encountered in the laboratory. Due to 
the Cunningham correction, the rate for 1 and 0.1 
micron particles would be increased to 12 and 21 % 
respectively. 

19.5.4 Coagulation and Stirred Settling 
Combined 

Elementary Theory 

The calculation of the rate of disappearance of 
particles due to both coagulation and settling is more 
complicated. 

In the early stages of the life of a stirred uniform 
particle size aerosol the decrease of particle concen¬ 
tration is given approximately by adding equation 
(20) to the differential equation of equation (2). 
That is: 

dn v 

- —= 5Cn 2 +-n. (23) 

dt h 

The solution of this equation is 



For times short compared to h/v, e vt/h = 1 + vt/h 
so that equation (24) becomes 



For particles of 1 ^ radius when h = 100 cm, h/v = 
10 4 sec. Therefore equation (25) is reasonably correct 
for a period of about 15 min provided the concentra¬ 
tion is not much over 10 5 per cubic centimeter. 

If \/n is plotted against time a straight line will be 
obtained having the slope 3C + v/h and the intercept 
1 /no. Thus if 3C is known r may be calculated, and 
conversely. 

This is the basis of a method of particle size meas¬ 
urement, described in Chapter 22, in which n is 
measured by measuring the intensity of light trans¬ 
mitted by the aerosol. 

General Equation 

The general equation of coagulation of a hetero¬ 
geneous aerosol in stirred settling was derived by 
Goldman. 14 It was assumed that the aerosol is com¬ 
posed of spherical fog droplets which coalesce on 
collision to form larger spherical fog droplets. 


SECRET 



BROWNIAN MOTION. COAGULATION 


307 


Let the distribution of particle size be given by 
dn(r) = n(r)dr = number of particles between r and 

✓»oo 

r + dr. Then j n(r)dr = N = total concentration. 

Since the distribution changes with time, n(r) = 
n(r,t). The total concentration N does not depend 
upon r, so that N = N(t). 

The Smoluchowski expression for the number of 
collisions per second between particles of radius n 
and r 2 in a heterogeneous smoke is: 
v(r h r 2 ) = 4 irkT[w(r i) + w(r 2 )](ri + r 2 ) • 

n(ri) drift (r 2 )dr 2 (26) 

w(r) is the mobility of the particle, given by the 
Stokes-Cunningham law, as: 


w(r) = 


r + a 
67 njr 2 


(27) 


where: a = Al; A = constant; l = mean free path 
of air molecule; rj = viscosity of air. 

Let JC 0 = (4:/3)(kT/rj), the coagulation constant 



TIME IN HOURS 


Figure 1. Coagulation and settling in stirred homo¬ 
geneous aerosol. 


for large particles, and let 

<Kri,r 2 ) = (~jT^ + /2 ' ^2 ( r i + r 2 ) . (28) 

Then 

jc 

v(r h r 2 ) = —° <j) (r h r^ n (n) dr in (r 2 ) dr 2 . (29) 

This is the general equation of coagulation 15 of 
which equation ( 21 ) is a special case. 

The number of particles of radius r settling out 
onto the floor per second [see equation ( 2 )] is 

v (r) = - n(r)dr . (30) 


h is the height of a rectangular box, or the ratio of 
the volume to the floor area, v is the Stokes-Cun¬ 
ningham velocity of fall: 

v = mgw(r), (31) 

where 


Let 


Then 


m — - ir rp. 
3 


2pgr . . , 

“ = ^T (r + a) 


p(r) = u (r) ft (r) dr. 


(32) 

(33) 


At each collision with one another the particles are 
destroyed as such, but a new particle is formed by 
coalescence having a radius corresponding to the 
sum of the masses of the two original particles. Hence 
the total rate of change of particles of radius r is: 


d C 1 f* 00 

—n(r)dr = — I p(r,x) + - I v ^ x tV) 

dt J x = 0 < 2iJx? J ry i =r i 

— u (r) ft (r) dr, (34) 
or 

= — — f <t>(r,x)n(r,t)n(x,t)dx 

dt 2 Jo 

+ — f <l>(.x,v)n(x,t)n(y,t) ^ dx 
4 dr 

— u(r)n(r,t) . (35) 

In the second integral the range of x is from 0 to r, 
and y is determined by the equation y z = r 3 — x 3 . 
This equation expresses the fact that, in coalescence, 
the volumes add. 

The above is the fundamental equation whose 
solution gives the number of particles of any size at 
any time when a given initial distribution is placed 
in the box. 


SECRET 






















308 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


This is a nonlinear integro-differential equation 
whose solution has been obtained in certain special 
cases, 16 namely: in an initially homogeneous aerosol 
when either the coagulation or the settling is pre¬ 
dominant. Since the equations are rather complicated 
they will not be given here. 

Figure 1 shows a numerical solution for a particular 
case of the differential equations derived from equa¬ 
tion (35). The smoke was initially homogeneous, of 
radius n = 0.83 micron, and concentration rii = 
5.8 X 10 5 per cubic centimeter. Terms ni(t) f n 2 (t), 
and ns(t) are the relative number of particles of radii 
ri, \^2 n, and present after time t. 


19.6 DEPOSITION IN CENTRIFUGAL 
FIELDS 


A particle in a field of force of acceleration a, will 
move with a terminal velocity v given by Stokes’ 
law [equation (1)] as follows: 


2 r 2 pa 
9 rj 


(36) 


As stated in Section 19.4.1, this equation will hold 
as long as vr<rj/pi = 0.15 for air. 

When vr 0.15 the motion becomes turbulent and 
the terminal velocity of the particle (relative to the 
air) is given by Newton’s law for bodies in turbulent 
motion: 



Here p is the density of the particle and pi is the 
density of the air. It is seen that the velocity is no 
longer dependent upon the viscosity of air. Allen 17 
found that this equation holds when vr is about 100 
times greater than rj/pi. 

If aerosol particles are given a sufficiently high 
centrifugal acceleration by causing a sudden change 
in the direction of flow, they can be precipitated out 
of the aerosol. Various forms of such precipitators 
have been constructed, such as centrifugal separators, 
impingers or impactors. They may be very effective 
for large particles but are frequently ineffective for 
small particles. 

The particles may be precipitated by directing a 
jet of aerosol against a collecting surface. In this type 
of precipitator the jet must have a high velocity and 
the change of direction must take place in a small 
distance in order that the acceleration may be high. 
Consequently the length of time during which the 


particle is in the high centrifugal field must of neces¬ 
sity be very small. 

The centrifugal acceleration a = V 2 /R , where R is 
the radius of curvature of the path of the particle, 
and V is the jet velocity. 

Substituting the value of the acceleration a, into 
equation (37) yields the following value for r, the 
minimum radius of the particle which will be 
precipitated: 


r 


3 pi v_ 
8 p V 2 


= 4.5 X 10~ 4 



(38) 


for a particle of unit density in air. 

If we replace v by d p /t, where d p is the distance the 
particle must travel relative to the jet of aerosol in 
order to reach the collector during the time t, and 
if we replace V by d a /t, where d a is the distance 
traveled by the jet of aerosol during the same time, 
we obtain: 

r = 4.5 X lO-^JR- (39) 

Consequently, if R or the ratio d p /d a or both are 
small, small particles will be precipitated. 

In the impinger or impactor, R is made small by 
placing the end of the jet tube near the collecting 
plate. 

The ratio d p /d a may be made small by passing the 
aerosol through a long spiral tube of moderately 
small radius. This results in a considerable separa¬ 
tion of the particles according to size, the larger 
particles being, of course, deposited first. The use of 
this type of separator is described by Abramson. 18 


19.7 ELECTRICAL EFFECTS. 

PRECIPITATION 

19.7.1 Charge on Homogeneous Smoke 
Particles 

The electrical charge on the particles of homo¬ 
geneous smoke was investigated. The homogeneous 
oleic acid fog produced in the usual way with electric 
spark (Chapter 20) is electrically almost neutral. 19 
Only 5 % of the particles are charged, mainly positive, 
and with small numbers of electronic charges (1 to 4) 
per particle. These observations were made in a 
Millikan oil drop apparatus using an electrical in¬ 
tensity of 500 v per cm. 


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COAGULATION BY SONIC AND SUPERSONIC VIBRATIONS 


309 


19.7.2 Unipolar Smoke 

Unipolar charged smokes are produced by a direct 
current corona discharge from a needle point at a 
potential of 10,000 v. This potential is obtainable 
from a 2V3G RCA rectifier tube. The needle point 
was placed in the center of a 2-1, three-neck flask 
through which the electrically neutral homogeneous 
smoke was passed. The other electrode consisted of 
an aluminum strip placed inside on the bottom of the 
flask. The characteristics of the negative unipolar 
charged smoke, obtained when the needle point was 
negative, are as follows: 

1. About 99% of the droplets are charged. 

2. Droplet charges are high, 25 to 50 electrons per 
droplet. These charges were observed in a Millikan 
oil drop apparatus using an electrical intensity of 
90 v per cm. 

3. Dilution with air from 1,000 to 32 fig per 1 has 
no significant effect on the droplet charge. 

4. High humidities have no effect on the droplet 
charge. 

5. The mass concentration of the neutral smoke 
may be decreased by as much as 65% due to passage 
through the corona discharge. 

6. The number of spectra (Chapter 21) in the 
Tyndall beam as counted by the naked eye may be 
decreased by 3^ to 1 spectrum on passage between 
the electrodes. 

7. This smoke disappears with great rapidity when 
introduced into a flask or other chamber. 

19.8 MOVEMENT OF PARTICLES IN A 
THERMAL GRADIENT 

Aerosol particles in a temperature gradient are 
acted on by a force directly proportional to the tem¬ 
perature gradient, 20 and inversely proportional to the 
absolute temperature. When introduced into a region 
between two bodies at different temperatures, par¬ 
ticles will move toward the colder body and deposit 
on it. 

The method of calculation of the force acting upon 
a spherical particle in a thermal force field depends 
upon the relative values of the particle radius r, and 
the mean free path l of the gas molecules. 21 When 
r»Z the force is proportional to ( l 2 rp/T)(dT/dx ), 
and when r < l the force is proportional to ( lr 2 p/T ) • 
(i dT/dx ), where p is the pressure and T the absolute 
temperature. 

It was found 21 that when r > 0.5 micron the 



0 0.5 1.0 1.5 2.0 

RADIUS IN MICRONS 

Figure 2. Thermal velocity vs particle radius. 

velocity is independent of particle size. In the region 
between 0.05 micron and 0.5 micron, there is a two¬ 
fold decrease in velocity with increasing particle 
radius (Figure 2). Hence there exists a definite possi¬ 
bility in this range of using a thermal gradient for the 
separation of smoke particles according to size, and 
thence obtaining the size distribution. 

Various types of thermal separators have been dis¬ 
cussed elsewhere. 21 - 22 Because of the limited size 
range of applicability, this method of size distribu¬ 
tion measurement has not as yet been developed ex¬ 
perimentally. 

A method of sampling smoke particles without 
separation according to size is described in Chapter 
22 . 

19.9 COAGULATION BY SONIC AND 
SUPERSONIC VIBRATIONS 

It is well known that sound of supersonic frequency 
and high intensity will cause the rapid coagulation of 
smoke. For example, Andrade 23 and Parker 24 ob¬ 
served the coagulation of magnesium oxide smoke 
using frequencies of 22,000 c, and Brandt and 
Hiedemann 25 coagulated tobacco and ammonium 
chloride smoke using frequencies of 10,000 to 20,000 c. 
St. Clair 26 found that a frequency as low as 4,000 c 
at an intensity of 0.2 w per sq cm (153 db) caused 
rapid coagulation of ammonium chloride smoke of 
1 micron radius. 

Large particle aerosols, including natural and 
artificial water fogs of droplet radii from 4 to 16 
microns, can be coagulated by sound of 250 to 1,000 c 
provided sufficient energy is generated. The available 


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310 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


theory of the phenomenon indicates that sound of 
350 c should cause nearly as rapid coagulation of 
natural water fog as any higher frequency. 

At such frequencies, the absorption of sound in air 
is negligible. At a frequency of 10,000 c, however, the 
sound intensity is reduced 10 db (a factor of 10) every 
150 ft. At higher frequencies, the adsorption is much 
greater. 

19.9.1 Theory 

The coagulation of an aerosol by sound vibrations 
is due to at least three effects: (1) the motion of 
different sized particles relative to each other, (2) at¬ 
tractive forces set up between particles by the air 
vibrating between them, and (3) vortex motion which 
occurs around large particles. 

These effects vary in different ways with the size 
and density of the particle and the frequency and 
intensity of the sound. 

1. For supersonic frequencies in small particle 
aerosols and for audible frequencies in large particle 
aerosols, the different size particles will vibrate with 
different amplitudes, the smaller particles having the 
larger amplitude. The largest particles will have 
practically zero amplitude. Consequently, the veloci¬ 
ties of the particles relative to one another will be 
increased and the probability of collision thereby 
increased. 

In order to determine the dependence of the par¬ 
ticle velocity upon frequency and particle size it is 
necessary to assume some law for the force on the 
particle moving through the gas. In an intense sound 
field the velocities vary from about 7 cm per sec at 
120 db (10~ 4 w per sq cm) to about 2,000 cm per sec 
at 170 db (10 w per sq cm). 

As stated above, Stokes’ law holds only when 
vr < rj / pi. In a sound field, v is the velocity of vibra¬ 
tion of the air relative to the particle. For air, 
v = 1.81 X 10~ 4 poise and pi = 1.2 X 10~ 3 g per 
cu m, so that rj/pi = 0.15. When r = 10 microns and 
v = 100 cm per sec, vr = 0.1 so that Stokes’ law is 
valid only for the smaller particle sizes and air 
velocities. When r = 1 micron or less, Stokes’ law is 
valid for much higher intensities. 

Koenig 27 has shown that, in general, the force de¬ 
pends upon the acceleration as well as the velocity. 
However, the approximate frequency necessary to 
obtain the maximum velocity of the particle relative 
to the air can be obtained by assuming Stokes’ law 
to hold. According to this law, the force of resistance 


acting on a spherical particle of radius r, moving 
through a viscous medium with velocity v is F = 
(Wrjrv . 

On this assumption St. Clair 26 has derived the 
following expression for v , the amplitude of the 
velocity of a particle relative to the air in a sound 
field. 

CO 


Here v Q is the velocity amplitude of the sinusoidal air 
vibration, co = 2r times the frequency and k = (9/2) 
(■ rj/r 2 p ) where p is the density of the particle. 



Figure 3. Relative velocity v/v 0} as a function of fre¬ 
quency and particle radius, r. 


Figure 3 shows v/v 0 plotted against r for several 
values of the frequency. It is seen that in the neigh¬ 
borhood of 440 c, the relative velocity has nearly 
reached its maximum at a radius of 10 microns. 

Various estimates 28 of the radii of natural fog 
droplets give the limits to be 4 to 40 microns, the 
large sizes predominating in radiation fogs. Although 
the above calculation may give only the order of 
magnitude of the relative velocity, it is evident that 
different sized particles will have different amplitudes 
and phases of vibration, which will increase the rate 
of coagulation. 

It should be pointed out that this particular effect 
is greatest for comparatively low frequencies. Figure 
3 shows that 100 c might be more effective than 440 c 
in a large droplet radiation fog. Droplets of 5 micron 
radius would have very low relative velocities and 
droplets of about 20 microns radius, very large 
relative velocities. On the other hand, at 5,000 c, all 
droplets above about 5 microns radius would remain 
motionless in the vibrating air. Smokes of particle 


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COAGULATION BY SONIC AND SUPERSONIC VIBRATIONS 


311 


radii less than 1 micron would require frequencies 
above 5,000 c to impart different relative velocities 
to the particles. 

2. The increased motion of the particles relative to 
each other appears to be of secondary importance in 
causing coagulation when compared to the hydro- 
dynamic forces of attraction between two particles re¬ 
sulting from the motion of the air between them. 
These forces are greatest when the relative velocity of 
air and particles is greatest, which does not neces¬ 
sarily mean when the particle is motionless. 

Due to the inertia of the particle, its vibrations are 
more or less out of phase with the vibration of the air. 
Consequently, when the relative velocity first reaches 
a maximum, the particle will not be standing still but 
will be vibrating with considerable amplitude, 180° 
out of phase with the air. For example, since the 
actual velocity amplitude u of the particle 26 is: 


u 


k 

Vo —==, 

Vk 2 + w 2 


(41) 


a 10-micron particle whose relative velocity ampli¬ 
tude is 0.95 Vo at 440 c has an actual velocity ampli¬ 
tude of 0.28 Vq. 

Koenig 27 derived the following equations for the 
components of force between two spheres in a sound 
field. Suppose the particles are stationary and lie in 
the X-Y plane, their line of centers making an angle 
0 with the Y axis, and the sound vibration is in the 
Y direction. The force components are then: 

X — —sin 0 (1-5 cos 2 0) (42) 

Y = ~ 3 ’l P !^ r2 -° COS e (3-5 cos 2 e) . (43) 


Here ri and r 2 are the radii of the particles, d is the 
distance between them, pi is the density of the air, 
and Vo is the velocity amplitude of the sinusoidal air 
vibration. 

The derivation of the above equations is also given 
by St. Clair. 20 It is interesting to note that the same 
distribution of forces exists around two magnets when 
their axes are parallel, at distances large compared to 
the lengths of the magnets. 29 

For two particles of the same size whose line of 
centers is|perpendicular to the air velocity (0 = 7r/2), 
the resultant force is an attraction along the line of 
centers of magnitude: 


X = 


SirpiT^vl 

2d 4 


(44) 


When the line of centers is parallel to the air velocity 
(0 = 0), the resultant force is a repulsion along the 
line of centers of magnitude: 


Y 


Srpir^vl 

<d 4 


(45) 


These forces have been checked experimentally by 
Georg Thomas. 30 

Some idea of the rate of coagulation caused by the 
hydrodynamic forces can be obtained by integrating 
the equation of motion of two particles attracted by 
the force X. Assuming that the motion of the par¬ 
ticles toward each other obeys Stokes’ law, St. Clair 26 
obtains the following expression for the time of ap¬ 
proach of two particles, separated by a distance d , 
whose line of centers is perpendicular to v 0 : 



(46) 


If d is the average distance of separation of the 
droplets in a uniform fog, t is the average time for 
each pair of droplets to collide once, thus halving the 
number of droplets. At constant mass concentration, 
the scattering per unit mass is inversely proportional 
to the radius for large particles (see Chapter 21). 
Therefore, halving the number of particles will in¬ 
crease the visibility by 26% since the radius will be 
increased by the factor y/2~ — 1.26. 

Expressing d/r in terms of c, the mass concentra¬ 
tion in grams per cubic centimeter, we have for an 
aerosol of spherical particles of unit density: 


0.66 

w 


(47) 


Thus for a given mass concentration, the time re¬ 
quired to halve the number of particles in a uniform 
aerosol is independent of the particle size, or the 
distance between them. 

This equation is based on the assumption that the 
concentration remains constant after coagulation, 
which, of course, it will not do because of precipita¬ 
tion of large coagulated particles. However, as dis¬ 
cussed below, the coagulation is quite rapid, par¬ 
ticularly for dense aerosols, so that the equation is 
valid for short times. 

Since the average acoustic energy per cubic centi¬ 
meter of air is y 2 piv%, the intensity of the sound is 
y 2 pivlV where V is the velocity of sound in air and 
is 3.44 X 10 4 cm per sec. Thus the time to halve the 
number of particles is inversely proportional to the 
sound intensity and to the five-thirds power of the 
mass concentration. 


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312 


STABILITY AND BEHAVIOR OF AEROSOL PARTICLES 


A dense water fog of 10 microns radius droplets, 
having a visibility of about 20 ft (99% of light 
scattered in 20 ft), has a concentration of about 10 
g per cu m. For a fog of this concentration, t would 
be of the order of 300 sec at 160 db and 3 X 10 4 sec 
at 140 db. 

In experiments on water fog, the observed time 
required to double the visibility was of the order of 
one hundredth the time calculated from the above 
theory. For example, a 43^ micron radius fog of 
50 ft visibility (c = 2 g per cu m) gave double the 
visibility in about 1 min at 135 db. 

This discrepancy is due in part to the assumption 
that d is the average distance of separation of the 
particles in a uniform aerosol. If the aerosol is not 
uniform the different sized particles will have dif¬ 
ferent amplitudes and phases relative to each other, 
as already described. Consequently, different sized 
particles will frequently approach much closer than 
the distance d (about equal to the amplitude of the 
sound vibrations). Since the force of attraction varies 
inversely as the fourth power of the distance, the 
small values of d will predominate in their effect on 
coagulation. For instance, if a value of %d were used 
in the above calculation, the time would be reduced 
by a factor of 32. 

St. Clair 26 found the same discrepancy between 
the calculated and observed time in his experiments. 
He observed the coagulation of 1 micron radius am¬ 
monium chloride smoke by sound of 4,000 c to be 
30 times faster than calculated according to the 
above theory. 

3. The third cause of coagulation, which has not 
been taken into account, is the vortex motion of the 
air around the larger particles which are not vibrating 
with the air. At the higher intensities, eddy currents 
are set up in the air around such particles. 

Andrade 31 has observed that vortex motion causes 
neighboring particles to be attracted or repelled de¬ 
pending upon their orientation relative to the sound 
field and their initial distance apart. He showed that 
vortex motion occurs around a large spherical par¬ 
ticle in air when vr > 0.35. Thus 10 microns radius 
particles would cause vortex motion when the veloc¬ 
ity exceeded 350 cm per sec or at about 155 db. 

Andrade showed also that vortex motion is the 
cause of the striations in the large dust particles in a 
Kundt tube. The distance between the striations is, 
consequently, not equal to twice the amplitude of the 
sound vibration as might be expected from the ex¬ 
periments of Koenig 27 and Robinson. 32 Therefore, 


the sound intensity cannot be obtained from the 
spacing of the striations. Andrade measured the sound 
intensity by observing the amplitude of vibration of 
the 0.25-micron radius particles in tobacco smoke 
which vibrate with the sound amplitude of the £ir. 

Vortex motion inhibits the hydrodynamic forces 
so that the Koenig equations for these forces do not 
apply when vr > 0.35. The anomalous experimental 
results obtained by Gorbatchev and Severnyi 33 are 
probably due to vortex motion. They observed the 
forces between two water drops, supported on sepa¬ 
rate glass threads in a wind tunnel, as well as in a 
“sound’’ field of frequency 10 -3 c. They found the 
directions of the forces to be just the reverse of those 
given by the Koenig theory. In the wind tunnel ex¬ 
periments the wind velocity was 15 cm per sec and 
the droplet radius of the order of 0.5 mm, so that vr 
was of the order of 0.75. The anomalous results ob¬ 
tained by several other investigators have been 
shown by Andrade 31 to be due to vortex motion. 

The results of the theory may be summarized as 
follows. 

1. No accurate value of the absolute rate of coagu¬ 
lation of an aerosol by sound can be calculated from 
the present theory. 

2. The relative rate of coagulation of uniform 
aerosols varies directly with the sound intensity, and 
inversely with the five-thirds power of the mass 
concentration of the aerosol. 

3. Insofar as the coagulation is due to the relative 
motion of different sized particles, there may be an 
optimum frequency for which the coagulation rate of 
a nonuniform aerosol is a maximum. 

19.9.2 Experiments 

Laboratory experiments at Columbia University 
and field tests at Lunken Airport, Cincinnati, Ohio, 
have shown that sound of audible frequency (300 to 
700 c) and high but practicable intensities (130 to 
160 db) will dissipate natural water fog and artificial 
sprays having the mass concentration and particle 
radius found in nature. 

In field tests at Lunken Airport, a radiation fog was 
partially cleared by four Chrysler-Bell victory sirens. 
The visibility was increased by the sound from 200 ft 
to 300 or 400 ft. 

The clearing occurred in about one minute over a 
region 300 ft long and 75 ft wide, where the average 
sound intensity was 140 to 150 db at a frequency of 
440 c. The height of the clearing was not measured 


SECRET 



FILTRATION — GENERAL 


313 


but, from the known intensity distribution of the 
sirens, probably extended about 50 ft upward. The 
droplet radius of this fog, measured microscopically 
(see Chapter 22), ranged from 4 to 16 microns and 
the mass concentration was about 1.0 g per cu m. 

In the experiments in a Columbia University 
tunnel, the visibility of a continuously produced spray 
of 43^ microns radius droplets was increased from 
35 ft to 70 ft by a 2-hp Federal Electric Company 
siren. The average sound intensity was 135 db at a 
frequency of 600 c. 

In a small-scale laboratory experiment, a spray 
of the same droplet radius but of much higher con¬ 
centration was completely dissipated in 15 sec by 
sound of 150 db intensity and a frequency of 500 c 
emitted by a loudspeaker. 

The details of these and other tests are described 
elsewhere. 34 

19.10 FILTRATION — GENERAL 

19 . 10.1 Effect of Particle Size 

Numerous experimental measurements 35 have 
shown that particles of radius about 0.17 micron 
penetrate most readily an ordinary type of smoke 
filter such as rock wool, glass wool, asbestos paper 
or cellulose paper (a- web). The Canadian wool-resin 
filter does not show this effect. 

The results of some measurements are shown in 
Figure 4. Curve 1 shows that as the particle radius 
is decreased from 0.3 micron to 0.1 micron, the pene¬ 
tration of a wool-resin filter rises from 0.016% to 
1 %. Curve 2 shows a comparison series of measure¬ 
ments on an ordinary Mine Safety Company type of 
canister, for which the maximum penetration occurs 
at 0.15 micron radius. 

19.10.2 Electrical Effects 

In general, the negative unipolar smoke described 
in the preceding section has a negligible effect on the 
penetrability of filters. The optical mass-concentra¬ 
tion meter (Chapter 22) was used to measure the 
penetration of a variety of filters, including a German 



Figure 4. Penetration of wool-resin and Mine Safety 
Company canisters. 


filter paper and a Canadian wool-resin, and the pene¬ 
tration found to be practically the same for the uni¬ 
polar as for the uncharged homogeneous smoke. 
However, the smoke penetration through a glass wool 
filter was decreased 90% or by a factor of 10. With 
rock wool filters, the penetration decreased 15% in 
one case and 36 % in another. 

The per cent penetration of the charged smoke as a 
function of time for Canadian wool-resin filters re¬ 
mained constant over a period of 30 min. A low 
smoke concentration, about 2.5 jug per 1, was used 
in this latter test since the Canadian wool-resin is 
readily broken down by oleic acid. 

These filter materials have only a slight effect on 
the electrical properties of the smoke. With filters of 
low penetrability, the dilute issuing smoke is mostly 
uncharged, with a few particles carrying com¬ 
paratively small charges, whether charged or un¬ 
charged test smokes are used. When a filter of high 
penetrability is used (10% or larger), the electrical 
characteristics of the issuing smoke are practically 
the same as those of the entering smoke. 

A detailed discussion of filtration is given in 
Chapter 23. 


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Chapter 20 

FORMATION OF AEROSOLS 

By David Sinclair 


20.1 CONDENSATION METHODS 

20.1.1 Condensation in Vapor Jets 

A erosols of very uniform particle size may be 
produced in the laboratory by slow and uniform 
condensation of vapor, well mixed with air, contain¬ 
ing condensation nuclei. The size of the particles is 


The substance from which the smoke or fog is to 
be formed is contained in the boiler , a 2-1 Pyrex flask 
(see Figure 1). The flask and contents are heated 
electrically in an asbestos board box to between 100 
and 200 degrees C depending upon the substance and 
the particle size desired. 

The condensation nuclei are formed in the ionizer , 



determined by the ratio of the mass of condensable 
vapor to the number of nuclei. When the cooling and 
other pertinent factors are carefully controlled, it is 
possible to produce aerosols having a particle size 
which does not vary by more than 10% from the 
average, as shown by direct microscope measure¬ 
ment of the droplets. 


a 1-1 Pyrex flask fitted with two electrodes sealed 
into standard tapered joints. The ionizer is mounted 
above the heater box and connected to the boiler by 
a standard tapered joint. The condensation nuclei are 
formed by a high-voltage electric spark or an elec¬ 
trically heated coil of wire which has been dipped in 
sodium chloride. 


314 


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THE DISPERSAL OF PRE-GROUND SOLIDS 


315 


The reheater is a 2-1 Pyrex flask in an adjacent 
asbestos box heated electrically to about 300 C. A 
double walled Pyrex glass chimney 20 in. long is con¬ 
nected to the reheater by a large standard tapered 
joint. The boiler and reheater are connected by a 
Pyrex tube having a standard tapered joint at each 
end. The outlet of this tube into the reheater con¬ 
sists of a jet having two holes of 2-mm diameter. 

Smoke is produced by bubbling air through the hot 
liquid in the boiler, through the glass tube shown in 
the diagram. At the same time, air is blown in 
through the ionizer. The total rate of flow is usually 
from 1 to 4 1pm. The mixture of nuclei, spray, and 
vapor-laden air then passes through the two jet 
holes into the reheater. Here the spray is vaporized 
and the nuclei well mixed with the vapor. 

The mixture then rises through the chimney, the 
vapor condensing uniformly upon the condensation 
nuclei. The smoke which issues from the chimney is 
found to be of quite uniform particle size. When the 
column of smoke is examined in front of a white light 
it is seen to be brilliantly colored, the colors varying 
markedly with the angle of observation. 

The smoke has a high mass concentration, about 
1 to 10 mg per 1, depending upon the particle size. In 
order to avoid destroying the uniformity of particle 
size by coagulation, the smoke should be immediately 
diluted 10 or 100 times with dry, filtered air. Small 
tubes or jets should not be used for this purpose since 
turbulent flow destroys the uniformity of size. 

The particle size is increased by increasing the 
temperature of the boiler, or by increasing the flow 
of air through the liquid relative to that through the 
ionizer, or by decreasing the rate of production of 
ions. A little practice with any given piece of ap¬ 
paratus will show the conditions that will yield the 
most uniform smoke of a given particle size. 

The temperature can be automatically maintained 
constant by a thermal regulator inserted directly into 
the liquid or into the heater box. The air must he 
dried and well filtered. If it is not, the moisture, dust 
and oil fog droplets in the air from a compressor, or 
even a tank, will provide so many condensation 
nuclei that the control of particle size by the ionizer 
will be lost. 

To produce the larger particle sizes above 1 or 2 
microns radius, it is necessary to increase the propor¬ 
tion of vapor by bubbling the air through a porous 
disk beneath the liquid surface. Care must be taken 
to avoid decomposition of the material by excessive 
heating. 


A substance having a range of boiling points or an 
impurity, particularly of higher vapor pressure, is not 
suitable for producing uniform smoke by this method. 
The different components condense at different rates 
in the chimney, causing nonuniformity in the particle 
size. A volatile impurity' sometimes condenses so 
readily that it forms sufficient nuclei to destroy the 
control of size by the ionizer. 

Uniform aerosols have been produced from oleic 
and stearic acid, triphenyl and trichresyl phosphate, 
rosin, menthol, ammonium chloride, lubricating oil 
and Aroclor. The range of particle radii is from 0.1 
to 5.0 microns. Smaller sizes may be produced, but 
it is difficult to measure the size or uniformity. In 
general, the large particle aerosols are more uniform 
in size. 

The condensation nuclei may be ionized air mole¬ 
cules or molecules of such compounds as N0 2 , H 2 , 0 2 , 
or NH 3 . When a too intense, flaming spark is used, 
N0 2 is readily detectable by its odor and color. 

The construction and operation of this generator 
is described more fully elsewhere. 1 

20.2 THE DISPERSAL OF PRE-GROUND 
SOLIDS 

20.2.1 Air-Jet Dispersion 

Pneumatic dispersion is capable of producing 
aerosols of solid particles whose size is as small as 
the primary size of the ground material. This method 
does not usually break up single particles but does 
tear apart aggregated particles. The method is very 
inefficient in that a very large volume of air is re¬ 
quired, producing a dilute aerosol. 

One form of apparatus, 2 called the geyser (see 
Figure 2) has been used to produce aerosols of litho- 
pone, Kadox (zinc oxide), and egg albumin, of mass 
concentration up to 30 /zg per 1. Using Kadox of pri¬ 
mary particle size 0.1 to 0.3 micron, the particles dis¬ 
persed by the geyser are 0.3 to 0.5 micron on the 
average. Egg albumin was dispersed down to its pri¬ 
mary particle size of 0.5 to 10 or 15 microns radius. 

It is quite necessary to use well dried and filtered 
air for the dispersal. The water vapor and oil fog in 
raw air from an air compressor cause materials such 
as lithopone to pack into an intractable mass. 

The filter and powder chamber are both made of 
standard 3 in. galvanized iron pipe although they 
have been drawn to different scales in the diagram. 
The connections are all made with standard H-in. 
pipe fittings, as shown. 


SECRET 



316 


FORMATION OF AEROSOLS 



Two spray nozzles of different types, made by the 
Binks Manufacturing Company of Chicago were 
adapted to this apparatus. The No. 174 nozzle, which 
gives the final dispersal, was altered by removing the 
air cap and the needle, and drilling out the central 
hole to 3^6 in- diameter. 

In order to eliminate a constriction and a right- 
angle bend, the hole that carried the needle adjust¬ 
ment was enlarged and the pipe from the powder 
chamber connected to this opening. The regular inlet 
(stamped WAT on nozzle) is closed off. With this 
arrangement the powder comes straight from c out 
through the No. 174 nozzle without any turns. This 
eliminates a tendency of the powder to collect at the 
turns and then break loose later in large pieces. 

The Binks No. 38 nozzle was altered by removing 
the screw cap and soldering in its place a flat disk 
having a 1-mm central hole concentric with the 
central air outlet. All the air from this outlet flows 


out through the 1-mm hole. In addition, the plate 
has three symmetrically placed holes to which bent 
tubes in. ID are attached as shown in the 
diagram. 

The air from these tubes serves to stir up the 
powder. Air from the central hole of the Binks No. 
38 nozzle blows up through the nozzle above at c, 
Avhich should be tapered. This air stream carries more 
or less of the powder-laden air with it, depending 
upon the adjustments a and b. The upper nozzle at 
c is a convex cone having a M6~i n - diameter hole. 

The top plate of the powder chamber is sealed with 
a gasket and fastened with screws which are loosened 
slightly while the adjustments are being made. Three 
horizontal adjusting screws b are used for lateral ad¬ 
justment, and adjustment at a is made by loosening 
the union directly above it and screwing the pipe 
up or down a small amount. 

The rate of flow out of the No. 174 nozzle is about 


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THE DISPERSAL OF PRE-GROUND SOLIDS 


317 


140 1pm. Most of this air flows through valve No. 3 
and is used to disperse the aggregates blown up from 
the chamber. 

A more convenient, portable form of geyser was 
made by attaching a Binks 174 nozzle to a DeVilbiss- 
type GB flock gun. The powder is stirred in the flock 
gun by a thin stream of air and the concentrated 
aerosol dispersed by the Binks nozzle as in the above 
described model. 


20.2.2 Gas Ejection Bomb 

A bomb of 22 cc capacity was used to disperse 
Kadox, egg albumin and lycopodium spores in a 
22-cu m room. The particle size in the Kadox aerosol 
was greater than obtained with the geyser. With egg 
albumin and lycopodium, a primary dispersion was 
obtained, when using a bursting pressure of 1,800 
psi. 3 (See also Chapters 22 and 35.) 


SECRET 



Chapter 21 

OPTICAL PROPERTIES OF AEROSOLS 

By David Sinclair 


21.1 SCATTERING OF LIGHT BY A 
SINGLE SPHERICAL PARTICLE 

T he scattering of light by spheres has been 
extensively studied, both theoretically and ex¬ 
perimentally. In the case of transparent dielectrics, 
that is, nonabsorbing substances, the scattering 
properties have been found to provide convenient 
measures of particle size and size distribution. 

The theory of scattering by a spherical particle was 
originally developed from Maxwell’s equations by 
Gustave Mie 1 in 1908. Since that time, numerous 
calculations 2 have been made of the total energy, 
and the angular distribution of the intensity of light 
scattered by both transparent and absorbing par¬ 
ticles. The derivation of the equations is given in a 
compact form by Stratton . 3 

Since the calculations available in the literature 
were incomplete, additional calculations on both 
absorbing and transparent particles were made by 
the Bureau of Standards. Most of the calculations on 
transparent particles have already been published . 4 
The calculations on absorbing particles and addi¬ 
tional calculations on transparent particles are 
described in following text. 

Numerous experimental measurements have amply 
confirmed the Mie theory, with one exception, de¬ 
scribed in the discussion that follows. 

For transparent, spherical particles that are small 
compared to the wavelength of light, the Mie theory 
is in complete agreement with the more elementary 
theory of Rayleigh , 5 derived to account for the blue 
of the sky. According to this theory the total amount 
of light of wavelength A scattered by a small sphere 
of radius r per unit intensity of illumination (unit 
energy per unit area) is 



Here V is the volume of a small particle, and m is its 
refractive index relative to that of air (= 1 ). S is 
thus the effective scattering area of one particle. 

This equation holds for extremely small particles 
such as air molecules. For such sizes the particles 
need not be spherical. The equation holds for spheri¬ 
cal particles when r < 0.1X. It is seen that the total 


scattered energy varies directly as the sixth power of 
the radius, and inversely as the fourth power of the 
wavelength, so that blue light is scattered much more 
than red. 

Consequently, the diffuse light of the sky is blue 
when free of haze. However, when the sun is near the 
horizon the skv may exhibit other colors even when 
free of haze as explained in the following text. 

When the particle is illuminated with unpolarized 
light, the intensity scattered at an angle y to the 
incident light is 


Iy 


9tt 2 

2R 2 



V 2 

— (1 cos 2 7 ) . 


( 2 ) 


R is the distance from the particle to the point of ob¬ 
servation. This equation holds only when R is very 
large compared to the radius of the particle. The 
angle 7 is the angle between the direction of propaga¬ 
tion of the scattered light and the reversed direction of 
propagation of the incident light. 

When observing at right angles to the incident 
light, i.e., when 7 = 90°, the scattered light is plane- 
polarized with the light vibrations perpendicular to 
the plane of observation. The plane of observation is 
the plane containing the direction of observation and 
the incident beam. 

If a very small particle is illuminated by polarized 
light the intensity of light scattered at an angle \f/ is 4 



Here \p is the angle between the direction of observa¬ 
tion and the direction of the electric vibrations in the 
incident polarized light. The scattered light is plane- 
polarized, no matter what the direction of observa¬ 
tion . 4 

As the particle radius increases to about the same 
size as the wavelength of the light, the scattering be¬ 
comes a very complicated function of the radius, 
wavelength, and refractive index. The Mie theory 
shows that the total scattering by one spherical 
particle per unit intensity, is: 


S 


X 2 y^/ oj + fA 

2v+ 1 J 


( 4 ) 


318 


SECRET 






EFFECTIVE AREA 


SCATTERING OF LIGHT 


319 



0 

0.1 

0.2 

0.3 

0.4 

0.5 0.6 

r IN MICRONS 

0.7 

0.8 

0.9 

1.0 

1.1 

0 

0.6 1.2 

2.4 

3.6 

4.8 

6.0 7.2 

CL 

8.4 

9.6 

10.8 

12.0 

13.2 


3.14 1.57 

0.785 

0.524 

0.393 

0.314 0.262 

0.224 

0.196 

0.174 

0.157 

0.143 


X IN MICRONS 

Figure 1. Scattering coefficient for spherical particles. K vs «, r and X. 


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320 


OPTICAL PROPERTIES OF AEROSOLS 



Figure 2. Angular distribution of intensity of light 
scattered by a spherical particle. i\ and u vs y. 


The aj s and p/s are functions of a = 2n r/X and 
/3 = 2n rm/\. 

The scattering coefficient K, the scattering per unit 
cross-sectional area of particle, is obtained by divid¬ 
ing equation (4) by nr 2 . Thus: 


oo 



V =1 


* + 7 


(5) 


K is therefore a function of r/X. This means that 
once the scattering coefficient is known for a par¬ 
ticular value of r and a particular value of X, it will 
be known for all values of r and X which bear the 
same ratio. 

Since the functions are extremely complicated and 
have already been published, 3 - 4 they will not be 
given here. 

The scattering coefficient for particles of different 
radius and refractive index is shown in Figure 1. The 
ordinates are the scattering coefficient K, and the 
abscissas are a = 2n r/X. The radii corresponding to 
a wavelength of X = 0.524 micron and the wave¬ 
lengths corresponding to a radius of 0.3 micron have 
also been given as abscissas, so that these curves 
show the variation of total scattering with radius at 
a constant wavelength, and with wavelength at a 
constant radius. 



Figure 3. Angular distribution of intensity of light 
scattered by a spherical particle. i\ and z 2 vs y. 


It is seen that the peak of the curve, and therefore 
the radius for maximum scattering, moves toward 
smaller radii as the refractive index increases. There 
is also a secondary peak in the neighborhood of 1 
micron or less. 

The angular distribution of intensity varies ac¬ 
cording to the same function of r/X. For Rayleigh 
scattering by small particles, the angular distribution 
as shown by equation (2) is symmetrical about a 
plane normal to the incident illuminating beam. That 
is, as much light is scattered backward as forward. 
As the particle radius increases, the forward scatter¬ 
ing becomes much greater than the backward. For a 
particle whose radius is equal to or greater than the 
wavelength of light, the ratio of forward to backward 
scattering may be 1,000 or more. 

The angular distribution of intensity is an ex¬ 
tremely complicated function of the scattering angle 
7 , and the complexity increases markedly with in¬ 
crease in particle size. Numerous equations and 
angular distribution curves are given in references. 2 - 3 

The Mie theory predicts, and observations confirm, 
that the scattered light is partially polarized. That is, 


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SCATTERING BY SPHERICAL AEROSOLS 


321 


the scattered light is composed of two incoherent 
plane-polarized components, whose planes of polari¬ 
zation are mutually perpendicular. One of these 
components, of intensity i lf has its light vibrations 
perpendicular to the plane of observation; the other, 
of intensity i 2) has its light vibrations parallel to the 
plane of observation. 

Figures 2 and 3 show the angular distribution of 
intensity scattered by spheres of different sizes and 
materials when illuminated by unpolarized light of 
X = 0.524 micron. Figure 2 is for a 0.1 micron radius 
water droplet (index 1.33). Figure 3 is for a 0.33 
micron radius oil droplet (index 1.50, taken from a 
paper by Blumer 2 ). 

The angular distribution of intensity varies Avith 
wavelength. For example, a 0.2 micron radius A\ r ater 
droplet Avould have, for a wavelength of 1.048 micron, 
an intensity distribution like that of Figure 2. This 
results from the reciprocal relationship betAveen 
radius and AvavelengthAvhich states that the intensity 
distribution is constant AA-hen r/\ is constant. 

The plane-polarized component, i u is the com¬ 
ponent observed in Rayleigh scattering at an angle 
7 = 90°. At this angle, i 2 is zero, as shoAAm by equa¬ 
tion (2), since the cos 2 y term in the brackets is pro¬ 
portional to i 2 . The unity term is proportional to ii, 
so that ii alone is constant for all angles of observa¬ 
tion in Rayleigh scattering. 

21.2 SCATTERING BY UNIFORM PAR¬ 
TICLE SIZE SPHERICAL AEROSOLS 

In aerosols, the particles scatter light independ¬ 
ently of one another Avhen the distance betA\ r een the 
particles is 10 or preferably 100 times the radius of 
the particle. In small particle aerosols, of radius 1 
micron and number concentration 10 6 per cc, the 
ratio of distance of separation to radius is 10 _2 /10~ 4 
= 100. HoAA-ever, for a 10-micron particle aerosol of 
the same concentration the ratio is reduced to 10. 
In such an aerosol some interference betAveen the 
scattering by neighboring particles Avould be ex¬ 
pected, but such high concentrations are not found 
in practice. 

In a Avater fog of 10 microns radius droplets having 
a number concentration of 10 3 per cc, the mass 
concentration Avould be 4.2 mg per 1. This is a con¬ 
centration found in dense natural fogs. HoAvever, 
the usual concentration found in screening oil fogs 
and in the laboratory is a feAv hundred micrograms 
per liter or less. Consequently, the optical properties 


of a single spherical particle can be obser\ r ed by a 
study of the optical properties of a uniform particle 
size aerosol. 

21.2.1 Angular Distribution of Color 

Observations of the scattering Avere made on a 
spherical flask of uniform droplet-size fog traversed 
by a bright and hearly parallel beam of light (called 
a Tyndall beam), about 1 in. in diameter. The fog 
Avas produced in the homogeneous aerosol generator 
described in Chapter 20. 

The angular distribution of color in the scattered 
light AA r as found 6 to agree closely Avith the theory. 
Oleic and stearic acid fogs Avere illuminated with un¬ 
polarized, AAdrite light, and the plane-polarized com¬ 
ponent ii Avas observed as the angle of observation 0 
(measured from the forward direction, i.e., 0 = 
180° — 7) Avas varied from near 0 to near 180°. The 
component i 2 exhibits a different and less distinct 
series of colors. 

As the angle of observation is varied from the for- 
Avard toAvard the backAvard direction, a series of colors 
is seen Avliich resembles the spectrum of AAdiite light. 
The order of the colors is violet, blue, green, yelloAV, 
orange, and red. This series may then be repeated 
several times, depending on the particle size. Near 
90° the order of colors reverses, becoming red, orange, 
yelloAV, green, blue, and violet. This reverse series 
may then be repeated until the backAvard direction 
is reached. 



RADIUS IN MICRONS 

Figure 4. Number of reds vs particle radius. 

The purity and brightness of the colors increases 
Avith the uniformity of particle size. The number ^of 
times the color sequence is repeated increases Avith 
particle size. This is the basis of a method of particle 
size measurement, according to Avhich the particle 
size is given by the number of times red, the most 
distinctive color, is repeated (see Chapter 22). 

In Figure 4, curves A and B are the experimental 


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322 


OPTICAL PROPERTIES OF AEROSOLS 


curves obtained with oleic acid fogs and sulfur 
smokes, showing the number of times red is ob¬ 
served as a function of particle size. 

Calculations for radii up to 0.5 micron and for 
indices of refraction 1.33, 1.44, 1.55, and 2.0 show 
that the number of reds corresponding to a given 
radius is independent of refractive index. Curve C, 
Figure 4, shows the calculated curve which differs 
throughout from the experimental curves by about 
0.025 micron. Since the curves for all indices of 
refraction approximately coincide up to 0.5 micron, it 
seems likely that they will continue to coincide up to 
1.0 micron. 

The calculated curves were obtained from the Mie 
theory as follows. A curve was plotted for each 
particle radius showing the ratio of the intensity i\ 
in the red (X = 0.629 micron) to the intensity i\ in 
the green (X = 0.524 micron) for scattering angles 
from 0 to 180°. The number of maxima of magnitude, 
greater than 0.45, is taken equal to the number of 
reds observed visually, for the following reason. 

The calculated values of i\ refer to unit intensity 
of illumination at all wavelengths in the incident 
beam. Since, in sunlight (i.e., white light) the in¬ 
tensity ratio of red to green at the above wave¬ 
lengths is 0.9, it was assumed that the observed 
scattered light would have a reddish hue when the 
ratio i\ (red) to i\ (green) was greater than 0.9. In 
the tungsten light used for observation, the intensity 



Figure 5. Angular position vs number of reds. 

ratio of red to green was 2.0. Consequently a calcu¬ 
lated ratio ii (red) to i\ (green), greater than 0.45, 
would correspond to an observed red since the ratio 
i\ (red) to i\ (green) in the observed scattered light 
would be greater than 2 X 0.45 = 0.9. 

Figure 5 shows the angular position of the reds 


seen in i\ in stearic acid smokes of 1 to 7 spectra. The 
ordinates show the number of reds and the abscissas 
their angular position, 0. With the exception of sulfur, 
most of the calculated points for other indices of 
refraction lie on the stearic acid curves to within ± 5°. 

21.2.2 Polarization 

The polarization for various angles 0 was found, 
both experimentally and theoretically, to vary in a 
regular manner from the Rayleigh region up to 
about 0.2-micron radius. The relative intensity of 
i<i to ii was found to vary from a low value up to 
greater than one. The polarization can thus be used 
as a measure of particle radii up to 0.2 micron (see 
Chapter 22). Above 0.2-micron radius, the polariza¬ 
tion varies more rapidly with particle radius and is 
multiply valued. 

The polarization may be conveniently measured 
with a polarization photometer. A Tyndall beam of 
approximately monochromatic light is observed 
through a bipartite disk with its dividing line parallel 
(or perpendicular) to the plane of observation. The 
bipartite disk is a plane-polarizer having one half of 
its plane of polarization perpendicular to the divid¬ 
ing line and the other half parallel to the dividing 
line. One half of the bipartite disk, therefore, trans¬ 
mits ii and the other half transmits i 2 . Between the 
observer and the bipartite disk is a plane polarizer, 
called the analyzer, which can be turned so that its 
plane of polarization makes a given angle with the 
plane of observation. 

The analyzer is turned so that the intensities of the 
two halves of the bipartite disk are equal. If the 
angle between the direction of the light vibrations 
transmitted by the analyzer and the plane of obser¬ 
vation is </>, then: 

— = tan 2 <f> • (6) 

h 

Figure 6 shows the calculated values of 0 as a func¬ 
tion of radius for five different refractive indices when 
the angle of observation 0 = 90° and X = 0.524 
micron. Figure 7 shows 0asa function of radius for 
four different values of 0 when the index of refrac¬ 
tion m = 1.44 and X = 0.524 micron. 

The blue tobacco smoke that rises from the end 
of a cigarette exhibits Rayleigh scattering approxi¬ 
mately when illuminated with white light (X = 0.4 
to 0.7 micron). If a Tyndall beam is examined in a 
direction at right angles to the beam through a plane 


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SCATTERING BY SPHERICAL AEROSOLS 


323 



RADIUS IN MICRONS 


Figure 6. Calibration curves for Owl. Analyzer angle 
<f> at 0 = 90°, vs refractive index. 

polarizer, it will be seen to be virtually extinguished 
when<£ = 0°. 

When fresh, the particles of tobacco smoke are 
0.15-micron radius or less. If this smoke is allowed to 
age in a flask, or if exhaled smoke is examined, much 
less polarization will be observed. Aged tobacco 
smoke particles are 0.2 or 0.25-micron radius, due to 
the accumulation of moisture. Such smoke may be 
sufficiently uniform in size to exhibit some color 
when examined through a polarizer. 

21 . 2.3 Total Scattering 

Measurements were made of the angular distribu¬ 
tion of intensity of the light scattered by uniform 
stearic acid and oleic acid fogs. The details of the 
method of measurement have been given elsewhere. 7 

A fog of known concentration (measured by weigh¬ 
ing a known volume of fog collected in a glass wool 
filter) was observed while streaming out of the gener¬ 
ator. A suitable volume was uniformly illuminated 
and the intensity scattered into a given small solid 
angle was measured with a photometer. Measure¬ 
ments were made at angles from 3 to 175° at frequent 
intervals. The intensities were then integrated over 
all possible directions. In order to obtain the total 
scattering coefficient, the integrated scattering was 
compared with that of a diffuse reflector of known 
reflectivity. 

The results are given in Figure 1. The dotted curve 
shows the experimental measurements made on uni¬ 
form particle size stearic acid fog, refractive index = 



Figure 7. Calibration curves for Owl. Analyzer 
angle at refractive index 1.44 vs 0. 


1.43. The agreement with the theoretical curve for 
index 1.44 is considered to be satisfactory. The dis¬ 
crepancy is due to the difficulties inherent in this 
type of measurement. 

It was found that the theoretical values of both 
total scattering and angular distribution of intensity 
are too high by a factor of 2 when the particle is 
illuminated by unpolarized light. This was due to a 
mistake made in the original derivation of the theory 
when transferring from polarized to unpolarized 
light. 4 The error was made originally by Rayleigh 5 
and was first pointed out by Stiles 8 in a paper, which 
was brought to the author’s attention after reference 
4 had been distributed. Rayleigh’s original error has 
been propagated unchanged in a number of texts. In 
the Handbuch der Physik, the error is compensated by 
making an improper integration over the sphere. 9 

The values of the scattering coefficient given in 
Figure 1 are the correct values. They are equal to the 
values obtained directly from the Mie theory when 
derived for polarized light, and to half the values 
given by the Mie theory for unpolarized light. 

The total amount of light scattered by 1 cc of 
aerosol is equal to the product of the amount of light 
scattered per particle and the number concentration 
n. Figure 8 shows S the scattering cross section per 
particle (X10 8 ) as a function of particle size and wave¬ 
length for water (index = 1.33), screening oil (Diol, 
index = 1.50) and sulfur (index = 2.0). These curves 
may be obtained from equation (4), or they may be 
obtained from the curves of Figure 1 by multiplying 
the values of the scattering coefficient K by the cross- 
sectional area of the particle 7rr 2 . The scattering per 
cc is then Kirr 2 n = Sn. 


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SCATTERING AREA PER PARTICLE IN SQ CM X 10 


324 


OPTICAL PROPERTIES OF AEROSOLS 



or 

3.14 1.57 0.785 0.524 0.393 0.314 0.262 0.224 0.196 0.174 0.157 0.143 

X IN MICRONS 


Figure 8. Total light scattered per particle. S per particle vs a, r and X. 


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13 

12 

11 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 


SCATTERING BY SPHERICAL AEROSOLS 


325 











n 


N 




















! 

i 













































FOR r 
FOR X 

SCALE 

SCALE 

X =0.52 
r = 0. 3 /j 

4/x 

L 








V „ 















Lz 

2 \ 











k SULFU 

m = 2.0 

R 

0 



DIOL i 

WATERi 

m=1.50 

p = 0.912 

ti =1.33 - 
/)=l.00 










0.1 

0.2 

0.3 

0.4 

0.5 0.6 

r IN MICRONS 

0.7 

0.8 

0.9 

1.0 

1.1 

1.2 

2.4 

3.6 

4.8 

6.0 7.2 

a 

8.4 

9.6 

10.8 

12.0 

13.2 

1.57 

0.785 

0.524 

0.393 

0.314 0.262 

0.224 

0.196 

0.174 

0.157 

0.143 


X IN MICRONS 


Figure 9. Total light scattered per gram of particles. S per gram (= J) vs a, r and X. 


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326 


OPTICAL PROPERTIES OF AEROSOLS 


The total scattering may also be expressed in terms 
of the scattering per gram of material. This is the 
quantity most important in determining the per¬ 
formance of a screening smoke. Figure 9 shows the 
scattering cross section in square meters per gram 
for some of the materials of Figure 8. These curves 
were obtained from Figure 8 by dividing the scatter¬ 
ing per particle by the mass of one particle. Thus, 
the scattering per gram is J = SK/^rp, where p is 
the density of the material. 

21.2.4 Transmission 

The total scattering may be more conveniently 
obtained by measuring the decrease of intensity of 
the transmitted beam. For small particles, the in¬ 
tensity of the transmitted beam of wavelength X de¬ 
creases exponentially with the distance traversed 
through the aerosol, that is: 

I = I 0 e~ Snl = Ioe~ Jc '. (7) 

Here l is the distance, and c is the mass concentration 
of the aerosol in grams per milliliter. The term Snl 
(.Snl = J cl) is defined as the optical density D. 

The intensity / transmitted through a given dis¬ 
tance l in a stirred homogeneous aerosol will decrease 
exponentially with the time, due to the decrease in n, 
according to equation (2), Chapter 19. Combining 
equation (2) with equation (7), 

logy = Snl = Snl 0 e- Wh) - (8) 

Thus the optical density D = Snl will decrease 
exponentially with the time. However, for times 
short compared to h/v the change will be small. If the 
concentration n is maintained constant by replenish¬ 
ing the aerosol from a homogeneous generator, the 
transmitted intensity will be constant. 

A beam of monochromatic light was passed into a 
photocell through a homogeneous aerosol of constant 
concentration, and the transmission measured as a 
function of particle size and wavelength. The con¬ 
centration and distance were also measured and the 
scattering coefficient then calculated from equation 
(7). Good agreement was found between experiment 
and theory for oleic acid 4 (index = 1.46), sulfur 4 
(index = 2.0), and Diol 10 (index = 1.5). 

In the case of oleic acid and sulfur, it was con¬ 
venient to plot curves showing the variation of 
J\[_ oc i£(X/r)] with r/X. These curves are similar in 
form to the K vs a curves of Figure 1. 

For Diol a series of curves showing the variation of 


log J with log X at constant radius was plotted. It was 
found that the slope of these curves varied markedly 
with particle size. For the wavelength 0.65 micron, 
the slope was —1.9 at r — 0.3 micron {a = 2.9), 
reached a maximum of +2.1 at r = 0.7 micron 
(a = 6.8) and fell to +1.7 at r = 0.76 micron 
(a = 7.3). 

At r = 0.1 micron or less the slope should reach 
the value —4, according to the Rayleigh equation 
[equation (1)]. The curve of scattering per gram for 
Diol (Figure 9) shows a variety of slopes of positive 
and negative values. 

A negative slope means that the scattering per 
gram decreases with increasing wavelength. In other 
words the transparency of the aerosol increases with 
increasing wavelength. This is the general situation 
for aerosols whose particle radii are smaller than the 
radius (or radii) corresponding to the principal maxi¬ 
mum of the scattering curve. Conversely, aerosols 
whose particles are somewhat larger than this 
optimum size will be more transparent to shorter 
wavelengths. 

It has been observed that the color of the sun’s 
disk, viewed through a cloud of Diol fog produced in 
the field, is red when the droplet radii are less than 
0.23 micron, and blue or green when the radii are 
greater than 0.3 micron. Inspection of Figure 9 shows 
that the optimum radii for Diol are between the 
above values (for green light, X = 0.524 micron). 

The observations should be made when the sun’s 
light is nearly extinguished, since the residual rays 
will exhibit the most distinctive color. The purity of 
the color will vary with the uniformity of particle 
size. It is evident that a considerable range of sizes, 
great enough to span the peak of the curve, would 
exhibit little or no color. This is a simple criterion for 
estimating the particle size and size distribution of a 
fog (see Chapter 22). 

If the particles are all considerably smaller than 
the optimum size, they may have a large range of size 
and still produce a red color in the transmitted light. 
The setting sun appears red, usually because of the 
small particles of haze Avhich exhibit approximately 
Rayleigh scattering. And the color of the sun deepens 
as it sets, due to increased selective scattering, until 
the residual color becomes a deep red just before the 
sun is extinguished. 

Even when free of haze the color of the sky at sun¬ 
set will differ from the usual blue. The sky color will 
vary with the color of the transmitted sunlight, which 
varies with the path length as follows: 


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SCATTERING BY NONUNIFORM SPHERICAL AEROSOLS 


327 


Combining equations (1) and (2) into an equation 
of the form of equation (7), 

9**/m*-l\V* 

7 ~ 2R 2 \m 2 + 2/ X 4 

(1 + cos 2 7) exp £ - 24ir> + 2 ) ^7 n ^\' ( 9 ) 

This equation is a maximum when 
X = jftaVH 

where 



Thus the wavelength of maximum Rayleigh scat¬ 
tering increases with the particle radius, the length 
of path and the number concentration. 

This phenomenon is very striking when observed 
in a dense homogeneous aerosol exhibiting Mie scat¬ 
tering. The color of the Tyndall beam varies from 
blue through green and orange to red, before it is 
extinguished. 

The particle radii may be obtained quite accu¬ 
rately by measuring quantitatively the transmission 
as a function of wavelength. This is the principle of 
an instrument called the Slope-o-meter described in 
Chapter 22. 

21.2.5 Scattering by Large Particles 

The Mie equations hold, theoretically, for any 
value of the radius. However, when a is greater than 
10 or 12, the practical difficulties of calculation be¬ 
come excessive. Consequently Figure 1 shows no 
points beyond a = 12. 

However, when r is extremely large, approximation 
methods show 3 that K approaches the value 2. At 
first sight this appears false since it says that a very 
large sphere scatters twice as much light as falls on it. 
Brillouin 11 has recently shown theoretically that the 
light scattered by a relatively large metallic sphere 
(r > 12 microns) could be divided into two equal 
parts, that scattered into a small solid angle around 
the forward direction (i.e., into the geometrical 
shadow), and that scattered in all other directions. 
This means that although the correct value of the 
scattering coefficient is 2, the actual value, measured 
experimentally, will be 1 for very large spheres, since 
for such spheres the angular divergence of the 
shadow is extremely small. 

This result was confirmed by the following experi¬ 
ment. A cloud of lycopodium spores was allowed to 


settle on to a glass plate. The radii of these spores 
were found to be very uniform, 15.0 ± 1 micron. The 
plate was then placed in a parallel beam of light in 
front of a photocell, and the transmitted intensity 
measured at different distances between plate and 
photocell. The reading of the photocell increased by 
the factor 2.1 when the distance from the plate to the 
photocell was decreased from 18 ft to 6 in. Calcula¬ 
tion checked this result and showed that at 18 ft the 
observed scattering cross section was 2irr 2 and at 
6 in. it was ir r 2 . At 6 in., half of the scattered light 
(i.e., that part scattered into the geometrical shadow) 
was picked up by the photocell. 

This conclusion is further confirmed by a considera¬ 
tion of diffraction by large obstacles. According to the 
theory of diffraction, the total amount of light dif¬ 
fracted by an opening is equal to the area of the 
opening (in the case of unit intensity of illumination). 
For a circular hole of radius r, the amount of light 
diffracted would be tt r‘ 2 . 

According to BabineUs principle, a circular ob¬ 
stacle of radius r will diffract the same amount of 
light as a circular hole of radius r. But the obstacle 
will also intercept an amount of light equal to its 
area tt r 2 . Consequently the total amount of light, both 
intercepted and diffracted, is 2tt r 2 , and the transmis¬ 
sion experiment described above will yield a scatter¬ 
ing cross section of 27rr 2 , provided the distance from 
the obstacle to the measuring device is made large 
enough. 

However, for very large obstacles, this condition is 
not realizable in practice. The diffraction pattern is 
so small that all the light contained in it is received 
by the collector. The collector then measures only the 
amount of light intercepted by the geometric cross 
section t r 2 . 

Therefore, it is evident that the total amount of 
light absorbed and scattered (i.e., diffracted at any 
angle from its original direction) is 2-7rr 2 , as the Mie- 
Stratton theory shows. However, any experimental 
measurement of a very large particle will yield the 
value tt r 2 , the amount of light absorbed by an opaque 
disk, or in the case of a reflecting sphere, light scat¬ 
tered outside of the geometrical shadow. 

21.3 SCATTERING BY NONUNIFORM 

PARTICLE SIZE SPHERICAL AEROSOLS 

Ordinary aerosols, having a large range of particle 
size, exhibit the scattering which would be observed 
from a mixture of a large number of uniform particle 


SECRET 







328 


OPTICAL PROPERTIES OF AEROSOLS 


size aerosols, mixed in varying proportions. The dif¬ 
ferent colors in the scattered light overlap so that the 
aerosol appears more or less white depending on how 
much one particle size predominates. The polariza¬ 
tion is also a mixture of that from many sizes, the 
effect of the large particles predominating because of 
the great increase of intensity with size. 

If a nonuniform aerosol, such as tobacco smoke, is 
allowed to settle in a convection-free chamber, con¬ 
siderable separation of sizes will occur. If the upper 
layers of the cloud are examined with a beam of white 
light, various colors will be seen depending upon the 
height and direction of observation. An approximate 
idea of the size and size distribution of the smoke 
particles can be obtained by examining the colors and 
polarization at different heights and angles. 



Figure 10. Angle scattering as function of particle 
size, p vs r in eq. A I = kr p An at 0 = 45°. 


21.3.1 Scattered Intensity vs Particle Radius 

The intensity scattered at any wavelength by a 
given volume of smoke at a fixed height will decrease 
with time since the number of particles in that volume 
will decrease due to differential settling as explained 
in Chapter 19. If coagulation is negligible, the rate of 
decrease of intensity at any time depends upon the 


particle size and size distribution, and the scattering 
as a function of size. 

The change in the scattered light intensity, A I, 
observed at a given angle and wavelength is propor¬ 
tional to the change in the particle concentration An, 
and the radius raised to some power p, that is 

A I = kr p An. (11) 

The value of p at a given value of r and angle of 
observation, 0, is obtained from the calculations of 
the angular distribution of intensity referred to 
above. 4 The values of log (ii + i 2 ) vs log r were 
plotted and the value of the slope pas a function 
of r was obtained for several angles. 

Figure 10 shows the variation of p with r at 
0 = average of 40°, 45°, 50°, for refractive index 1.44, 
and 1.55 at the wavelength 0.524 micron. It. is seen 
that p has the value 6 for radii below 0.1 micron as 
is to be expected in the region of Rayleigh scattering. 
The region of negative values of p corresponds 
roughly to the region of the curves of Figure 8 where 
the slope is negative. Sufficient calculations are not 
available to carry these curves beyond r = 0.5 
micron. 

Similar curves were drawn showing p as a function 
of r for total scattering. For Rayleigh scattering, p 
should again have the value 6, and for very large 
particles, the value 2. These curves were found to be 
quite different from those of Figure 10 in the useful 
range from 0.1 to 1 micron so that they cannot be 
used to supplement the curves of Figure 10. 

The use of these curves in conjunction with the 
differential settler for the determination of particle 
size and distribution is described in Chapter 22. 

21.3.2 Transmission in Tranquil Settling 

The intensity transmitted by an aerosol in tranquil 
settling will vary in a similar manner. However, the 
practical difficulties of this measurement were found 
to be insurmountable. In order to obtain sufficient 
optical density and avoid coagulation, the smoke 
chamber must be large in order that the path length 
may be large since n must be not over 10 5 per cc. It 
has been found impossible to eliminate convection 
currents in anything but a chamber so small that the 
transmission is very nearly 100% when n has a 
suitable value. 

21.3.3 Transmission in Stirred Settling 

The optical density D = Snl, of a homogeneous 
aerosol in stirred settling and undergoing coagula- 


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SCATTERING BY NONUNIFORM SPHERICAL AEROSOLS 


329 


tion, will vary according to equation (24), Chapter 
19, as follows. 



For times short compared to h/v, this becomes 


l = l_ / JC v \ 

D D 0 + \Sl + hD 0 ) 1 ’ 


(13) 


If 1/D is plotted against time a straight line will be 
obtained, having the slope 3C/SI + v/hD 0 . The 
quantities l, h, D, and Z) 0 are readily measurable. If 
the particle radius is known, v, S, and 3C may be 
calculated, or if 3C is known, then v, S, and r may be 
calculated. (See Chapter 22.) 

This equation neglects the change in particle size 
(but not the change in number) due to coagulation. 
As a result of coagulation, v and S would not be quite 
constant. 


21.3.4 Heterogeneous Aerosol without 
Coagulation 

The total scattering cross section of N spherical 
particles of different sizes can be obtained by measur¬ 
ing the optical density D = SIN. In a heterogeneous 
aerosol, S is the scattering cross section of an average 
particle. In the range of particle sizes where K is 
nearly constant and equal to 2 (r > 1 micron, see 
Figure 1), S will be the scattering cross section of 
the sphere having the average geometrical cross 
section. Therefore, according to equation (6), Chap¬ 
ter 19, the scattering cross section per cc at zero 
time is 

S 0 = -N 0 K 2 dl, (14) 

4 


and according to equation (8), Chapter 19, the 
scattering cross section at time t is: 

S t = ~K 2 f d 2 rid exp (— — ) <5 log d. (15) 
4 Jo \ h / 


Here K 2 is the scattering coefficient of the sphere of 
diameter d 2 . 

Equation (15), Chapter 19, may then be trans¬ 
formed to: 


|logS, = 1.3 X 
dt h K 2 d 2 


(16) 


or 

-|lo g S,= 1.3X10^ §4- (17) 

Thus d 6 can be obtained by measuring the average 


scattering cross section provided A 4 and K 2 can be 
determined. 

The scattering per gram at zero time A 0 is ob¬ 
tained by dividing equation (14) by equation (7), 
Chapter 19. 


Ao 



^N 0 K 2 d% 

lN 0P dl 

b 


3 #2 

2 pC?5 


(18) 


making use of equation (5), Chapter 19. 

A further useful relationship is obtained by divid¬ 
ing equation (16) by equation (14), Chapter 19. 
Writing d/dt log M t = u m and d/dt log S t = u 8 we 
have 


Us_ = K± 4 d% 
u m K 2 d\ d 2 


Multiplying equation (19) by A 0 [equation (18)] 
gives 


^ u$ 3 d 4 

u m 2 p d\ 


3 Ka 

2 pdg 


( 20 ) 


making use of equation (5), Chapter 19. 

The use of these equations for particle size meas¬ 
urement is described in Chapter 22. 


21.3.5 Complete Analysis of Scattering 

The complete analysis of the light scattered or 
transmitted by a heterogeneous aerosol is extremely 
difficult. The absence of distinctive color in the scat¬ 
tered light is an indication of heterogeneity, but the 
distribution curve cannot be obtained by this means. 
Similarly, the polarization in the range of radii below 
0.2 micron, may be used to detect the presence of a 
distribution of sizes, although it is extremely difficult, 
if not impossible, to obtain any quantitative results 
by this means. 

The general theory has been discussed elsewhere. 12 
The conclusions reached may be summarized as 
follows. 

The determination from scratch of the non¬ 
homogeneity of a smoke is possible only in principle. 
But if we already know enough about the size and 
distribution of a heterogeneous smoke, the knowledge 
of the scattering functions of homogeneous smokes 
will enable us to find out more. For example, the 
determination of the proportions of a mixture of two 
homogeneous smokes of known particle size is rela¬ 
tively easy. 

The relative proportions of a mixture of two homo- 


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330 


OPTICAL PROPERTIES OF AEROSOLS 


R 


= tan 2 </>. (21) 


geneous smokes of known radii less than about 0.2 
micron can be obtained by measuring the polariza¬ 
tion at the scattering angle 0. Let x and 1 — x be 
the proportion of particles of radius n and r 2 respec¬ 
tively. Let iiixifl) and f 2 (n,0) be the intensities of 
the polarized components scattered per particle of 
radius n at the angle 0, with similar expressions for 
r 2 ; and let the wavelength be X. 

Then the ratio of the intensities observed at the 
angle 0 will be according to equation (6) 
xi 2 (r h 0) + (1 — x)i 2 (r 2 ,0) 
xii(n,d) + (1 —x)fi(r 2 ,0) 

Since the i 2 s and the tVs are known from the Mie 
theory, this equation may be solved for x. 

If the radii w r ere unknown they could be obtained 
by observing the polarization at three different 
angles 0. 

For radii greater than about 0.2 micron this method 
would not yield a unique solution since the absolute 
values as v r ell as the ratio of the intensities are 
multiple valued. 

Usually, however, no such simple distribution of 
sizes is encountered. Calculations have been made 
showing the effect of various size distributions on the 
polarization. 13 The conclusion is that this method 
cannot be used to obtain the size or size distribution 
of heterogeneous smokes. 

One can merely determine whether or not the 
smoke is homogeneous by observing the polarization 
at several angles. If, for example, the polarization of a 
stearic acid smoke were observed at 90°, 80°, and 70°, 
and the same size were obtained from each of the 
corresponding curves of Figure 7, then the smoke 
w^ould evidently be homogeneous. 14 However, this 
method w r ould fail for radii near 0.15 micron where 
the curves cross. 

Similarly, the color of the transmitted light serves 
as an approximate measure of the particlq size, and 
an unsaturated color indicates a distribution of sizes 
(see preceding text and Chapter 22); but the distri¬ 
bution curve cannot be obtained from the wave¬ 
length intensity distribution of the transmitted light. 


21.4 THE SCATTERING OF LIGHT BY 
SOLID PARTICLES 

21.4.1 Polarization 

The angular distribution of intensity of the light 
scattered by irregularly shaped particles has not been 
analyzed in detail. The Rayleigh theory is applicable 


to extremely small particles no matter what their 
shape. However, for larger particles near the limit 
of the Rayleigh region, shape and internal structure 
have an effect on the scattering. The ratio i 2 /i\, 
called the depolarization factor , is greater than for 
spherical particles. Lotmar 15 has shown that the 
internal crystal structure of solid particles has a much 
greater effect on the polarization than does the ex¬ 
ternal shape of the particle. 

When very small particles are illuminated by 
polarized light the Rayleigh theory shows [equation 
(3)] that i 2 is zero everywhere. For larger spheres 
exhibiting Mie scattering, or for irregular particles 
exhibiting depolarization, i 2 is not zero. Krishnan 16 
has shown theoretically and experimentally that the 
component i 2 (scattered w r hen the incident light is 
polarized w ith its electric vibrations perpendicular to 
the plane of observation) is equal to the component i\ 
(scattered w T hen the incident light is polarized with 
its electric vibrations parallel to the plane of ob¬ 
servation). These twn components will be referred to 
as the rotated components. This relationship holds 
for a mass of particles of all shapes and sizes, and for 
all angles of scattering, provided the orientation of 
the particles is random. 

The Mie theory for spherical particles shows that 
the rotated components are both equal to zero. 4 
Consequently when the incident light is unpolarized, 
the component i 2} w hich is observed, is produced by 
the incident electric vibrations w hich are parallel to 
the plane of observation, and the component i\ is 
produced by the incident electric vibrations which 
are perpendicular to the plane of observation. 

However, w r hen irregularly shaped particles are 
illuminated by unpolarized light, the rotated compo¬ 
nents are no longer equal to zero. Consequently, com¬ 
parison of the polarization of the light scattered by 
particles when illuminated with unpolarized and 
polarized light w T ould provide a measure of the shape 
or anisotropy of the particles. 

It W'Ould be expected that the polarization by par¬ 
ticles of a given form could be used as a measure of 
their size, provided a calibration could be obtained. 
This would require a series of smokes of uniform size. 
Attempts w'ere made to produce or obtain solid 
particle smokes sufficiently uniform for this purpose, 
but they were not successful. 

21.4.2 Scintillating Particles 

Some useful qualitative information can be ob¬ 
tained by observing the effect of Brow-nian rotation. 


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SCATTERING OF LIGHT BY SOLID PARTICLES 


331 


When a bright Tyndall beam is observed in a solid 
particle smoke, the particles will be observed to 
scintillate due to random reflections from the crystal 
faces. Large particles, which are observed to fall 
rapidly, produce intermittent flashes at a much lower 
frequency than those from the more slowly falling- 
particles. Stearic acid smokes that have been aged 
for an hour or more exhibit these scintillations, while 
fresh smokes do not. This indicates that in the course 
of time the supercooled stearic acid droplets crystal¬ 
lize. 

21.4.3 Transmission in Stirred Settling 

The optical density of solid particle smokes in 
stirred settling may be analyzed according to the 
methods described in preceding text. 

The aerosol, composed of irregularly shaped ag¬ 
gregates of a wide range of sizes, is compared with a 
hypothetical aerosol of equivalent spherical particles 
having a logarithmic-probability distribution of sizes. 
Microscope examination of Kadox (see Figure 1, 
Chapter 22) and albumin particles has shown them 
to be fairly compact aggregates that show no tend¬ 
ency to form filamentary particles; particle size 
exhibits a distribution curve that follows approxi¬ 
mately the logarithmic-probability law. 

In ground materials it is probable that the number 
of particles at very small sizes is greater than appears 
from the measurements, due to the difficulty of ob¬ 
serving them. However, since the scattered light de¬ 
creases with the sixth power of the radius for par¬ 
ticles below about 0.1-micron radius, and the contri¬ 
bution to the mass decreases as the third power of the 
radius, such particles are relatively unimportant so 
that the approximation appears to be good enough 
for practical purposes. Bailey has found a logarithmic 
probability distribution in ground pigments. 17 

Consequently one can calculate various average 
diameters in a manner similar to that described in 
Chapter 19. The average scattering cross section and 
scattering per gram may be expressed as described in 
preceding text, provided the scattering coefficient is 
known. 

In the case of Kadox and other small particles less 
than about 2-micron diameter, the Mie theory shows 
(see Figure 1) that the scattering coefficient usually 
has a value between 2 and 4 except for extremely 
small particles exhibiting Rayleigh scattering. It was 
found empirically by Bailey 17 that if the values of the 
diameter are multiplied by (m 2 — l)/(m 2 -f-2), where 


m is the refractive index, then all the scattering- 
curves approximately coincide. 

It has been found that this relationship is also 
approximately true for the scattering curves calcu¬ 
lated from the Mie theory. Figure 11 shows the 
average of the curves obtained by plotting the values 
of K in Figure 1 against the corresponding value of 
d{m 2 — l)/(m 2 +2). It is seen that maximum values 
of the scattering coefficient occur when d(m 2 — 1)/ 
(m 2 + 2) =0.2 and 0.5 micron (dashed line in Figure 
11). Figure 11 is a universal scattering curve for all 



o.oi o.i i io 

Figure 11. Universal scattering curve for all trans¬ 
parent materials of any refractive index. 

transparent materials of any refractive index. The 
heavy line was drawn to average out the trough and 
minor peak since they are within the precision of 
measurement. (See Chapter 22.) 

Since solid aerosol particles are aggregates of small 
primary particles, they will have an effective density 
and an effective refractive index less than the true 
density and refractive index of the material. The ef¬ 
fective density has been found experimentally to be 
about equal to the density of the powder before dis¬ 
persal, i.e., the average of the density of the solid 
particles plus the air in the spaces between the par¬ 
ticles. The effective refractive index has been found 
to be given approximately by the same average. 

The author has found that the effective density p 
and effective refractive index m are related according 
to the Lorenz-Lorentz relation, p = Constant X 
(m 2 — l)/(m 2 + 2). The value of the constant for 
a given aerosol material is found by substituting the 
true density p 0 and the true refractive index w 0 into 
the equation. The constant is equal to 11 for Kadox 
and 4 for albumin. It is seen that the factor (m 2 — 1)/ 
(m 2 + 2) is the factor which brings the scattering- 
curves for all materials into approximate coincidence. 


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332 


OPTICAL PROPERTIES OF AEROSOLS 



Figure 12. Scattering curve for Kadox. K vs pd. 


as a single large particle showing Mie scattering. In 
the case of albumin the particles are all so large that 
the refractive index has little effect on the scattering, 
K having the constant value 2 as explained in pre¬ 
ceding text. 

Figures 12 and 13 may be used to obtain the par¬ 
ticle size and size distribution as described in Chap¬ 
ter 22. 

21.5 SCATTERING BY LIQUID OR 
SOLID PARTICLES WHICH 
ALSO ABSORB 

21.5.1 General Characteristics 



Figure 13. Scattering curve for albumin. K vs pd. 


Two curves (Figures 12 and 13), one for Kadox 
and one for albumin, were plotted, showing the varia¬ 
tion of the scattering coefficient K with 



Such a curve will yield the scattering coefficient of a 
loosely aggregated particle of a given material when 
the product pd of the diameter and effective density 
is known. 

It has been assumed that the effective density is a 
constant for all sizes of aggregated particles formed. 
This means that the packing of the primary particles 
is the same for all aggregates, which seems probable 
since most of the aggregates contain large numbers of 
primary particles, 20 or more. 

The assumption that the refractive index of the 
aggregated particle is a smeared out index appears to 
be justified since the primary Kadox particles are 
about one-fifth to one-tenth the wavelength of light. 
Since the primary particles are packed in contact 
with each other, they will not individually give rise 
to Rayleigh scattering but will behave collectively 


The scattering of light by colored particles is a 
combination of the selective scattering by trans¬ 
parent particles having a real refractive index, plus 
the selective absorption by absorbing particles having 
a complex refractive index. In selective scattering all 
the light not scattered is transmitted, but with 
selective absorption, some of the light not scattered 
is also not transmitted. 

In colored materials the absorption and the re¬ 
fractive index vary markedly with wavelength. For 
example, solutions of the orange dye (Calco Oil 
Orange Y-293) used in orange smoke signals have a 
low value of absorption in the yellow and red, a high 
value in the green and blue and an intermediate value 
in the violet. This means that, for the green and blue 
wavelengths, dye particles and oil droplets containing 
dye will have complex scattering and absorbing 
properties, while for the red and yellow wavelengths 
such particles will exhibit approximately the selective 
scattering by transparent particles. 

At wavelengths of low absorption the optimum 
particle size of a colored particle will be approxi¬ 
mately the same as that of a transparent particle of 
the same real refractive index. In the case of dye dis¬ 
solved in oil of real refractive index 1.50, the optimum 
particle size would be about 0.3 micron for red and 
yellow. Since the absorption of green and blue is 
higher, the refractive index at these wavelengths 
will be higher, and therefore, the optimum particle 
size will be smaller since it decreases with increasing 
refractive index. (See Figure 9.) 

The exact form of the dispersion curve for pure 
Y-293 dye is not known. The refractive index of the 
pure dye for red and yellow is 1.8. For green and blue 
it is probably higher; for violet, probably lower. In 
any case, the optimum particle size is lower than for 
Diol or for dye dissolved in Diol. It is probably near 


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SCATTERING BY PARTICLES WHICH ALSO ABSORB 


333 


that of sulfur, index = 2.0, for which the mean 
optimum particle radius is 0.15 micron. (See 
Figure 9.) 

The observed optical density of pure dye smoke (of 
unknown particle size), measured with blue light 
(X = 0.44 micron) outdoors, 18 was about one-half the 
observed and calculated optical density of both sulfur 
and Diol for green light (X = 0.524 micron) at the 
optimum particle size. Diol has a scattering cross 
section of 11 to 12 sq m per g (see Figure 9) for radii 
between 0.22 and 0.34 micron, and sulfur has about 
the same scattering cross section for the radii 0.12 to 
0.18 micron. The dye smokes should have at least 
the same scattering cross section at their optimum 
radius (probably about 0.2 micron). The fact that the 
observations on the dye smoke were made for blue 
light and the measurements on sulfur were made 
with green light does not invalidate this statement 
since the optical density of sulfur smoke near the 
optimum particle size (r = 0.12 to 0.18 micron) is 
practically the same for all visible wavelengths. This 
can be seen in Figure 9 by dividing the X scale by 2 
to correspond to r = 0.15 micron. 

The indications are that the dye smoke particles 
produced by the orange smoke signals are smaller 
than the optimum size when produced outdoors and 
larger when produced indoors. The dye smoke par¬ 
ticles produced indoors were examined with a high 
power microscope of high resolution. They were too 
small to be measured accurately but appeared to be 
not greater than 0.3 or 0.4 micron in radius. The 
particles produced outdoors appeared smaller for 
the following reasons. 

In a dye smoke, the color of the transmitted light 
is an indication of the size just as it is in the case of 
transparent particles. For example, the dye smoke 
produced by burning the orange signals in a 22-cu m 
room appeared pale green by transmitted light. This 
occurred because the particles had grown large due to 
rapid coagulation of the dense smoke. They became 
somewhat greater than the optimum size so that the 
transmitted light appeared green as it does through 
a screening oil fog whose droplets are somewhat 
greater than the optimum size (green sun’s disk). On 
the other hand, deep red or orange is frequently trans¬ 
mitted by the dye smoke produced outdoors showing 
that the particles are smaller than the optimum size. 

It has been observed frequently that the color of a 
cloud of dye or other colored smoke becomes paler 
with dilution. This is a necessary consequence of the 
absorbing properties of such smokes. A dense cloud Qf 


small orange dye particles appears orange by scat¬ 
tered light and deep red or orange by transmitted 
light. The cloud transmits red and yellow as does an 
oil solution of the dye, and the color of a cloud be¬ 
comes paler with dilution, as the color of a solution 
becomes paler with dilution. 

A dense cloud of small orange dye particles ap¬ 
pears orange because of multiple scattering and ab¬ 
sorption, and not because of primary scattering, 
which is practically colorless. At each rescattering, 
slightly more green than red is abstracted from the 
light by selective absorption in a particle, so that the 
light which is finally scattered from the interior of a 
dense cloud has had much of the blue and green ab¬ 
stracted from it and consequently appears red or 
orange. In a dilute cloud, however, the multiple 
scattering is greatly decreased. A great deal of pri¬ 
mary scattering is seen, which is practically colorless. 

However, in a cloud of large particles, the color 
decreases less rapidly with dilution. Due to greater 
selective absorption, larger particles abstract a 
greater proportion of blue at each scattering process 
so that less multiple scattering is required to produce 
a strong orange color. Again, as with the dye smoke 
produced indoors, if the size is somewhat greater than 
the optimum, then selective scattering may cause the 
transmitted light to appear green. 

21.5.2 Tables of Calculations 

Tables of calculations, based on the Mie theory for 
absorbing particles, have recently been completed. 
They can be used to obtain the total scattering by a 
droplet of transparent oil of real refractive index 
ra 0 = 1.50 containing dye in solution. When the 
absorption index k of the dye solution is known 
as a function of wavelength, the total scattering can 
be calculated for a complex refractive index m, rang¬ 
ing in value from m = 1.44(1 — ik) to m = 1.55 
(1 — ik) for values of a up to 6.0. The index k 
can have values up to 0.03, which corresponds to high 
absorption. These calculations cannot be used for 
pure dye smokes whose real refractive index is 1.8. 

It should be pointed out that these calculations 
will also yield the total scattering by a transparent 
particle of refractive index from 1.44 to 1.55 whenfc 
is made equal to zero. Approximately correct values 
will be obtained for refractive indices as small as 
1.33 and as large as 1.65. 

These tables have been published by the Mathe¬ 
matical Tables Project. 19 


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Chapter 22 

MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 

By David Sinclair 


22.1 MICROSCOPIC EXAMINATION 

22.1.1 Light Microscope 

T he light microscope has long been the standard 
method of observation of the particle size and 
distribution of smokes. It possesses the advantage 
that the true shape and size of the particles can be 
obtained, provided the radii of the primary particles 
are not less than 0.3 micron. It has the disadvantage 
that a long and tedious series of measurements is re¬ 
quired to obtain a distribution curve. 

Solid particles are usually composed of more or 
less loosely bound aggregates of primary particles 
too small to be resolved by the light microscope. To 
reveal the true structure of such particles, the elec¬ 
tron microscope is required. 

When liquid droplets are observed on slides, the 
true diameter is not observed since the drop is flat¬ 
tened, more or less, by its weight. The amount of 
flattening depends to a marked extent on the prop¬ 
erties of the surface of the slide as well as the nature 
of the droplet. If a carefully cleaned slide is used, a 
definite relationship exists for a given drop material, 
between the observed diameter of the flattened drop 
and its focal length. 

May 1 has given equations and curves from which 
the true diameter can be read when the lens diameter 
and focal length have been measured. The amount of 
flattening of the drop can be reduced by coating the 
slide with an oleophobic film. 2 

This method has sometimes been found unreliable. 
Observation of 4 microns radii droplets (determined 
by the gravity fall method and also by weighing a 
known number of droplets) gave results 25% too 
small when the radius was calculated from micro¬ 
scope measurements of the lens diameter. 

Volatile droplets on slides may evaporate so rapidly 
that the true diameter cannot be obtained. This 
may be avoided by allowing the drop to settle into 
a viscous liquid film in which it is insoluble. 1 

This method has been successfully applied to the 
measurement of the radii of water fog droplets. 3 A 
small drop of castor oil is placed in a depression slide 
and spread into a film. The water drops are allowed 
to settle onto the oil and then immediately covered 


with a cover glass coated with oil. The water drops 
are thus imprisoned and may be observed at leisure. 
The true diameter of the drops is observed, since 
they assume a spherical form while floating in the oil. 

Because the density of castor oil is 4% less than 
that of water, the droplets will finally sink to contact 
with the slide. They will usually spread and change 



4 + 



Figure 1 . Electron microscope photo of ZnO particles. 


their shape. This may occur for large drops before 
thejr can be measured. The spreading may be pre¬ 
vented by coating the depression with a thin, trans¬ 
parent film of paraffin. 

The light microscope may be used to measure 
smoke particles in situ. This method has been in¬ 
vestigated in great detail by Whytlaw-Gray. 4 The 
difficulties of this method have been analyzed and 
some of the defects corrected by Stumpf. 5 

In general, the light microscope is most useful as 
an auxiliary to other methods. These methods, de¬ 
scribed below, make possible rapid measurements on 
a mass of particles in their actual state of dispersion, 
either in the laboratory or in the field. 


334 


SECRET 



SAMPLING METHODS 


335 


22.1.2 Electron Microscope 

The electron microscope reveals details of the 
shape, structure, and size of particles completely un¬ 
observable by any other method. For example, some 
magnesium oxide particles of 1 or 2 microns diameter, 
as seen in the light microscope, are found to be irregu¬ 
lar aggregates of a large number of cubical crystals as 
small as 0.01 micron on a side (see Figure 1, Chapter 



Figure 2. Electron microscope photo of lithopone. 


18). Carbon particles are found to be long filaments 
of extremely small spherical particles (see Figure 3, 
Chapter 18). Similarly, the structure of particles of 
zinc oxide and lithopone are revealed by such photo¬ 
graphs as Figures 1 and 2. Extensive observations of 
the structure of aerosol particles have recently been 
made with the electron microscope by Eyring, 6 Mc- 
Grew, 7 and others. 

The electron microscope has some of the disad¬ 
vantages suffered by the light microscope. The par¬ 
ticles are not observed in the dispersed state and may 
be altered during or after sampling. This is especially 
true of fog droplets which are evaporated and dis¬ 
torted by the energy in the electron beam. For this 
reason, particles must have a vapor pressure at room 
temperature of not over 10 -5 cm of Hg, if they are to 
be observed in the electron microscope. The problems 
presented by various sampling methods are described 
in the next section. 

The difficulties of obtaining a true particle size dis¬ 
tribution curve are even greater with the electron 
microscope than with the light microscope. Because 
the magnification is high, the field of view of the 
electron microscope is so small that a large number 
of photographs must be taken in order to obtain a 


representative picture. This greatly increases the 
time and labor involved in making a count. 

Furthermore the details of individual particles 
observable with the electron microscope are often 
unimportant, or are averaged out in the mass of 
particles in an aerosol. For example, the obscuring 
power of a smoke of solid particles is determined by 
the average cross section of the particles, their shape 
and structure being unimportant. For such problems 
a method of size measurement is desired which will 
yield the particle area distribution as rapidly as 
possible. 

Similarly, the rate of fall of particles is determined 
by their geometric cross section and particle density 
(generally less than the true density of the solid 
material), so that these quantities can be obtained by 
suitable measurements of the rate of fall. It would be 
extremely tedious if not impossible to obtain the 
particle cross section and density from electron 
microscope photographs. 

In general, the method of measurement should be 
adapted to obtaining the properties of the aerosol of 
particular interest. 

The electron microscope, even more than the light 
microscope, is not suitable for measurements in the 
field. For these reasons the electron microscope, like 
the light microscope, is most useful as an auxiliary to 
the methods of measurement of particle size and dis¬ 
tribution in the aerosol state, described in following- 
text. 

22.2 SAMPLING METHODS 

22.2.1 Centrifugal Separation 

The cascade impactor is a form of centrifugal 
separator developed at Porton Experimental Sta¬ 
tion. 1 It is suitable for particles above 1-micron 
radius. The aerosol is forced in succession through a 
series of jets directed at microscope slides perpen¬ 
dicular to their surface. For each succeeding jet the 
velocity of flow V is increased by decreasing the area 
of the jet opening; and the radius of curvature R of 
the path of flow is decreased by placing the jet nearer 
the surface of the slide. 

Particles having a radius equal to or greater than ri 
[given by equation (39), Chapter 19] will be thrown 
out onto the first slide. Particles having a radius equal 
to or greater than r 2 will be thrown out onto the second 
slide, and so on, where > r 2 > r 3 • • •, Vi < V 2 < V s 
• • •, Ri > R 2 > Rs • • •. 

As stated in Chapter 19, the values of r h r 2 , r 3 , • • • 


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336 


MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 


may be determined by the construction of the ap¬ 
paratus, which determines the length of time the 
particles are in the given centrifugal field, as well as 
by the values of V and R. The apparatus is usually 
constructed so that all the particles down to 1 micron 
radius are collected in four stages. Smaller particles 
may contribute a large amount to the total number 
of particles but they contribute a negligible amount 
to the total mass of large particle aerosols. 

In order to obtain a constant range of sizes on 
each slide the velocity of flow must be kept constant. 
This can be done by drawing the air through a 
critical pressure orifice. For example, this may be an 
opening in a glass tube, adjusted so that the pressure 
drop across it is appreciably greater than one-half an 
atmosphere when the flow has the desired value. 8 
Under these conditions, moderate changes in the 
pumping rate have no effect on the flow through the 
orifice. 

The cascade impactor, like the impinger, 9 has the 
disadvantage that the particles are likely to be dis¬ 
torted by the violent impact with the slide. Solid 
particles are frequently broken, resulting in too high 
a count of small particles, and droplets are spread out 
and greatly distorted from their spherical shape. 
Consequently, only an approximate idea of the true 
size can be obtained by direct microscope measure¬ 
ment of the impinged particles. An independent 
measure of size should be made so that the instru¬ 
ment can be calibrated for a given rate of flow and 
particle density. The cascade impactor has the ad¬ 
vantage of compactness, and rapidity and ease of 
operation in the field. 1 

22 . 2.2 Thermal Precipitator 

The thermal precipitator is particularly suitable 
for sampling heterogeneous smokes of particle radii 
less than 1 micron. As described in Chapter 19, aero¬ 
sol particles will move in a temperature gradient from 
a hot body toward a colder body with a velocity 
directly proportional to the temperature gradient. 
With a high temperature gradient, the force acting 
on a particle is many times the force of gravity and 
the particle is deposited quickly. By placing the hot 
and cold bodies close together, the temperature 
gradient can be made high when the temperature 
difference is low (50 to 100 C). 

All the particles can be removed quickly from a 
small volume of smoke in a few minutes so that a true 
sample can be obtained. Thus, this method is su¬ 


perior to deposition by gravity, which discriminates 
against small particles because of their lower rate of 
fall. 

This method is superior to centrifugal separation of 
solid particles since it does not shatter or distort the 
particles by high velocity impact. It is not suitable 
for collecting volatile droplets because the hot body 
causes evaporation. 

A type of precipitator that gives 100% precipita¬ 
tion is described by Watson. 10 A similar piece of ap¬ 
paratus was constructed at Columbia University and 
used to sample both solid and liquid smokes, which 
were also analyzed with the differential settler. 

The apparatus consisted of a heated wire 0.007 in. 
in diameter, placed midway between two cold micro¬ 
scope cover glasses which were 0.015 in. apart and 
mounted with their planes vertical and parallel. Each 
cover glass was supported on one end of two brass 
plungers which fitted into a brass cylinder. The wire 
was stretched across the center of the cylinder, 
perpendicular to the axis. The wire was insulated 
from the cylinder and was heated to about 100 C by 
an electric current. The plungers carrying the cover 
glasses were inserted at opposite ends of the cylinder 
and held against stops so that each cover glass was 
at a distance of about 0.004 in. (about 100 microns) 
from the surface of the wire. 

The method of sampling was as follows. The flask 
of smoke from which a sample was taken for the dif¬ 
ferential settler was immediately connected by a 
rubber tube to the thermal precipitator. Smoke was 
then drawn in between the cover glasses through an 
inlet tube in the top of the cylinder. The direction of 
flow was at right angles to the length of the wire. The 
smoke particles were all deposited on each of the 
two cover glasses in a strip parallel to the wire and a 
little ahead of a line opposite the wire. 

The rate of flow was kept constant at about 3 cc 
per min by allowing water to flow slowly out of a 
reservoir connected to an outlet tube in the bottom 
of the cylinder. One to three minutes were required 
to obtain a sample, depending on the particle con¬ 
centration and size of the smoke. 

The efficiency of collection was tested by drawing 
the air from the precipitator through a spherical 
flask illuminated by an intense Tyndall beam. Any 
particles, even extremely small ones, can be readily 
detected by this method. When the flow was less than 
about 5 ml per min, no particles could be found in the 
flask. 

The deposits were measured and counted, using a 


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SAMPLING METHODS 


337 


microscope having an objective of numerical aperture 
about 0.85 and magnification of 120 diameters. This 
was used with a micrometer eyepiece, magnification 
20 diameters, which was calibrated with a Zeiss stage 
micrometer. One division on the ocular micrometer 
= 0.86 micron. The diameter of particles of 0.3 
micron radius and larger could be read to ±0.1 
division or about ±0.1 micron in diameter, i.e., 
±0.05 micron in radius. Particles below 0.3 micron 
radius could only be estimated. 

Distribution curves were obtained by counting 
about 200 particles. A count of a larger number of 
particles would be necessary for an accurate distri¬ 
bution curve, but the number counted seemed suf¬ 
ficient for the purpose of testing the performance 
of the differential settler. 

There was some indication of separation of sizes 
along the direction perpendicular to the hot wire. 
The smaller particles seemed to be deposited sooner 
than the larger, in conformity with the theory (Chap¬ 
ter 19). Consequently, in order to obtain as true a 
count as possible, the counts were made along several 
lines which completely traversed the deposit. 

The particles were deposited in two strips about 
1 mm wide and 1 cm long, i.e., over an area of 0.2 
sq cm. In 2-min flow at a rate of 3 cc per min, a 
smoke of 10 5 particles per cc would yield a deposit 
of 6 X 10 5 particles. These 6 X 10 5 particles of 1 mi¬ 
cron radius have a total cross-sectional area of 0.002 
sq cm, or 1 % of the area on which they are deposited. 
Thus 1 % of these particles should be expected to touch 
and form some sort of double particle. An equal 
number of smaller particles are less likely to touch, 
and the time of sampling can be shortened for larger 
particles. 

The normal appearance under the microscope of a 
deposited smoke prepared from undecomposed stearic 
acid is that of solid spheres, which are probably 
supercooled liquids of high viscosity. (The melting 
point of pure stearic acid is 69 C.) Frequently, how¬ 
ever, the particles were not spherical. There were a 
few doublets which could have been formed either by 
coagulation in the aerosol or by collision at the time 
of deposition. Sometimes the slides showed many 
crystals, either leaves oftetrahedra. These were most 
numerous when using an old batch of stearic acid 
which had turned dark brown from the decomposi¬ 
tion products. 

Crystallization may have occurred in the aerosol, 
but more probably at the time of deposition on the 
slide. (It was frequently found that particles, origi¬ 


nally deposited as spheres, had changed their shape by 
the following day.) Scintillating crystal particles are 
always observed in an aged smoke and only rarely in 
a freshly made heterogeneous smoke. No scintillating 
particles were observed in many fresh smokes which, 
after deposition on the microscope slide, showed leaf 
or tetrahedral crystals. It seems probable, therefore, 
that the condition of the surface of the cover glass 
caused the observed variety of shapes of the particles. 

As has already been mentioned, drops will spread 
when deposited on a hard surface so that the diameter 
observed in the microscope will be too large. 

The thermal precipitator was also used to obtain 
deposits of lithopone and zinc oxide on electron 
microscope slides. A brass disk, having a depression 
cut to fit an electron microscope screen, was used in 
place of one of the light microscope cover glasses. 
This method was found to be very unreliable since 
most of the particles were deposited onto the plastic 
film on top of the wires where they could not be ob¬ 
served. Furthermore, the heat from the wire tended 
to break the film on the screen. 

A microscopic examination of the plastic film on a 
new screen revealed the fact that the film sagged be¬ 
tween the wires. The center of the film was as much 
as 20 microns lower than the part touching the wires. 
This is one-fifth of the distance between the screen 
and the hot wire of the thermal precipitator. The re¬ 
sult is that the thermal gradient is 25 % greater over 
the wires than over the center of the film, so that the 
particles tend to deposit on top of the wires. 

Figure 1 shows one of the few good thermal de¬ 
posits of ZnO obtained. The sample for Figure 2 was 
prepared from a liquid dispersion of lithopone. The 
latter appears to be the only reliable method of pre¬ 
paring electron microscope screens. 

22 . 2.3 Gravity Settling 

Gravity settling yields a slide on which the particle 
number distribution usually differs from that in the 
aerosol. Unless the slide is left in so long that all the 
particles settle out, the number of particles of smaller 
radii which settle out will be less than the true dis¬ 
tribution in proportion to the square of the radius. 
[See equation (1), Chapter 19.] In general, it is im¬ 
practical to wait for all the smallest particles to settle 
out. 

Consequently, the slide is usually placed in the 
aerosol for a few minutes and the number distribution 
corrected by multiplying the observed number of 


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MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 


particles of radius r by r\/r 2 . This correction is valid 
only in tranquil settling, and is applied only to par¬ 
ticles of radius r < r 0 where r 0 is the radius of the 
particle for which the distance of fall during the time 
of exposure of the slide is equal to the distance from 
the slide to the top of the settling chamber. 

According to equation (2), Chapter 19, in stirred 
settling the fraction f s of particles having a given 
velocity v, which settle out during the time t of ex¬ 
posure of the slide is 

fs = 1 - e~ vt!h . (1) 

Consequently, the correct number distribution can 
be obtained by dividing the number of particles of a 
given size by the corresponding value of f s . 

In general, the type of settling of an aerosol in a 
closed chamber is somewhere between tranquil and 
stirred settling, so that an exact correction cannot be 
applied unless care is taken to maintain either tran¬ 
quil or stirred settling. For small particles, gravity 
settling is not suited to obtaining a representative 
sample because of the length of time required. 


illumination is used. The light scattered forward at 
angles from about 5 to 30° is observed, instead of that 
scattered at 90°. As the Mie theory shows, the ob¬ 
served intensity may thus be 100 or even 1,000 times 
greater. The instrument was developed for measure¬ 
ment of filter penetration. 12 

A schematic diagram of the apparatus is shown in 
Figure 3. The source S is a 6-v, 32-cp automobile 



Figure 3. Schematic diagram of optical mass-concen¬ 
tration meter. 


22.2.4 Mass Concentration 

The mass concentration of an aerosol can usually 
be readily measured by collecting a known volume in 
a glass wool filter and weighing. A small drying tube 
is half-filled with fine fiber glass wool, which should 
be packed in fairly tightly. The aerosol is drawn 
through the tube for a given length of time at a rate 
of about 10 1pm, measured with a flow meter, or a 
critical pressure orifice. 

The efficiency of collection is observed by drawing 
the filtered air through a spherical flask illuminated 
with a Tyndall beam. If an appreciable number of 
particles are observed, more glass wool should be in¬ 
serted, or the rate of flow decreased. Small particles 
pass through more readily than large particles. 

This method is suitable for aerosol concentrations 
down to about 10 jug per 1. At this concentration and 
a flow rate of 10 1pm for 30 min, an efficient filter 
would collect 3 mg, which can be measured with fair 
accuracy. For lower concentrations a microfilter, 
developed at Porton, 11 may be used. 

22.2.5 Optical Mass-Concentration Meter 

The optical mass-concentration meter may be used, 
when calibrated, to measure concentrations from 
200 ng per 1 down to 10~ 3 ^g per 1. The instrument is a 
form of Tyndall meter, modified so that dark field 


headlight bulb. L\ and L 2 are aspheric condenser 
lenses of about 23 ^-in. focal length and 23 ^-in. di¬ 
ameter. The source is placed at the focal point of L\. 
A high intensity image of the source is formed by L 2 
at its focal point. At this point the conical beam 
passes through a diameter aperture A in the 

screen S c . The smoke enters through a glass tube be¬ 
low A, passes through A and several peripheral holes 
in the screen and leaves the chamber through the 
tube above A . 

A black, opaque disk D of about 3^-in. diameter is 
painted or glued onto the lens L 2 . This disk D blocks 
out a cone of central rays. Observation along the axis 
of the cone through the window W (about Ji-in. 
diameter) shows the smoke brilliantly illuminated, 
but no direct rays reach the eye. The observer sees 
only the rays which are scattered along or near the 
axis of the cone, the direct rays from the source being 
absorbed by the blackened end of the chamber. Stray 
light is reduced to a minimum by blackening the 
whole of the interior of the chamber, preferably with 
soot. 

When no smoke or dust particles are present, the 
observer sees only the black background of the disk 
D, provided the aperture A is small enough. The 
.aperture A must be so small that no scattered light 
from the edge of D or from dust particles on the 
lenses reaches the window. The aperture A must be 
larger than the image of the source. When the lenses 


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METHODS BASED UPON GRAVITY SETTLING 


339 


are not achromatic, violet rays strike the edge of 
A but are so faint that the resultant stray light is 
quite weak. 

The sensitivity of the apparatus is such that the 
dust in ordinary room air appears brilliantly il¬ 
luminated. Consequently, the chamber must be air¬ 
tight. The zero reading for no smoke in the chamber 
is made while well filtered air is passing through. 

The instrument is calibrated for a given smoke by 
observing the intensity at several concentrations high 
enough to be measured by collection in a glass wool 
filter. The concentration of more dilute smokes is then 
directly proportional to the intensity. 

Because of turbulence the smoke fills the chamber 
completely. For this reason, a smoke of concentration 
higher than about 200 Mg per 1 should not be used. 
At higher concentrations the loss in intensity of the 
direct beam due to scattering becomes appreciable, 
so that the linear relationship between observed in¬ 
tensity of scattered light and concentration no longer 
holds. 

The calibration is correct over a wide range of mass 
concentrations provided the particle size remains un¬ 
changed. For this reason the smoke must not be so 
dense that appreciable coagulation occurs. This sets 
an upper limit to the mass concentration which de¬ 
creases with particle size. Because of the short time 
of flow the maximum allowable number concentration 
is 10 6 per ml (see Chapter 19). Therefore, a 0.5 mi¬ 
cron radius homogeneous smoke will not show appre¬ 
ciable coagulation up to 500 Mg per 1 while a 0.15 
micron radius smoke must not be over 14 Mg per 1 (see 
preceding text). 

The measurement or other purpose for which the 
aerosol is used must not change the particle size ap¬ 
preciably. For example, when using heterogeneous 
smoke to measure filter penetration, the dilute smoke 
which issues from the filter usually has a smaller 
average particle size than the more concentrated 
smoke entering the filter (see Chapters 19, 23, and 
24). Consequently a fairly homogeneous smoke is 
particularly necessary when measuring filter penetra¬ 
tion with the optical mass-concentration meter. 

22.3 METHODS BASED UPON GRAVITY 
SETTLING 

22.3.1 Measurement of Individual Particles 

The velocity of fall of particles under gravity may 
be used in a variety of ways to measure their size. The 


simplest method is to observe with a low power 
microscope the individual particles when brightly 
illuminated in a small closed chamber. The radius 
may be calculated from the observed velocity of fall 
by means of the Stokes-Cunningham law of fall. (See 
Chapter 19.) 

This method is suitable pnly for qualitative meas¬ 
urements. In order to obtain quantitative results a 
large number of particles must be observed and it is 
difficult to make the measurements representative. 
The tendency is to select the larger, brighter particles. 
Furthermore, the smaller particles are difficult to 
follow because of Brownian movement and the larger 
particles are likely to fall out before they are ob¬ 
served. 

22.3.2 The Homogeneous Smoke Settler 

The particle size of a homogeneous smoke may be 
conveniently measured by observing the rate of fall 
of the top of the cloud in a settling chamber free from 
convection currents. (See Chapter 19.) The observa¬ 
tion is made with a Tyndall beam from a source which 
may be held in the hand or mounted so that it can 
be moved up and down conveniently. If care is taken 
to shield the chamber from radiation, the top of the 
smoke cloud will remain quite flat and sharp for an 
hour or more. 

A form of settling chamber, previously described, 13 
consisted of a 3-in. diameter Pyrex tube 18 in. long, 
closed at the bottom with a rubber stopper and at 
the top with a brass plate cemented to the glass. This 
chamber is submerged in distilled (dust free) water 
contained in another glass cylinder and kept at a 
uniform temperature by stirring. 

Smoke is introduced through two brass tubes 
soldered to holes in the brass top of the settling 
chamber and extending above the water level. These 
tubes contain needle valves which are operated from 
above the water level by wires or strings. This ap¬ 
paratus avoids mechanical and temperature dis¬ 
turbances. 

Tranquil settling may best be obtained by placing 
the chamber in a darkened room free from draughts 
or other causes of rapid temperature change. A water 
cell should be used to remove the heat from the Tyn¬ 
dall beam, which is turned on only when a reading is 
being taken. 

The height of the cloud is recorded at suitable 
time intervals by sighting along the top of the cloud 
and marking the position on the wall of the water 


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MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 



jacket with a wax pencil. A precision of 5% or better 
can be obtained readily from four successive read¬ 
ings. 

This method can be used for rates of fall from about 
4 cm per hr up to 160 cm per hr, corresponding to 
radii from 0.3 to 2 microns for a material of unit 
density, and radii from 0.2 to 1)^ microns for ma¬ 
terial of density 2 g per cc, such as sulfur. 


Radii down to 0.1 micron may be measured by 
observation (with a low-power microscope) of the 
individual droplets in a small chamber. Frequently, 
the microscope observation can be made on the top 
of the cloud. Although the top becomes considerably 
spread due to Brownian movement (see Chapter 19), 
an average position can be measured with fair ac¬ 
curacy. This method yields sufficiently accurate re- 


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METHODS BASED UPON GRAVITY SETTLING 


341 


suits with a few measurements in the case of a 
homogeneous smoke. 

For radii below 0.1 micron the Brownian move¬ 
ment becomes so large that the results are unreliable. 

22.3.3 Differential Settler 

The differential settler is an instrument designed to 
measure the size and size distribution of a heterogene¬ 
ous smoke. As described in Chapters 19 and 21, the 
rate of change of the number of particles, An/At, at a 
fixed height in an aerosol in tranquil settling is pro¬ 
portioned to the rate of change of the scattered light 
intensity Al/At. 

Figure 4 is a diagram of the apparatus constructed 
and used to measure the size distribution of a variety 
of smokes having spherical particles. 14 

The settling chamber consists of a hollow brass 
cylinder closed with brass end plates, 3 in. in diameter 
and 2 in. high, inside dimensions. The walls of the 
chamber are 34 m - thick. 

The smoke is illuminated and observed through 
plane glass windows cemented over circular holes 
bored in the side of the chamber. The chamber is 
submerged in distilled (dust free) water contained in 
a brass water jacket and kept at a uniform tempera¬ 
ture by a stirrer (not shown in diagram). The water 
jacket also carries windows, located opposite the 
windows in the settling chamber. 

Smoke is introduced through two brass tubes 
soldered to holes in the top of the settling chamber 
and extending above the water level. These tubes 
contain needle valves which are operated from above 
the water level by wires. This apparatus avoids 
mechanical and temperature disturbances. 

In order to make reliable intensity measurements 
and also to prevent convection currents, it is neces¬ 
sary to reduce stray light to a minimum. For this 
purpose, clear plane windows consisting of polarime- 
ter tube cover glass 23.7 mm in diameter are used. 
By means of a slit 2 mm high and 8 mm long, the 
illuminating beam is made small enough so that it 
enters one window and leaves by a diametrically 
opposite window without touching the chamber walls. 
The light is made roughly monochromatic with a 
green filter and is completely screened off between 
readings. 

The illuminated smoke is observed at an angle 0 of 
45° ± 5° to the incident beam, as shown in the dia¬ 
gram. The intensity is measured with a Luckiesh- 
Taylor brightness meter. The 8-mm depth (in the 



0.3 0.4 0.5 0.6 


RADIUS IN MICRONS 



0.2 0.3 0.4 0.5 


RADIUS IN MICRONS 

Figure 5. Corrected and uncorrected differential set¬ 
tler curves. 

direction of observation) of the illuminated volume 
of smoke provides sufficient intensity of scattered 
light for accurate measurement. The smoke should be 
as dilute as possible in order to prevent coagulation 
during the time of a run. With fine particle smokes, 
this time may be as much as an hour or more. 

The 2-mm thickness (in the vertical direction) of 
the illuminated volume is the least that will provide 
a large enough field of view for good matching with 
the Luckiesh photometer. The thickness of the illumi¬ 
nated region should be kept as small as possible rela¬ 
tive to the height of the top of the chamber above the 
illuminated region. A convenient height is 1.5 cm. A 
greater height makes the length of some runs exces- 


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MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 


sive, and a smaller height introduces too large an error 
in the determination of the starting time of a short 
run. With the above dimensions the intensity ob¬ 
served at any one time is that due to all particles 
within the region 1.5 ± 0.1 cm from the top. This 
introduces an error such that a smoke of uniform 
particle size appears to have a spread in size of about 
7%. This is not considered excessive. 

When the particle density is known, the particle 
size can be calculated from the relative intensity at 
any time provided the law of scattering of light with 
particle size is known. In the previous measurements 
described elsewhere, 14 it was assumed that the law of 
scattering for spherical particles was given with 
sufficient accuracy by making p [see equation (11), 
Chapter 21] equal to 3 for all values of the radius. 
This yielded a distribution curve which was not even 
approximately correct in some cases. 



Figure 6. Corrected and uncorrected differential set¬ 
tler curves. 


The true law of scattering is given in Figure 10, 
Chapter 21. Some of the distribution curves, pre¬ 
viously given, were corrected by means of Figure 10, 
Chapter 21. The results are shown in Figures 5 to 8 
which show the relative number of particles dn of 
radius r microns. 

It will be seen that some of these curves, notably 
those in Figures 6 and 8, are completely altered. It is 
not certain that the curves of Figure 10, Chapter 21, 
are the proper correction curves. In correcting the 
distribution curves, the observed 7% spread in 
particle size as well as the 10° spread in angle was 
taken into account as far as possible. 

A more reliable method would be to obtain an ex¬ 
perimental calibration curve using very homogeneous 
smokes. In addition, a type of illumination similar to 
that used in the optical mass-concentration meter 




RADIUS IN MICRONS 


Figure 7. Corrected and uncorrected differential set¬ 
tler curves. 


might be used. This would provide a greater angular 
spread in illumination which would tend to smooth 
out the calibration curve. 

Furthermore, more intense illumination would 
make it possible to use smokes of low concentration, 
thus avoiding coagulation which may have been a 


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OPTICAL METHODS 


343 


disturbing factor in the measurements made with 
the differential settler thus far. 

22.3.4 Stirred Aerosols 

The equations to be used in the measurement of 
particle size and size distribution of uniformly 
stirred aerosols have been given in Chapter 21. 

Homogeneous Aerosol with Slow Coagulation 
If the aerosol is initially homogeneous and under¬ 
goes slow coagulation, equation (13), Chapter 21, de¬ 
scribes the early stages in the life of the aerosol. 
Some experimental results obtained by this trans¬ 
mission method have been described elsewhere. 15 



RADIUS IN MICRONS 

Figure 8. Corrected and uncorrected differential set¬ 
tler curves. 

Heterogeneous Aerosol without Coagulation 
When a heterogeneous aerosol is sufficiently dilute 
so that coagulation is negligible, equations (14) to 
(20), Chapter 21, may be employed. This transmission 
method has been used 16 to obtain the initial size dis¬ 
tribution of aerosols of zinc oxide and egg albumin 
dispersed with the geyser and with the gas ejection 
bomb described in Chapter 20. 

The average diameters of the equivalent spheres 
(see Chapter 21), that is, spheres having the density, 
rate of settling, refractive index and scattering cross 
section of the actual particles, were obtained from 
measurements of the initial scattering per cc of 
aerosol, S t [equation (15), Chapter 21], and the mass 
concentration, M t [equation (9), Chapter 19]. The 
values of S t and M t were plotted on semi-log paper. 

Extrapolation of these curves to zero time gives the 
initial scattering per cubic centimeter, S 0 , and the 
initial mass concentration, M 0 , from which the 


initial scattering per gram, A 0 = So/M 0 [equation 
(18), Chapter 21], is obtained. The slopes of these 
two curves at zero time give the initial values of 
u s = d/dt log S t [equation (17), Chapter 21], and 
u m = d/dt log M t [equation (16), Chapter 19]. 

In order to facilitate the analysis of the experi¬ 
mental measurements, figures were drawn from which 
the values of p, d g and a g can be picked off when the 
experimental quantities u 8 , u m and A 0 are known. 
These figures were calculated by means of equations 
(5) and (16), Chapter 19, and (18) and (20), Chapter 
21, as described in following text. They are particu¬ 
larly useful when the particles are so small that the 
scattering coefficient is greater than 2. This is the 
case for all Kadox particles and for the smaller sta¬ 
tistical diameters of egg albumin, although in the 
latter case K 2 is only a little greater than 2. 

Figure 9 shows the values of a g and pd g correspond¬ 
ing to a set of values of A 0 and R for egg albumin, 
where R = u m /u s . To obtain this figure, appropriate 
values of a g and pd g were chosen and from these, 
pd 2 , pd 4 , pdb, and pd 9 were calculated by means of 
equation (5),Chapter 19. Using Figure 13,Chapter 21, 
K 2 and Ka corresponding to pd 2 and pd\ are read off, 
and these values, together with pd 5 and pd 9 , are 
substituted in equations (18) and (20), Chapter 21, to 
calculate A 0 and A 0 (u s /u m ). 

Figure 10 shows the values of p corresponding to a 
set of values of pd 8 and hu m calculated by means of 
equations (5) and (16), Chapter 19. 

The figures are used by finding on Figure 9 the 
value of a g and pd g corresponding to the experimental 
values of A 0 and R = u m /u s . Using the value of a g 
and pdg thus obtained, pd 8 is calculated by means of 
equation (5), Chapter 19. Using this value of pd 8 and 
the experimental value of hu m , the value of p is ob¬ 
tained from Figure 10. The weight median diameter 
de, or other statistical diameter may then be calcu¬ 
lated from equation (5), Chapter 19, using the values 
of (T g and d g just found. This calculation of d 6 may 
be checked by means of equation (17), Chapter 21. 

22.4 OPTICAL METHODS 

22.4.1 The Owl 

As described in Chapter 21, the colors and polari¬ 
zation of the scattered light may be used to deter¬ 
mine the particle size of a homogeneous smoke of 
spherical particles. An instrument, called the Owl, 
has been constructed and used for this purpose. 17 It 


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MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 



yodg-► 

dg IN MICRONS 

Figure 9. Values of a Q and pd 0 for values of A 0 and R for albumin. 


consists of an observation chamber and light source 
which may be held in the hand and rotated while 
observing the smoke through a low power micro¬ 
scope. 

The observation chamber is a hollow metal cylinder 
3 in. in diameter and 1 in. high (ID) having flat end 
plates, Figures 11 and 12. A window 3^ in. high is 
cut in the side for an angular distance of a little more 
than 150°. Over this is cemented a section of a 
cylinder of uniform glass whose inside diameter is 
equal to the outside diameter of the chamber. This 
window enables observations to be made at all angles 
between 15 and 165° by rotating the chamber (and 
attached illuminator) about an axis through its 
center. The axis of rotation is perpendicular to the 
plane of observation. 

The illuminator is constructed from microscope 
eyepieces and an automobile headlight bulb as shown 
in Figure 11. The arrangement shown provides a 


sufficiently intense light beam, parallel to ±3°. 
When the illuminator is properly adjusted, the light 
beam just clears the open end of the light trap. 

On the opposite side of the chamber from the 
illuminator is a light trap consisting of a ^-in. 
diameter tube 23 ^ in. long with the far end closed 
with a metal plate. Except for the window, the inside 
of the chamber should be blackened with high quality, 
dull black optical lacquer and, preferably, also covered 
with soot. This can be conveniently done by means 
of the flame from burning camphor. 

A semicircular scale, graduated in degrees, is 
mounted on the bottom of the chamber as shown in 
Figure 11. The illuminator should be located at 180° 
and the light trap at 0° to within 1°. A fiduciary mark 
should be placed on the supporting bar, extended, for 
reading the angle of observation, 0. The chamber is 
rotated by using the light trap as a handle. 

By means of an atomizer bulb, smoke is blown in at 


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OPTICAL METHODS 


345 


dg IN MICRONS 

P<*6 -* 


2 3 4 5 6 7 0 9 10 II 12 13 14 15 



h * HEIGHT OF SMOKE CHAMBER IN CM 

Figure 10. p vs hu m for values of pd%. 


the bottom and out through the top of the chamber. 
A ball valve is located at the bottom of the bulb, and 
another at the top of the chamber. A type of valve 
which does not stick easily is required. 

The observations are made through a long focus 
microscope, of magnification 6X, constructed from 
ordinary microscope eyepieces as shown in Figure 11. 
The microscope is focused on the smoke particles in 
the center of the chamber. 

The polarization photometer (see Chapter 21) is 
made by mounting a bipartite Polaroid disk in the 
eyepiece of the microscope, in good focus, with the 
dividing line parallel to the plane of observation to 
±1°. This setting may be made as follows. Remove 
the chamber and illuminator from their supports and 
mount the illuminator so that the direct beam can be 
seen through the photometer and microscope. Mount 
a Polaroid (hereafter referred to as the polarizer) be¬ 
tween the illuminator and telescope. The polarizing 
axis of the polarizer is set parallel (or perpendicular) 
to the plane of observation and the analyzer (see 
following paragraph) is set perpendicular (or parallel) 
thereto. When the polarizer and analyzer are thus 
crossed and the bipartite disk is oriented correctly, no 
light (except for the residual violet always trans¬ 


mitted by Polaroids) will be transmitted. If any 
white light is transmitted, rotate the bipartite disk 
until extinction is obtained, and fix it in this position. 

The bipartite disk was made by the Polaroid Cor¬ 
poration (Cambridge, Massachusetts) using their new 
Polaroid-H laboratory-type film which, they report, 
gives about 99.99% polarization throughout most of 
the visible region. The polarizing axes of the bipartite 
disk are respectively perpendicular and parallel to 
the dividing line to ±1°. The dividing line between 
the two halves should be as inconspicuous as possible. 

The analyzer is placed in front of or in the eyepiece 
between the bipartite disk and the observer. It consists of 
a piece of Polaroid-H laboratory glass mounted so as 
to be readily rotated about a horizontal axis. The 
angular setting, (f >, is read off a quarter circular scale 
graduated in degrees. The scale is mounted so that 
the setting of the analyzer is accurate to ± 1°. When 
(f> = 0° the vibration or polarizing axis of the analyzer 
lies in the plane of observation. 

A piece of Wratten 58B green gelatin filter is also 
mounted in front of, or in, the eyepiece. This filter 
should be fastened to the front face of the analyzer. 
Both the analyzer and filter should be readily re¬ 
movable out of the line of sight. 


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346 


MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 



In order that observation may be made in day¬ 
light, the microscope objective and window should be 
completely covered. One satisfactory method is to 
use a conical bag of opaque black cloth open at both 
ends. The small end fits over the microscope so that 
it does not interfere with the rotation of the chamber. 

A tapered metal sleeve extending to just in front 
of the window is fitted over the microscope. This pre¬ 
vents the black cloth from obstructing observation. 
In addition, a black cloth hood is fastened around the 
eyepiece end of the microscope and thrown over the 
observer’s head. 

The foregoing description refers particularly to 
models made at Columbia University. Another model 
has been made commercially which is of improved 
design. Among other features, this model has a fine 
adjustment for setting the analyzer, and a facepiece 
which eliminates the need for the black cloth hood. 

The particle radius corresponding to the observed 
angular setting of the analyzer is given in the calcu¬ 
lated calibration curves, Figures 6 and 7, Chapter 21. 
The polarization at a radius of 0.11 micron for sulfur 
and at 0.17 micron for oleic acid has been checked 


experimentally by observing the rate of fall of 
homogeneous smokes under gravity in the small 
settling chamber described in preceding text. 

The calibration curves extend down to 0.05 micron 
but readings below 0.10 are not reliable. It must be 
emphasized that these curves can be used only for 
small particle smokes of radii below 0.2 micron (for 
sulfur and tryphenyl phosphate only below r = 0.15 
micron). In other words, they should not be used 
Avhen the number of spectra (reds) observed is two 
or more. 

For measurement of particles of radii from 0.20 up 
to 1.0 micron, remove the analyzer and green filter 
and count the number of times red is seen in i\ as the 
observation chamber is turned from near 0 to near 
180°. The description of the colors observed is given 
in Chapter 21, and the calibration curve is shown in 
Figure 4, Chapter 21. 

The observations of the number of reds must be 
made on the scattered component i x alone, since the 
component i 2 exhibits a different series of spectra. 
The component i\ is seen when the vibration axis of 
the analyzer is vertical. In a Polaroid-H disk, this 


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OPTICAL METHODS 


347 



axis is parallel to the diameter through the diamond 
etched on the disk. 

When observing without the analyzer, the two 
spectral series in i x and i 2 are seen simultaneously and 
adjacent to each other and the contrast between them 
frequently aids in the analysis of rather heterogeneous 
smokes. 

When observing the spectra, attention should be 
paid to the angular position of the reds (Figure 5, 
Chapter 21) as well as their number. It is seen clearly 
how the position of the first red shifts from 100 to 20° 
as the number of spectra increases from one to seven, 
i.e., as the particle radius increases from about 0.1 to 
0.7 micron. 

22.4.2 Coronae 

The radii of transparent fog droplets of 5 or 10 
microns and over can be obtained by observing the 
diffraction rings or coronae formed around either a 
point source of light located in the fog, or, preferably, 
a beam of light shining through the fog. These diffrac¬ 
tion rings are similar in appearance to the colors ob¬ 
served in Mie scattering by smaller droplets, except 
that the angles at which the colors appear are much 
smaller. 

According to the theory of diffraction for opaque 
disks, the angular radius 0i of the first bright ring is 
given by sin 6 X = 0.819X/r where X is the wavelength 
of the light and r the radius of the droplet. 18 The 
second bright ring is given by sin 0 2 = 1.346X/V, the 
third by sin 0 3 = 1.858X/r, and the fourth by sin 0 4 = 


2.362X/r. The relative intensity of the first four rings 
is approximately 1 , Ko> Mo- 

The angular radii of the dark rings are given simply 
by sin 0 = (n + 0.22)X/2r where n is the order of the 
ring. 

The rings are observed most clearly in a fog of 
uniform droplet size. Experience has shown, however, 
that the uniformity need not be so great as in the 
case of Mie scattering. Kohler 19 has used this method 
for the measurement of the droplet size in water fogs 
of about 8 microns radius. He found that the rings 
are usually produced by the predominant size, with 
the larger sizes being favored since they produce the 
smallest and brightest rings. The writer has observed 
several colored rings in water fogs which contained 
droplets varying in radii from 4 to 16 microns or 
greater. 

It is seen that the size of the rings is independent 
of the index of refraction of the droplets. This is so 
because the equations are derived for diffraction by 
opaque disks. For this reason, Wilson 20 states that 
the equations are not accurate for radii less than 10 
microns and scattering angles 0 greater than 10°. 

For accurate measurement of radii below 5 or 10 
microns, down to 1 micron (below which the Mie 
scattering can be used) the coronae radii could be 
calibrated against droplets of known size. However, 
an approximate value of the radius can be obtained 
for radii between 2 and 10 microns by the use of the 
above equations. 

For this purpose Humphreys 18 gives a calculated 
curve showing the angular radii of the first and 


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348 


MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 



/ 


5 
\\ 

4 - 


n 


I! 

i 


Pi* RCA 922 PHOTOTUBE (RED SENSITIVE) 

P--RCA 929 PHOTOTUBE (BLUE SENSITIVE) 

F,-WRATTEN 88 A FILTER 

Fg-CORNING 554 

L|-2"0IA ,4"f LENS 

L2'2"DIA ,2"f ASPHERIC CONDENSER 


Mi - HALF-SILVERED MIRROR 

M 2 -MIRR0R 

B - 6 - 8 V. 6 CP BULB 

P - HARD RUBBER RADIO PANEL 

G- GLASS PANE 

C - CARRIAGE MOUNT FOR BULB 


UNLESS INDICATED, ALL CONSTRUCTION IS 5 PLYWOOD 


SEIn 


Figure 13. Slope-o-meter (layout of parts). 


second red rings as a function of the radii of water 
droplets between 1 and 10 microns. It will be seen 
that these two curves are roughly extensions of the 
first two curves of Figure 5, Chapter 21. 

The coronae were used to measure the size of lyco¬ 
podium spores of fairly uniform size. The radius of 
these spores, as measured in a light microscope, was 
found to vary from 13.6 to 16.0 microns. 

The spores were allowed to settle on a glass plate 
which was then placed in a beam of light of parallel 
rays and also in a slightly divergent beam from a 
point source. Measurements were made of the angu¬ 
lar diameter of two orders of both the light and dark 
diffraction rings in both red and green light. From 
these measurements the spore radius was calculated 
to be 15.5 ± 0.2 microns, in good agreement with the 
microscope measurements. 

Similar measurements were made on a uniform 
droplet size oil fog in a flask. The radius, as measured 
by two independent methods was 4.0 ±0.1 microns. 
The agreement here is less good, as is to be expected 
for such small, transparent spheres. 

22.4.3 The Slope-o-Meter 

The particle size of a homogeneous smoke, or an 
average size of heterogeneous smoke, may be ob¬ 
tained by measuring light transmission as a function 


of wavelength (Chapter 21). An instrument, called 
the Slope-o-meter, has been constructed and used for 
this purpose. 21 

The instrument is essentially a photoelectric spec¬ 
trophotometer which compares the intensity of light 
transmitted at two wavelengths through a sample 
of smoke. Extensions of the same mechanical and 
electrical system may be used to compare the trans¬ 
mission at three or more wavelengths. Two types of 
Slope-o-meter designated as Type I and Type II have 
been constructed. The following is a description of 
Type II. Type I is described elsewhere. 21 

Method 

Photo-emissive photoelectric cells of the vacuum 
type are used to measure (1) the intensity of blue 
light (wavelength, 4400 A) transmitted through the 
aerosol sample, and (2) the difference between the 
intensities of infrared light (wavelength, 8000 to 
9000 A) and blue light transmitted. 

Construction 

The optical and electrical systems have been as¬ 
sembled in a single box, one compartment of which 
serves as a smoke chamber (Figure 13). A second box 
contains three 45-v portable B batteries and an 8-v 
portable storage battery. Power is transmitted to 
the optical and electrical systems via a six-wire cable 


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OPTICAL METHODS 


349 


TUNING EYE 

6J7GT 6 E 5 



Figure 14. Slope-o-meter (wiring diagram). 


and suitable plugs and jacks. The optical system 
consists of a 6-cp automobile bulb (Mazda No. 81), a 
condensing lens which sends a beam of light through 
the smoke and a semitransparent mirror directing it 
finally onto the phototubes. The purpose of the semi¬ 
transparent mirror is to enable a single beam of light 
through the smoke to suffice for both phototubes. 
Color filters are interposed between the semitrans¬ 
parent mirror and the phototubes. 

Rigid mounting of all parts of the optical system is 
necessary for reliable operation. The possibility of 
warping should be reduced to a minimum, although 
slight warping is corrected by the normal adjust¬ 
ment of the Slope-o-meter. 

The electrical system (Figure 14) consists of suita¬ 
ble resistance loads (R h R 2 , and R 3 ) for the phototubes, 
selector switch Si and a slide-back vacuum tube volt¬ 
meter. Three 45-v B batteries provide plate and 
slide-back voltage and an 8-v portable storage battery 
provides current for the 6-cp lamp and for the heaters 
of the vacuum tubes. 

The resistors, R u R 2 , and R 3 , vary from one ma¬ 
chine to the other but are selected so that with no 
smoke in the chamber, and with the 6-cp bulb 


operating at its proper current, the emf developed by 
each photocell is just below 22.5 v, the maximum 
slide-back voltage. The proper current is selected so 
that it can be maintained constant for all working 
voltages of the storage battery through adjustment 
of R~. 

When the selector switch Si is at position 1, the 
grid of the 6J7 GT is connected through R 4 to ground 
and the slide-back potential is zero. •Rg may then be 
adjusted so that the shadow of the tuning eye (6E5) 
is open to some selected angle near the middle of its 
range. This angle is marked and used for all subse¬ 
quent balancing operations and indicates that zero 
emf is impressed on the grid of the 6J7 GT. 

When the selector switch is at position 2 or 4, the 
emf developed by the blue sensitive phototube (RCA 
929) is impressed on the grid of the 6J7 GT and this 
may be balanced manually by the slide-back emf de¬ 
veloped in R b . The dial reading of R b is a measure of 
the total amount of blue light striking the phototube. 

When the selector switch is at position 3 the dif¬ 
ference between the emfs developed by the blue and 
and by the infrared light is impressed on the grid 
6J7 GT and the slide-back potential is again zero. The 


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350 


MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 


load resistance (R 2 + R 3 ) of the infrared sensitive 
phototube may then be adjusted to bring the tuning- 
eye to the balance position. The effect of this opera¬ 
tion is to make the response of the instrument to blue 
light the same as the response to infrared light. This 
compensates for changes in the color of the light 
emitted by the lamp as it ages and for other changes 
in the apparatus such as drift in the value of the 
phototube load resistors or small amounts of warping. 

When the selector switch is at position 5 or 6, the 
difference between the emf s developed by the infra¬ 
red and by the blue light may now be balanced by the 
slide-back potential developed inR b . With the selector 
switch in these positions, however, the magnitude of 
the slide-back voltage corresponding to full scale of Re 
has been reduced by the insertion of Re. The in¬ 
crease in sensitivity is desirable here because a dif¬ 
ference between two quantities is measured which 
may often be small. 

Operation 

1. Adjustment: No smoke in smoke chamber. 

a. Switches S 2 and S s are thrown to “on” posi¬ 
tion. 

b. Selector switch on l. Adjust R& to balance. 

c. Selector switch on 2. Set Re on preselected 
value near maximum. Adjust R 7 and R\ 2 to 
balance. 

d. Selector switch on 3. Adjust R 2 to balance. 

2. Measurement: Put smoke in smoke chamber. 
For field use, open the door of the smoke chamber 
while in the smoke and close it. 

a. Selector switch on 4. Adjust R b and note dial 
reading. 

b. Selector switch on 5. Adjust R b and note dial 
reading. If no balance is possible, turn selector 
to position 6, balance with Re and note dial 
reading. 

The dial readings of Re for selector switch positions 
4 and 5 (or 4 and 6) fix the particle concentration 
and the radius (respectively) of the smoke in the 
chamber. See typical calibration curve in Figure 15. 

The concentration lines on the calibration curves 
were obtained by means of calculations based on the 
Mie theory. As described in Chapter 21, the Mie 
theory yields the droplet radius from observations 
of the color and polarization of the scattered light. 
The theory also gives the scattering coefficient for a 
known droplet size and wavelength, so that the con¬ 
centration can be obtained by observing the decrease 


of intensity at a known wavelength and known length 
of light path through the smoke. 

Measurement of Particles Below 0.18 Micron 
Radius 

For very fine particles the sensitivity of the Slope- 
o-meter decreases markedly. For instance, all smokes 
fine enough to exhibit Rayleigh scattering fall on the 
same particle size calibration line. Accordingly, for 
fine particles the Owl described previously should be 
used to determine the particle size, and the Slope-o- 
meter used to measure concentration. For this pur¬ 
pose, it is necessary to measure only the transmission 
of blue light (dial reading of Re for selector position 4). 

Limitations and Precautions 

For particles above 0.5-micron radius, index of 
refraction 1.50 to 1.55, the particle size calibration 
curves are duplicates of the curves obtained for 
smaller particles. 

It is apparent that a reading of particle size and 
concentration will be obtained no matter how in¬ 
homogeneous the smoke may be. For a homogeneous 
smoke, which shows orders in the Owl,the results will 
be as accurate as the initial calibration. For hetero¬ 
geneous smokes, a complex weighted average is ob¬ 
tained, where the effect of particles larger than the 
average tends to cancel the effect of particles smaller 
than the average, provided there are few particles of 
0.5-micron radius or larger. The smoke from large- 
scale generators of the coil or combustion gas type is 
apparently homogeneous enough and the particle 
sizes are within the proper range for use of the 
Slope-o-meter. 

22.4.4 Color of the Transmitted Light 

Visual observations of the color of white light 
transmitted through an aerosol provide a measure of 
the particle size (Chapter 21). It must be emphasized 
that this method does not provide an absolute, but 
only a relative measure of size relative to the 
optimum size for material of a given refractive index. 

If the residual rays transmitted by a Diol fog are 
blue or green, it indicates that the average radius is 
greater than 0.33 micron, the optimum radius for 
Diol. However, a similar observation through sulfur 
smoke indicates an average particle radius greater 
than 0.17 micron, the optimum radius for sulfur. If 
the residual rays are red, it indicates an average 
radius less than 0.33 micron for Diol fog and less 


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DIAL READING NO. 6 DIAL READING NO 


OPTICAL METHODS 


351 



Figure 15. Slope-o-meter (calibration curves). Note: Diol m = 1.50. 


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352 


MEASUREMENT OF PARTICLE SIZE AND SIZE DISTRIBUTION 


Table 1 


Date 

Generator 

Owl radius, 
microns 

Slope-o-meter 
radius, microns 

Sun’s disk color 

Comments 

Nov 10, 1942 am 

Esso 

0.18 

0.15 


Fairly homogeneous 



0.16 

0.16 



Nov 10, 1942 am 

Servel 

0.29 



Moderately homogeneous 



0.33 




Nov 10, 1942 pm 

Servel 

0.29 

0.28, 0.33, 0.22, 0.33. 






After turning off and 






on again: 0.20 



Nov 10, 1942 pm 

Haslar 

0.5 






estimate 


Blue 

Brownish color, heterogeneous 

Nov 23, 1942 pm 

Servel 50 gal 

0.32 


Purple 

15 ft from generator 



0.40 


Blue 

115 ft from generator 

Feb 23, 1943 pm 

Servel 25 gal 

0.22 


Red 

30 ft from generator, some carbon 

Feb 23, 1943 

Chrysler 



Lavender 

Sample unobtainable. Blower 





White 

sends smoke 35 ft up 

Feb 23, 1943 

DeVilbiss 

estimate 


Lavender 

Heterogeneous 



medium size 


White 


Feb 24, 1943 am 

Esso 

0.3 


Lavender 

Owl colors indistinct 





White 


Feb 25, 1943 am 

Hickman 

0.4 approx 

0.5 approx 

Blue 

Heterogeneous 



0.3 approx 



Standard nozzle 

Feb 25, 1943 pm 

Hickman 

0.27 

0.30 

Lavender- 

Multiple-hole nozzle 



0.22 

0.26 

white to red 


Feb 25, 1943 pm 

Williams 

0.20 

0.18 

Red 

Multiple-hole nozzle 



0.25 

0.25 

Red 


Feb 25, 1943 pm 

Williams 

0.32 

0.35 

Red 

Multiple-hole nozzle 



0.35 


Blue 


Feb 25, 1943 pm 

Hickman 

0.29 

0.31 

Too cloudy 

Multiple-hole nozzle 

Feb 25, 1943 pm 

Hickman 

0.35 

0.38-0.42 

Too cloudy 

Standard nozzle 

Feb 25, 1943 pm 

Esso 

0.29 

0.25 

Reddish white 

50 ft from generator 

Feb 24, 1943 

Esso 

0.27 

0.24 

Red 

18 mph wind from propeller 



0.22 

0.19 

Red 



then 0.17 micron for sulfur smoke. A magenta color 
indicates the optimum particle size. 

Langmuir has developed a set of color filters which 
enable this measurement to be made more precisely. 
Several transparent filters, whose colors match the 
residual colors of the sun when the droplet radius of 
Diol fog is at or near the optimum, are mounted in 
a frame and viewed against a white background. The 
particle size can then be obtained by matching the 
observed color of the sun with the color of one of the 
filters. 

22.4.5 Field Measurements 

During November 1942, and again in February 
and March 1943, optical methods were used to 
measure the droplet size of oil fogs from screening 
smoke generators operated at Edgewood Arsenal, 
Maryland. The droplet radii in the fog produced by 
the Esso, Servel, Haslar, Chrysler, DeVilbiss, Hick¬ 
man, and Williams generators, using Diol 55 as the 
fog oil, were measured with the Owl and the Slope-o- 


Table 2. Esso generator. 


Owl Nozzle Diol 

radius, diameter temperature 


microns Sun’s disk 

inches 

degrees F 

Remarks 

0.2 

Red 

3/16 

1,000 

Homogeneous 

0.2 

Red 

3/16 

950 

Homogeneous 

0.25 

Red 

3/16 

900 


0.3 

Lavender 

3/16 

850 

Indistinct 

0.3 

Lavender 

3/16 

800 

Indistinct 

0.3 

Red 

1/4 

900 


0.3 

Lavender 


900 


0.3 

Lavender-white 

5/16 

1,020 

Homogeneous 

0.35 

Blue 

5/16 

1,000 


0.3 

Lavender 

5/16 

900 

Homogeneous 

0.3 

Blue 

5/16 

800 

Homogeneous 

0.3 

Red 

3/8 

1,000 

Homogeneous 

0.35 

Lavender-white 

3/8 

900 

Indistinct 

0.4 

Purple 

3/8 

800 


0.4 

Blue 

3/8 

825 

Indistinct 


meter. Observations of the color of the sun’s disk 
were made whenever possible. 

The results are summarized in Table 1. They 
represent only the results obtained for the particular 


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OPTICAL METHODS 


353 


settings of the generators and are not to be taken as 
the only particle radius that may be obtained from 
these generators. At the bottom of the table it is 
shown that an 18 mph wind decreased the droplet 
radius 0.05 micron. 

Special tests were performed on the Esso generator 
to test the effect of high wind, of nozzle diameter and 
of oil temperature as shown in Table 2. The standard 
nozzle diameter in the Esso generator is in. When 
the diameter wag doubled to % in. the average drop¬ 
let radius was increased by 0.1 micron, provided the 


temperature of the oil was constant. For a given size 
nozzle, when the Diol temperature was raised from 
800 to 1000 F, the average droplet radius was de¬ 
creased by 0.1 micron. The pressure was not ob¬ 
served. It is seen that the droplet radius could be 
increased from 0.2 to 0.4 micron by doubling the 
nozzle size and lowering the temperature simul¬ 
taneously. 

Additional field and laboratory measurements 
made on various types of smokes are described in 
an unpublished report. 


SECRET 



Chapter 23 

FILTRATION OF AEROSOLS 

By W. H. Rodebush 


23.1 INTRODUCTION 

A s has been pointed out in Chapter 18, aerosol 
filters do not behave as sieves or screens which 
stop particles larger than the mesh and let through 
smaller particles. It is theoretically possible to con¬ 
struct such a filter, but it would offer so much re¬ 
sistance to the flow of air that it would be useless 
from a practical point of view. Thus, the filter papers 
used in analytical chemistry for the separation of 
precipitates are very inefficient as aerosol filters. All 
mechanical aerosol filters must, in practice, be of 
open construction, with the openings large compared 
to the size of the particles to be removed, in order to 
reduce the resistance offered to the flow of air. The 
removal of the particles is therefore by chance 
collision rather than positive action, and the per¬ 
centage removed is a statistical function of the thick¬ 
ness of the filter; a filter of infinite thickness would be 
required to remove 100% of the particles from the air 
stream. 

In practice all mechanical filters are made up of 
fibers, some of which must be of small diameter (i.e., 
comparable to the diameter of the aerosol particles) 
if the filter is to be efficient. An efficient filter may be 
defined as one which offers a low resistance and at the 
same time a low penetration. These two quantities 
are mutually interdependent variables, and for a 
given filter material one can be decreased only at the 
expense of the other. 

It will be obvious from the theory of filtration why 
an efficient filter must be made up of fibers. The ideal 
filter would consist of a series of grids of fibers parallel 
to each other and at right angles to the direction of 
air flow. In practice it is impossible to obtain any 
such perfect orientation of the fibers although, in 
general, thej^ will lie at right angles to the direction 
of flow. 

In theory, the smaller the fiber diameter the better 
the performance, but it is clear that if the fiber 
diameter is too small the fiber will not have sufficient 
mechanical strength to resist the air currents. Fur¬ 
thermore, the forces which cause a particle to adhere 
to a fiber must depend to some extent upon the area 
of contact, and a very small fiber would not retain 


a large particle against the forces exerted by gravity, 
air currents, etc., which would tend to remove it. In 
practice, there is a limit to fiber diameter, but fibers 
of 0.01 micron or less prove to be v.ery effective. 

23.2 THE MECHANISM OF THE 
FILTERING ACTION 

It has been pointed out in Chapter 18 that small 
particles adhere to any surface with which they come 
in contact, because of van der Waals forces. If elec¬ 
trical charges are present the adhesion forces may be 
increased; but electrical behavior will be discussed 
in a separate section. Mechanical filtration depends 
upon the actual impingement of the particles on the 
fibers of the filter. In order to consider the mechanism 
of the filtering action, consider a single fiber placed 
at right angles to the air stream. Assume in this dis¬ 
cussion that the velocity is low enough so that the 
flow is nonturbulent, since it can be shown that this 
condition must hold in any filter that operates with 
a reasonably low pressure drop. There are several 
different mechanisms which may bring about the 
impingement of the particle on the fiber. 

23.2.1 Direct Interception 

Imagine the center of the particle of radius r to lie 
on a stream line which passes within a distance r of 
the fiber, in which case the particle will be caught. In 
the limit of the fiber diameter d, approaching zero, 
the particle will be removed from a cross-sectional 
area = 2r per unit length of fiber. For larger fiber 
diameters the number of particles removed will not 
be greatly increased and will be independent of 
velocity, since the stream lines do not change with 
changes in flow rates. Direct interception is restricted, 
however, to particles whose centers remain in coin¬ 
cidence with a given stream line. This will occur only 
if the particles are too large to show appreciable 
Brownian motion and too small to have an appreci¬ 
able Stokes’ law rate of fall. There is no particle size 
for which the Brownian motion and the Stokes’ law 
rate of fall are both zero, and simple calculations 
show that the efficiency of filters is far greater than 


354 


SECRET 


MECHANISM OF THE FILTERING ACTION 


355 


could be accounted for by direct interception . 1 These 
two effects, which prevent particles from following 
the stream lines around a fiber, evidently play an 
important role in the mechanism of filtration, and 
each will be considered in turn. 

23.2.2 Stokes’ Law Deposition 

If a particle is large enough so that it has an ap¬ 
preciable Stokes’ law rate-of-fall, its path will no 
longer coincide with any particular streamline in the 
air flow. It might be assumed, at first thought, that 
Stokes’ law deposition would not in itself be im¬ 
portant, since a particle is likely to fall away from, as 
well as toward, a fiber of the filter. The following- 
consideration, however, shows that the Stokes’ law 
fall is important in deposition. Suppose that the air 
flow through a filter be suddenly stopped. Within a 
short period, all of the larger particles which are 
present will be deposited on the upper surfaces of the 
fibers of the filter; and this period will be short be¬ 
cause the distances through which the particles must 
fall are short. Although the same process goes on 
without interruption when the air is moving through 
the filter, it appears that it will make no difference 
whether the direction of flow is horizontal or vertical. 
The rate of deposition will vary with the particle size 
and concentration, and the total area that the upper 
surfaces of the fiber project into a horizontal plane. 
The flow will maintain the concentration uniform lo¬ 
cally, but the concentration will decrease with increas¬ 
ing depth of-penetration of the filter. If the particle 
is below 0 . 3 -micron radius, the Stokes’ law rate of 
fall is so low that this mechanism of removal is likely 
to prove unimportant. The rate of deposition is not 
affected by variation in the rate of flow, but im¬ 
portant inertial effects appear at higher velocities 
(particularly with larger particles), which give rise to 
another mechanism of filtration. 

23 . 2.3 The Inertial Effect 

If a streamline bends sharply around a fiber, a 
heavy particle at high velocity will not follow the 
sudden bending but will tend to continue in a direct 
course and collide with the fiber. 

The extent to which a particle may be carried by 
its own inertia across the stream lines may be meas¬ 
ured by the so-called stopping distance. The stopping- 
distance, S, is the distance a particle with a velocity 
F and a mass m will penetrate a gas which is assumed 


to be at rest before being brought to rest by the 
viscous forces. The force resisting the motion of the 
particle through the gas is / = 6x777* F. Since 

_ djviV) 

dt 1 

integration gives 

V = V Q e ~ 6wr,rt/m , 

where F is the velocity of the particle at the time t, 
and F 0 the initial velocity. Integration of 



gives the value 

s _ m V 0 = 2 r‘ 2 pF 0 
i)Trrjr 9r; 

where p is the particle density. Substituting the val¬ 
ues 77 = 1.8 X 10 ~ 4 for the viscosity of air, particle 
density unity, and a velocity of 3.5 cm per sec (a 
reasonably high rate of flow), the following table of 
values in centimeters is obtained: 

r, cm S, cm 

0.5 X 10 - 4 10 - 5 

5 X 10 - 4 10 - 3 

S is the maximum distance that the particle could 
travel across stream lines if the stream lines bent at 
right angles. One sees that this distance could have 
no consequence for impingement if the particles were 
of 0.5-micron radius, but that with particles of 5-mi¬ 
cron radius a considerable increase in the number 
impinging on a given fiber could be expected. Fur¬ 
thermore, an increase in velocity will increase the 
number caught. 



Figure 1. Stream lines around fiber and effective di¬ 
ameter b as compared with actual diameter d. 


The effective diameter of a fiber may be defined as 
the width b between the bordering stream lines such 
that particles initially located in them will just clear 
the fiber (see Figure 1). Particles lying within this 
boundary will impinge upon the fiber. The ratio b/d is 


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356 


FILTRATION OF AEROSOLS 


always less than unity and may approach zero for low 
velocity of flow, large fiber diameter, or small particle 
diameter. If the dimensionless ratio, Vr 2 p/dr), where 
V is the velocity of flow, r the particle radius, p the 
particle density, d the fiber diameter, and 17 the 
coefficient of viscosity, is plotted against the ratio 
of the effective diameter b to the actual fiber diame¬ 
ter a curve of the form given in Figure 2 is obtained. 



Figure 2. Inertial effect for large particles. Ratio of 
effective diameter to actual diameter, b/d , plotted 
against dimensionless ratio ( Vr 2 p)/(di\ j). 


For particles of large diameter, the effects of direct 
interception become appreciable and must be super¬ 
posed on the curve of Figure 2 to give an increased 
filter efficiency. The effective diameter b is in this case 
increased by the amount 2r. When the particle diame¬ 
ter is of the same order of magnitude as the fiber di¬ 
ameter, this correction becomes very important. 

23.2.4 Diffusion 

The Impingement of Small Particles 

For particles of 1 micron diameter or less, inertial 
effects should not be important, and this is confirmed 
by the fact that penetration increases rather than de¬ 
creases with increasing velocity. Similarly, the direct 
interception effect ( 2 r) becomes very small for small 
particles. Yet, provided the fibers are of small 
diameter, the filtration efficiency is high and in¬ 
creases with decreasing particle size. The diffusion 
coefficient D varies inversely as the radius, and this 
quantity may be combined with the fiber diameter 
and velocity of flow in a dimensionless ratio D/dV to 
plot the ratio of effective diameter to actual diameter, 
as before (Figure 3). The value of b/d now becomes 
greater than one; but b no longer represents a sharp 


boundary between particles which impinge and those 
which escape, since on account of the Brownian mo¬ 
tion, the probability of impingement is a matter of 
chance which decreases with increasing distance 
measured at right angles to the axis of the fiber and 
the direction of flow. 

Actually, 6 is a mean distance; the total number of 
particles impinging on the fiber is equal to the 
number lying within the limits of 6 , but many of the 
particles within these limits do not impinge and many 
of the particles impinging come from outside these 
limits. The ratio b/d is of course greater, the greater 



Figure 3. Diffusion effect for small particles. Ratio of 
effective diameter to actual diameter, b/d , plotted 
against dimensionless ratio D/dV. 


the diffusion constant. The number impinging is 
greater the slower the velocity of flow, since the 
particles remain in the neighborhood of the fiber for 
a longer time. The ratio also increases as d approaches 
zero because b does not approach zero but a finite 
value which depends upon the mean distance of 
diffusion. 

23.3 THE THEORY OF FILTRATION 

It is practically impossible to give an exact mathe¬ 
matical theory of filtration. In the first place the 
differential equations can be solved only in an ap¬ 
proximate manner, either for the inertial or the 
diffusion mechanism . 2 ’ 3 

Even if satisfactory solutions are obtained for the 
behavior of a single fiber, a filter is made up of fibers 
with a random deposition and orientation, which 
cannot be taken into account in any exact manner. 
However, certain general considerations can be de¬ 
duced, and these conclusions have been verified in a 
general way. 

For example, very small particles will be removed 


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FILTER MATERIALS 


357 


effectively by the diffusion mechanism 4 and very 
large particles by the inertial effects. It would be ex¬ 
pected, therefore, that particles of intermediate size 
would be most difficult to remove. This prediction 
has been confirmed by experiment, but the size with 
a radius of about 0.2 micron 5 turns out to be the most 
difficult to remove. This maximum of penetration 
appears to be independent of fiber size. The decrease 
in penetration for particles above 0.2 micron radius 
can scarcely be due to the inertial effect, which was 
shown previously to be unimportant even for par¬ 
ticles of 0.5 micron radius. It has been suggested that 
the effect of direct interception must account for the 
decreasing penetration of particles of greater than 
0.2 to 0.3 micron radius, and it can readily be seen 
that the direct interception will contribute to the 
filtering action as the particle size increases. It would 
not appear however that a sharp maximum of pene¬ 
tration should be found which is apparently quite 
independent of rate of flow and fiber diameter. 

The answer to the question seems to be given by 
experiments with glass plates, where the filtering 
action at lower particle size must be entirely due to 
diffusion and the filtering action for large particles 
can only take place through Stokes’ law deposition. 
The same sharp maximum of penetration in the 
neighborhood of 0.2 to 0.3 micron is observed. Hence 
it must be concluded that the decrease in penetration 
above 0.2 micron is due to the increasing rate of 
Stokes’ law deposition. 

The effect of velocity on filtering efficiency depends 
upon the particle size. Small particles are removed 
more effectively at low velocities by diffusion, while 
large particles are removed more effectively at higher 
velocities by inertial effects. At some point in the 
intermediate range, perhaps in the neighborhood of 
1 micron radius, the filtering efficiency will not be 
affected by changes in velocity. 

Small fibers are more effective than large fibers in 
collecting particles from an air stream, because the 
smaller the diameter of the fiber the closer the 
streamlines lie to the fiber surface. A fiber maybe con¬ 
sidered to be surrounded by an envelope of nearly 
stationary air which is thicker the larger the periph¬ 
ery of the fiber. Also, the stream lines bend more 
sharply when the fiber diameter is smaller which will 
make the inertial mechanism of filtration more ef¬ 
fective. The correctness of the foregoing statement 
has been demonstrated experimentally with fibers of 
1 micron diameter and particles in the range 0.2 to 0.5 
micron radius. It is possible that the statement is not 


true for very small particles whose diffusion range is 
very large, but these particles are so readily removed 
by a filter that they do not constitute a problem. 

From the foregoing, one sees that a filter made up 
of a given number of fibers disposed in a certain way 
will be more effective when the fiber diameter is 
smaller, and at the same time the resistance will be 
less. Actually, a filter made up of smaller fibers will 
be more closely packed and have a higher resistance. 
Hence, if very small fibers are used, in order to avoid 
too high a resistance it is necessary to support the 
fine fibers on a loose network of coarser fibers. 

23.4 FILTER MATERIALS 

Most naturally occurring fibers, such as cotton, 
wool, and silk, are 10 to 20 microns or more in diame¬ 
ter. These fibers are much too large to be effective, 
and filters made of these materials will have to be 
very thick and have a high resistance, if the penetra¬ 
tion is to be reduced to a low figure. 6 

Paper is a particularly unsuitable material for a 
filter, since the fibers are flat and ribbon-like and are 
matted together in such a way as to offer a minimum 
porosity. Certain fibers obtainable in tropical coun¬ 
tries, such as esparto grass, are narrower than the 
fibers of ordinary paper stock, and papers made of 
these fibers are more open and have less resistance 
to the passage of air. In general, however, these fibers 
can be used only as a supporting grid for finer fibers 
such as asbestos. 7 There is no apparent limit to the 
fineness of dispersion which may be obtained with 
asbestos fibers, and mixtures of asbestos fibers with 
wool or paper are in use, and make excellent filters. 8 
If paper is used, it must be very porous and, hence, of 
little mechanical strength, but this defect is easily 
remedied by a backing of gauze. 

23.4.1 Glass Wool 

Glass fibers of diameter down to 1 micron can be 
produced by special methods. By coating the glass 
fibers with a suitable binding, they can be matted 
into a paper-like web which is very strong and shows 
excellent filtering characteristics. Such a material is 
relatively expensive, but is unexcelled in many re¬ 
spects as a filter material. 9 

23.4.2 Rock Wool 

Rock wool is composed of glass fibers which are 
produced from blast furnace slag or special limestone 


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358 


FILTRATION OF AEROSOLS 


silica mixtures. The material is fused in a cupola 
furnace, and the fibers are produced by blowing the 
molten fluid. The material is produced in carload lots 
for use as thermal insulation at a cost of a few dollars 
a ton. By control of the process, it is possible to pro¬ 
duce fibers of a few microns diameter, and the ma¬ 
terial has great possibilities for use as a filter, 10 par¬ 
ticularly where bulk is not limited. 

23.4.3 Synthetic Fibers 

Various types of synthetic textile materials such 
as cellulose acetate, polyvinyl acetate, or polyvinyl 
chloride, can be produced in the form of fibers of very 
small diameter. 11 The methods for producing these 
fibers are either a modification of the ordinary proc¬ 
ess of spinning and drawing, or electrostatic spinning. 
These materials have not been produced on a com¬ 
mercial scale, but experimental samples show the 
excellent performance that is to be expected. In order 
to use these very fine synthetic fibers, it is necessary 
to support them on a gauze backing. 

23.4.4 Methods of Testing Bulk Filter 

Materials 

The testing of a material in bulk in order to deter¬ 
mine its suitability for use as a filter material is a 
different process from the testing of a fabricated filter. 
It is desirable to test the material at varying rates 
and over long periods of time. In order to detect 
clogging or breakdown, the penetration and resistance 
must be recorded as a function of the time. 

A filter material majr be conveniently tested in the 
form of layers or pads of uniform thickness arranged 
in series. The pads are compressed together to a suit¬ 
able degree by means of metal gauze placed at the 
front and back of the series of pads. A radioactive 
smoke such as triphenyl-phosphate is passed through 
the material for a length of time, after which the pads 
are separated and each one counted separately with 
a Geiger counter. During the run, the pressure drop 
through the series of pads is recorded at intervals. 

If the pads are of uniform thickness and homogene¬ 
ous, and the smoke itself is homogeneous, each layer 
will remove from the smoke a constant fraction of the 
number of particles entering the layer. Thus if the 
number entering the nth layer is A r n , and the number 
entering the n plus first layer is N {n + n, then their 
ratio is given by: 


where k is the stopping coefficient per unit thickness, 
and AX is the thickness of the pad. If the logarithm 
of the numbers of counts per pad is plotted against 
the ordinal number of the pad, a straight line results 
with a slope S = kAX. If the pressure drop per pad 
is p, then the ratio s/p becomes an index for the 
filtering efficiency of the material; the higher the 
value of s/p, the better the performance of the ma¬ 
terial. Since, in general, both s and p will vary with 
the velocity of flow, it is necessary to test the ma¬ 
terial at various flow rates. 

23.4.5 Clogging and Breakdown 

An increase in pressure drop during a run is an 
indication of clogging. The filtering efficiency may or 
may not be affected, but the resistance will continue 
to go up until the filter becomes inoperable. 

Breakdown of a filter material is often observed 
with liquid smokes. It is characterized by the fact 
that the plot of the logarithm of the counts is no 
longer a straight line but is a convex upward as 
shown in Figure 4. This is because the penetration 



Figure 4. Plot of quantities of smoke caught by suc¬ 
cessive layers of a filter showing evidence of breakdown. 


has gone up in the first layers which have become 
“saturated” with the smoke. This saturation effect is 
presumably due to the fact that the liquid wets the 
fine fibers of the filter and draws them together by 
surface tension forces, thus leaving open passages 
through the filter. 

23.4.6 Electrostatic Filters 

It is a matter of common observation that filters 
show a higher penetration when the relative humidity 
is high. The explanation of this must be that at low 
humidit ies static charges are accumulated on the filter 


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FILTER MATERIALS 


359 


fibers and these charges are effective in collecting 
particles from the air even though the particles may 
be uncharged. Certain types of materials will retain 
static charges even at high humidities, and the Cana¬ 
dian wool-resin filter furnishes us with a striking ex¬ 
ample of this behavior. The wool-resin filter is made 
by carding various types of naturally occurring or 
synthetic resins into wool. The resulting material has 
excellent filtering power with, of course, a very low 
resistance. It retains this power for long periods of 
time at high humidities and, if the filtering power is 
lost, it may be restored by recarding the wool of the 
filter. There seems to be no question that the action 
of this filter is electrostatic. Wool and resin are 
classical materials for the production of static charges 
by friction, and the carding process undoubtedly 
produces high static charges on the filaments. In the 
neighborhood of the filaments the field intensities 
would rise to thousands of volts per centimeter. 


Most of the particles in a smoke are uncharged, 
but they will be polarized in these strong fields and 
attracted to the filament. The polarization varies as 
the cube of the radius of the particle, whereas the 
resistance to motion through a viscous fluid is in¬ 
versely proportional to the radius. The situation is 
the same, therefore, as with the fall due to gravity 
according to Stokes’ law. The velocitj^ with which a 
particle is drawn toward a filament will be propor¬ 
tional to the square of the radius. Large particles will 
be removed much more effectively than small par¬ 
ticles. The filters are very effective, however, for 
particles in the ordinary smoke range of 0.2 to 0.5 
micron radius (see Figure 4, Chapter 19). 

Oil smokes appear to break the filter by dissolving, 
or perhaps merely wetting the resin. Some resins are 
more resistant to oil smokes than others. 

Methods of testing fabricated filters are described 
in Chapter 24. 


SECRET 



Chapter 24 


METHODS OF TESTING SMOKE FILTERS 

By Frank T. Gucker, Jr., Hugh B. Pickard, and Chester T. O’Konski 


24.1 GENERAL PRINCIPLES OF SMOKE 
FILTER TESTING 

T he principles discussed in the preceding chap¬ 
ters clearly indicate that, for use against troops 
equipped with the U.S. masks or any Service smoke 
filter except the wool-resin type employed by the 
British and Canadians, the most penetrating toxic 
smoke which could be set up in the field would con¬ 
sist of nearly uniform liquid particles about 0.3 mi¬ 
cron in diameter. The production of such a smoke is 
a problem for the maker of CW munitions. 

The most effective mechanical filter for this smoke 
should consist of fine fibers, e.g., of asbestos, supported 
on a web of larger fibers which give the filter mechani¬ 
cal strength and allow passage of the air with mini¬ 
mum resistance. The production and comparison of 
such filter materials and the manufacture and testing 
of completed filters is a problem for the CW defense. 

The critical evaluation of a smoke filter should 
include many different considerations. The smoke 
penetration and pressure drop should be determined 
over a considerable range of flow rate, including any 
to which the filter would be subjected in use in the 
field. The smoke penetration should also be studied 
over a range of particle size, and correlated with 
toxicity studies which should indicate both the total 
number of particles and the total mass of smoke 
which could be tolerated. Other important charac¬ 
teristics of a filter are its capacitj^ to remove smoke 
before clogging and its resistance to breakdown due 
to severe climatic conditions, CW agents, or other 
factors met in the field. 

Once the general characteristics of a filter material 
are known, routine tests of pressure drop and filtra¬ 
tion can be made under a single set of conditions if 
these are suitably chosen. 1 

Since filter penetration depends on the flow rate, 
the standard flow rate should be chosen after con¬ 
sideration of actual field conditions. A rate of 32 1pm 
was used in many of the tests at the beginning of the 
war. However, studies of breathing rates showed 
that a man exercising vigorously breathed at an 


average rate of 50 or 60 1pm, and that the instan¬ 
taneous rate at the peak of the cycle may be as high 
as 200. 2 The rate of 85 1pm was taken as a standard 
for measurement of pressure drop and filter efficiency 
of canisters, and 320 cm per sec of linear flow for 
testing filter material, at a pressure drop of 30 mm of 
water. 

The measurement of pressure drop is simple enough, 
and discussion will be confined to the measurement 
of smoke penetration. Here the test smoke should be 
of the most penetrating size. The test apparatus must 
include a reliable smoke generator and a rapid and 
sensitive method of measuring inlet and outlet smoke 
concentration. For poor filters, chemical or other 
methods of analysis of samples filtered from the 
smoke are adequate, although the process is ex¬ 
tremely slow. Such methods are totally inadequate 
for the best types of modern filter, which require 
much more sensitive analytical methods, usually 
based on the measurement of the light scattered from 
the smoke. Such methods are more rapid as well as 
more sensitive. Instead of giving the average penetra¬ 
tion integrated over a long period of time, they give 
instantaneous values of effluent concentration. Un¬ 
less the instrument is differential and compares inlet 
and effluent concentration simultaneously, it must 
be used with a smoke generator which is adjusted to 
produce a smoke of constant size and constant mass 
concentration. With any type of instrument the test 
smoke must be homogeneous or nearty so, otherwise 
the filtration will cause a change in the particle-size 
distribution. The particles of the more penetrating 
sizes will comprise a larger proportion of the effluent 
than of the original smoke, and the light scattered in 
the two cases may not be strictly proportional to the 
respective quantities of smoke. 

The actual development of methods of testing 
smoke filters paralleled the increased understanding 
of the process of filtration and the improvements in 
filter material which took place during World War II. 
The production of test smokes will be taken up first, 
then the methods of smoke-filter testing designed for 
laboratorjr use, and finally those which were adapted 
to production-line testing. 


360 


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LABORATORY TEST METHODS 


361 


24.2 CHEMICAL TEST-SMOKE 
GENERATORS 

Most of the generators used for the production of 
uniform test smokes employed condensation of super¬ 
saturated vapors, as described in Chapter 20. 

24.2.1 The NDRC Homogeneous 

Aerosol Generator 3 

This apparatus already has been described in 
Chapter 20. In the hands of a skilled operator it pro¬ 
duces smokes which are beautifully homogeneous as 
judged by their spectra. However, this generator is 
temperamental, is not easily adjusted to give fine 
smokes, and cannot be run for long tests without 
continuous care and adjustment. 

24.2.2 The MIT—E1R7 Smoke Generator 

The CWS Development Laboratory perfected a 
standard test-smoke generator which was widely 
used in smoke filter testing. The MIT-E1R7 genera¬ 
tor 4 employs a stream of humidified air at 88 1pm. 
This is divided so that a flow of 171pm passes through 
a heated chamber where it picks up dioctvlphthalate 
vapor from an open cup. The vapor-laden air is mixed 
with the larger stream of air at a Venturi orifice, 
under highly turbulent conditions (Reynolds number 
of 45,000 to 50,000) so that the rapid cooling yields a 
fine smoke. The mass concentration is adjusted to 
about 100 jug per 1 by regulation of the boiler tem¬ 
perature. The particle size is adjusted if necessary by 
means of a small filament heater in the large air 
stream, so that the MIT-E1R2 particle-size meter 
(see The Owl, Chapter 22) gives a reading of 29° 
(±1°). This corresponds to the standard smoke of 
0.3 micron diameter. The generator is connected to 
convenient clamp holders for canisters and sheets of 
filter paper. The generator furnishes a sample of 31pm 
of raw smoke for the penetrometer and 85 1pm for 
the filter test. 

24.2.3 The NRL Smoke Generator 5 

Work at the Naval Research Laboratory paralleled 
that at the CWS Development Laboratory. The MIT 
smoke generators were tested and several basic modi¬ 
fications were made, which added to the stability of 
operation. The MIT generators were designed to 
furnish a test smoke under pressure, which was 
forced through the filter. The insertion of the filter 
increased the resistance in the line and this changed 
the concentration and characteristics of the smoke. 


The NRL generator was designed to furnish smoke 
to a 5-gal reservoir at a rate somewhat greater than 
that required for test. Excess smoke escaped to the 
atmosphere through a vent, while that required for 
test was sucked through the filter by a vacuum 
connection. Although this arrangement required a 
tight test system to avoid diluting the test smoke or 
introducing dust from the room air into the filtered 
smoke line, the NRL group considered that it stabi¬ 
lized the test smoke by keeping the pressure in the 
generator constant, and by allowing the smoke to cool 
to room temperature before it was used. 

A propeller stirrer in the reservoir of dioctyl- 
phthalate helped improve the control of temperature 
and rate of evaporation of the liquid. Later, a water 
jacket was put around the quenching air stream to 
keep its temperature constant, and this also helped 
to stabilize the particle size of the smoke. 

24.2.4 Smoke Materials 

The material for a test smoke should be a liquid 
with a low vapor pressure at room temperature. It 
should be stable for long periods of time at the boiler 
temperature. Triphenyl phosphate [TPP] was used 
in much of the earlier work. It has the disadvantage 
of being a solid melting at 50 C. Although it forms a 
supercooled liquid smoke, this solidifies when it de¬ 
posits in any cool parts of the generator, and even¬ 
tually clogs the apparatus. Oleic acid also was used in 
the early work. It has a lower melting point than 
TPP and also supercools to form a liquid smoke. It 
has the disadvantage of decomposing at the tem¬ 
perature of the boiler. Tricresyl phosphate [TCP] 
has the advantage of being a liquid at room tempera¬ 
ture, and was used to some extent, but later was 
given up because of its tendency to decompose and 
the fact that it is somewhat toxic. Dioctylphthalate 
[DOP] was the most useful smoke material, and be¬ 
came a standard test material by the end of the war. 
It is liquid at room temperature and is fairly stable, 
although it decomposes somewhat after a considera¬ 
ble time in the boiler. 

24.3 LABORATORY TEST METHODS 

When the United States entered the war, the CWS 
at Edgewood Arsenal used two standard laboratory 
methods of testing smoke filters. The first employed 
toxic test smokes [DM or DA], the second utilized 
nontoxic methylene blue [MB] introduced by the 
British. 


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362 


METHODS OF TESTING SMOKE FILTERS 


24 . 3.1 DM and DA Smoke Tests 6 

Smokes of DM 7 are produced by dripping a 1 % 
solution of DM in acetone upon a hot plate held at a 
temperature of about 245 C. The smoke is generated 
in a closed box, which is kept at a temperature of 
45 to 50 C. The resulting smoke particles are solid 
crystals. Microscopic examination on a thermal- 
precipitator slide showed a particle-size distribution 
curve with a peak at 0.2 micron diameter, which is 
only slightly smaller than the most penetrating size 
(0.3 micron diameter) and no particles larger than 0.6 
micron diameter. The smoke, at a concentration of 
about 50 Mg per 1, is passed through the test filter at 
32 1pm. The effluent smoke is analyzed for arsenic 
by a modified Gutzeit method sensitive to 0.01 /xg 
per 1, or 0.02% penetration. 8 A charcoal bed is placed 
between the filter and the analyzer to absorb any 
DM vapors which may come from the generator. 
This arrangement improves the consistency of the 
results, but removes 20 to 25% of the DM smoke. 
The test therefore does not yield absolute per cent 
penetration, although it can be used to grade a series 
of canisters or samples of paper. Additional disad¬ 
vantages of this test are the toxicity of the agent, the 
excessive time required to carry out the chemical 
analyses, and the fact that solid smokes with irregu¬ 
larly shaped particles are less penetrating than liquid 
smokes with the same number of spherical particles. 

The DA test 9 obviates this difficulty, since this 
material forms a liquid smoke. The method of pro¬ 
duction is similar to that for DM smoke. An acetone 
solution of about 2.6 g per 1 is dropped at the rate of 
80 drops per minute on a hot plate to form the smoke. 
Experimental tests also were run with DC smoke 
produced in the same way. 

24 . 3.2 The Methylene Blue Test 10 

In the methylene blue test carried out at Edgewood 
Arsenal in the EA-E1 meter, 11 the smoke is generated 
by atomizing a 1% aqueous solution of methylene 
blue and evaporating the water by mixing the spray 
with a larger quantity of dried air. Microscopic exami¬ 
nation showed that most of the particles were nearly 
spherical with a diameter of 0.2 micron, and only 
a few were larger than 0.4. The smoke is drawn 
through the filter or canister at a rate of 32 1pm and 
then passes through a strip of filter paper for a 
definite length of time. The test strip is “developed” 
by exposing it to steam and the color is compared 


with a set of standard stains. One disadvantage of 
this method of comparison is that the rate of drawing 
off standards is different from the rate used in making 
a test strip. This may lead to error, since velocity has 
a considerable effect upon the penetration of smoke 
through paper, especially the alpha-web paper which 
is used as the standard strip. The lower limit of the 
methylene blue test is about 0.005% penetration. 

The CWS Development Laboratory at MIT de¬ 
signed the MIT-E2 methylene blue penetration 
tester 12 to overcome some of these difficulties in the 
testing of filter paper. The MB smoke, generated as 
before, is passed through a pad of a number of sheets 
of the filter paper under test and the stains produced 
on the single sheets are compared. The penetration 
per sheet can be calculated from the filtration law. A 
series of tests at Edgewood Arsenal 13 indicated that 
the MIT-E2 tester gave less reproducible results than 
the EA-E1 tester, was not sufficiently sensitive to 
discriminate closely between filter papers of different 
filtering qualities, and required 25 min for a test, 
compared with an average of 4 min per test on the 
EA-E1. It can be used only for filters in sheet form. 
An indirect method, which is still less sensitive, must 
be used when the filter sheet is colored. 

24 . 3.3 The Radioactive Smoke Test 1416 

Early in the NDRC smoke program (November 
1940) a method of testing the filtering power of sheets 
of paper or bulk material was devised, using radio¬ 
active test smokes. The sheets, or bulk material made 
into pads of uniform thickness, are arranged in series, 
and the test smoke (e.g., triphenyl phosphate con¬ 
taining radiophosphorus) is passed through these. 
After a sufficient length of time the sections are tested 
separately with a Geiger counter which registers 
counts proportional to the amount of smoke removed 
by each section. This test served to compare the filter¬ 
ing power of many materials and played an important 
role in the early NDRC smoke program. It suffers 
from the disadvantage of requiring radioactive mate¬ 
rials and techniques, and later was given up in favor 
of more rapid, simple, and sensitive optical methods. 

24 . 3.4 Optical Smoke Penetration Meters 17 

The NDRC Optical Mass-Concentration 
Meter 25 

Before the introduction of photoelectric meters, the 
NDRC optical mass-concentration meter was devel- 


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LABORATORY TEST METHODS 


363 


oped and used for many of the decisive tests on var¬ 
ious filter materials. An appreciation of the advantage 
of small-angle forward scattering, and thorough 
familiarity with optical systems led to the design of 
the instrument already described in Chapter 22. It 
was operated in a small dark room and, in the hands 
of a skilled operator, was sensitive to 0.001 /zg per 1 
of a 5 order (1 micron diameter) oleic acid test smoke 
or the standard DOP smoke of 0.3 micron diameter 
and 100 jug per 1. Thus, the instrument was sensitive 
to 0.001 % penetration. The optical comparisons were 
very tiresome for the operator, and required con¬ 
siderable skill and experience as well as time. 

The MIT-E1R1 Optical Mass-Concentration 
Meter 1819 

An optical system nearly identical with that of the 
NDRC optical meter was developed independently 
at about the same time at the CWS Development 
Laboratory and used in the MIT-E1R1 optical 
meter. This was designed as a rapid, portable, and 
simple instrument for testing filter papers or canisters 
with liquid smoke furnished by the MIT-E1R7 
generator 4 described in a previous section. It utilized 
two smoke cells, with identical lamps and identical 
optical systems, employing small-angle forward scat¬ 
tering. Unfiltered smoke passes through one cell and 
filtered smoke through the other. The light scattered 
from the filtered smoke passes directly through a small 
rectangular hole in the center of the silvered face of a 
prism forming one half of a photometer cube, while 
that scattered from the raw smoke is reflected from 
a single prism and then from the opposite side of the 
silvered face. Thus the field, viewed by a low-power 
microscope, consists of the central rectangle of light 
coming from the filtered smoke, surrounded by the 
light from the raw smoke. Before measuring smoke 
penetration, raw smoke first is passed through both 
smoke cells, and a neutral screen filter in the optical 
system is adjusted to give uniform illumination of the 
photometer cube. Then filtered smoke is put into 
one cell and the intensity of the light scattered from 
the raw smoke is reduced by means of a calibrated 
optical gradient until the field is again uniform. The 
penetration is read directly from a 3-cycle logarithmic 
scale on the same shaft as the optical gradient. If the 
filtered smoke concentration is very low, the in¬ 
tensity of the light from the raw smoke can be further 
reduced by means of optical filters to 0.1, 0.01, or 
0.001 of the reading on the gradient. 

This instrument is compact, portable, and simple 


to operate. A small light shield over the eyepiece 
allows it to be read in the ordinary daylight. It gives 
absolute penetrations, and has the advantage of any 
comparative method in that a single reading gives 
relative light scattering, and gradual changes in the 
concentration of the test smoke are compensated. Its 
chief disadvantage is that it requires visual com¬ 
parison of two fields, which is tedious. It was the 
experience of the Division with the instrument fur¬ 
nished that under optimum conditions individual 
readings vary by as much as 10%, and a series of 
readings are required for 5% accuracy. The limit of 
sensitivity of this instrument was found to be about 
0.05% of a 100 )ug DOP smoke, being determined 
chiefly by stray light in the effluent smoke cell which 
could not be reduced below this value. 

24 . 3.5 The Australian Ionization 

Penetrometer 20 

An ionization penetrometer was developed at the 
Munitions Supply Laboratories, Maribyrnong, Aus¬ 
tralia. A 1% solution of sucrose is sprayed under a 
pressure of 30 psi to give a cloud of charged particles. 
Mobility measurements indicate a mean diameter of 
0.03 micron. The spray is diluted to a flow of 1 cu ft 
per min, yielding a positive ion concentration of 
about 400,000 per ml. The electrical conductivity of 
the smoke is measured before and after filtration. 
The sensitivity of the penetrometer is 0.0002% per 
mm deflection on the scale, on the highest sensitivity 
range. Four to five minutes are required per test. The 
ions are found to be only about one-fifth as penetrat¬ 
ing as a carbon smoke at a carbon penetration of 0.1 % 
and only one-hundredth as penetrating as methylene 
blue. Comparative tests of this method apparently 
have not been made in this country, but it should be 
investigated, since it might be useful either for the 
study of the penetration of very fine smokes, or if 
larger ions could be produced, as a penetrometer for 
use with the standard smoke of 0.3 micron diameter. 

24 . 3.6 Photoelectric Smoke Penetrometers 

Hill’s Photoelectric Smoke Penetrometer 21 

At the start of the war, the most sensitive labora¬ 
tory instrument available was the photoelectric 
smoke penetrometer developed by A. S. G. Hill for 
the testing of commercial dust respirators, which is 
described in the British Journal of Scientific Instru¬ 
ments. Hill’s test smoke consisted of carbon particles, 


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364 


METHODS OF TESTING SMOKE FILTERS 


which he stated had an average diameter of 0.16 
micron. The smoke was made by the carefully con¬ 
trolled incomplete combustion of butane in a bunsen 
burner. The smoke contained 6.8 X 10 9 particles per 
liter, at a mass concentration of about 25 Mg per L 
The absorption of light by a 50-cm column of this 
smoke was measured by means of a photocell con¬ 
nected to a triode amplifier, the plate current of which 
was balanced with a suitable resistor and a highly 
sensitive galvanometer. Although the total absorp¬ 
tion of the raw smoke was only about 9%, penetra¬ 
tions could be read to 0.02% (1 mm galvanometer 
deflection). This arrangement required careful ad¬ 
justment of the flame to give a uniform smoke, and 
careful regulation of the light current and the bat¬ 
teries, in order to measure the minute changes in the 
intensity of the transmitted light. 

English and Canadian Carbon-Smoke Penetrom¬ 
eters 22t 23 

In the early days of the war, a carbon-smoke 
penetrometer was developed and used in England for 
testing gas mask filters, and was employed in Canada 
as an acceptance test. The English apparatus was 
sensitive only to 0.5% and was superseded by the 
MB test. A penetrometer, using carbon smoke also, 
was developed at the Pulp and Paper Research Insti¬ 
tute of Canada. Butane is burned in a bunsen jet with 
a variable amount of air bled into the gas stream be¬ 
fore combustion. The penetrometer consists of two 
smoke cells separated by a filter holder. The light, 
scattered by the smoke in either cell, is measured by 
means of an RCA 929 vacuum photbtube and a 
balanced d-c amplifier of the cathode follower type. 

It was found that the penetration of rayon-asbestos 
filters increased markedly as the amount of air bled 
into the gas stream was increased. Electron micro¬ 
scope photographs showed only a slight increase in 
the relative number of particles of optimum size as 
the gas is diluted. This change was not considered 
great enough to account for the large increase in 
penetration. It was concluded that the phenomenon 
was a mass-concentration effect, the carbon smoke 
forming a pre-filter upon the rayon asbestos fibers. 
The more concentrated the smoke, the greater was 
the pre-filtering action. 

Since the mass concentration must be controlled 
with care to insure significant penetration data, and 
since liquid smokes are 50 to 100 times more pene¬ 
trating than carbon smoke, the carbon penetrometer 
seems to be of little practical use. 


The Kimberley-Clark Nephelometer 24 

This instrument was developed for testing samples 
of filter paper. A single 50-cp automobile headlight 
supplied light to two smoke cells set at right angles 
to each other. In each cell the light was focused by 
means of a lens system upon a small area where the 
light, scattered from the smoke at right angles, was 
viewed by a Type 931 photomultiplier tube. The 
stray-light current in each cell was balanced out 
electrically. Raw smoke flowed through one cell and 
filtered smoke through the other. The current due to 
the scattered light in each case was read and the ratio 
of the two gave the smoke penetration. The sensi¬ 
tivity of the instrument was about 0.1% penetration 
when using the standard 100-jug test smoke. 

By 1943, smoke filters were improved to the point 
where they transmitted only a few hundredths of a 
per cent of a standard DOP smoke, of 0.3 micron 
particle diameter (as judged by a 29 degree Owl read¬ 
ing). At a standard concentration of 100 Mg per 1 for 
the test smoke, the effluent from such a filter could 
not be measured by means of the MIT-E1R1 optical 
mass-concentration meter. The NDRC optical mass- 
concentration meter has the necessary sensitivity 
only in the hands of a skilled operator. However, a 
penetrometer for routine testing, sensitive to 0.001 %, 
was evidently needed, and tests in this range are ex¬ 
tremely difficult by any visual method. Neither the 
Kimberley-Clark nephelometer nor any of the photo¬ 
electric photometers then in use by the Armed Forces 
in this country, Great Britain, or Canada, had the 
desired sensitivity. The only photoelectric penetrom¬ 
eter of sufficient sensitivity was that of Hill to which 
reference has been made. 21 This instrument, however, 
measured the absorption of light and required extreme 
control of light intensity as well as an extremely sensi¬ 
tive galvanometer. Since only about 10% of the light 
was absorbed by the raw smoke, the intensity of the 
light had to be kept constant to 0.002% in order to 
obtain Hill’s sensitivity of 0.02% in the penetration. 
If the scattered light is measured, however, the varia¬ 
tion in light intensity can be of the order of the de¬ 
sired accuracy of measurement, e.g., 1%, provided the 
background light intensity is kept low. Hill’s instru¬ 
ment also required a galvanometer with a sensitivity 
of 1,500 mm per m&, which cannot be used con¬ 
veniently except in a research laboratory. 

As a result of the need for a sensitive and simple 
penetrometer for routine tests, several instruments 
were developed for photoelectric measurement of 
the intensity of the light scattered from the standard 


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LABORATORY TEST METHODS 


365 


test smokes, using electronic amplification and small 
rugged galvanometers which could be operated any¬ 
where. 

The NDRC Balanced Photoelectric Smoke 
Filter Penetrometer 25 

This apparatus was developed from the NDRC 
optical mass-concentration meter already described. 
A single 50-cp bulb supplies light to two of the for¬ 
ward-angle scattering cells placed at 130° to each 
other. The scattered light falls on two Type 931 
photomultiplier tubes. With raw smoke in one cell 
and filtered smoke in the other, the currents from the 
scattered light in the two cells pass through resistors, 
one of which can be varied so that the IR drops are 
balanced in a bridge circuit. If the currents are pro¬ 
portional to the smoke concentrations in each case, 
the ratio is the smoke penetration. Careful tests 
showed, however, that the Type 931 tubes were far 
less reliable than had been expected, when appreci¬ 
able currents were drawn. Individual tubes also 
varied widely in their characteristics and suffered 
fatigue so that a current of 0.5 ma would fall off by 
25% to 50% in an hour of steady illumination. This 
meter was studied in some detail at the Central 
Laboratory of Division 10, but reliable results below 
0.05% penetration never could be obtained. There¬ 
fore the use of the Type 931 tube in such an arrange¬ 
ment was given up in favor of the more stable 
vacuum-type phototube in conjunction with suitable 
amplifying circuits. 

The NDRC-E1R2 Smoke Penetrometer 26 

This compact, direct-reading photoelectric pene¬ 
trometer, designed especially for rapid and accurate 
readings to 0.001 % of the standard DOP smoke, is 
shown schematically in Figure 1. It was developed 
between March 1943 and June 1944. The photoelec¬ 
tric current passing through the resistance R pro¬ 
duces across it a potential drop E R which can be 
balanced by means of the potentiometer so as to 
bring the galvanometer in the plate circuit of the 
amplifier tube to zero. 

The smoke-cell arrangement is shown in Figure 2. 
The smoke from any suitable generator can be used. 
The CWS Development Laboratory MIT-E1R7 
generator 4 was widely used for test purposes. The 
smoke enters at A and leaves the cell at B. The con¬ 
verging beam of light from the aspheric lens system 
C illuminates the smoke intensely at the focus D 
where the image of the filament falls. Stray light is 


reduced to a minimum by use of the light trap E to 
absorb the diverging beam, the baffles F, G, and the 
slits H, H, which limit the field of view of the photo¬ 
cell. This reduction of background compensates for 
the reduction of intensity in using right-angle instead 
of small-angle forward scattering. 



Figure 1 . Schematic diagram of penetrometer circuit. 


The Type 929 vacuum phototube was removed 
from its base to reduce leakage currents and con¬ 
nected through a very high resistance to the grid of 
a Type 38 tube which serves as a single stage of d-c 
amplification. As the photocurrent is reduced (to 
5 X 10 -13 a for a smoke concentration of 0.001 jug 
per 1), the potential drop is kept within the range of 
measurement by increasing the high resistance by 
decimal steps from 10 7 to 10 10 ohms. A special circuit 
was introduced, which compensates for any deviation 
of the high resistors from their nominal values. 

A photograph of the instrument is shown in Figure 
3. To make a measurement, the switches are turned 
on, the grid bias is adjusted and the stray light knob 
is turned to balance the stray light electrically. Then 
raw smoke is passed through the cell, the scale switch 
is set on 1 (connecting the 10 7 -ohm resistor in the 
circuit), the per cent penetration dials are turned to 
100, and the sensitivity is adjusted to give a zero 
reading on the galvanometer. Next the filtered smoke 


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366 


METHODS OF TESTING SMOKE FILTERS 



Figure 2. Smoke cell arrangement 


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LABORATORY TEST METHODS 


367 


is passed through the cell, the scale switch turned to 
the appropriate value, and the per cent penetration 
dials adjusted to balance the galvanometer. The re¬ 
sulting readings give the penetration directly. Thus 
85% on scale 0.001 (10 10 -ohm resistor) corresponds to 
0.085% penetration. On this scale a change of 0.001 % 
gives a galvanometer deflection of 1 mm, which is 
significant. 



Figure 3. NDRC-E1R2 smoke penetrometer. 


Auxiliary circuits are supplied to check the adjust¬ 
ment of the scale switch to decimal steps, to check 
the emf of all cells, and to read the stray light, grid, 
and leakage currents. Arrangements are also made 
for reading plate currents, so that the characteristics 
of the Type 38 amplifier tubes can be determined. 
The unit is self contained, and all these readings are 
made without auxiliary equipment. 

In addition to the NDRC-E1R2 smoke penetrome¬ 
ter built and used in the Central Laboratory of 
Division 10, at Northwestern University, three in¬ 
struments were furnished to the Services. The first 
was sent to the CWS Development Laboratory at 
MIT, the second to the Naval Research Laboratory, 
and the third to Edge wood Arsenal. 

The CWS Photoelectric Smoke Penetrometer, 
MIT-E2 27 

This apparatus was developed between June 1942 
and August 1945 by adapting the optical system of 
the MIT-E1R1 optical smoke penetration meter to 
the measurement of light intensity with an electrical 
system using a Tj^pe 931 photomultiplier tube. It was 
designed not as a penetrometer but as a versatile 
instrument for studying the optical properties of 
smokes at low light intensity. It is sensitive to 
0.001% of the standard 100-jug DOP smoke, but is 


more complicated than the instruments designed as 
penetration test meters. 

The apparatus included two separate smoke cells 
for measuring forward scattering, with a separate 
Type 931 tube and associated circuits for each. Great 
care was taken to supply a regulated constant voltage 
to the dynodes of each tube, the output of which was 
kept to 50 /za or less, and amplified by a cathode- 
follower circuit. Compensation of the stray light and 
leakage current was accomplished by means of an 
adjustable compensating lamp and Type 926 photo¬ 
tube. Arrangements were also made to calibrate the 
intensity of the light falling on the Type 931 tube 
by means of an incandescent lamp which could be 
compared with a standard lamp. 

In practice, one optical system was used to measure 
the intensity of the light from the raw smoke. This 
light was cut to 1 % by means of an optical attenuator. 
The other optical system was used for measuring the 
intensity of the light from the filtered smoke, and the 
ratio of the two intensities gave the penetration. 

The NRL Smoke Penetration Meter E2 5 

This meter, developed at the Naval Research 
Laboratory for laboratory use and factory tests of 
filter paper, comprised the NRL smoke generator 
previously described, an Owl particle-size meter, a 
smoke cell, and an indicator unit. The smoke cell, 
based on the NDRC optical mass concentration 
meter, employed small-angle, forward scattering. 
Careful arrangement of light baffles reduced the stray 
light to 0.008% of that from the standard 100 /ug 
DOP test smoke. The light was focused upon a Type 
931 photomultiplier tube. At first, the output current 
was measured with a galvanometer sensitive to 
0.03 /za per division. Later a vacuum-tube current 
amplifier was used with a microammeter in a bridge 
arrangement in the plate circuit, so that the indicator 
would be immune to the vibrations of factory opera¬ 
tion. 

In order to insure stable operation of the Type 931 
tube by limiting its output photocurrent to 30 jua, the 
light from the raw smoke was reduced by means of a 
calibrated optical filter, made from a perforated disk 
of metal inserted between the condensing lenses so 
that it was perpendicular to the light beam. 

The stray light was compensated electrically. Ad¬ 
justment of a sensitivity control made the galva¬ 
nometer read directly in per cent penetration. A 
scale switch allowed the range to be reduced by 
factors of 0.01 or 0.001, so that readings could be 


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368 


METHODS OF TESTING SMOKE FILTERS 


made to 0.001% penetration of a standard DOP 
smoke. The whole operation was rapid and con¬ 
venient. 

24.3.7 Comparative Tests of Various 
Penetrometers 

The photoelectric penetrometers are so sensitive 
that independent tests by other means are difficult. 
However, careful comparisons were made at the 
CWS Development Laboratory 27 and at the NRL. 5 
Penetrations were measured by collecting standard 
DOP smoke for a sufficient length of time on a 
weighed glass-fiber filter, and comparing the penetra¬ 
tions so measured with the readings of the photoelec¬ 
tric meter on the same sheets. In each case, the re¬ 
sults agreed within a standard deviation a of ± 3 %, 
which is less than the experimental uncertainty. 
These comparisons could not be made with any ac¬ 
curacy for penetrations less than a few per cent. 

Each of the penetrometers was tested individually 
for self-consistency by measuring the penetrations of 
a series of filter papers singly and in series. Plots of 
the logarithm of the penetration against the number 
of sheets showed a straight line as required by the 
filter law. 

In November 1943, two series of measurements 
were made with the NDRC-E1 penetrometer. This 
was the original model from which the direct-reading 
E1R2 was developed. Measurements of 2, 4, 6, 8, and 
10 sheets of Brown and Company paper gave pene¬ 
trations of 33 to 0.4%, with a standard deviation of 
±6.6% from the average penetration for 2 sheets. 
Omitting one result, the standard deviation was 
±3.4% for the other 9 sheets. A similar series of ex¬ 
periments on 1 to 12 sheets of paper at MIT gave 
penetrations of 50 to 0.01%, with a standard devia¬ 
tion of ±5.5% from the mean penetration per sheet. 
Two series of measurements at the NRL on 1 to 5 
sheets gave penetrations of 50 to 2 %, with a standard 
deviation of ±3.7% from the mean penetration per 
sheet. These results tested simultaneously the smoke 
generator and the uniformity of the filter paper as 
well as the penetrometer. The observed deviations 
include errors due to variations and inhomogeneity in 
the smoke and paper, as well as experimental errors 
in the penetrometers. 

The self-consistency of the MIT-E2 meter was 
checked in a series of twenty consecutive tests on a 
group of canisters over a period of four months. The 

a Defined as the square root of the average values of the 
individual deviations. 


standard deviation of the results on any one canister 
averaged ± 8% at penetrations of 0.04 to 0.14%. The 
results for a series of canisters all appeared to vary 
in the same direction from one day to another, sug¬ 
gesting that a change in the smoke may have caused 
the differences. 

Tests with two different NRL meters showed a 
standard deviation of ±3% for the penetration of 
the same canister measured with the same meter 
over a period of about a month, and ±2% standard 
deviation for the penetration of a single canister 
measured with the two meters over a period of seven 
months. The excellent agreement of this series of re¬ 
sults shows the advantage of the close control of the 
smoke generator which was developed at the NRL. 

A series of 27 comparisons of filters and papers, 
using the same smoke and two different indicator 
units, gave an average ratio of 1.01 with a standard 
deviation of ±0.03% over the range from 0.01 to 
73% penetration. A comparable series of experiments 
with two completely separate meters, each including 
its own smoke generator, cell, and indicator unit, 
gave an average ratio of 1.02 with a standard devia¬ 
tion of ±0.06%. This indicates that about half of 
the observed differences were due to difference in the 
smoke. However, the agreement is very satisfactory, 
and speaks well for the operation of both NRL smoke 
generators and indicator units. 

A number of comparative tests of the different 
penetrometers were made. The CWS Development 
Laboratory 27 made a series of comparisons between 
their E2 photoelectric meter and their E1R1 optical 
meter, and NDRC-E1R2 photoelectric penetrometer 
and an NRL-E2 meter. The results were given in 
terms of the average value of the ratio of the reading 
of any meter, referred to the corresponding reading 
of the MIT-E2 meter. These values are given in 
Table 1 together with the corresponding standard 
deviations [SD] of the individual pairs of readings. 
A series of comparisons was also made at the NRL 
between their E2 meter and an NDRC-E1R2 meter. 
The average of these results, most of which are given 
in the NRL Report, 5 is also given in the table. Since 
the NRL-E2 meter gives results which are about the 
average of the others, all of the values have been 
calculated on the basis of 1.00 for this meter. These 
results are given in the last column of Table 1. 

The Particle-Counting Smoke Penetrometer 

By the spring of 1944, work at Camp Detrick had 
shown that the best canister smoke filters gave almost 


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LABORATORY TEST METHODS 


369 



Table 1. Summary of comparative tests of penetrometers. 


Meter 

Experiments 

Range (%) 

Average ratio 

SD 

Average/NRL 

NDRC-E1R2 

29 

0.07-55 

NDRC/NRL 1.05 

0.09 

1.05 

NDRC-E1R2 

140 

0.002-50 

NDRC/MIT 1.05 

0.19 

1.01 

NRL-E2 

36 

0.01-30 

NRL/MIT 1.04 

0.07 

1.00 

MIT-E2 





0.96 

MIT-E1R1 optical 

17 

0.15-50 

MIT-E1R1 /MIT-E2 0.97 

0.04 

0.93 


perfect protection against the BG spores which were 
being used as simulated BW agents. Many canisters, 
however, which showed low penetration for the 
standard DOP smoke, leaked an appreciable number 
of the BG spores. These spores, which are elliptical in 
shape with major axis of about 1.2 microns and minor 
axis of about 0.8 micron, evidently were stopped al¬ 
most completely by the filter paper but penetrated 
any cracks due to faulty crimping of the edges of 
the filter paper, or pinholes in the paper or the metal 
can. 

The method of determining penetration at Camp 
Detrick was to collect the spores from the effluent 
air on a cotton-wad impinger, wash them off onto an 
agar plate, and count the number of colonies which 
developed in 24 hours’ time. There was urgent need 


for a rapid method of detecting defective canisters 
and of comparing the best canisters, which only allow 
the passage of a few particles per minute. Some indi¬ 
cation of defective canisters was obtained by in¬ 
creasing the size of the DOP test smoke and decreas¬ 
ing the flow rate used in production-line tests with 
the MIT-E1 canister tester. This is because smoke 
penetration through the filter paper decreases with 
decreased flow rate much more rapidly than leakage 
through pinholes. However, a more direct method 
was needed, comparable both in sensitivity to the 
biological test and in rapidity to the ordinary photo¬ 
electric penetrometer. The problem was solved by 
developing the photoelectric particle-counting pene¬ 
trometer described below. 

Preliminary tests were made with a uniform DOP 


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370 


METHODS OF TESTING SMOKE FILTERS 




Figure 5. Cell unit of particle-counting penetrometer. 


Figure 6. Time recorder and power supply unit. 


smoke of 0.4-micron radius from a generator 3 like 
that described in Chapter 20. When this smoke was 
used in the NDRC-E1R2 photoelectric penetrometer 
described in a previous section, the lower limit of 
measurement was found to correspond to the light 
from only about 10 smoke particles. The sensitivity 
for counting individual particles therefore did not 
seem unattainable, particularly if the added in¬ 
tensity of small-angle forward scattering were utilized 
instead of the right-angle scattering of the photoelec¬ 
tric penetrometer. The d-c electronic amplifier of the 
earlier penetrometer could not be used, but an a-c 
pulse amplifier and counter had the advantage of 
eliminating the effect of any nonfluctuating stray- 
light background. 

The smoke cell contained a dark-field system of 
illumination similar to that in the NDRC optical 
smoke penetration meter described in Chapter 22. 
The general arrangement is shown in Figure 4. The 
smoke enters the cell A through G, the smaller of the 
two concentric tubes, while a sheath of filtered air 
flows through the outer tube H at the same linear 
rate and prevents the smoke stream from spreading 
out before it passes into the tube /. The well-defined 
smoke stream is narrower than the light beam at the 
focus. Hence every smoke particle is illuminated and 
scatters light into the conical shadow beyond the 
focus. Most of this light, indicated in Figure 4 by 
the inner dashed lines, enters the lens J and is focused 
on the photosensitive cell K to produce an electrical 
impulse of about 0.003-sec duration for each particle. 
The vents L, L, are used to flush the cell with filtered 
air before use. The cell K, coupling condenser and 


resistors, and first amplifier tube (Type 1603) are 
mounted in an airtight brass box, desiccated with 
silica gel to reduce electrical leakage. 

The 50-cp automobile headlamp C was held in a 
massive clamp. The cell was of heavy construction, 
mounted on a solid brass plate U which rested on a 
felt pad. These precautions eliminated mechanical 
vibrations of the lamp filament which would lead to 
optical microphonics and spurious counts. The ap¬ 
pearance of the cell unit is shown in Figure 5. 

In preliminary tests neither vacuum nor gas-filled 
phototubes were found to give a high enough signal- 
to-noise ratio to allow successful counting. Even the 
best available RGA Type 931 electron-multiplier 
phototube gave a ratio so small that counting was 
unsatisfactory because of the background. Fortu¬ 
nately a thalofide cell, 28 developed in Division 16 of 
the NDRC, was made available for this work. This 
cell gave a high enough signal-to-noise ratio so that 
background counts could be reduced to one every few 
minutes and the operation of the counter became 
practical. 

The original pulse was fed into the Type 1603 
amplifier, chosen for its low microphonics, followed 
by two Type 6SJ7 tubes, giving a maximum ampli¬ 
fication of about 500,000. The output of the amplifier 
was fed into a thyratron trigger circuit which acti¬ 
vated the mechanical recorder. A control of the grid 
bias of the thyratron regulated the size of the pulse 
needed to fire the tube. The amplifier and thyratron 
voltages were taken from a rectifier with a filter and 
a number of VR (voltage regulator) tubes which gave 
a closely-regulated, stable power supply. Filters were 


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PRODUCTION-LINE TESTERS 


371 



Figure 7. Rear view of time recorder and power sup¬ 
ply unit. 


used to eliminate the feedback between the stages of 
the amplifier. 

The success of the particle counter depended upon 
three things: (1) the use of the thalofide cell with its 
high signal-to-noise ratio, (2) the construction of a 
compact and rigid optical system which eliminated 
optical microphonics due to vibrations, and (3) the 
development of a remarkably stable amplifier which 
eliminated electrical background counts. 

Two mechanical recorders were used, in order to 
provide a check of their functioning. These and an 
electric timer were so arranged that in a normal test 
a single button started the recorder and timer which 
were then stopped after 100 counts by a contact on 
the counter. The time for 100 counts thus recorded 
was determined with a statistical uncertainty of 
not over 10% in each experiment. Figures 6 and 7 
show the timer, recorder, and power supply units. 

Although the electrical stray counts were reduced 
to a negligible quantity, the background due to dust 
blown from the filter was troublesome unless the 
filter was blown off for 5 min or more before a test. 
Then the counts could be reduced to a value of about 
1 to 5 per min which is negligible for most tests. 

The particle counter was tested by measuring the 
penetration of the same filter paper, first with smoke 
of standard concentration and the photoelectric 
penetrometer, and then with greatly diluted smoke 
of known dilution and the particle-counting pene¬ 
trometer. The results agreed up to about 1,000 
counts per min, above which an increasing number 
of the counts were lost. 


The range of the instrument is from about 3 to 
1,200 counts per min. If the inlet smoke concentra¬ 
tion is 10 8 particles per 1, which is attainable with 
BO, one count per min corresponds to 10 -e per cent 
penetration. Hence the sensitivity range of the instru¬ 
ment is 3 micro-per cent to 1.2 milli-per cent. 

A particle-counting smoke penetrometer, E1R2, 
was made for use at Camp Detrick, where it was 
compared with the BG tester. The work at North¬ 
western Universit}' is being continued under a con¬ 
tract with the War Department and should yield re¬ 
sults of considerable interest. 

24.4 PRODUCTION-LINE TESTERS 

24.4.1 The Edge wood Arsenal E3 

Canister Tester 30-33 

The EA-E3 meter, employing an oil smoke, was 
used extensively at the beginning of the war for pro¬ 
duction-line filter testing. The oil smoke is produced 
by spraying amyl stearate into an electrically heated 
furnace mounted on one side of a large smoke cham¬ 
ber. The furnace is heated to about 450 C, and the 
smoke is formed by condensation of the oil vapor in 
the large chamber. The smoke is sucked through the 
canister at 40 1pm and then through a cell where the 
light, scattered at right angles from a Tyndall beam, 
is measured, using a Westinghouse Type SK-60 
phototube and a Wheatstone bridge circuit amplifier. 
The meter is standardized by the use of master 
standard filters and used as a pass-reject instrument. 
The mechanical arrangements of the canister holder 
are well designed for rapid and convenient produc¬ 
tion-line tests by unskilled operators. 

The concentration of the oil smoke originally used 
in the E3 meter was maintained as uniform as possi¬ 
ble, but was not determined accurately. According to 
the estimate of H. Scherr, it was about 40 mg per 1. 
With this inlet smoke concentration, the sensitivity 
of the E3 meter was better than 0.02%. 34 

NDRC tests 25 about April 1941 showed that oil 
smoke caused considerable deterioration of the car¬ 
bon-impregnated paper then used in the smoke filter. 
Apparently this is because the liquid smoke wets the 
fine carbon filaments bridging the openings in the 
filter paper, causing these fine filaments to coalesce 
with the coarser cellulose fibers. Later, considerable 
attention was paid to the harmful effect of oil screen¬ 
ing smokes on filters. 35-38 

When the highly concentrated test smokes were 


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372 


METHODS OF TESTING SMOKE FILTERS 


shown to be harmful to the filters on the production 
line, the concentration of the test smoke was reduced 
to about 2 to 5 mg per l. 39 However, this reduced the 
sensitivity of the meter to somewhat better than 
0.2% penetration. 

24.4.2 The CWS Development Laboratory 
MIT-E1 Canister Tester 40 * 41 

The great improvement in Service canisters 
rendered the EA-E3 meter obsolete, and the much 
more sensitive MIT-E1 canister tester was developed 
to take its place on the production line. This tester is 
provided with the MIT-E1R1 generator 4 which pro¬ 
duces a liquid smoke of DOP. A stream of air is 
bubbled through the liquid DOP in a boiler main¬ 
tained at a constant temperature within ±0.5 C by 
a thermostat. The vapor-laden air is cooled rapidly 
as it is mixed with a large volume of diluting air in a 
Venturi tube. By proper adjustment of the tempera¬ 
tures of the boiler and diluting air, the smoke-particle 
size is maintained at about 0.3-micron diameter, as 
measured by an Owl reading of 30° (± 1°). Originally, 
the smoke concentration was between 200 and 250 /xg 
per 1, at a flow of 85 1pm in the MIT-E1 canister 
tester. Later, the flow was cut to 32 1pm and the 
concentration was increased to 750 ng per 1 in the 
MIT-E1R1 canister tester. This change was made in 
order to make the tester more sensitive to pinhole 
leaks and canister imperfections, as explained in dis¬ 
cussing the particle-counting smoke penetrometer. 

All the smoke stream put through the canister also 
traverses the smoke cell. Hence it is flushed out 
almost instantly. The cell is designed to minimize 
fouling of the lenses by smoke or by lint blown off 
from the filters, so as to allow long periods of opera¬ 
tion before the background light becomes too high. 
Since the test-smoke concentration is reduced to 
avoid damage to the filter, and the scattered light 
from the smoke cell is viewed at right angles to reduce 
background scattering as much as possible, the 
amount of light scattered from the filtered smoke is 
so minute as to require a very sensitive photoelectric 
circuit. A Type 929 photocell is employed. A light 
chopper between the lamp and the smoke cell gives 
90-c pulses from the Type 929 tube, which are fed to 
a 4-stage 90-c amplifier operated at a gain of about 
2 X 10 6 . Thus the small current due to the light 
pulses scattered by the filtered smoke is separated 
from the much larger d-c leakage current in the Type 


929 tube. The background light, scattered by the 
cell, is compensated by a zero adjustment. 

When the instrument has been calibrated against 
a standard filter, the percentage penetration may be 
read directly. However, in a production line, it is 
used as a pass-reject instrument. The rejection limit 
may be set as low as 0.01% penetration. 

Another advantage of the tester is its speed. Since 
only about 5 sec are required per canister, it is well 
adapted for use on a production line. The disad¬ 
vantages are the complicated electronic circuits, 
which make the initial cost high and require main¬ 
tenance men who are specialists in electronics to 
service the meter. 

24.4.3 The NRL E3 Smoke Penetration 
Meter 5 

This meter employed the smoke generator, small- 
angle forward scattering cell, and indicator units of 
the NRL-E2 meter described in an earlier section, 
adapted to rapid production-line testing. The volume 
of the smoke cell was reduced by a wooden sleeve, 
which filled most of the space around the cone of 
light, so as to reduce the time for equilibration of the 
cell. With a test smoke of 125 to 150 jug per 1, this 
instrument had a sensitivity of 0.001 % and measured 
absolute penetrations. This was an advantage over 
the MIT-E1 canister tester, which was calibrated 
against a standard filter. 

The validity of standard filters is always open to 
some question, due to change of penetration with use. 
The CWS Development Laboratory supplied stand¬ 
ard canisters with filters of glass fiber, which is less 
affected by DOP smoke than paper filters. The 
MIT-E1 canister tester, calibrated with such a 
standard, was found to give results with other glass 
fiber filters which agreed well with the NRL-E1 
meter (the original laboratory model from which the 
production-line tester NRL-E3 was developed). 
However, the penetrations of paper filters measured 
with the MIT-E1 meter were nearly twice as large 
as those obtained with the NRL-El meter. All the 
measurements were in the range 0.05 to 0.10% 
penetration. The discrepancy was greatly reduced 
when the MIT test smoke was used with both indi¬ 
cators. This fact suggested that the test smokes were 
not equally uniform, and that selective filtration was 
different with the two filter materials. Even with the 
same test smoke, unless it were homogeneous, the 
selective filtration could cause a different reduction of 


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PRODUCTION-LINE TESTERS 


373 


the intensity of the light viewed at right angles in the 
MIT-E1 meter, and at small forward angles in the 
NRL-E1 meter. 

The complete explanation of all these facts awaits 
the development of a method of measuring particle 
size distribution in these fine smokes before and after 
filtration. If such a method were comparable in ease 
with the owl reading for average particle size, it would 
give a tremendous amount of useful information. 
However, a practical solution in this case was ob¬ 
tained by using paper filters as primary standards for 
the MIT-E1 meter, and the glass wool filters as 
secondary standards which were checked against the 
primary ones and then used for routine tests the rest 
of the day. The primary standards were replaced 
frequently. 

24.4.4 The Carbon-Smoke Penetrometer 42 

This instrument, which has been described in a 
previous paragraph, was used by the British and the 
Canadians as a production-line tester. The sensitivity 
of the British apparatus was only 0.5%. The Cana¬ 
dians employed a photoelectric detector sensitive to 
0.01% penetration. However, the penetrometer had 
the disadvantage of using a solid smoke consisting of 
many chain-like particles made up of small primary 
carbon nuclei. These particles are less penetrating 
than spherical liquid particles of the same mass. Also, 
they tend to clog the filter, decreasing its penetration 
for the moment by impregnating it with fine carbon 
filaments. However, this improvement disappears in 
the presence of oil smokes, which wet the carbon fila¬ 
ments and cause them to coalesce with the larger 
fibers of the filter, as explained in the discussion of 
the Edge wood Arsenal E-3 canister tester. 

24.4.5 The Sodium-Flame Penetrometer 43 

The sodium-flame apparatus was developed by the 
British 44 - 45 as a 100% filter tester for use in the pro¬ 
duction of canisters. The smoke is generated by 
atomizing a 2% solution of salt and diluting the spray 
with air, allowing the drops to dry to a smoke of solid 
sodium chloride. As originally designed, the appa¬ 
ratus employed visual comparison of the intensities of 
sodium light from two hydrogen flames, one burning 
in the unfiltered smoke, the other in the effluent leav¬ 
ing the test filter. A comparison spectroscope is used 
so that the D lines of the two flames appear to be 
separated by a dividing line. The intensity of the 


flame burning in the unfiltered smoke is cut down by 
means of an optical wedge to match that of the test 
flame. At balance, the percentage transmission of the 
wedge is a measure of the concentration of the filtered 
smoke. Since the intensity of the flame may not be 
proportional to the concentration of salt in the air 
about the flame, and since the intensity may change 
with the alignment of the spectroscope with respect 
to the flames, the value at balance is not absolute but 
only relative. Thus, one of the disadvantages of this 
type of tester is that it yields percentage penetrations 
only after it is calibrated with filters standardized by 
some other method such as the methylene blue tester. 
A second disadvantage is that it requires visual com¬ 
parisons of intensities, which is rather fatiguing, al¬ 
though the British reported no complaints of eye 
strain from the observers in their factories. 

The advantages of this tester are its high sensi¬ 
tivity, the rapidity with which canisters can be 
tested (over 400 an hour by one observer), and its 
simplicity, which reduced the initial cost and required 
a smaller amount of strategic materials than did more 
complicated testing apparatus. 

The sodium-flame apparatus was later modified by 
the Canadian Chemical Warfare Laboratories 46 so 
that visual comparisons are replaced by the use of the 
RCA Type 931 electron-multiplier type phototube, 
the output of which is passed through a microamme¬ 
ter. The meter can be made to give absolute penetra¬ 
tions by comparison with a standard filter, the pene¬ 
tration of Avhich has been measured by means of a 
methylene blue tester. The hydrogen flame is ad¬ 
justed so that 1 jua corresponds to a penetration of 
0.005%. After a careful study of the penetration of 
wool-resin filters, it was concluded that the sodium- 
flame penetrometer gave results as consistent as did 
the methylene blue and DOP penetrometers. The 
sodium-flame penetrometer might well be adopted as 
a production-line tester if all canisters were tested 
against a solid smoke. 

24.4.6 Possible Use of a Particle-Count¬ 
ing Canister Tester 

The particle-counting smoke penetrometer has 
definite possibilities as a production-line tester, if the 
need should arise for such an apparatus. The control 
of test smoke concentration by a photoelectric device 
is now under investigation at Northwestern Univer¬ 
sity under a contract with the Army Service Forces at 
Camp Detrick. The smoke cell and electrical circuits 


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374 


METHODS OF TESTING SMOKE FILTERS 


would require little change to arrange for a count of 
5 or 10 sec duration. The chief problem would seem 
to be removal of all dust from the filter, which might 
be accomplished by blowing filtered air through the 


canisters on the assembly line before they reached 
the testing station. The maintenance and servicing 
of the electronic apparatus probably would be simpler 
than for the MIT-E1 canister tester. 


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Chapter 25 

SMOKE SCREENS 

By W. H. Rodebush 


25.1 INTRODUCTION 

smoke screen is an artificially generated cloud 
of smoke particles, or more usually fog droplets, 
produced for the purpose of obscuring vision. Be¬ 
cause of the scattering of light by the individual drop¬ 
lets, the visibility of an object in or beyond the cloud 
may be reduced to a low value or to zero. A small or 
dilute cloud produces a diffuse glare of light between 
the object and the observer which decreases the con¬ 
trast between the object and its surroundings (see 
Chapter 27). A large or dense cloud may provide a 
completely opaque screen. 

25.2 TYPES OF SMOKE SCREENS- 
BLANKET SCREENS AND CURTAIN 

SCREENS 

A smoke screen laid over an area to conceal it from 
aerial observation may be termed a blanket screen. 
A smoke screen laid along the ground to conceal ob¬ 
jects at ground level from observers on the ground 
may be termed a curtain screen. If a curtain screen 
rises to a sufficient height it may interfere with aerial 
observation, and a blanket screen becomes a curtain 
screen if it settles to the ground. The distinction is 
important only for defensive screening. In the of¬ 
fensive use of smoke, where the object is to blind 
the enemy by enveloping him in a dense cloud at 
ground level, the distinction between blanket and 
curtain screens no longer exists. 

25 . 2.1 Meteorological Conditions Favor¬ 
ing Different Types of Screens 

It is often stated that stable air conditions are 
favorable to the use of smoke, but this is by no means 
necessarily the case. If smoke is being produced by a 
number of generators under strong inversion condi¬ 
tions with a wind blowing over a smooth terrain, the 
smoke plumes will not spread enough to merge and 
will not rise to great enough height to form a satis¬ 
factory curtain screen. A blanket screen is entirely 
out of the question under such conditions. 

On the other hand, by the proper choice of muni¬ 


tion, one may produce a curtain under any condi¬ 
tions. Under high inversion a cluster type munition of 
white phosphorus will give a continuous screen and a 
sufficient rise, because of the large quantity of heat 
liberated. If the wind direction happens to be parallel 
to the screen, a long screen can be generated by a few 
munitions. It is, of course, equally possible to produce 
a curtain screen under unstable conditions using a 
cluster type munition, but one giving less heat than 
white phosphorus is to be preferred. Under neutral 
conditions a long curtain screen downwind may be 
produced by a single generator. 

25 . 2.2 Blanket Screens 

The first use of blanket screens in World War II 
was by the British who used the orchard heater to 
produce a black or brown carbon smoke by burning 
fuel oil. These screens were used to protect industrial 
areas from night bombing raids. They were satis¬ 
factory for the following reasons. 

While the orchard heaters are very inefficient 
smoke producers, only a small quantity of smoke is 
required to produce obscuration at night. The smoke 
is dark colored, so that the canopy was not con¬ 
spicuous by moonlight. It is necessary that the smoke 
blanket lift off the ground to permit visibility and 
movement, and that the cloud rise to a sufficient 
height to cover tall objects. Under the inversion con¬ 
ditions usually prevailing at night, the large amount 
of heat produced by the generators served to cause 
the smoke blanket to rise to a considerable height and 
then level off, as is characteristic of smokes which 
consist of carbon in an atmosphere of carbon dioxide. 

The oil vapor smoke generator, which has largely 
replaced the orchard heater because of its increased 
efficiency, behaves in a very different manner. Be¬ 
cause of the large volume of brilliant white smoke 
produced, it is better adapted for daytime screening. 
Furthermore, since there is little heat liberated in the 
smoke production process there is little tendency for 
the smoke to rise. Unstable air conditions will be re¬ 
quired to form a defensive blanket screen. If these 
generators are used at night under inversion condi¬ 
tions, the smoke will cling to the ground and paralyze 



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375 


376 


SMOKE SCREENS 


traffic. Conditions of extreme instability are not de¬ 
sirable, of course, because a blanket screen which 
has risen to a height of five or six thousand feet is of 
little use. 

25.3 SMOKE COVERAGE 

The smoke coverage may be defined as quantity of 
smoke per unit area of a blanket screen necessary to 
give obscuration. It may be stated in terms of grams 
per square meter, or pounds or gallons per square 
mile. (1 g per sq m = 5,700 lb per sq mile.) As 
pointed out in Chapter 27, the smoke coverage will 
vary enormously with the varying conditions of 
illumination, contrast of target, etc. An amount of 
0.25 g of oil smoke per square meter, when dispersed 
in optimum particle size, will give obscuration under 
severe conditions. This is equivalent to 200 gal of oil 
per square mile. 

25.3.1 The Number of Generators Re¬ 
quired to Give a Stated Smoke Coverage 

If Q is the output of a generator (gallons per hour), 
C the smoke coverage (gallons per square mile) re¬ 
quired, and V the wind velocity in miles per hour, 
then the number n of generators per mile of front re¬ 
quired to maintain this smoke coverage is 


The foregoing statement requires qualification. The 
smoke plumes will not merge until the smoke has 
traveled a long way downwind, particularly under 
stable air conditions over smooth terrain. The smoke 
will never be distributed uniformly over the area, 
because of local variations of wind direction, so that 
the minimum smoke coverage for obscuration will 
not give obscuration. Finally, the smoke blanket 
usually spreads out over an increasing width of 
terrain as it travels downwind, so that the actual 
coverage is less than the calculated. 

25.3.2 Rule of Double Output 

Hence, if complete obscuration at all points is de¬ 
sired, double the output given by equation (1) will 
give a moderate factor of safety. 

25.3.3 Degree of Obscuration Required 

for Protection 

It is by no means necessary in all cases to obtain 
complete obscuration for adequate protection. Com¬ 


plete obscuration may be a disadvantage. Thus, in 
the Italian campaign near Salerno, it was found 
possible to protect a rear area several miles in extent 
by maintaining a haze over this area. This reduced 
visibility to a few hundred yards, but still permitted 
free mobility of vehicles and troops in the congested 
area on the ground. There was good visibility between 
an airplane directly overhead and the ground, but 
this was of advantage to the ground forces since it 
enabled them to direct antiaircraft fire, whereas it 
was a disadvantage to the attacking plane because 
its pilot must have visibility at an angle in order to 
begin a bombing run. A plane can do little damage 
to an objective that is only visible from directly 
above. 

25.4 SMOKE MATERIALS 

The primary requirement is that the material be 
cheap and available. Since the only methods of pro¬ 
ducing a satisfactory smoke are by vaporization and 
condensation, the material for this must volatilize 
without decomposition and at the same time have a 
low enough vapor pressure so that a few hundred 
pounds will saturate a cubic mile of atmosphere. 
These last requirements are almost contradictory, 
and the only materials that can be used practically 
are the stable petroleum oils with a boiling range in 
the neighborhood of 400 C. 

Sulfur is an interesting material in that it is cheap 
and available and has almost ideal volatility. It has 
a high refractive index and the optimum particle size 
is about 0.15 micron radius (see Figure 9, Chapter 
21). The difficulty with the use of sulfur is that this 
particle size is very critical and lies in a range which 
is difficult to obtain. 

Since heavy lubrication stock oils are about the 
only materials available for the production of smoke, 
it follows that the onfy feasible method for setting up 
large-scale smoke screens is the vapor condensation 
method. 

25.4.1 Practical Considerations Con¬ 
cerning Particle Size of Oil Smokes 

Oil vapor smoke generators obtain particle size 
control by the rapid dilution of the oil vapor with 
cool air. As the mixing and cooling occurs, the vapor 
condenses with a high degree of supersaturation. We 
must assume that sufficient nuclei are present, «o 
that many more particles are formed than are finally 


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OIL VAPOR SMOKE GENERATORS 


377 


present in the smoke. A very rapid rate of coagulation 
occurs for a very short time, and the particle size 
grows to the proper size without developing any ap¬ 
preciable heterogeneity of particle size. The dilution 
occurs so rapidly that the process of coagulation is 
checked after a few thousandths of a second. 

It is, of course, a matter of coincidence that the 
condensation process produces particles within the 
proper size range when the oil vapor is allowed to 
escape through a jet with a few pounds excess pres¬ 
sure at temperatures slightly above the boiling point. 
This conclusion is confirmed by the fact that it has 
not been possible to increase the particle size, e.g., to 
1 micron. The vapor issues at high velocity, at or 
near the boiling temperature, and is rapidly diluted 
with cold air. It must be assumed that the high de¬ 
gree of supersaturation produces a very high con¬ 
centration of very small particles, and that these 
particles grow by coagulation to their final size in the 
first few feet of travel. Since the time of coagulation 
is very short, a remarkably narrow range of particle 
size results. 

The particle size is variable within limits, possibly 
over a tenfold range, but it is very difficult to produce 
a particle size greater than 1 micron diameter. This is 
understandable if we grant the initial high concentra¬ 
tion of very small particles. Whatever may be the 
nature of the nuclei which produce the condensation, 
they appear to be present in large numbers, and there 
is no obvious method of controlling them. The oil is a 
mixture of many different hydrocarbons and it is 
possible that very large molecules may act as con¬ 
densation nuclei. Some control of particle size is 
obtainable by varying the rate of mixing with the air, 
which varies the length of the period of coagulation 
(see Table 3, Chapter 22). In view of the fact that 
each tenfold reduction in particle number (corre¬ 
sponding to a little more than a twofold increase in 
particle diameter) requires ten times as long as the 
previous tenfold reduction (Table 1, Chapter 18), 
it is seen that a given design of nozzle cannot be 
operated to give any great range of particle size. A 
thousandfold change in coagulation time would be 
required to produce a tenfold change in particle size. 
Furthermore, a long coagulation period must result 
in a nonuniform particle size. 

25.4.2 Inflammability 

When the vapor of a high-boiling oil is rapidly 
diluted with cold air, the zone of inflammability 


(where the vapor concentration is within the limits to 
support combustion) is very narrow and fluctuating. 
Consequently, even if the jet is ignited with a hand 
torch, it will blow out almost instantly. This freedom 
from inflammability depends on the proper operation 
of the equipment. There are several conditions which 
will almost certainly result in spontaneous flaming 
of the vapor jet. One of these is the cracking of the 
oil to produce light hydrocarbon vapors plus carbon 
particles. The danger of this is obvious. 

A second cause of flaming is the occurrence of large 
drops. If a slug of unvaporized liquid is thrown out 
into the air, it retains its heat until it is completely 
surrounded by pure air. While the flash point of the 
oil is high because of the low vapor pressure, the 
combustion temperature is probably lower than for 
the lighter hydrocarbons. The large drop will there¬ 
fore inflame spontaneously. 

A final cause of flaming occurs in the combustion 
type of oil vapor smoke generator when the excess 
oxygen present exceeds 100% or more. Under these 
conditions ignition occurs directly from the combus¬ 
tion chamber, and by the time the oxygen present is 
consumed, the jet has become mixed with additional 
air which continues to support combustion. In other 
words, a combustible mixture exists through the 
vapor cloud instead of merely in a narrow zone 
bordering the issuing jet. 

25.5 OIL VAPOR SMOKE GENERATORS 

Two general types of oil vapor smoke or fog genera¬ 
tors have been built. These may be referred to as the 
coil type and the combustion type. The coil type was 
perfected first, and examples of this type are the 
Esso Jr., the Beslar, and the DeVilbiss. In the coil- 
type generator the oil is vaporized in a coil which re¬ 
sembles that of a tubular steam boiler. In order to 
avoid coking and to reduce the amount of decom¬ 
position of oil in the coil, the standard refinery prac¬ 
tice of introducing a small amount of water along 
with the oil is followed. The oil vapor and steam mix¬ 
ture escapes through jets into the atmosphere with 
an excess pressure of atm or more to insure a high 
velocity. The combustion type of smoke generator is 
illustrated by the Williams (never perfected), the 
York-Hession, and the Todd. In the combustion 
type, the fog oil is sprayed directly into the combus¬ 
tion gases from an oil fire. The resulting mixture of 
gases issues from relatively large apertures at a fairly 
high velocity but only slightly in excess of atmos¬ 
pheric pressure. 


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378 


SMOKE SCREENS 


25.5.1 Advantages and Disadvantages 
of the Two Types 

From the operational standpoint the coil has a 
great advantage, since the oil is separated from the 
fire and the control of combustion and oil flow can be 
carried out independently. From the standpoint of 
mechanical durability, however, the coil is a liability. 
Because of the high boiling point of the oil, the heat 
transfer per unit area is very low compared with that 
for a tubular water boiler. Since the coil is in direct 
contact with the fire, local superheating is likely to 
occur, with the deposition of coke and the formation 
of a “hot spot” which will quickly burn through. 
Unless a large, heavy coil is used, it must be replaced 
at frequent intervals. 

Since light weight is usually an important con¬ 
sideration in the design of a smoke generator, the 
combustion-type generator possesses obvious ad¬ 
vantages. Still further reduction in weight can be 
achieved by the use of air cooling in this type, but the 
design involves difficulties. Since the combustion 
must be carried out with a small excess of oxygen, the 
temperature of the combustion chamber is very high, 
and heat resistant metal must be used for the cham¬ 
ber. Cooling fins must be placed on the outside of the 
chamber, and a rapid circulation of air maintained 
over these fins. 

25.6 SMOKE MUNITIONS 

The standard smoke munitions used by the Chemi¬ 
cal Warfare Service (such as FS, HC, and WP) are, 
in general, hygroscopic or deliquescent substances, or 
produce substances of this character by a chemical 
reaction. The resultant smoke is a fog composed of 
droplets of a concentrated water solution with a 
refractive index 1.40 or thereabouts. Such droplets 
constitute an effective obscuring screen, and, since 
the water is condensed from the air, a small quantity 
of the original material will produce a great deal of 
smoke. From the standpoint of logistics therefore, 
these munitions would be very satisfactory were it 
not for one difficulty. There is no satisfactory control 
of the particle size produced by these munitions, and 
it is generally much too large to give an efficient area 
of obscuration per unit weight of material. 

25.7 METHODS OF LAYING SMOKE 

SCREENS 

There are three general methods of laying smoke 
screens. 


25.7.1 Smoke Screens Drifted into 

Position 

This is the method commonly used in defensive 
area screening. A line of stationary oil generators or 
smoke pots is placed upwind of the area to be 
screened. A high steady wind is more favorable than 
a low variable wind, since it takes less time to develop 
the screen and there is less danger of sudden shifts in 
the wind. In the use of this method it is necessary to 
anticipate sudden shifts in the wind direction, which 
may prove disastrous. With no wind this method 
becomes practically useless. 

25.7.2 Smoke Laid from Moving Craft 

Smoke may be laid from generators mounted on 
moving planes or boats. When planes are used, one 
attains the practical results of the third method in 
that the smoke is laid right where it is wanted within 
a matter of a minute or two. The lead plane in a 
smoke mission is exposed to fire, but once a screen 
is established, it may be maintained with a minimum 
of exposure. Boats are so much slower that their use 
in laying smoke screens involves the character of the 
first method to a considerable extent. The smoke may 
be produced either from generators mounted on the 
boat or from floats which are thrown overboard at 
intervals. The latter method anchors the screen to a 
fixed point or line of generation. If the generator is 
mounted on the boat, a straight plume of smoke 
trails from the boat in a straight line in the direction 
of the relative wind, i.e., the direction recorded by an 
anemometer mounted on the boat. Such a screen 
maintains its direction, i.e., travels with the boat, so 
that to the stationary observer it becomes a curtain 
screen with a lateral drift. Because of the relatively 
low speed of a boat, the laying of screens from boats 
calls for a degree of anticipation, and, hence, some 
uncertainty occurs in the results. 

25.7.3 Projected Munitions 

The third method of laying screens is by projected 
munitions, such as bombs, shells, or rockets. This 
method has the advantage of the placement of the 
screen exactly where it is needed (within the limits 
of accuracy of aim) at the instant that it is needed, 
and without undue exposure to enemy fire. In order 
to get a proper distribution of smoke, a bursting mu¬ 
nition is desirable, but if the screen is to have any 


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OPERATIONAL TACTICS 


379 


duration, a slow-burning munition is necessary. The 
ideal munition is a combination of the two, and for 
use in landing operations it should also be amphib¬ 
ious, i.e., function either on land or water. 

25.8 OPERATIONAL TACTICS 

The primary use of a smoke screen is obscuration 
of vision, and to the extent that viewing devices 
render the obscuration futile, a smoke screen is use¬ 
less. Military tactics have always depended heavily 
upon the protection afforded by darkness or natural 
fog. The smoke screen affords the same protection as 
darkness or natural fog plus the advantage that it 
can be placed where it is wanted and be initiated and 
discontinued at will, so that the user need not have 
his own movements handicapped by poor visibility. 
For many operations, it would be desirable to dupli¬ 
cate natural conditions of poor visibility rather than 
to produce a dense screen, but the processes of at¬ 
mospheric diffusion are too slow and uncertain to 
achieve the former. 

With respect to the disposition of the screen and 
the occasion of its use, smoke screens may be classi¬ 
fied as defensive or offensive. 

25.8.1 Defensive Screens 

A blanket screen placed over an area as a protec¬ 
tion against aerial bombing is a common example of 
a defensive screen. Such screens vary greatly in their 
effectiveness depending upon the area to be defended 
and the equipment of the attackers. For example, 
when fixed installations are subjected to pattern 
bombing, the attackers are able to use navigational 
and viewing instruments to do about as good a job as 
if the screen were not there, and, once fires are 
started, they will be able to judge the results by 
photographs. On the other hand, with mobile targets 
such as troops on the ground or ships in a transparent 
area, blanket screens may prove to be of very great 


actual protection, since the enemy can form no 
adequate picture of the disposition of the targets, 
which are being constantly relocated. 

It should also be mentioned that an area screen 
(provided it is maintained at such an elevation that it 
does not reduce the visibility at the surface to a point 
where it hampers movement) is likely to be a great 
aid to the morale of the men working in the area. 

25.8.2 Offensive Screens 

Offensive smoke screens find their greatest use in 
assault or landing operations where personnel are 
exposed to directly aimed enemy fire. In the offen¬ 
sive use of smoke, the purpose is to blind the enemy, 
and to achieve this purpose the smoke should be 
placed immediately upon him. The second or third 
method of laying smoke screens must be used here 
as a rule, and special attention must be given to the 
probable wind directions. With the wind blowing in 
the face of the assault troops, the smoke will be 
blown back and blind the assault troops instead of 
the enemy. 

Blinding the enemy serves two purposes: (1) it pre¬ 
vents directly aimed fire against the assault troops, 
and (2) it handicaps the enemy’s movements, cuts 
down his efficiency, and affects his morale. The im¬ 
portance of the second effect above should not be 
minimized. Anyone who has attempted to work in 
dense smoke will realize how difficult it is to work 
effectively. 

The argument commonly urged against the use of 
smoke in assault operations, namely, that it inter¬ 
feres with the effective fire of the attacking troops, 
is fallacious. While they are advancing, their fire will 
be badly aimed and ineffective; when they have 
reached a hold point where they have some protec¬ 
tion, the smoke screen can be lifted. A smoke screen 
placed upon an enemy does not reduce the accuracy 
or effectiveness of general fire at him by more than 
a small percentage. 


SECRET 



Chapter 26 

TRAVEL AND PERSISTENCE OF AEROSOL CLOUDS 

By W. H. Rodebush 


26. L FORMATION AND TRAVEL OF 
SMOKE CLOUDS 

T he behavior of smoke (when used, for example, 
for the purpose of obscuring vision) is subject to 
the same laws of micrometeorology which apply to 
gases liberated for military purposes. As in the case 
of the gases, the smoke is usually emitted from the 
generator in a jet of considerable velocity, so that 
mechanical turbulence produces a rapid mixing with 
the air. This effect quickly damps out and is no 
longer effective at a distance of a few feet from the 
generator. More persistent effects are due to differ¬ 
ences in density. The ordinary toxic gases are usually 
vapors of molecular weight much greater than air. In 
addition, because of the absorption of the heat of 
vaporization, the gas is much cooler than the air with 
a resultant tendency for the gas cloud to settle. 

With a smoke, the situation is quite the opposite. 
The density of a smoke cloud is but little greater 
than that of air (smoke density of 1 mg per 1 is a very 
dense cloud), and the formation of smoke is usually 
accompanied by the liberation of sufficient heat which 
more than offsets any increase in density. In the case 
where smoke is formed by burning oil or white 
phosphorus, for example, the heat liberation is so 
great that the smoke exhibits a very strong tendency 
to rise because of the reduced density. Even in the 
case of an oil vapor smoke or chlorosulfonic acid, the 
condensation of the oil vapor or of moisture from the 
air causes a rise in temperature sufficient to more than 
compensate for the increase in density due to the 
smoke particles present. 

Table 1 is self-explanatory. A temperature rise of 
0.25 C will offset an increase in density of 1 mg per 1. 

26.1.1 Thermal Behavior of Smokes 

It will be seen from Table 1 that there will be a 
tendency for smoke to rise in every case, this tend¬ 
ency being especially pronounced for white phos¬ 
phorus. 

When a smoke appears to be “heavy,” there is 
usually a gas of high molecular weight present. For 
example, even on hot sunshiny days, the black smoke 
from a factory chimney usually rises at first, but may 


occasionally fall to the ground after some travel. 
This happens because the carbon dioxide present 
loses its heat by radiation and then sinks because it 
is heavier than air. The carbon dioxide receives no 
heat directly from the sun because there is sufficient 
carbon dioxide in the air above to remove all the 
radiation of the wavelength that is absorbed by 
carbon dioxide. Particles of soot will, of course, ab¬ 
sorb heat and tend to prevent the cooling effect which 
causes the smoke to fall. 

26.1.2 Atmospheric Diffusion 

The initial condition of turbulence, which accom¬ 
panies the generation of smoke, disappears by the 
time the smoke has traveled a short distance from the 
generator. The buoyancy effect resulting from the 
higher temperature of the smoke will continue to be 
effective, causing the smoke cloud as a whole to rise. 
As the smoke becomes more and more diluted with 
the cooler air, this effect will be less and less observ¬ 
able, unless (as in the case of white phosphorus) 
there is a very great initial rise in temperature when 
the smoke is formed. 


Table 1. Effect of temperature rise on density; relative 
humidity, 70%; smoke density, 1 mg per 1. 


Material 

Per cent by wt of condensed 
water in smoke 

Temperature 

rise 

Oil vapor 

0 

1.0 

FS 

66 

1.6 

HC 

60 

2.2 

WP 

83 

7.0 


The process by which the smoke is diluted and 
mixed with air is called atmospheric diffusion. This 
process is often termed eddy diffusion to distinguish 
it from molecular diffusion, since eddy-like motions 
of one to many feet in diameter are commonly ob¬ 
served. Eddy diffusion takes place at the same rate 
for a gas as for a smoke while molecular diffusion de¬ 
pends upon the size of the molecule or particle. The 
rate of atmospheric diffusion is measured by the 
angle of rise and angle of spread of the smoke plume 
as it travels downwind from the source. 

Photographs taken at right angles to the smoke 


380 


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FORMATION AND TRAVEL OF SMOKE CLOUDS 


381 



Figure 1. Angle of rise of smoke plume (from photo¬ 
graph). 


plume, both horizontally and vertically, furnish a 
convenient method of measuring the angle of rise and 
angle of spread (see Figures 1 and 2). Such photo¬ 
graphs show that the smoke plume usually has initial 
angles of rise and spread which differ from the angles 
farther away from the point of generation. It has al¬ 
ready been indicated that the initial behavior is a 
transient effect of the heat and turbulence resulting 
from the process by which the smoke is generated. 
Its behavior-as the smoke travels farther away from 
the generator depends upon the meteorological condi¬ 
tions prevailing, and these require detailed discussion. 

26.1.2 Meteorological Factors 

The principal meteorological factors affecting the 
travel of a smoke cloud are wind speed, direction, and 
turbulence, in the lower atmosphere. These are, of 
course, the same micrometeorological factors that 
affect the behavior of war gases, but the effects are 
not the same, and the conditions favorable to the use 
of one may not be favorable for the other in a given 
set of circumstances. 

If it is desired to cover an area with smoke from 
a limited number of stationary sources, a wind 
velocity of fixed speed and direction is desirable. Too 
high a wind speed will require an excessive rate of 
production of smoke to maintain any sort of coverage. 
On the other hand, too low a wind speed means that 
too long a time will be required to develop the screen 
in the first place. 

If there is no wind, the smoke screen can only be 
obtained by laying the smoke from a moving vehicle 
such as a plane or boat, or by projecting smoke 
munitions into the area. The latter method is usually 
only feasible in offensive operations. 

Conditions of very low wind speed are likely to 
be accompanied by sudden variations in the wind, 
which may carry the smoke into areas in which it is 
not desired. 



Figure 2. Angle of spread of smoke plume (from photo¬ 
graph). 


When smoke is emitted by a stationary generator 
in a steady wind, the smoke plume travels downwind 
with the speed of the wind, and the axis of the plume 
is parallel to the wind direction. The density of the 
smoke at any point downwind will be, in general, 
inversely proportional to the wind speed, but this 
statement is only approximately true because of other 
factors which must be taken into account. 

When smoke is laid from a moving source, the 
above statements will still be true if one substitutes 
the relative wind speed and velocity for the true wind 
speed and velocity. By the relative wind speed and 
velocity, one means the wind speed and velocity as 
recorded by an anemometer that is mounted on the 
vehicle carrying the smoke generator. Thus, if a boat 
carrying a smoke generator moves due south with a 
speed of ten knots when the wind is blowing from 
due east at ten knots, the smoke plume will appear to 
an observer on the boat to lie exactly downwind, i.e., 
northwest, and to have a density corresponding to a 
speed of 14.14 knots. The above statement, however, 
is not so simple as it sounds, and it only holds for an 
observer on the boat. To a stationary observer, the 
smoke plume no longer lies with its axis parallel to 
the wind (see Figure 3). 

If the wind speed and direction are recorded by 
sensitive instruments, very rapid and violent fluctua¬ 
tions of both quantities will often be observed. Thus, 
the exact direction of the wind can be established 
only as an average measurement over a considerable 
time, and the wind may momentarily veer by as 
much as 180°. Zero wind may be recorded momen¬ 
tarily. The wind vane records variations only in the 
horizontal component of wind velocity, but, if a vane 
is mounted to turn in a vertical plane, vertical com¬ 
ponents of velocity will be observed. These latter 
must, of course, approach zero as the measuring 
instrument approaches the ground surface. 

The unsteadiness in wind velocity and direction 
can be considered, therefore, as being due to pulsa¬ 
tions taking place in three directions, namely, in the 
general direction of the wind, and in horizontal and 
vertical directions at right angles thereto. The mean 


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382 


TRAVEL AND PERSISTENCE OF AEROSOL CLOUDS 


values of these pulsations in the different directions, 
measured over a period of time, would be expected to 
be equal if the motions of the lower air were isotropic, 
but the vertical direction is unique in this respect. 
If thermal instability exists, strong vertical gusts 
may be expected at considerable altitudes. At the 
ground level, however, the vertical component must 
fall to zero. 

The sum total of the pulsations in the different 
directions measures the gustiness or turbulence of the 
atmosphere. 

26.1.3 Causes of Turbulence 

One obvious cause of turbulence is mechanical. 
The higher the wind velocity, the greater the tur¬ 
bulence, particularly over a rough terrain. Over a 
smooth surface of water there will be no turbulence 
produced by mechanical causes at low wind speeds. 
Wind speeds greater than 10 to 11 knots, however, 
will produce waves which in turn will produce me¬ 
chanical turbulence in the lower air layers. 

26.1.4 Thermal Stability 

The most important factor in producing turbulence 
is thermal instability in the lower atmosphere. During 
the day, in bright sunshine, the ground surface re¬ 
ceives a great deal of heat from the sun, and since 
the earth is a poor conductor, the temperature of the 
surface will rise many degrees. The layer of air in 
contact with the ground is heated in turn, and be¬ 
coming lighter by expansion, it rises. Since the warm 
lower layer of air cannot rise everywhere uniformly, 
it must break through the upper cooler layers some¬ 
what as bubbles burst upward through a liquid. The 
actual driving force is, of course, the weight of the 
cooler air, which settles toward the ground to be 
heated in turn. These upward convective currents 
cause the bumpiness of the air which is noticeable in 
an airplane, and, if there is sufficient humidity, 
cumulus cloud formation is likely to take place at 
moderate altitudes. 

On clear nights the ground loses heat by radiation 
and cools the lower layer of air so that the density 
is greater near the ground, and a condition of ex¬ 
treme stability prevails. When the sky is overcast, 
heat is neither received nor lost by the earth, and a 
neutral condition prevails in which there is no tend¬ 
ency for upward convection. 


The foregoing statements do not hold for changing 
weather conditions. The passage of a warm or cold 
front may completely alter the temperature relation 
between ground surface and air and produce stability 
or instability regardless of time of day or sky condi¬ 
tions. 


> 

h 

o 

o 

-I 

UJ 

> 

Q 

z 

i 


BOAT VELOCITY 



The situation over large bodies of water is also 
different. Water is a heat reservoir of great capacity, 
so that there is no significant variation in temperature 
between day and night. On the other hand, the air is 
usually not at the same temperature as the water, so 
that we may expect to find conditions of stability or 
instability prevailing continuously (throughout the 
twenty-four hours) for long periods. Changes in 
stability will usually take place only with changes in 
wind direction or in seasons. Thus, a wind blowing 
offshore from the New England coast will probably 
produce stable air conditions in summer and unstable 
air conditions in winter, over the ocean. Near the 
equator the ocean receives so much heat from the sun 
that a considerable degree of instability is likely to 
prevail. 


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FORMATION AND TRAVEL OF SMOKE CLOUDS 


383 


26.1.5 Thermal Gradient 

Although stability relations have their cause in 
differences in temperature between the earth’s sur¬ 
face and the lower layers of the air, the actual sta¬ 
bility conditions are determined by the temperature 
gradient in the air itself. If the temperature decrease 
with height is more than 1 C per 100 m, the air will 
be unstable, that is to say, the lower layer of air will 
tend to rise and to keep on rising as long as this 
condition prevails. This is caused by the rising mass 
of air which, even though it expands and cools as it 
rises, will be warmer and lighter than the surrounding 
air at any altitude. On the other hand, if the gradient 
is less than —1C per 100 m, i.e., zero or positive, 
there will be no tendency for the air to rise, because 
a mass of air carried upward would be colder and 
heavier than the surrounding air. 

It is, of course, not an easy matter to measure the 
temperature gradient, but it is usually much exag¬ 
gerated near the ground, so that unless the gradient 
is near zero a temperature difference of a degree or 
more will be observed between two thermometers 
placed a few inches and a few feet, respectively, above 
the ground. 

This critical gradient of — 1 C per 100 m is termed 
by the meteorologist the adiabatic lapse rate for dry 
air, and the degree of stability or instability will de¬ 
pend upon the extent to which the temperature 
gradient departs in one direction or the other from 
the critical value. The extreme condition, when the 
temperature gradient is actually positive, is known 
as inversion and is characterized by extreme stability 
of the lower atmosphere. (See Figure 4.) 


26.1.6 Stability Relations at Land- 
Water Boundaries 

Since a diurnal cycle of stability exists on land and 
no such variation occurs over water, it might be 
anticipated that a sharp discontinuity in meteoro¬ 
logical conditions might occur at land-water bounda¬ 
ries, which would greatly complicate the use of smoke 
in landing operations, for example. It turns out, how¬ 
ever, that this is not the case, except for discontinui¬ 
ties due to such terrain as high cliffs or other sharp 
differences in elevation. There is a tendency for the 
air to be stable over beaches which are bordered by 
low-lying terrain. This comes about in the following- 
way. The diurnal variation in stability relations 
often results in the so-called land and sea breezes. 



20 21 22 23 24 25 26 

TEMPERATURE IN DEGREES C 


INVERSION 


Figure 4. Thermal stability and instability. This 
gradient is 1 degrees centigrade per 100 meters. 


During the day, the air over the land becomes 
heated and the cooler, stable air from the sea flows 
in over the beach. This air mass must in turn become 
heated and unstable by contact with the ground sur¬ 
face, but the instability will not be set up until the 
air mass has penetrated some distance inland. 

On the other hand, at night the land is cooled by 
radiation, and a cool air mass flows from inland out 
over the beach. This air mass may be cooler than the 
water and may, therefore, become unstable as it 
travels to sea, but the air in the vicinity of the beach 
will remain stable. 

The foregoing generalizations are only statements 
of tendencies. There will be many departures from 
this regularity, and the whole situation may be il¬ 
lustrated by a discussion of the stability conditions 
prevailing over the east coast of Florida in summer. 
Very few fronts pass through the subtropical regions 
of the world in summer. This is particularly true in 
the neighborhood of large water areas where the 
disturbances due to land areas are at a minimum. 
Under these conditions the highs and lows are static, 
and the gradient wind which blows along the isobars 
maintains a steady velocity day after day. At sea, 
this wind prevails practically down to the sea surface, 
where it is known as a trade wind. Off the east coast 
of Florida a northeasterly wind blows throughout the 
summer. The warm Gulf Stream lies some distance 
off the coast, and the air mass becomes unstable over 
the Stream. This instability is evidenced by the 


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384 


TRAVEL AND PERSISTENCE OF AEROSOL CLOUDS 


cumulus clouds which can nearly always be seen 
from the shore. 

The water mass between the Gulf Stream and the 
shore is cooler, so that the air mass may be cooled 
enough to become stable over this intervening water. 
When it passes across the beach over the land in the 
daytime, it will become unstable before it has 
traveled very far inland. On the other hand, the air 
at night becomes cooled over the land and flows out 
to sea as a land breeze. This land breeze is usually 
strong enough to oppose the gradient wind, but its 
effect does not extend very far out to sea, nor to a 
very high altitude. The gradient wind still blows a 
few hundred or a few thousand feet aloft. At some 
time during the forenoon, the gradient wind will 
overcome the land breeze and blow across the beach 
once more as a sea breeze. The exact time at which 
this happens depends upon the relative strengths of 
the two winds, and it cannot be forecast with exact¬ 
ness. Similarly, when the air temperature is near that 
of the water, the change from stability to instability 
over the water may take place with slight changes in 
wind velocity or other variables. The temperature of 
the water itself is likely to undergo sudden changes 
such as an offshore wind which may bring up cooler 
water from below near the beach. 

26.1.7 Theory of Atmospheric Diffusion 

In order to describe the travel of smoke clouds, it 
would be desirable to develop a mathematical theory 
in terms of such certain measurable quantities that 
when the meteorological structure of the lower air is 
known, it is possible to calculate the smoke concen¬ 
tration at any point downwind. The British meteorol¬ 
ogists have developed such an equation (on a frankly 
empirical basis) for gas clouds, and it has been pro¬ 
posed to apply this equation to the travel of smoke. 
Certain very serious limitations exist, however, to 
the use of such an equation. 

In the British equation the degree of turbulence 
existing in the air is taken account of by the so-called 
R ratio which is the ratio of the wind velocity at 2 m 
to the wind velocity at 1 m. Actual values of the R 
ratio vary from about 1.05 for very unstable air to 
1.30 for stable air over a very smooth terrain. 

Such an equation, however, has a very limited ap¬ 
plicability. If the air is thermally unstable, a smoke 
cloud will lift clear of the ground before it travels 
very far. This will happen as soon as it encounters an 
upward convection current, but the point at which 


it will occur cannot be predicted by a statistical equa¬ 
tion. On the other hand, under stable conditions over 
a smooth terrain, there is no natural tendency for a 
smoke cloud to rise or spread. This conclusion is 
supported by the evidence of many photographs 
which have been made of smoke streamers under 
stable air conditions. The only use that remains for 
the British equation which applies to smoke is to 
take account of the mechanical turbulence produced 
by rough terrain. This is done by means of on-the- 
spot measurements of R made at ground level. Such 
measurements will not apply to the smoke cloud after 
it has reached an elevation of 100 ft. The British 
equation is, of course, not calculated to take care of 
the initial transient rise and spread of a smoke cloud 
which is due to the heat and turbulence produced by 
the smoke generator. 

26.2 BEHAVIOR OF SMOKE CLOUDS 
UNDER VARIOUS METEOROLOGICAL 
CONDITIONS 

26.2.1 Stable Conditions 

Under inversion conditions over a smooth terrain 
such as calm water, the only tendency shown by the 
smoke cloud to rise and spread is the initial transient 
effect due to the heat and turbulence produced by the 
smoke generator. The turbulence is quickly damped 
out but the heat produced may be sufficient to cause 
a very pronounced rise as is the case with white 
phosphorus smoke munitions. In the case of oil smoke 
where the heat produced is small, the temperature of 
the smoke at any dilution is only slightly greater than 
the temperature required to produce a buoyancy suf¬ 
ficient to offset the increase in density caused by the 
presence of the smoke material. As the smoke rises, 
the temperature falls because of two effects, namely, 
further dilution with cool air, and the adiabatic ex¬ 
pansion due to the decrease in barometric pressure. 
Since, in an inversion, the temperature of the sur¬ 
rounding air increases with increasing altitude, an ele¬ 
vation is soon reached at which the smoke is stable; 
having the same density as the surrounding air, it has 
no tendency either to rise or sink. 

Oil vapor smoke is often observed to level off 
(Figure 5) at an elevation of approximately 100 ft 
under stable air conditions. Certain types of smoke 
will show an erratic behavior because of abnormal 
density. Examples of these are (1) the smoke pro¬ 
duced by burning oil in an orchard heater, in which 


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BEHAVIOR OF SMOKE CLOUDS 


385 



Figure 5. Smoke leveling off under inversion condi¬ 
tions. 


particles of carbon and carbon dioxide are present, 
and (2) HC smoke, in which large particles of zinc 
chloride and other heavy materials are formed. While 
a good deal of heat is produced in the formation of 
these smokes, a good deal of it is quickly lost by 
radiation, particularly at night. 

Since the heat produced in the generation of the 
smoke will usually cause the smoke cloud to rise, even 
under the most stable conditions, it may be antici¬ 
pated that the cloud will lift entirely off the ground 
after a short distance of travel. If, however, a wind 
of considerable velocity is blowing, this lifting from 
the ground will not occur for reasons which will be 
explained later. 

Although the heat produced in the smoke generator 
produces a rise, it has little effect upon the spread of 
the smoke cloud. Such spread as takes place is due 
to the initial turbulence, and this soon damps out. 
Consequently, if it is desired to produce continuous 
clouds of smoke from a series of individual generators, 
it is necessary to place the generators very close to¬ 
gether, otherwise the individual plumes may not 
merge for a long way downwind. This situation holds 
for smooth terrain. If, however, the terrain is covered 
with shrubbery, for example, the lateral spread of the 
cloud is greatly increased as a result of the mechanical 
turbulence produced by the wind flowing through the 
shrubbery. 

26.2.2 Behavior of Smoke Under Un¬ 
stable Conditions 

When the air current is turbulent because of ther¬ 
mal instability, atmospheric diffusion takes place to 
such an extent that the initial transient -behavior of 
the cloud due to the heat and turbulence of the 
generator is of little significance. The smoke cloud 
continues to rise and spread as it travels downwind 
until the cloud becomes so thin that its boundaries 
are no longer distinguishable to the eye. If a time 
exposure were to be taken of the cloud it would ap¬ 


pear as a cone with its apex at the generator and its 
axis rising at an angle from the horizontal, the angle 
of rise depending upon the degree of instability and 
the wind velocity. An instantaneous view of the cloud 
will show that it is furrowed and broken by variations 
in wind direction and sudden upward convective 
currents. 

26.2.3 Convective Pattern 

As has been stated previously, when the air is 
thermally unstable, upward convective currents 
occur. Over a rough terrain these currents are apt to 
be located at certain points. An upward current may 
be anchored at the windward brow of a hill, for ex¬ 
ample. Over a smooth terrain the convective currents 
are constantly shifting, and the distance between two 
upward currents depends upon various factors such 
as wind velocity and degree of instability. (Some idea 
of the convective pattern may be obtained by ob¬ 
serving cumulus clouds.) Between these convective 
upbursts, the atmosphere is slowly settling over the 
whole area. Hence, the smoke cloud will appear to 
hug the ground until it encounters an upward cur¬ 
rent, when it will appear to change direction sud¬ 
denly and rise at a considerable angle. The dimension 
of the convective patterns (distance between up cur¬ 
rents) may be as much as 3^ mile over a very smooth 
terrain. Since the convective pattern involves a com¬ 
plete circulation of the air, it might be supposed that, 
eventually, smoke which has been carried upward 
would be widely diffused and brought back down 
with the descending air. This must happen eventu¬ 
ally, but whether or not it happens within a short 
distance from the point of generation depends upon 
the height of the convective ceiling. 

26.2.4 Convective Ceiling 

The lower air is thermally unstable when a nega¬ 
tive temperature gradient greater than 1 c per 100 m 
of elevation exists at the ground level. This negative 
gradient may continue indefinitely upward. Thus, in 
thunderstorms, cumulus clouds often rise to a height 
of several miles, and a smoke cloud would be carried 
to the same height. 

Under other circumstances, a current of warmer 
air may be blowing at an elevation of a few hundred 
feet, so that the temperature gradient may become 
zero or even positive, giving an inversion at this ele¬ 
vation. There is no tendency for the lower air to rise 


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386 


TRAVEL AND PERSISTENCE OF AEROSOL CLOUDS 


through this warmer lighter layer, and a definite ceil¬ 
ing will be established for the convective turbulence. 
Within this layer the atmosphere turns over and over, 
and the smoke may become diffused throughout the 
layer before it has traveled very far. It must be re¬ 
membered, of course, that eddy diffusion always 
takes place at the boundaries of the upward con¬ 
vection currents, so that some smoke will become 
diffused throughout the settling layer of cooler air 
even with a high convective ceiling. 

26.2.5 Angle of Rise 

The rate of rise of the convective current increases 
with the thermal instability. The angle of rise of the 
smoke cloud (as a statistical average) is inversely 
proportional to the wind velocity. With zero wind, 
the convective currents rise directly upward. As the 
wind increases, the direction of the convective current 
must incline more and more away from the vertical. 

26.3 EVAPORATION AND DEPOSITION 
OF AEROSOLS 

Travel of smoke clouds has been discussed in the 
first part of this chapter, from the standpoint of 
meteorological conditions. Since the particles of 
which screening smokes are composed are too small 
to fall out appreciably by Stokes’ law, and have too 
low a vapor pressure to evaporate, screening smokes 
will persist almost indefinitely, i.e., until the cloud is 
so diluted by atmospheric diffusion that it is no 
longer apparent to the observer. Naturally occurring 
fogs, however, disappear both by evaporation and by 
Stokes’ law deposition, and clouds of aerosols may be 
set up which are subject to attenuation by one or 
both processes. 

The fundamental factor in estimating the rate of 
either process is the concentration of aerosol at the 
ground level or at some stated height above the 
ground. The difficulties that arise in estimating this 
quantity have been emphasized and need not be 
reiterated here. Rather, the discussion will be limited 
to conditions where some sort of satisfactory estimate 
of concentration over a considerable area can be 
made. The discussion will be limited to the following 
conditions. 

1. The thermal gradient at ground level is positive, 
or in the limit, neutral, so that the lower atmosphere 
is stable. 

2. Wind velocity is moderate. 


3. Terrain is level with uniform vegetative cover. 

4. The aerosol drops are not larger than 5 microns 
radius. 

If the foregoing conditions are satisfied, the only 
turbulence in the air will be the mechanical turbu¬ 
lence produced by the vegetative cover of the terrain. 
The drop size is large enough so that Stokes’ law 
deposition occurs, but not large enough so that a 
major portion will fall out before the transient effects 
of the generator have disappeared and the clouds 
have become stabilized. The concentration will de¬ 
crease from the ground upward and, under the con¬ 
ditions postulated, will probably become negligible 
at a point two to three times the height of the 
vegetative cover. It is not possible to judge the height 
of the cloud by the eye, since considerable concentra¬ 
tions of the larger drops will be inconspicuous 
while a small amount of smoke of smaller drops 
(about 1 micron) will be very noticeable. If the cloud 
is generated from a plane, the initial height of the 
cloud will be very much greater than if the generators 
are located on the ground. 

26.3.1 Approximate Rule for Concen¬ 

tration in Cloud 

Under the stable air conditions assumed above, and 
with a line of generators at right angles to the wind, 
one may use the following approximate rule. Assume 
that the height of the cloud is the same as the height 
of the vegetative cover and that the concentration 
does not vary with height. This will be approximately 
true for fog of uniform particle size. The concentra¬ 
tion near the ground will then be the concentration 
expected, if the foregoing conditions are satisfied. 

To illustrate, suppose that with a wind velocity of 
5 m per sec, 100 g of aerosol are generated per sec 
per m of front, and that the height of the vegetative 
cover is 25 m. The mass concentration to be expected 
when the cloud is initially diffused is 0.8 mg per 1. 

The foregoing rule may lead to errors of 100% or 
more, and it becomes meaningless when applied to 
nearly bare ground. When measurements of R can be 
made, the British diffusion equation may be used to 
give a more exact result. But, unless the measure¬ 
ments are made on the spot, the use of the equation 
is not likely to decrease the error very much. 

26.3.2 The Evaporation of Aerosols 

A satisfactory formula for the evaporation of drops 
whose vapor pressures range from that of water to 
nitrobenzene appears to be the equation of Fuchs, 


SECRET 



EVAPORATION AND DEPOSITION OF AEROSOLS 


387 


dn 2 tt kd 


dt 


RT 


(:Po - v)- 


(i) 


Here dn/dt equals the rate of formation of vapor in 
moles per second per drop, k the diffusivity of the 
vapor in air, d the drop diameter, R the gas constant, 
T the absolute temperature, p 0 the vapor pressure of 
the liquid, and p the actual partial pressure of the 
vapor present in the air; CGS units are required for 
the formula. 

The mass rate of evaporation is proportional to the 
drop diameter. The rate of change of drop diameter 
at a constant mass rate varies inversely as the square 
of the diameter. Thus, if both sides of equation (1) 
are multiplied by M/p where M is the molecular 
weight and p the liquid density, 

M dn dv 2irkMd 

7 Tt = -Jt = -^ ip °- p) - (2) 

Here v is the volume of the liquid drop. Substituting 
2r for d, 

4irr 2 dr 4irkMr 

(po-p) • (3) 


dv 

dt 


Hence, 


dr 

dt 


dt 

kM 
' pRT 


P RT 




This may be integrated to 
0 2 kM 

P RT 


r L = r„ 


(Po —p)<, 


or 


d 2 = dl 


8 kM 
~ P RT 


(: Po-p)t . 


(4) 


(5) 


( 6 ) 


Hence, as the drop evaporates, the rate of decrease of 
drop diameter varies inversely as the drop diameter. 
A curve showing the decrease of drop diameter with 
time is shown in Figure 6, plotted from the data 
shown in Table 2. As the drop size becomes smaller 
the drop decreases in diameter more and more 
rapidly. 

Table 2. Diameter of evaporating drop as a function 
of the time for a typical liquid. 

Mol wt = 100; density = 1; k = 0.1 cm 2 per sec; 

Po = 0.01 mm; p = 0; T = 298 K. 


Drop diameter (microns) 

Time (seconds) 

10.0 

0 

7.5 

10 

3.7 

20 

3.09 

21 

2.24 

22 

0.95 

23 

0 

23.2 



Figure 6. Evaporation of 10-micron drop. 

If it is desired to estimate the vapor concentration 
in equilibrium with an aerosol, an estimate must be 
made of the original concentration, and a step-by- 
step integration must be made to estimate the change 
in concentration with time and distance of travel 
downwind. 


26.3.3 


Deposition of Aerosols 


If the concentration is known at any point in an 
aerosol cloud, the rate of deposition per unit area 
through Stokes’ law fall can be estimated. Let V 0 = 
the Stokes’ law rate of fall for the particular aerosol 
particles forming the cloud. Then the rate of deposi¬ 
tion per unit area is 

F 0 C, 

where C is the concentration per unit volume. If the 
cloud is assumed to be of uniform concentration at 
all times, and of height h, then the rate of change of 
concentration with time is 

dC v j£ . (7) 


dt 


Integrating 


In 


/C 0 \ = TV 

\C/ h 


(8) 


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388 


TRAVEL AND PERSISTENCE OF AEROSOL CLOUDS 


The concentration at any point downwind could be 
calculated if the wind velocity were known. 

The above calculation assumes a single surface for 
deposition and would hold for a cloud traveling over 
bare ground. When the area is covered with vegeta¬ 
tion, the area of deposition may be doubled. 

26.3.4 Inertial Effects 

With wind velocities of several miles per hour, 
inertial effects become very important in deposition, 


especially because the leaves of many plants are 
covered with hairs of small dimensions, which prove 
to be very effective in filtration. The deposition due 
to inertial effects in dense vegetation may prove to be 
several times that due to Stokes’ law deposition. 
When one considers that an aerosol will usually not 
be of uniform particle size and that the concentration 
at any point in the cloud is a highly variable quan¬ 
tity, one sees that the estimate of rate of deposition 
from an aerosol cloud in a jungle area may be in 
error by several hundred per cent. 


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Chapter 27 

THEORY OF OBSCURATION 

By W. H. Rodebush 


27.1 THE CONTRAST LIMEN 

I n addition to physiological and psychological 
factors affecting visibility of a target through fog 
or smoke clouds, there are at least two physical 
factors of fundamental importance. These are the 
contrast offered by the target and the amount of light 
scattered by the cloud. The contrast of the target is 
measured roughly by the reflectivity of the target, 
although color affects the contrast to a degree. The 
ordinary smoke box experiments are usually made 
with a target consisting of a white square on a black 
background. The white square has a reflectivity near 
unity and the black background is near zero, so that 
the contrast is nearly equal to the intensity of illumi¬ 
nation of the target. With actual targets, however, 
which are usually camouflaged to a certain extent, 
the differences in reflectivity may not be more than 
10%. An exception is the case of the wake of a vessel 
viewed from the air, where the contrast becomes very 
great. 

If the reflectivity of target and surroundings is 
n and r 2 respectively, then the contrast C may be 
defined as the difference in intensity of the reflected 
light, that is, 

C = (rx-r*) It = A rl t (1) 

where 1 1 is the intensity of illumination on the target 
and its surroundings. 

The contrast limen is defined as the critical ratio 
C/Ii necessary for visibility. C is now the observed 
difference in intensity and Ii is the total intensity of 
light received by the eyes from the general direction 
of the target. The contrast limen depends upon the 
total intensity of illumination, the angle subtended 
by the target, and various other physical and physio¬ 
logical factors. It is not the same for different ob¬ 
servers, nor for the same observer at different times. 
However, under ordinary daylight conditions, it may 
be stated that for complete visibility C/I i must not 
be less than 1% and for complete obscuration not 
greater than 0.3%. 

27.1.1 Visibility in a Natural Fog 

When both target and observer are enshrouded in 
a natural fog, the intensity of illumination reaching 


the target and entering the eye of the observer is the 
same. The contrast ratio C/I\ becomes, therefore, 


(1-cQA rh 

h 


4 (l-a)Ar, 


( 2 ) 


where 1 — a is the fraction of the light reflected by 
the target that reaches the eye of the observer with¬ 
out being scattered. If it were not for the fog, the 
eye would receive only the light reflected from the 
target, but because of the scattering and diffusion of 
light by the fog, the intensity of illumination is 
uniform everywhere. 


27.1.2 The Extinction of Light by a Fog 

The transmission factor, 1 — a, for light traveling 
a distance l centimeters through a fog is given by an 
expression of the general form, 1 — a = e~ Kl where 
k is the scattering coefficient per unit distance in a 
fog. Since [from the theory of scattering (Chapter 
21)] the effective scattering area for small drops is 
known, it is possible to calculate by statistical 
methods with a fair degree of approximation the 
scattering coefficient for a fog. 

Assume that the fog consists of drops of uniform 
size, each drop having an effective scattering cross 
section of 1/N sq cm and that there are n drops per cc. 
Imagine a cross section of 1 sq cm at right angles to 
the line of vision to be divided into N equal squares 
Avith area equal to the effective scattering area of a 
drop. If only one drop is present, the chance that 
the center of this drop will lie in any of these small 
squares is 1/N, and the probability that the center 
of the drop will not lie in any specified small square 
is 1 — 1/N. If there are n drops per cc, the probability 
that no drop will have its center in a specified square 
is (1 — 1 /N) nl . The total area of squares per sq cm in 
Avhich the center of a drop does not lie xvill be just 
(1 — 1/N) nl . Since nl and N are large, this expres¬ 
sion becomes e~ nl/N . 

This result does not mean that a fraction of the 
total area equal to e~ nl/N will be unobstructed for vi¬ 
sion, for there will be overlapping of drops whose 
centers lie in areas adjacent to a vacant square. In 
order to appraise the extent of this overlapping, the 


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390 


THEORY OF OBSCURATION 


assumption will have to be made that the squares 
adjacent to an empty square contain the average 
number of drops randomly distributed. This cannot, 
of course, always be the case, but the errors intro¬ 
duced will perhaps be as often positive as negative, 
and the estimate will be a good first order approxi¬ 
mation. By a process of counting, the fractional ob¬ 
scuration due to overlap is estimated to be 0.3 nl/N 
where nl/N is the average number of drops per 
square. The fraction of light transmitted unscattered 
becomes 

l-« = (l -0.3|)e" n,/Ar - (3) 

This formula agrees with reported results. For ex¬ 
ample, it is reported that visibility is 200 m in a 
natural fog of 0.18 g water per cu m. This would 
correspond to n = 8 drops of 35 microns diameter 
per cc. Taking the effective scattering area for the 
drop as 2t r 2 (Chapter 21), nl/N = 3.1, which ap¬ 
proaches the limiting value, and 1 — a — 0.32%. 
One notices that when nl/N becomes 3.33, the result 
indicates that even a square in which no centers of 
drops lie will be completely obscured. One, therefore, 
concludes that when the effective obscuring area of 
the drops present in a region is 3.33 times the actual 
area measured at right angles to the line of vision, the 
visibility will be zero. 

27.1.3 The Extinction of Light by a 
Screening Smoke 

Since 1/N = a, the effective scattering area for a 
drop, equation (3) may be written 

1 - a = (1 - 0.3 nla)e~ nla (4) 

The expression nla represents the total effective 
scattering area of all the drops that lie in the line 
of sight, per unit of cross-sectional area. This expres¬ 
sion is equivalent to, and may be replaced by, the 
expression Aw, where A is the total effective scatter¬ 
ing area per unit weight of the material as dispersed, 
and w is the weight of material dispersed per unit of 
cross-sectional area. Since the expression is dimen¬ 
sionless, any units may be used as long as the same 
units are used for A and w; w is often expressed in 
grams per square meter. 

Thus, for Diol 55 dispersed in particles of optimum 
size for screening smoke (about 0.3-micron radius), A 
is about 10 sq m per g. The expression for extinction 
[equation (4)] then becomes 

1 -a = (1 - 0.Sw)e~ 10w . (5) 


27.1.4 Conditions Approaching Extinction 

The remarkable property of a fog or smoke of 
considerable density is that an object either appears 
visible or disappears completely, there being no ap¬ 
preciable zone of partial visibility as long as the 
illumination is adequate. This is partially due to the 
sharpness of the contrast limen, but it is also due in 
part to the effect of the overlapping drops. The 
formula above shows that, as the exponent ap¬ 
proaches a value which is estimated to be in the 
neighborhood of 3.33, the light transmission, instead 
of continuing to fall off exponentially with the in¬ 
creasing depth of fog penetrated, suddenly becomes 
zero. This result agrees with experience. It will not be 
possible to check this expression by observations of 
visibility in natural fogs because of the difficulty of 
estimating the exact number and size of drops 
present per cubic centimeter of air, but it may be 
taken as a reasonably reliable formula. 

27.1.5 Variation of Visibility with 

Concentration 

It has been assumed in the foregoing considerations 
that the interference of a fog with vision depends 
only upon the total number of fog particles per unit 
area of cross section that lie in the line of vision and 
in no way upon the distribution in space of these 
particles. That is to say, a high concentration along 
a short path would produce the same obscuration as 
a low concentration over a long path. This assump¬ 
tion is at least approximately correct, and it follows 
that the limiting distance for visibility for a given 
drop size will be given by the relation 

lo ~ - t 
n 

where n is the number of drops per cubic centimeter. 
In very dense fogs the visibility is likely to be re¬ 
duced, because the contrast limen depends upon the 
total intensity of illumination. 

27.1.6 Visibility in Artificial Fogs; 

Smoke Screens 

The artificially produced fog cloud differs from the 
naturally occurring fog in that it may occupy only a 
relatively narrow region between the target and the 
observer, with both the target and observer entirely 
out of the cloud. Under these circumstances, the in¬ 
tensity of illumination may be very different at the 
target and at the eyes of the observer. Because of 
this fact, the quantity of fog or smoke required for 


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THE CONTRAST LIMEN 


391 


complete obscuration is a highly variable quantity, 
and no reasonable figure can be given that will be 
adequate under all conditions. 

The general formula for visibility may be written 

Ah _ (1 - a)ArI t 

77 - h (6) 

Here I t is the intensity of light on the target and h 
the total intensity of light reaching the eye of the 
observer. The contrast at the target is A rl t , and 
Ah = (1 — a)ArI t is the contrast perceived by the 
observer as diminished by the screen. Ah/h must be 
less than 0.003 for complete obscuration. For a 
screening smoke of Diol 55, 1 — a is given by equa¬ 
tion (5). 

The greatest difficulty lies in estimating the values 
of I t and Ii. Before we can estimate values for these 
quantities, we must consider the penetration of light 
in fog. The fraction of the total intensity that pene¬ 
trates a fog without being scattered is a far different 
quantity from the total intensity of light that pene¬ 
trates a fog after repeated scattering. Because of the 
complicated way in which it is scattered as a function 
of angle, and because multiple scattering occurs, it is 
not possible to calculate the penetration factor 
exactly, but an approximation is given by the fol¬ 
lowing considerations. Imagine the cloud to be made 
up of a large number of single layers of particles. 
Light which is scattered by one of these layers is 
scattered in all directions, but a major fraction of it 
is scattered in the forward direction. On the other 
hand, a certain fraction 1/k is scattered in the back¬ 
ward direction. A complete analysis of the problem 
shows that the total fraction of incident light re¬ 
turned by m layers is 


fm 


m 


m k — 1 

Hence, the fraction that penetrates m layers is 
k - 1 


1 ~fm = 


m + k — 1 


(7) 


( 8 ) 


It has been shown that the equivalent of more than 
three continuous layers of drops is required for com¬ 
plete obscuration. Estimating a value of 1/k = 1/4, 
one sees readily that the equivalent of three layers 
would not reduce the penetration to less than one- 
half. If the cloud is of sufficient depth and concentra¬ 
tion to correspond to many layers, practically all the 
light entering a cloud must be returned to the same 
side of the cloud which it entered and from which it 
is now scattered in a backward direction. Thus, a 


thick cloud must behave as a perfectly white body, 
one which returns by diffuse reflection (scattering) 
100% of the light which falls upon it. The upper 
surface of a cumulus cloud appears a brilliant snowy 
white in the sunshine while the under side of the 
cloud may appear black because of the failure of light 
to penetrate. 



Figure 1. Obscuration by a blanket screen. 7 0 = in¬ 
cident light. fl 0 - light scattered back by cloud. 
(1 —/)/o = light reaching target. 


It is possible now to set up the expression showing 
the exact dependence of the degree of obscuration by 
a blanket screen upon the various factors. Referring 
to Figure 1, the contrast ratio will be 

Ah = (1 - /)Ar/ 0 (l - 3 w)e~^ 
h flo U 

The greatest amount of smoke will be required when 
both sun and observer are directly overhead. Assume 
w = 0.25 g per sq m. Assuming Ar = 0.1, then Ah/h 
= 0.0025, which is below the limen for obscuration. 
On the other hand, a greater contrast (larger Ar) 
would not give obscuration. A Ar of 0.1 might be 
expected in an area which has been camouflaged to 
give low visibility. A dark object on snow or the wake 
of a ship against quiet water would, on the other 
hand, give values of Ar approaching unity. 

When the sun and the observer are at angles less 
than 90° with the horizon, the quantity of smoke 
required will be less. The effective value of w will be 
increased in the ratio 1/sin 0, where 0 is the angle with 
the horizon. The penetration will be less for smaller 
values of 0, and in particular, if the sun and observer 
are at 180° azimuth, the value of / in the denominator 
will no longer be the same as the value for / in the 
numerator, but will be much greater. 

At low angles for sun and observer, when the ob¬ 
server is facing the sun, the cloud behaves as if it 
were a mirror giving specular reflection, because of 


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392 


THEORY OF OBSCURATION 


the tendency toward forward scattering. The top of 
the cloud will then have a brightness several times 
that of a perfectly white body. 

Thus it happens that the amount of smoke re¬ 
quired for obscuration by a blanket screen is greatly 
reduced: (1) by the reduction in illumination of the 
target, and (2) by the glare thrown back from the 
top of the cloud into the eye of the observer. If the 
cloud is of small extent and high, the illumination of 
the target will not be reduced, and any artificial 
illumination of the target at night, for example, will 
require a larger quantity of smoke for obscuration. 

With curtain screens, the illumination of the target 
will not be reduced, and the second effect mentioned 
above will be present only when the observer and 
sun are on opposite sides of the screen. 

27.2 COLORED SMOKE 

The theory of the scattering of light by absorbing 
or reflecting particles has not been perfected to the 
same degree as the theory for transparent particles. 
Hence, it is not possible to make positive statements 
as to the variation of the effective scattering area as a 
function of particle size and wavelength. Certain 
thermally stable dyes can be vaporized to give colored 
smokes. Such smokes may show some of the char¬ 
acteristics of solutions, such as fluorescence and 
selective reflection. If the particle size is too small, 
the color may not be that of the original dye. For 
colored smoke signals it is satisfactory to produce a 
particle size somewhere between 1 and 5 microns 
diameter. 

27.2.1 Colored Smoke Screens 

White smoke screens (transparent particles) may 
be very conspicuous, particularly on moonlight nights 


or over water, so that they serve to point out the 
target rather than to conceal it. It would be desirable 
to produce screens of neutral or pastel tints ranging 
from blue-green to dark brown or black for tactical 
operations. Dyes are obviously too expensive to be 
used in a pure state on such a scale. 

It is evident that the high screening efficiency per 
pound of material that is obtained with Diol 55, for 
example, is due to the very careful control of particle 
size, a particle being produced which has an effective 
screening area several times its geometrical area. 
About the only materials that can be used for making 
smoke are transparent or nearly colorless materials 
such as hydrocarbon oils. Carbon is, of course, a 
cheap and available material, but carbon smoke can¬ 
not be produced in the particle size desired, and even 
carbon black is a relatively expensive material. 

A few per cent of oil soluble dye dissolved in a fog 
oil will give a smoke which in high concentrations 
shows a good deal of color. When the smoke thins 
out to a screening concentration, however, the color 
fades and the smoke appears to be white or nearly so. 
The explanation for this behavior is not difficult. 
Very little absorption takes place when light is 
scattered by a particle of the optimum particle size 
for scattering, but after repeated scattering, enough 
absorption will have occurred to give a pronounced 
color. If the smoke cloud is of great density and 
depth, all of the light will be thrown back by re¬ 
peated scattering, and a strong color will be observed. 
As the cloud thins out, much of the light penetrates 
clear through the cloud, and the light that is scat¬ 
tered backward has undergone only two or three 
scatterings. The cloud now behaves as a white body 
of poor reflecting power, but it is scarcely less 
conspicuous than if the dye were not present. 


SECRET 



PART IV 


NEW MUNITIONS FOR SMOKE AND TOXIC GASES 


SECRET 



Chapter 28 

INTRODUCTION 

By H. F. Johnstone 


28.1 ORGANIZATION 

arly in the preparation for World War II, 
work was started on the development of new 
methods for dispersing smoke and toxic aerosols. 
Some of the first contracts supported by Section B5 
of NDRC were on the development of new smoke 
generators and improved munitions for dispersing 
DM and CN. Later, following the inauguration of an 
extensive field testing program in which concentra¬ 
tions of toxic gases from standard munitions were 
measured, and estimates made on the munition re¬ 
quirements for various tactical situations and mete¬ 
orological conditions, Section B6 was requested to 
undertake work on the improvement of gas munitions. 
When the two sections were reorganized as Division 
10, the munitions work was concentrated in one con¬ 
tract at the University of Illinois which operated 
under Service Projects: CWS-1, “Aerosols: Their 
Generation, Stabilization and Precipitation/’ and 
CWS-27, “Simple and Unusual Munitions for Set¬ 
ting up Field Concentrations of Chemical Warfare 
Agents.” In this section the technical aspects of 
several new-munitions and devices, which were de¬ 
veloped for dispersing smoke, toxic and insecticidal 
aerosols, and toxic gases, will be discussed. 

28.2 NEW SMOKE MUNITIONS 

Fundamental studies on the evaporation of liquids, 
carried on in connection with the development of new 
designs of the DM candle and CN generators, led to 
suggestions of new methods for the dispersal of 
aerosols. These formed the basis of several new muni¬ 
tions which were developed later. It was shown that 
extremely rapid rates of heat transfer could be ob¬ 
tained by finely atomizing a liquid as it was injected 
into a hot gas stream. The atomization was accom¬ 
plished by injecting the liquid at the throat of a 
Venturi through which hot gases were passed at high 
velocities. In this way, complete evaporation of rela¬ 
tively high boiling liquids could be accomplished 
within a few milliseconds, so that decomposition of 
heat-sensitive agents was reduced to a minimum. 
Several new oil smoke generators were developed on 
this principle. These included smoke pots and floats 


and a smoke generator to be attached to the exhaust 
of airplane engines. The possibility of setting up oil 
smoke clouds in this way was especially attractive 
because, as a substitute for HC, it eliminated the 
toxicity and the glow of the burning pyrotechnic mix¬ 
ture, both of which were serious handicaps to the 
standard pot. During the later stages of World War 
II, when it was necessary to set up smoke screens of 
long duration, the need for the oil smoke pot became 
particularly pressing and the work on the new de¬ 
velopments proceeded under high priority. 

The lightweight exhaust generator for airplanes 
had an output of 40 to 50 gal of fog oil per min, when 
installed on the single engine 1,900-hp TBM-3 plane. 
It produced satisfactory smoke screens of 2 to 10 min 
duration under all meteorological conditions when the 
plane was flying at a speed of 200 knots. The possi¬ 
bility of using a formation of planes with this equip¬ 
ment, for providing rapid protection of harbors and 
task forces at sea, was recognized as a possible de¬ 
fense against kamikase attacks, and equipment for 72 
planes was procured during the summer of 1945. 
These planes were not used, however, before the war 
ended. 

The extensive use of phosphorus smoke munitions 
in the Sicilian and Italian campaigns resulted in an 
urgent request in the fall of 1943 for work on the im¬ 
provement of this type of smoke filling, especially 
with the view of eliminating the pillaring characteris¬ 
tic. The possibility of mechanically reinforcing the 
filling with steel wool, gauze and tubes had been tried 
with only partial success. The idea of incorporating 
the phosphorus granules in a matrix of rubber was 
then suggested and this resulted in the development 
of plasticized white phosphorus [PWP]. Field tests 
on the new smoke agent in bombs, rockets, and mortar 
shells were carried on during the summer and fall of 
1944. Its superior quality finally led to its adoption 
as a standard smoke-filling in place of WP for all 
nonrotating projectiles and rockets used by the Army 
Ground Forces, as well as for the 4.2-in. chemical 
mortar and for the 3.5-in. and 4.5-in. Navy rockets, 
and for the M-47 bomb. 

The thermal generator method described above 
was also adapted for evaporating heat-sensitive 



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395 


396 


INTRODUCTION 


organic dyes for new and efficient target identifica¬ 
tion markers and floating distress signals. This was 
the basis of a new target identification bomb (Bomb, 
Target Identification, Smoke, Mark 72, Mod 2), 
which was demonstrated in June 1945. A number of 
these bombs were manufactured for Service test. 

Because of the possibility of a short supply of 
chemicals for the hexachloroethane smoke mixture, 
in 1942 an intensive study was made of possible 
substitutes. New mixtures were developed containing 
the anhydrous chlorides and complexes of more 
readily available salts. A sulfur nitrate smoke mix¬ 
ture was also developed and demonstrated to the 
Chemical Warfare Service. Attention was also given 
to a sulfur smoke generator built on the thermal 
generator principle. A successful model of this device 
was completed in May 1943. The unit, although 
quite light, had only a small capacity, and the limita¬ 
tions imposed, coupled with considerable improve¬ 
ment in the oil smoke generators at the same time, 
made it undesirable to continue with the project. 
The information obtained, however, was valuable in 
the development of the direct combustion-type oil 
smoke generator, such as the Hesson-York unit, 
which utilized the Venturi design. 

28.3 TOXIC VAPORS AND AEROSOLS 

While toxic gas was not used during World War II, 
considerable effort was spent in developing new 
weapons for dispersing it in the most effective man¬ 
ner. With the improvement of the gas mask and other 
protective measures, it was realized that either agents 
of much greater toxicity must be found, or else much 
greater concentrations of the known agents must be 
established to be of value in tactical situations. The 
value of dispersing the liquid agents as aerosols to 
establish high concentrations was recognized by both 
sides. The Germans had made elaborate field studies 
in which they demonstrated the potency of mustard 
gas and Tabun (MCE) when dispersed from shells 
and bombs with extremely heavy bursters which 
shattered the chargings into fine droplets, most of 
which remained airborne until evaporated. The im¬ 
portant tactical use of these weapons was mainly to 
set up high initial concentrations to achieve casual¬ 
ties before protection could be gained. The Germans 
claimed that a single 250-kg bomb charged with 
H-arsenol mixture, with a 34-lb TNT burster, could 
produce a lethal area of 4,000 to 4,500 sq m for a 
1-min exposure. 


The great potency of mustard vapor was recog¬ 
nized even in World War I. A method for taking full 
advantage of this effect was developed in the form 
of a thermal generator bomb which operated on the 
Venturi principle already described. Field tests indi¬ 
cated that it was easily possible to set up mustard 
vapor concentrations which exceeded the lethal 
dosage even of masked men within less than a minute, 
using clusters of bombs identical in size with the oil 
incendiary bombs and having the same dispersion 
pattern. Tests on cave fortifications with similar de¬ 
vices showed that dosages could be established with 
a small expenditure of munitions which exceeded the 
best protection of impregnated clothing. While the 
limitation of the small thermal generator bomb 
(designated E29R1) was recognized in that it must 
impact and remain in a vertical position in order to 
function properly, a larger bomb was developed near 
the end of World War II which did not have this 
restriction. 

Work similar to that of the Germans on dispersing 
aerosols by means of an HE burster was also carried 
on by the Munitions Development Laboratory 
[MDL]. In this case, however, the size of the bomb 
was intentionally made small so that it could be 
carried in standard clusters and take the maximum 
effect of the burster. It was contemplated that this 
bomb might also be used for dispersing solutions 
of insecticides from airplanes over enemy-held terri¬ 
tory. 

Because of the considerable interest in the develop¬ 
ment of new highly toxic powders, work on a new 
munition for dispersing these agents was also carried 
on. Several of the materials considered were quite 
sensitive to even moderate temperatures and to ex¬ 
plosive shocks. It was desirable, therefore, to find 
other means of dispersing the powders than by high 
explosives. Preliminary tests showed that good dis¬ 
persal could be obtained by the sudden release of a 
gas under high pressure through the agent compart¬ 
ment. This principle was incorporated in a bomb 
which used either a small cylinder of air at 4,000 lb 
pressure or a cylinder of liquid carbon dioxide. The 
gas was released by the action of a mechanical fuze, 
or an explosive train. 

Work on several miscellaneous devices and muni¬ 
tions was also carried on at the MDL. Some of these 
proved to be unsuccessful and were abandoned, while 
others were developed with the utmost dispatch but 
failed to be used during the war, either because they 
were developed too late or because need for them did 


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TOXIC VAPORS AND AEROSOLS 


397 


not arise in the later campaigns. One of the interest¬ 
ing problems on which the staff of the MDL co¬ 
operated, because of its experience in the dispersal 
of solid particles, was the development of means for 
dispersing herbicides. It was decided that the most 
feasible method of dispersal was by means of an 


aimable air burst bomb. This necessitated a study of 
the fall of granules of the material through air and 
the measurement of dosage patterns to determine the 
most desirable size of the particles and the containers. 
Here again, the sudden ending of World War II in the 
Pacific made use of this weapon unnecessary. 


i 


SECRET 



Chapter 29 

ATOMIZATION OF LIQUIDS 

By H. F. Johnstone 


29.1 INTRODUCTION 

T he effectiveness of many liquid agents used in 
warfare depends upon atomization to produce 
small droplets. This is true not only of chemical 
agents, but also of smokes and insecticides and even 
applies to liquids used in other ways, since atomiza¬ 
tion is necessary for carburetion and combustion of 
fuels. The degree of atomization desired depends 
upon the nature of the agent and the use to which it 
is being put. In the generation of oil smokes, for in¬ 
stance, it was found that the optimum drop size for 
maximum obscuration is considerably below the 
range attainable by mechanical atomization. Conse¬ 
quently, it was necessary to evaporate the oil com¬ 
pletely and to produce the droplets by condensation 
following discharge of the vapor into the air. The 
evaporation of oil by heat transfer from hot gases 
takes place most rapidly when the liquid is atomized 
as completely as possible. On the other hand, in the 
application of insecticides it was found that the drop 
size useful for screening smokes is entirely too small 
to give efficient results. The optimum size occurs 
when the particles are just small enough to be dis¬ 
persed by the wind and still produce the maximum 
contact effect on insects as well as give an efficient 
coverage when they are deposited on foliage and 
water surfaces. The optimum drop size for this pur¬ 
pose appears to lie between 10 and 50 microns 
diameter. 

In the dispersal of the vesicant chemical warfare 
gases the so-called persistent effects for the denial of 
terrain and contamination of personnel are best ob¬ 
tained when the drops are fairly large, i.e., within 
the range of 1 to 5 mm diameter. During the war, 
the perfection of the gas mask and development of 
protective clothing shifted the emphasis to other 
tactical uses of these agents which depended upon 
surprise and the setting up of high concentrations of 
vapor and aerosols which would produce lethal 
dosages before the protection of the mask could be 
gained. Much attention was given to mechanical and 
thermal methods of dispersing mustard gas and other 
vesicant agents as aerosols. The atomization of liquid 
agents by high explosives was the principal method 


adopted for the dispersal of these agents by the 
Germans. 

In this chapter a review will be made of the princi¬ 
ples of atomization on the basis of present knowledge. 
These have led to the development of several new 
chemical and smoke munitions. 

29.2 ATOMIZATION BY NOZZLES 
29.2.1 Mechanism of Droplet Formation 

The basic mechanism of the formation of finely 
divided drops consists of drawing out the liquid into 
slender streams or filaments. Such filaments are un¬ 
stable and any slight displacement causes them to 
contract in some places and expand in others so that 
eventually they collapse into droplets. High-speed 
photographic studies show clearly the formation and 
disruption of the filaments in a manner which de¬ 
pends on the air velocity. At low velocities, the rela¬ 
tive motion between the air and the liquid stream 
produces a bead-like swelling and contraction with 
continuously increasing amplitude until the liquid 
jet finally breaks up into separate drops. As the veloc¬ 
ity of the air is increased somewhat, a fluttering 
action of the jet begins, forming a twisted ribbon of 
liquid. A portion of the ribbon is caught up by the 
air stream and, being anchored at the other end by 
surface tension, is drawn out into a fine ligament. This 
ligament is quickly cut off by the rapid growth of a 
dent in its surface and the separated mass is swiftly 
drawn up into spherical drops. At still higher air 
velocities, there is a flattening action of the twisted 
ribbon to form a cobweb-like film which is so thin 
that it is readily torn apart into microdroplets. 

There is some evidence that there is a minimum 
average drop size attainable in the atomization of a 
liquid by air. 1 Sauter 2 measured by photometric 
means the size of the drops formed when water is 
atomized in an air stream, and found that, at high air 
speeds, the mean diameter approaches asymptotically 
a value of about 12 microns at air velocities of 330 to 
400 fps. The idea of a limiting degree of atomization 
of liquids in air, however, is opposed by Littaye. 3 In 
any case, it is evident that, from a practical point of 


398 


SECRET 


ATOMIZATION BY NOZZLES 


399 


view, it is very difficult to secure complete atomiza¬ 
tion to the sub-micron range. It is true that a large 
percentage of the drops from an atomizing nozzle 
may exist in this range but the actual percentage of 
the mass of the liquid below 1 micron is very small. 
This conclusion, which is based on the amount of 
energy required to provide a high-velocity air stream 
with large ratio to the liquid rate, indicates that no 
air atomizing nozzle can be perfected which will 
efficiently produce a screening smoke from a non¬ 
volatile liquid. 

29.2.2 Types of Nozzles 

Spraying devices may be classified as pneumatic, 
hydraulic and mechanical, according to the principle 
employed in effecting the dispersion of the liquid. 
These types differ characteristically in the degree 
and uniformity of the dispersion produced and in 
their industrial applications. 

1 . Pneumatic nozzles in which compressed air or 
steam is used to effect atomization are capable of 
producing the finest dispersion. They are commonly 
used for paint spraying, humidification of gases and 
atomization of oil for burning. Industrial pneumatic 
nozzles are classified as internal mixing and external 
mixing, according to the relative positions of the 
liquid and gas jets. A nozzle is described as external 
mixing if the contact between the fluid and the gas 
takes place entirely outside the nozzle, and internal 
mixing if the contact occurs within a chamber from 
which the spray exits through an orifice. 

2. Hydraulic nozzles are available in a variety of 
forms and sizes. The most common is the so-called 
hollow-cone nozzle in which the liquid is led into a 
whirl chamber through tangential passages or through 
a fixed spiral so that it acquires a rapid rotation. In 
either case, the liquid emerges through a relatively 
large orifice which is placed at the axis of the whirl 
chamber. The basic principle is that of imparting 
angular motion to the liquid which causes it to be 
thrown out as a thin hollow cone moving at a high 
velocity. The relative volume of air which is engaged 
for atomization depends upon the angle of the cone 
and the design of the orifice. These nozzles are char¬ 
acterized by low power consumption and large capac¬ 
ity, but the atomization obtained is relatively poor, 
compared with air-atomizing nozzles, unless ex¬ 
tremely high pressures are used. In one form of 
hydraulic nozzle the liquid, under high pressure, is 
forced through a very small orifice or slit. This type 


of nozzle has found some application in diesel engine 
fuel injection. Another type of hydraulic nozzle 
which is used for special purposes and apparently 
gives good atomization, but still somewhat less than 
the pneumatic nozzle, is the impact nozzle. Here, a 
solid stream of liquid under pressure is caused to 
strike a solid surface or another similar stream to 
give the necessary dispersion. 

3. Mechanical nozzles are used when the liquid to 
be atomized has a high viscqsity or carries suspended 
particles which may clog a small orifice. Atomization 
is obtained by discharging the liquid onto a disk ro¬ 
tating at high speed. The centrifugal force hurls the 
liquid into the air, thus providing the velocity neces¬ 
sary to produce atomization. These devices have 
found extensive use in spray drying. 

29.2.3 Performance of Pneumatic Nozzles 

In spite of the importance of the degree of atomiza¬ 
tion obtained from commercial nozzles, there have 
been actually very few measurements made of the 
drop size distribution in a spray pattern. Few nozzle 
manufacturers are in position to report the actual 
degree of fineness produced by their products. Possi¬ 
bly the reason for this is the difficulty in collecting 
representative samples of the droplets from the spray, 
and in measuring the actual diameters after the drop¬ 
lets are collected. Some of the studies reported have 
used obviously imperfect methods which have led to 
erroneous conclusions regarding nozzle performance. 
The most complete study in this interesting field was 
made by two Japanese engineers, S. Nukiyama and 
Y. Tanasawa 4 at Tokyo Imperial University. This 
work led to two empirical correlations on the drop 
size distribution and performance of pneumatic 
nozzles. These have served as a basis for a more 
extended study made at the Munitions Development 
Laboratory in which it was found that the same 
methods of correlation could be used for large ex¬ 
haust atomizers, airplane sprays, and, in a limited 
way, to explosive bursts. 5 

Nukiyama and Tanasawa studied the atomization 
of several liquids of varying physical properties with 
small gas atomizing nozzles of various types operated 
with compressed air. They collected samples of the 
spray droplets from several points in the spray by 
means of a cylindrical shutter device which gave an 
exposure time of 0.002 to 0.01 sec. The drops were 
received on a cover glass coated with a film of oil 
which was then photographed under a microscope 


SECRET 



400 


ATOMIZATION OF LIQUIDS 


so that the size distribution could be measured. The 
following factors influenced the degree of atomiza¬ 
tion. 

1 . The effect of the relative velocity of the air past 
the droplets. 

2. The effect of the physical properties of the 
liquid, including surface tension, viscosity and 
density. 

3. The effect of the relative quantity of air ex¬ 
pressed by the ratio of the volume of air to the volume 
of liquid. 

Within a limited range of these variables, that is, 
for densities between 0.8 and 1.2, surface tensions 
between 30 and 73 dynes per cm, viscosities between 
0.01 and 0.3 poises, and for air velocities below the 
acoustic velocity, the following empirical equation 
represents the degree of atomization: 


D 0 = 585 ^ + 597 

vVp 


/ n \ OA5 ( 1,000 Ql Y 5 
\\Ato) \ Qa / > 


( 1 ) 


where D 0 = diameter, in microns, of a single drop 
with the same ratio of surface to volume 
as a representative sample of the drops 
in the spray; 

v = difference in velocity between air and 
liquid at the vena contracta , in meters 
per second; 

Qo/Ql = volume flow rate of air/volume flow rate 
of liquid; 

p = liquid density, grams per cubic centi¬ 
meter; 

p = liquid viscosity, poises; 

a = liquid surface tension, dynes per centi¬ 
meter. 


The distribution of the drop sizes in a spray can be 
represented by a relatively simple empirical formula 
of the type: 

dn 

— = ax p e~ hx<l , (2) 

ax 

where x = drop diameter, in microns; 

n = total number of drops in the sample with 
diameters between zero and x microns; 
a , b, p, and q are constants. 

Nukiyama and Tanasawa found that when the 
velocity and the quantity of the air were both high 
and sufficient, i.e., velocities above 450 fps and for 
air/liquid ratios greater than 5,000, the values of the 
constants were p = 2 and q = 1. For poor atomiza¬ 


tion, which is obtained at low air velocities and low 
air/liquid ratios, the value of q decreases to 3^ to 
but p appears to remain constant. 

The significance of the constants a and b in equa¬ 
tion (2) is of interest. These relationships follow from 
the fact that by definition, 



If p, q, D 0 , and the total volume of sample under con¬ 
sideration (or the total number of drops) are known, 
the integration can be carried out and the constants 
a and b determined. The relationships among 
a, b, q , D 0 , and the total volume of sample are shown 
in Table 1 for the case when p = 2. If l/q is an inte- 


Table 1. Relationship between q, a, 6, V , and D 0 , 
when p = 2. 



Do as a 

a as a function 

q 

function of b 

of 6 and V* 

2 

1.50 /Vb 

1.916 3 F 

i 

5/6 

1.59 X 10-W 

3 

110/6 2 

2.39 X lO-WV 

1 

3 

4,080/6 3 

1.79 X 10 -15 6 18 F 

1 

213,000/6 4 

1.84 X 10 _23 6 24 F 

1 

5 

14,300,000/6® 

5.32 X 10 _32 6 30 F 

1 

6 

l,170,000,000/6 6 

3.08 X lO-^F 

General case when 

(6/?)! 5 6-i/s 

(5 /q)\ A 6 

366«/« F 

1 /q is an integer 

(6/g)hr 


* V = total volume of sample in cubic microns. 


ger, the calculations may be performed by the usual 
methods of calculus and an ordinary integral table; 
but the labor is considerably less if a table of gamma 
functions is utilized. If l/q is not an integer, the use 
of table of gamma functions is advisable. 

The value of q is a measure of the flatness of the 
drop distribution curve. If q = 2, the curve has a 
relatively high and narrow apex. As q decreases, the 
peak of the curve becomes lower and flatter. Ac¬ 
cordingly, a high value of q means that most of the 
mass of the liquid lies within a narrow range of 
sizes, whereas a low value of q corresponds to a 
scattering of the drops over a considerable range of 
sizes. The volume frequency curves for three values 
of q are shown on a comparable basis in Figure 1. 
The corresponding cumulative volume curves are 
shown in Figure 2. For any given nozzle, it appears 
that q is constant over a wide range of operating 
conditions. However, q is affected markedly by the 


SECRET 











ATOMIZATION BY NOZZLES 


401 




Figure 1. Volume frequency curves for typical nozzle 
coefficients. 


Figure 2. Integrated volume distribution curves for 
typical nozzle coefficients. 


type and size of the atomizing device used. Hence its 
value must be determined experimentally for each 
type and size. Values thus far encountered range from 
to 1 for gas-atomizing nozzles and from % to 2 
for spray nozzles. 

For some purposes, it is of more interest to know 
the mass median diameter [MMD] of the droplets in 
a spray than it is to know H 0 . If the drop size distri¬ 
bution in a spray fits the empirical equation for 
dn/dx , and if p = 2, and 1/q is an integer, it can be 
shown mathematically that the ratio of the MMD to 
D o depends only on the value of q. 


MMD _ (6/8)1 6 /q 

Do (6/?)! 5 


(4) 


where Y is found by trial-and-error solution of the 
equation following. 


1 

2 



(5) 


These equations have been solved for the case when 
q = 1, for which it is found that MMD/D 0 = 1.14. 


If p = 2, then the equation for drop size distribu¬ 
tion can be written as follows: 



If sufficiently small intervals are used in the drop 
count, a plot of log ( l/x 2 )(An/Ax ) against x q should 
give a straight line with slope equal to — b/ 2.3. This 
relationship makes it easy to test experimental data 
to see if they fit the empirical equation, since the 
distribution data are normally available in terms of 
An, the number of drops in a small size range, Ax, at 
various values of x. Various values of q are assumed, 
and for each value, a plot is made of log (1/a; 2 ) 
(A n/Ax) vs x 9 . The correct value of q is the one that 
gives a straight line plot. The value of b is obtained 
from the slope of the straight line. From the values 
of q and b, one can then calculate D 0 through use of 
the second column in Table 1. Examples of the use 
of this method for various types of nozzles are shown 
in Figures 3, 4, and 5. 

It will be noted that, in some cases, deviations of 
some of the observed points from the straight lines 


SECRET 


















































402 


ATOMIZATION OF LIQUIDS 



x IN MICRONS 


Figure 3. Performance of exhaust Venturi atomizer 
on Dodge truck dispersing Diol 55 oil. 

occur in both the low and high ranges of drop sizes. 
These are to be expected since, with the usual 
methods of sampling, it is difficult to collect the very 
small drops and, unless an extremely large number of 
droplets is counted, a statistically significant number 
of large drops is not included in the area of the slide 
surveyed. In fact, this is one of the advantages of 
this method of analyzing drop count data since it is 
usually possible to determine the value of q and the 
slope of the line from a relatively few points deter¬ 
mined by counting the number of drops in small 
increments of diameter. For representative samples 
of sprays which are relatively homogeneous, the 
values of Z> 0 and MMD determined from the above 
formulas will agree quite closely with those obtained 
by summing up the actual drop counts. For less 
homogeneous sprays, however, when q is small, the 
value of Do may actually exceed the diameter of the 
largest drop measured if only a small number of 
drops is counted. In this case the graphical method 



0 12 3 4 5 

IN MICRONS 

Figure 4. Drop size distribution from a small air-atom¬ 
izing nozzle. 

permits extrapolation of the data, and gives a more 
exact picture of the drop spectrum. The value of q 
cannot be determined precisely by the trial-and-error 
method but this is of no great importance. Small 
errors in the determination of the slope of the line, 
however, may cause large deviations in the calcu¬ 
lated value of Do and the method of least squares 
should be used to determine the best line. 

29.2.4 Venturi Atomizer 

The air for most industrial pneumatic nozzles is 
supplied at pressures ranging from 20 to 150 psi and 
the liquid is supplied under only a small head. In 
spite of the large volume of air required and the low 
energy efficiency of these nozzles, the power require¬ 
ment generally is not excessive for industrial pur¬ 
poses. In munitions, which are usually limited to a 


SECRET 








































































ATOMIZATION BY NOZZLES 


403 



Figure 5. Drop size distribution from Spraco Type T nozzles. 


SECRET 



























404 


ATOMIZATION OF LIQUIDS 


small supply of gas from a pyrotechnic fuel block 
at low pressures, or when the exhaust gases from an 
airplane engine or the slipstream around a plane are 
employed for atomization, it is essential that the 
gas pressure be low. 

A practical device for providing high gas velocity 
and still maintaining low overall pressure drop is 
the familiar Venturi tube, consisting of a converging 
section, a high velocity throat and a tapered diver¬ 
gent section. The important element is the diver¬ 
ging section which should not have a total angle of 
more than 7°, while the converging section is the 
frustum of a cone with a vertex angle of 25 to 30°. 
The use of the Venturi tube to secure a zone of high 
velocity largely avoids the substantial loss of kinetic 
energy occasioned when the jet from a simple nozzle 
or orifice discharges downstream into a slowly mov¬ 
ing fluid. The pressure difference between the up¬ 
stream and the throat of the Venturi may be cal¬ 
culated from the usual adiabatic orifice formula. 6 
The overall pressure loss for a single-phase fluid, 
gas, or liquid, is from 10 to 20% of this difference. 
Design calculations for a Venturi used for the atomi¬ 
zation of oil by means of the exhaust gases from an 
airplane engine are shown in Chapter 33. It will be 
seen that it is possible to approach the acoustic 
velocity in the Venturi throat and still have an over¬ 
all pressure loss of only a few pounds per square inch. 
This loss is perhaps increased by a factor of 1.5 to 3 
when liquid is fed to the Venturi throat during atomi¬ 
zation depending on the ratio of liquid to gas and 
on the gas velocity. 

The Venturi atomizer is especially adaptable to the 
production of small droplets for high rates of evapora¬ 
tion in hot gases. Even with viscous oils it is possible 
to produce a spray in which essentially all of the 
droplets are less than 100 microns diameter and the 
value of Do is approximately 40. This will correspond 
to about 6,000 sq ft per gal of liquid fed to the 
atomizer. This type of pneumatic atomizer is espe¬ 
cially suitable for the dispersal of insecticides, since 
the exhaust gases from an internal combustion engine 
are readily available either for airplane spray or 
ground spray. The greatest use of the Venturi 
atomizer for war purposes, however, was contem¬ 
plated in the development of a new floating oil 
smoke generator and in munitions for the dispersal 
of vesicant gases, both of which depended upon the 
vaporization of a liquid by means of hot gases from 
a pyrotechnic fuel block. 

A brief study was made of the performance of 


Venturi atomizers in various sizes ranging in throat 
diameter from 0.11 in. to 3.3 in., and using gases of 
various densities and viscosities and several types of 
liquids. 7 For the small Venturis the atomization of oil 
in a stream of nitrogen was somewhat better than 
that indicated by equation (1). Since neither the 
viscosity nor the density of the gas is included in this 
equation, it was desirable to determine what effect 
these properties would have on the resulting atomiza¬ 
tion. From experiments using ethylene and helium, 
it was found that a decrease of gas viscosity at con¬ 
stant gas density improved the atomization of the 
liquid. A viscosity decrease of approximately 60% 
resulted in a decrease in D 0 of about 60%. On the 
other hand, a decrease in gas density at constant gas 
viscosity had an unfavorable effect on the atomiza¬ 
tion of the liquid. When the density was reduced to 
V by substituting helium for nitrogen the value of 
Do was increased by a factor of 2 to 3. 

In the case of the small Venturi atomizer, it was 
found that incomplete atomization of the liquid 
sometimes took place and resulted in dribbling of the 
liquid from the exit of the atomizer. This appeared 
to be a wall effect occasioned by the impingement 
of the droplets on the downstream section. It could 
be eliminated entirely by cutting off the Venturi so 
that the exit diameter was not greater than twice 
the throat diameter. 

For the large Venturis the agreement between the 
observed drop sizes and those predicted by the 
empirical equation of Nukiyama and Tanasawa was 
surprisingly good. In all cases for the Venturi atomi¬ 
zers operating at high gas velocities, the value of 
q was 1. This indicated that the atomization was good 
and that a relatively uniform drop spectrum was ob¬ 
tained. Figure 3 shows the correlation of the data for 
the atomization of Diol 55 oil in a Venturi attached 
to a Dodge truck engine. Although sampling of the 
aerosol from airplane dispersal using the Venturi 
atomizer was somewhat more difficult than for 
ground dispersal, surprisingly good agreement with 
the predicted drop sizes was also obtained when the 
drop count data from stationary and waved slides 
were analyzed by means of equation (2). 

In this work several types of nozzles were used to 
introduce the liquid into the Venturi throat. These 
included low-velocity jets which allowed the liquid 
to run along the wall of the Venturi throat, coarse 
spray nozzles which gave an initial break-up to the 
liquid, and a concentric axial spray jet. No particular 
difference was found in the performance of the Ven- 


SECRET 



ATOMIZATION BY NOZZLES 


405 


turi atomizers using these types of injectors, although 
in practice it is better to use large-diameter liquid 
jets so as to avoid clogging and the disadvantage of 
high liquid pressure. As long as the liquid jet dis¬ 
charges into the throat the angle of flow does not 
seem to make much difference. 

29.2.5 Performance of Hydraulic Nozzles 

The few complete measurements on drop sizes from 
commercial hydraulic nozzles which have been re¬ 
ported by Houghton 8 have been analyzed by means 
of equation (2). The results are shown in Figure 5. 
The data follow straight lines which converge at a 
point when the exponent q is From the slope of the 
lines the characteristic drop diameter is found to 
vary from 430 to 1,100 microns. It is apparent there¬ 
fore that this type of atomizing nozzle gives a rela¬ 
tively inhomogeneous coarse spray. The only data on 
fine sprays which have been analyzed by this method 
are those by Lee 9 who measured the atomization of 
fuel oil through nozzles with very small orifices at 
pressures up to 5,700 psi. The variables studied were 
the effects of oil pressure, air density, nozzle design, 
orifice diameter, and the ratio of orifice diameter to 
orifice length. It was found that the degree and uni¬ 
formity of atomization were favored by increasing 
the oil pressure and decreasing the orifice diameter, 
and were insensitive to air density and ratio of orifice 
length to diameter. With a given oil pressure and 
orifice diameter, modifications of the details of the 
nozzle construction appeared to have no effect on 
the average diameter of the spray, but did affect the 
uniformity of drop distribution. Analysis of the data 
from a typical series of runs shows the surprisingly 
high value of 2 for the exponent q in equation (2). 
Values of D 0 varied from 122 microns at 450 psi to 70 
microns at 5,700 psi. 

An attempt was made to correlate these results 
with equation (1) so that the performance of hydraulic 
nozzles could be predicted. In order to do this, it was 
necessary to estimate the interfacial velocity of the 
liquid leaving the nozzle and the relative volume of 
air effective in the atomization. Because of the 
limited amount of data, the correlations are only 
roughly quantitative. They are based on two assump¬ 
tions: (1) the velocity at which the conical sheet of 
liquid formed by the nozzle leaves the orifice is given 
by Bernoulli’s equation, i.e., v = 3.72\/p/pi, where 
v is the velocity of the sheet in meters per second, P is 
the pressure on the nozzle in pounds per square inch 


gauge, and pi is the density of the liquid in grams per 
cubic centimeter. The value of v estimated in this 
manner may be used for the velocity term in equa¬ 
tion (1); (2) the effective value of Q a , when applied to 
interaction between stagnant air and a high-speed 
sheet of liquid issuing from a spray nozzle, is propor¬ 
tional to the surface of the sheet and the rate at which 
it is traveling. This is equivalent to saying that 
Qa = cdy/p/pi, where d is the orifice diameter in 
inches and c is a constant. If QU and Q a are expressed 
in gallons per minute, the value of c for Houghton’s 
data appears to be about 85 and for Lee’s data ap¬ 
proximately 6,600. The wide discrepancy in these 
two values indicates the greatly different atomizing 
efficiencies of different types of hydraulic nozzles, but 
correlation with the design of the nozzle has not been 
attempted. 

29.2.6 Attempt to Produce Screening 
Smokes by Mechanical Atomization 

Early in the war it was suggested that artificial 
fogs could be produced by atomizing solutions or 
suspensions of nonvolatile materials in water. Favor¬ 
able results were obtained in laboratory experiments 
using solutions of sodium chloride and other salts 
and suspensions of bentonite clay in water. 10 It was 
also proposed that the refuse from the beet sugar 
industry, known as Steffen’s waste , could be dispersed 
through pneumatic nozzles to set up artificial fogs for 
the protection of large industrial areas. 11, 12 Various 
types of spray nozzles were evaluated, first according 
to the persistence of the suspension formed by spray¬ 
ing solutions of various concentrations into a large 
room, and second, on the basis of the power consumed 
in spraying. 13,14 It was possible to produce artificial 
fogs roughly equivalent to natural fogs, with visibility 
noticeably impaired at a distance of 20 ft in the 
laboratory when the concentration of one gram of 
sodium chloride per cubic meter existed. With the 
best hydraulic nozzles, however, not more than 2% 
of the total solvent sprayed at nozzle pressures up to 
5,000 psi remained suspended in the air longer than 
five min. 15 While no measurements of the drop sizes 
were reported, this observation alone indicates a half- 
life of about one min, for which it can be shown that 
the MMD of the initial cloud was between 20 and 
30 microns. a 

a The half-life of a coarse aerosol cloud dispersed in a 
closed room is a convenient method of measuring the MMD. 
See Figure 2 in Chapter 35. 16 


SECRET 






406 


ATOMIZATION OF LIQUIDS 


The most promising nozzles from the standpoint 
of fog production were the pneumatic types furnished 
by the Spraying Systems Company and the Binks 
Manufacturing Company, and the oil burner Nozzle 
SA-0 of the National Airoil Burner Company. Fogs 
produced by these humidifying nozzles in the labora¬ 
tory had a half-life of from 6 to 15 min, corresponding 
to MMD’s of 5 to 10 microns. The best operation was 
obtained with the nozzles operating on compressed 
air at 50 to 60 psi at which the consumption of air 
was 165 cu ft per gal of liquid sprayed. 

The futility of trying to produce screening smokes 
by mechanical atomization should be apparent on the 
basis of the preceding discussion. It is evident that, 
even if aerosols with MMD’s of 5 microns could be 
produced by the use of large quantities of air for 
atomization, less than 10% of the mass of the liquid 
would be below 2 microns, according to the curves 
in Figure 2. Even if dilute solutions were used, only 
the droplets of this size would evaporate to leave 
residues sufficiently small to produce light scattering. 
The whole process, therefore, is extremely inefficient 
and there is no possibility that mechanical atomiza¬ 
tion of this type could be used for the formation of 
screening smokes. 

29.3 ATOMIZATION IN AIRPLANE 
SPRAYS 

Aircraft may be used for the dispersal of smoke, 
insecticides, and vesicant agents by the discharge of 
the liquid into the slipstream. The degree of atomiza¬ 
tion depends upon the speed of the plane and the 
properties of the liquid. For FS smoke, it is desirable 
to atomize the liquid as completely as possible so that 
vaporization of the sulfur trioxide will take place 
readily as the drop falls through the air. The desirable 
limits of atomization for insecticides have already 
been mentioned. The problem in the dispersal of 
vesicant agents, however, is to prevent fine atomiza¬ 
tion from taking place so that the drops will remain 
of sufficient size to produce casualties. This problem 
has been thoroughly studied, and numerous measure¬ 
ments have been made on the drop-dispersal spec¬ 
trum from thickened and unthickened liquids. It is 
beyond the scope of this chapter to discuss the de¬ 
tails of this work since it is treated elsewhere in this 
series. This report will be concerned only with the 
mechanism of break-up and methods of increasing 
the efficiency of atomization when desired. 17 

The problem of break-up of liquids in an aircraft 


spray has been studied mathematically by the 
British. 18 ’ 19 The study of ripples on a liquid surface 
over which a steady stream of air is flowing shows 
that ripples of certain wavelengths are hydrodynami- 
cally unstable and grow rapidly in amplitude. An 
approximate theory of break-up was developed by 
correlating the wavelengths of the most unstable 
ripple with the diameter of the most frequent drop in 
the drop spectrum. This led to the conclusion that 
the main drop will have dimensions proportional to 
H % v~ 4/h o- Vz where n is the viscosity of the liquid, a is 
the surface tension, and v is the velocity of the air in 
the slipstream. Elaboration of this theory predicted 
drop-size distributions which were in fair agreement 
with those found experimentally. The theory was 
tested for a range of values of /z and v. A change in v 
gave a variation in drop sizes which was in satis¬ 
factory agreement with the theory, but there was less 
satisfactory agreement with the results in which /x 
was varied. These deviations may have been due to 
the existence of a tough surface film with the rubber 
gels used for increasing the viscosity. This would in 
a sense give a very large increase in a, and may ac¬ 
count for the" results with the thickened agents. 

29.3.1 Design of a Venturi Air Scoop 
for Atomization 

Several attempts have been made, by using a Ven¬ 
turi scoop, to increase the velocity of the air at the 
point at which the liquid is discharged, above that of 
the speed of the aircraft. The designs of suitable de¬ 
vices have been empirical for the most part, but they 
have been successful when used on a small scale. The 
problem of designing a large Venturi air scoop arose 
in connection with dispersing insecticide solutions at 
a high flowrate from the B-25 medium bomber, which 
has only a moderate speed. Because of the quantity 
of liquid to be atomized and the belief that it was 
necessary to secure as small droplets as possible, the 
size of the air scoop became quite large. Approximate 
design calculations were based on mechanical energy 
balances making allowances for the acceleration of 
the injected liquid b and the friction of the scoop. 
Calculations were made for a speed of the aircraft of 
300 fps (205 mph) and throat velocities of 600 and 
900 fps. The effect of friction loss in the Venturi itself 

b In these calculations it was assumed, on the basis of ex¬ 
periments made on small Venturis, that the liquid injected 
into the throat of the Venturi was accelerated to 61% of the 
velocity of the air in the throat. 


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ATOMIZATION IN AIRPLANE SPRAYS 


407 



) 2 3 4 5 6 


RATIO ENTRANCE AREA TO THROAT AREA 

F igure 6. Dimensions of Venturi air scoop for spraying 

DDT solutions. Throat velocity = 600 fps; plane ve¬ 
locity = 300 fps. 

was taken at 0, 10, 20, and 30% of the difference in 
head between the upstream and throat section to 
show T the degree of care needed in the fabrication of 
the unit. 

The results are shown in Figures 6 and 7 which 
give the entrance areas of the Venturi, as square feet 
per gallon of liquid sprayed per second, for different 
ratios of upstream to throat areas, to produce the 
indicated throat velocities. Several conclusions may 
be drawn from these curves. 

1. If it is desired to have an air velocity of 600 fps 
at the throat, or twice the IAS, the friction in the 
Venturi scoop is not serious; that is, the upstream 
area is not increased excessively if the overall pres¬ 
sure loss due to friction is 30% rather than 10% of the 
energy loss between the entrance and the throat. 
However, if it is desired to have a velocity of 900 fps 
at the throat in order to produce better atomization, 
it is necessary to keep the pressure loss due to friction 
to an absolute minimum, otherwise the area of the 
entrance becomes excessively large. 

2. For an air velocity of 600 fps at the throat, an 
entrance area of 13 ^ to 234 sq ft per gal of liquid 
sprayed per sec is sufficient, provided the throat area 
is one-third to one-fourth as large. 

3. It appears that it is better to have the throat 


32 



z 

UJ 


0 ----- 

3 * 4 5 6 7 8 

RATIO- UPSTREAM AREA TO THROAT AREA 

Figure 7. Dimensions of Venturi air scoop for spraying 
DDT solutions. Throat velocity = 900 fps; plane ve¬ 
locity = 300 fps. 

area too small than too large, as the entrance area 
required to produce a given air velocity at the throat 
decreases rapidly as the ratio increases and then 
reaches a broad minimum before increasing. 

Table 2 shows the dimensions of the Venturis re¬ 
quired for dispersing DDT solutions from a plane, 
assuming that 0.5 lb of agent is required per acre 
and that the plane can lay a swath of 100 ft when 
traveling at a speed of 300 fps and a velocity of 600 
fps at the throat is necessary for the atomization. 

The Venturi scoop, shown in Figure 8, was con¬ 
structed of Duralumin sheet riveted to 234 x 234 
x 34 i n - Duralumin angles. The solution to be 
sprayed was fed into the Venturi throat through two 
streamline distributing tubes with orifices in the 
downstream edges. 20 The Venturi was installed be¬ 
neath the fuselage of a B-25 plane at Wright Field. 
Flight tests were made to observe the degree of 
atomization when a solution of DDT in fuel oil was 


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408 


ATOMIZATION OF LIQUIDS 


Table 2. Dimensions of Venturi air scoop required for atomizing DDT solutions to give 0.5 lb f>er acre. 
Throat velocit}', 600 fps; speed of plane, 300 fps; swath width, 100 ft. 


Solution 10% Friction 20% Friction 30% Friction 

Tons of strength No. of Entrance Throat Entrance Throat Entrance Throat 

solution % DDT by Venturis diameter diameter diameter diameter diameter diameter 

per sq mile weight on plane in. in. in. in. in. in. 


3.2 

5 

1 

15.9 

9.20 

17.5 

10.1 

19.8 

11.5 

3.2 

5 

4 

7.95 

4.60 

8.75 

5.05 

9.9 

5.73 

0.8 

20 

1 

7.95 

4.60 

8.75 

5.05 

9.9 

5.73 

0.8 

20 

4 

3.98 

2.30 

4.38 

2.53 

4.97 

2.87 


fed by gravity to the distributor. 21 Unfortunately, no 
opportunity was provided in these tests for determin¬ 
ing the air velocity at the throat. The atomization 
was so fine, however, that, in turbulent air, recovery 
of the solution on the ground was poor. Because of 
the complexity of the unit, it was decided that a 
simple discharge tube cut at the exit at an angle of 
45° on the trailing side was suitable for dispersing 
DDT solution. While the atomization with this was 
admittedly much poorer than with the Venturi air 
scoop, the results over open terrain where there was 
no screening of the large drop sizes by the foliage ap¬ 
peared to be reasonably good. 22 



Figure 8. Rectangular Venturi spray device for at¬ 
tachment under fuselage of B-25 bomber. 

Later, a small Venturi scoop for dispersing DDT 
solutions was developed empirically for the Navy 
Bureau of Aeronautics by the Curtiss-Wright Re¬ 
search Laboratory. 23 The final unit had a throat area 
of 3.2 sq in. and an entrance area of 50 sq in. Its 
capacity was 0.5 gal fuel oil per sec for a plane speed 
of 300 fps. This device produced droplets from 115 to 
185 microns diameter. 

A considerable study was also made at Edgewood 
Arsenal on the atomization of DDT solutions of low 


viscosity when discharged from modified M-10 spray 
tanks. Chemical and physical methods were de¬ 
veloped for assessing the spray. It is interesting to 
note that the characteristic diameter of the spray 
spectrum could be determined by the graphical 
method outlined above. 24 

29.4 ATOMIZATION IN EXPLOSIVE 
BURSTS 

There is no difficulty in obtaining a satisfactory 
degree of dispersion with liquid chargings of low 
viscosity in shells and bombs. With gunpowder 
bursters, a mean drop size of 50 microns may be 
obtained, and with high explosives the mean size is 
10 to 20 microns. 19 The Germans had several shells 
of the 10.5-cm and 15-cm size equipped with heavy 
bursters ranging from 0.5 lb to 4.5 lb RDX/wax and 
1.7 lb TNT for dispersing mustard gas and other 
vesicant agents as aerosols. They also had bombs and 
rockets for the same purpose. Some of these contained 
bursters with as much as 15.5 kg of TNT for a 
250-kg bomb. 

29.4.1 Mechanism of Atomization by 
Explosion 

A study of the mechanism of atomization by ex¬ 
plosion was made by Whytlaw-Gray by means of a 
spark photographic apparatus. 25 - 26 From these ex¬ 
periments, it appeared that the fragmentation occurs 
before or at the moment of opening of the container, 
while subsequent shattering by projection of the 
liquid through the air is of little importance. In short, 
fragmentation is caused by cavitation of the liquid. 
It is not clear whether the passage of the explosive 
shock wave through the fluid leaves the highly 
cavitated liquid which is then ejected before the 
cavities have time to collapse, or whether the liquid 
under compression in the bomb forms cavities on sud- 


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ATOMIZATION IN EXPLOSIVE BURSTS 


409 


den release of the pressure. In either case fragmenta¬ 
tion is due to cavitation which, in turn, is due to the 
expansion of the liquid, giving tensions in excess of the 
tensile strength of the liquid. It was found that cavi¬ 
tation in the liquid can be inhibited by outgassing or 
by applying external pressure. Furthermore, water, 
which has a low compressibility and a high tensile 
strength, is fragmented much less than organic 
liquids under comparable conditions. 

Davies 27 found no evidence supporting the theory 
that pre-ejection effects such as cavitation play an 
important part in the atomization of chargings from 
a base ejection bomb. His experiments were carried 
out with liquids of varying viscosity in a small model 
bomb, one end of which was closed by a copper 
diaphragm which was burst by compressed air at 
45 atm pressure. Flash photographs of the order of 
10 -5 sec exposure were taken at various distances 
from the explosive release. The break-up of the liquid 
Avas brought about primarily by the shattering of the 
liquid plug which was ejected more or less intact 
from the bomb. The plug appears to fissure along 
planes parallel to the axis into rods of liquid held 
together by sheets. In normal liquids, unless the 
viscosity is very high, the sheets disappear rapidly 
and the rods break up into comparatively fine drops. 
It was found that the mean velocity of ejection of the 
viscous filling from the experimental bomb when the 
bursting pressure was 32 atm Avas 5,000 cm per sec. 
This velocity is probably much loAver than that at¬ 
tained in the burst of a high-explosive bomb, but it is 
likely that the mechanism of break-up of liquid 
charging from base ejection shells is essentially the 
same as that found for the experimental bomb. 

If it is assumed that the folloAving factors determine 
the degree of atomization in an explosive burst, di¬ 
mensional considerations may be used to define the 
conditions which account for the results. 


p = pressure Avithin the bomb at instant of fracture; 
p = density of liquid; 
v = kinematic viscosity of liquid; 
r = surface tension of liquid; 
d = diameter of bomb; 
l = length of bomb; 

a = length characterizing the drop spectrum. 


Then, assuming the atmosphere to be constant and 
no secondary disturbances to be present, dimensional 
reasoning indicates 


/ 


('-■ 

\ra 


o 

pv 2 p a/ 


( 7 ) 


Increasing any of these factors favors fine dispersion. 
In the case of base ejection from shells in flight, other 
terms involving velocity of spin may be required. 

29.4.2 Drop Size Distribution from 
Explosive Bursts 

Data available from field tests at Suffield Experi¬ 
mental Station on the dispersion of liquid chargings 
from bursting Aveapons have been analyzed by means 
of equation (2) to determine whether the distribution 
of drop sizes from an explosive burst is similar to that 
from an atomizing nozzle. In this test, Avhich is re¬ 
ported in Suffield Technical Minutes No. 37, 28 two 
double-day bombs, containing 2.82 1 of aqueous solu¬ 
tion of 5% egg albumin and 1% rhodamine B dye, 
were functioned simultaneously on separate layouts. 
The bombs Avere fitted Avith bursters of 723 g 
CE/TNT 30/70, 170 g CE, No. 8 detonator. One of 
the bombs was charged Avith C0 2 at 500 lb pressure in 
order to determine if the dissolved gas Avould aid in 
the atomization. The bomb used Avas an experimental 
type made from the British 30-lb light case Mk 1 
bomb and was characterized by the heavy axial 
burster Avhich runs the full length of the case. 28 



(x-STAIN DIAMETER IN MICRONS ) 2 


Figure 9. Analysis of drop size data from explosive 
bursts. 

The data shown in Figure 9 Avere taken from sAving- 
ing impactor samples collected on the 50-yd line, and 
are corrected for the efficiency (e) of the impactor as 


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410 


ATOMIZATION OF LIQUIDS 


shown in the report. They are presented here simply 
to show that the method of analysis of drop size data 
from nozzles is also applicable to atomization by 
explosive bursts. For the particular charging and 
conditions of these tests, the value of the coefficient q 
is The characteristic diameter D 0 of the stains, 
which is approximately twice that of the drops, is 
197 microns for the bomb containing C0 2 and 200 


microns for the other bomb. Since, for this drop 
spectrum, the mass median diameter is 25% larger 
than D 0 , the values of MMD is about 125 microns. 
The atomization of the charging was no better from 
the bomb containing C0 2 under pressure than from 
the bomb without C0 2 . It was concluded that less 
than 1% of the material at 50 yd is present as drop¬ 
lets smaller than 20 microns diameter. 


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\ 


Chapter 30 

THERMAL GENERATOR MUNITIONS 


By E. W. 

30.1 INTRODUCTION 

T hermal generators are devices which use a 
self-contained fuel as a source of heat to vaporize 
a substance with a relatively high boiling point. Sev¬ 
eral munitions of this type were available at the be¬ 
ginning of World War II or shortly thereafter. One 
example is the colored smoke grenade which uses an 
intimate mixture of a volatile organic dye and a fuel 
which carries its own oxygen supply. The 9-lb DM 
candle was another example. The agent and fuel in 
this candle were in separate compartments and the 
hot gases passed over the liquid agent and carried 
away its vapors. 

The thermal generators described in this chapter 
are an improved type and provide for highly efficient 
and short-time contact between the hot fuel gases and 
the agent. The improved design has increased the 
agent capacity and permitted the use of less volatile 
and also less thermally stable agents in the thermal 
generators. 

The improved thermal generator has been tested 
with a number of agents for setting up screening and 
toxic smokes as well as highly concentrated vapors. 
The materials which have been vaporized successfully 
are paraffin wax, oleum, sulfur, CN, DM, DC, 
tertiary butyl stearate, methyl salicylate, triethyl- 
phosphate, Glaurin, Diol and other high-boiling 
hydrocarbon oils, solutions of DDT in oil, and several 
varieties of mustard gas, including extracted Levin¬ 
stein, distilled mustard, and mustard from the 
thiodiglycol process. In every case an excellent aero¬ 
sol or concentrated vapor cloud was produced with¬ 
out undue decomposition of the agent. The design 
has been applied to pots, bombs, and larger genera¬ 
tors. 

30.2 FUNDAMENTAL PRINCIPLES 

Every thermal generator design must meet certain 
general requirements in addition to the special re¬ 
quirements of each individual application. These 
general requirements are discussed below. 

Thermal Stability of the Agent. The agent to be 
vaporized will begin to decompose when it is heated 
above a temperature range which is characteristic of 
each agent. The amount of decomposition depends on 


Comings 

the temperature and the time the agent is held at this 
temperature. Relatively high temperatures in this 
range will result in little decomposition if the time of 
exposure is very short. The capacity of the generator 
will be greater if the agent is heated to quite high 
temperatures for the shortest possible time rather 
than to lower temperatures for a longer time. 

Heat Requirements. The heat from the fuel is 
needed for several purposes. 

1. It raises the temperature of the agent to the 
vaporizing temperature range. This is the range in 
which the agent has an appreciable vapor pressure. 
It may be well below the boiling point. 

2. It supplies the latent heat of evaporation of the 
agent. 

3. It raises the temperature of the agent vapor to 
the final temperature of the hot emerging gases. 

4. If the agent is initially solid it supplies the 
latent heat to melt it. 

5. It heats the metal components of the generator 
and supplies heat lost through the walls of the 
generator. 

6. The fuel gases themselves leave the unit at an 
elevated temperature, and the fuel must supply the 
heat in these exit gases. When these gases leave the 
unit, saturated with agent vapor, this heat require¬ 
ment is at a minimum for a given fuel burning tem¬ 
perature. When the gases carry out less vapor than 
that needed to saturate them, the exit gas tempera¬ 
ture will be higher and this heat requirement greater. 
A higher fuel burning temperature will also result in 
a higher exit gas temperature, but if this gas is 
saturated with vapor the heat requirement will be 
less when compared on the basis of a unit weight of 
agent evaporated. This is so because less fuel gas is 
needed to carry off a unit weight of agent vapor. The 
higher the fuel burning temperature and the more 
nearly saturated the exit fuel gases, the lower will be 
the fuel requirements. 

7. In some cases inert materials such as carbonates 
have been added to the fuel to reduce the fuel burning 
temperature in order to avoid decomposition of the 
agent. The fuel must then heat these materials and 
in some cases supply additional heat to decompose or 
vaporize them. These additions increase the fuel re¬ 
quirements by absorbing heat and by increasing the 


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411 


412 


THERMAL GENERATOR MUNITIONS 


heat requirements of exit fuel gases due to the lower 
fuel burning temperatures. These additions to the 
fuel have been avoided where possible in the im¬ 
proved thermal generator designs. Thermal decom¬ 
position of the agent has been avoided by reducing 
the time that the agent is exposed to the higher 
temperatures. 

Heat Transfer. The design must provide for the 
transfer of the heat supplied by the fuel to the agent. 
Merely making the heat available is not enough. The 
design must insure that it reaches the agent at a 
fairly uniform rate. Direct radiation from the fuel to 
the agent compartment may provide for part of this 
transfer. It is preferable to transfer the heat through 
the liquid surface in direct contact with the hot gas. 
The transfer will be more rapid if a large area of 
liquid surface is exposed and also if the gas velocity 
over this surface is high. A large amount of experi¬ 
mental and theoretical evidence indicates that these 
conditions are best provided by a spray of small 
liquid drops in a high-velocity gas stream. 

Vapor Transfer. The agent vapor is transferred 
from the liquid surface to the gas stream. The condi¬ 
tions which permit this transfer to take place readily 
are the same as those which promote the transfer of 
heat from the gas to the liquid, namely, a large liquid 
surface area and a high gas velocity over this surface. 
Thus, a spray of small liquid drops in a high-velocity 
gas stream also provides the best conditions for the 
transfer of vapor. 

Experiments on the vaporization of high boiling 
organic liquids from flat surfaces into a stream of hot 
gas 58154 indicated that the same principles apply as 
when evaporating lower boiling liquids. An excessive 
extent of surface is needed to obtain practical evap¬ 
oration rates by this means. Evaporation from the 
surface of packing material, such as used in a com¬ 
mercial absorption tower, also requires more space 
than can be allotted in a compact munition. 

Carrier Gas. The agent vapor is carried out of the 
thermal generator by the gases from the fuel. The 
supply of a large volume of carrier gas is an important 
function of the fuel. The amount of vapor which the 
gas will carry is limited to the vapor which will 
saturate the gas at its exit temperature. A large 
volume of fuel gas will permit operation of the 
generator at a lower temperature and protect the 
agent from decomposition. Thus, a fuel that supplies 
heat but does not give a large volume of gas is not a 
satisfactory fuel for thermal generators. The fuels 
selected for the improved thermal generators provide 


a maximum amount of heat and carrier gas and a 
minimum of solid residue and slag. 

30.3 PERSISTENCE OF THE AEROSOL 

The agent vapor mixed with the gases from the fuel 
issues from the thermal generator in jets. These jets 
entrain the surrounding air and are chilled rapidly to 
a temperature approaching that of the atmosphere. 
The vapor condenses during this cooling and forms 
an aerosol cloud. 

When a liquid aerosol cloud is formed by condensa¬ 
tion of vapor or by mechanical disintegration of 
liquid, the cloud is carried downwind and diluted by 
the turbulence of the air and by precipitation of the 
large droplets onto vertical and horizontal surfaces. 
Evaporation of the droplets commences as soon as the 
partial pressure of the vapor in the cloud falls below 
the saturation value. The rate of evaporation de¬ 
pends primarily on the size of the droplets and on the 
difference between the saturation vapor pressure and 
the actual partial pressure of the substance in the air. 
Only when the concentration of droplets is high and 
their diameter is small will the rate of evaporation be 
sufficient to maintain the air in the cloud essentially 
saturated. 

With highly nonvolatile agents such as fog oil, very 
little vapor is needed to saturate the air and the 
cloud will persist for long distances before it is diluted 
sufficiently to evaporate all the aerosol. The oil smoke 
generators depend on this nonvolatile characteristic 
of fog oil for the persistence of the smoke screen. The 
factors influencing the persistence of screening smoke 
have been discussed in connection with the large oil 
smoke generators. 1 ’ 2 With more volatile agents, the 
aerosol cloud will be less persistent. 

The cloud of mustard gas aerosol from a thermal 
generator is very similar to a cloud of nonpersistent 
gas. The degree of saturation of the cloud has been 
predicted from differential equations 3 written for the 
rate of evaporation of an aerosol cloud based on the 
British equations for atmospheric diffusion and the 
laws of vaporization of spherical droplets. Both con¬ 
tinuous point and infinite line sources were con¬ 
sidered. Step-wise integration of these equations 
showed that the degree of saturation of mustard gas 
aerosol clouds depends very much upon the diameter 
of the drops, the source strength, and the atmospheric 
conditions. An approximate solution to determine 
the maximum initial drop diameter that will main¬ 
tain essentially saturated conditions throughout the 


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PERSISTENCE OF THE AEROSOL 


413 



DISTANCE FROM SOURCE IN YARDS 


Figure 1. The effect of distance from a point source on 
the degree of saturation of a mustard gas aerosol cloud 
for particles of various initial sizes. 

life of the cloud has shown that the droplets in aero¬ 
sols generated by mechanical spray nozzles or by ex¬ 
plosive bursts are much too large. Only thermally 
generated mustard gas aerosols may be expected to 
be saturated. Nonvolatile impurities soluble in the 
agent reduce the rate of vaporization of the agent and 
leave a persistent cloud of droplets with a residual 
drop diameter of the same order of magnitude as the 
original droplet. 

Figures 1 and 2 show some typical integral curves 
for point and line sources for several different atmos¬ 
pheric conditions, source strengths, and initial drop¬ 
let sizes. The curves on the right show the distance 
from the generator at which the droplets in a 
homogeneous aerosol of pure mustard gas would 
disappear. They represent also the total concentra¬ 
tion of mustard gas as vapor plus aerosol, at any 
distance from the source. Thus, they do not end at a 
fraction of saturation of unity, but could be extended 
to the source position through the region in which 
the aerosol would exist, regardless of the size of the 
droplets. 

30.3.1 Effect of Temperature on Vapor 
Concentration in the Cloud 

The shape and location of the integral curves repre¬ 
senting the degree of saturation in the cloud are af¬ 
fected little by changes in air temperature since the 
diffusivity of the agent vapor changes only slightly 



O 10 20 30 40 50 60 70 80 


DISTANCE FROM SOURCE IN YARDS 

Figure 2. The effect of distance from a line source on 
the degree of saturation of a mustard gas aerosol cloud 
for particles of various initial sizes. 

with changes in temperature. This means that a 
homogeneous aerosol cloud from a given source, and 
under fixed meteorological conditions, should have 
the same percentage saturation of vapor at all air 
temperatures. The actual concentration of vapor will 
increase with temperature in proportion to the 
volatility of the agent. The aerosol cloud will persist 
longer at lower temperatures. After all the droplets 
evaporate and the aerosol cloud has disappeared, the 
vapor concentration becomes independent of temper¬ 
ature and depends solely on the strength of the source 
and on the meteorological conditions. 

30.3.2 Maximum Drop Size to Maintain 
the Aerosol Cloud Essentially Saturated 

It is of interest to know the maximum initial size 
of drops in a homogeneous aerosol cloud that will 
maintain a saturated condition throughout the life of 
the cloud. If only the vapor is effective as a casualty 
agent, it is evident that the larger droplets would be 
undesirable because the concentration and dosage 
during the passage of the cloud from a given source 
would be decreased by the slower rate of evapora¬ 
tion. 

Only infinitesimal droplets can keep the cloud 
completely saturated at all distances up to that at 
which the cloud disappears. Small droplets maintain 
high degrees of saturation. Figures 3 and 4 show the 
largest original diameter of uniform drops that will 
keep the cloud better than 90% saturated throughout 
its life for several atmospheric conditions. The values 


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414 


THERMAL GENERATOR MUNITIONS 



SOURCE STRENGTH IN LBS PER MIN 


Figure 3. The maximum initial drop diameter which 
will maintain essentially saturated conditions in a mus¬ 
tard gas cloud from a point source. 

of wind velocity chosen for the high “R” values in the 
figures are about the maximum to be expected. 18 
Consequently, these charts show the upper limit of 
drop sizes that may be used for essentially saturated 
clouds. Aerosols containing large drops could be 
saturated only under conditions of low atmospheric 
turbulence. Under such conditions, however, these 
drops would settle out rapidly. Since the drop sizes in 
mists from explosive bursts and from all commercial 
spray nozzles are considerably larger than 10 mi¬ 
crons, 19 it is evident that mustard gas aerosols from 
such sources cannot be saturated. The only method 
known at present for the field generation of aerosols 
with droplets less than 1 micron in diameter is the 
thermal generator. 8 It appears that all mustard gas 
clouds from such munitions will remain essentially 
saturated under all atmospheric conditions as long 
as the aerosol of mustard gas droplets persists. 

30.3.3 Effect of Nonvolatile Impurities 

If the aerosol droplets contain a nonvolatile residue, 
the aerosol cloud will not disappear by evaporation. 
The appearance of such a cloud produced from Levin¬ 



0.1 0.2 0.3 0.4 0.6 0.8 1.0 


SOURCE STRENGTH IN LB PER MIN PER YD 

Figure 4. The maximum initial drop diameter which 
will maintain essentially saturated conditions in a mus¬ 
tard gas cloud from a line source. 

stein mustard is apt to be misleading. The drop 
diameter then decreases to such a small extent, when 
only the nonvesicating impurity is left in the drop, 
that it may still form a screening smoke. Even ma¬ 
terials of high purity, when dispersed as aerosols, may 
leave visible clouds after the evaporation is essen¬ 
tially complete. Figure 5 shows the residual diameter 
of drops containing various percentages (by volume) 
of nonvolatile impurities. 

The rate of evaporation of a droplet is decreased by 
the presence of a soluble impurity due to the lowering 
of the saturation vapor pressure. If the vapor pres¬ 
sure follows Raoult’s law, as in the case of Levinstein 
mustard, 4 the differential equations can be modified 
to allow for this impurity. These equations 3 can be 
integrated in a step-wise manner. Such an integration 
has been performed for a certain field test at Edge- 
wood Arsenal on a mustard thermal generator. The 
candle was charged with Levinstein mustard. The 
calculated axial concentration of mustard gas vapor 
in the cloud is shown in Figure 6 in comparison with 
the curve calculated for a pure mustard charging. 
The initial uniform drop diameter used in the calcu¬ 
lations was 0.6 micron, which is the average size 


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CALCULATION OF EVAPORATION OF AEROSOL CLOUD 


415 



0.1 0.2 0.4 0.7 1.0 2.0 4.0 7.0 10 20 40 70 100 

ORIGINAL PERCENT BY VOLUME OF IMPURITY 


Figure 5. The effect of small amounts of nonvolatile 
impurity on the residual drop diameter. 



Figure 6. Comparison of calculated concentrations of 
mustard gas vapor in clouds from thermal generator. 
Test No. 1, Edgewood Arsenal, February 1943. 


measured for simulant clouds set up in the same way. 
It is evident from the curves that the vapor concen¬ 
tration in the Levinstein cloud is considerably less 
than that of a cloud from pure mustard gas. Further¬ 
more, whereas the cloud of pure mustard gas should 
have visibly disappeared at about 30 yd, the evapora¬ 
tion of the Levinstein droplets was still continuing at 
100 yd. The calculated residual diameter of the drop¬ 
lets is shown in the upper curve in Figure 6. 

30.4 CALCULATION OF EVAPORATION 
OF AEROSOL CLOUD 

30.4.1 Derivation of Equations 

For aerosols of small particles, the effect of gravity 
is negligible. The cloud is diluted in the same way 
as a gas cloud and the same laws of turbulent dif¬ 
fusion are applicable. The theory of atmospheric 
diffusion derived by the British workers requires a 
knowledge of the wind velocity, the vertical gradient 
of wind velocity, and the components of gustiness 
near the ground. 16 The axial, or peak, concentration 
of gas near the ground is given by the equations 

c = ^ for a continuous point source; (1) 

Aux m 

c = ——— for a continuous infinite line source. (2) 
Bux m / 2 

For a gas cloud, Q is the source strength in grams per 
second, or grams per second per centimeter, respec¬ 
tively, u is the wind velocity near the ground, and 
x is the distance from the source, both in cgs units. 
The index m is determined from the velocity gradient 
and is conveniently expressed in terms of the “R” 


value, which is the ratio of the wind velocity at 2 m 
to that at 1 m, 


log 2 

The scale factors of diffusion, A and B, are actually 
complicated functions of the wind gradient, wind 
velocity and gustiness. Various simplifying approxi¬ 
mations have been made in the use of these equations, 
such as for the concentration range slide rule 47 for 
field use, where A and B are assumed to be unique 
functions of the wind gradient and velocity. For the 
solution of the equations derived in the following 
text, a step-by-step integration is required, and even 
the above simplification is not sufficient to avoid labor¬ 
ious computations. Consequently, for this calculation 
A and B have been considered constants for all values 
of “R” and wind velocities. Actually, proofing of the 
equation against the Service slide rule has shown that 
the concentrations calculated will not deviate by more 
than 30% from the values based on the closer ap¬ 
proximation, even for a large range of wind gradient 
and velocity. Since it is desired here to obtain only 
the approximate degree of saturation of the cloud and 
the effect of the droplet size, this simplification is 
warranted. Accordingly, the values of the constants 
were calculated from the slide rule for neutral con¬ 
ditions, “R” = 1.15, and for u = 5 mph (223 cm 
per sec), whence A = 0.34 (for axial concentrations) 
and B = 0.31. 

For an aerosol cloud, N will be considered as the 
source strength expressed as number of particles per 
second (or number per second per centimeter fora line 
source), and c is the number of particles per cubic 


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416 


THERMAL GENERATOR MUNITIONS 


centimeter at any point. The volume of air associated 
with one particle of the aerosol for a point source, 
therefore, is 


1 Aux m 



(4) 


Applying the gas law, the number of moles of vapor 
already evaporated from the droplet in this volume 
of air is 


p Aux m 
RT ' ~N~ 


(5) 


The rate of vaporization of small droplets in moving 
air has been investigated by Frossling, 17 who meas¬ 
ured the evaporation of aniline, nitrobenzene, naph¬ 
thalene, and water. All his data were correlated by 
means of the dimensionless equation 

Nu' = 2(1 + 0.276 Re Vi Sc A ). (6) 


Here the dimensionless groups are 


Nu' = 


RTkgd 

~~k~ 


Re = 


dVpg 


Sc = 


where d = diameter of the drop; 

k — molecular diffusivity of the vapor in air; 
p g = density of gas; 

v = interfacial velocity of the drop in the air; 
p = viscosity of air; 
k g = molar mass transfer coefficient. 

When Nu' = 2, the rate of vaporization is 




, 27i -kd 

P) = ~RT 


V) 


(7) 


which is identical with the equation of Fuchs for the 
evaporation of a spherical drop in still air, where 
p s = saturation vapor pressure of the liquid at the 
drop surface; 

p = actual partial pressure of the vapor in the 
ambient air. 

The value of the Schmidt group, Sc, for mustard 
gas in air is 2.25. Since the inertial effects of the at¬ 
mospheric eddies on the droplets of an aerosol are 
negligible, any interfacial velocity of air past the 
drop must be essentially that due to gravity fall. 
From Stokes’ law, a 50-micron mustard gas drop falls 
at the rate of 9.5 cm per sec and Re = 0.393. For a 
20-micron drop, the fall is 1.5 cm per sec and Re = 
0.025. Thus, for any mustard gas aerosol cloud con¬ 
taining drops which do not readily settle out, Nu' is 
essentially equal to 2, and the Fuchs equation for 
evaporation in still air is satisfactory. 


= (d 3 - 


The diameter of the drop at any time is related to 
the original diameter D at the source by 

( 8) 

Substituting equations (5) and (8) in equation (7), and 
letting / represent the fraction of saturation, p/p 8 , 
gives the equation for a cloud from a point source, 

d(fx m ) _ 2irkN /^ 3 _ 6 Au p s M 

' \ ~^N ’ RTf^i ’ X 


dt 


*) v, a- 


/) 


Equation (9) may be simplified by noting that 

v —=w 

RT 


(9) 


( 10 ) 


which is the saturation concentration of the vapor, 
and 

-7T- = Q> ( 11 ) 


where Q is the liquid volume rate of generation of the 
aerosol, which is here assumed to be perfectly 
homogeneous, and also that 

udt = dx . 

Then 

1/3 (i -/) 


4f_ 12 kQ( 1 AuW, y 
dx Au 2 D 2 \ Qpi ) 


mf 

x 


( 12 ) 


This represents the equation for the degree of satura¬ 
tion in an aerosol cloud at any distance from the point 
source up to the disappearance of the droplets. It is 
convenient to write the equation in the form 


dx x m 


X 


where 


K, = 


12 kQ 


and Ko = 


AuWs 


Au 2 D 2 Qpi 

The analogous equation for a line source is 




dx 


where 


K[ = 


12 kG 
Bu 2 D 2 


and Kn = 


BuWs 

Qpi 


(13) 


(14) 


(15) 


(16) 


30.4.2 Integration of Equations 

No general solutions of equations (13) and (15) 
have been obtained. Consequently, the integration 
has been performed by a step-wise method. The par¬ 
ticular method used was as follows. 


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CALCULATION OF EVAPORATION OF AEROSOL CLOUD 


417 


As a starting point, it was assumed that/ = 1 when 
x = 100 cm. This means essentially that the cloud 
is saturated very near the source, although a few 
trials with / = 0 at x = 100 showed that the condi¬ 
tions at the start are not critical as the curves 
originating from these extremes converged rapidly. 
Values of Ki and K 2 (or K{ and K 2 ) were chosen 
for the conditions of the atmosphere, and source 
strength, and the particle size. Then df/dx at Xi was 
found. The increment Axi corresponding to A/i was 
then found from 

Ax - A/l 
1 (df/dx) x 

A new point on the curve was then determined from 
— fi + A/i 
x 2 = Xi + Axi 


and ( df/dx) 2 were found by substitution. The process 
was repeated indefinitely to give the integrated curve. 
If the chosen values of A/ were sufficiently small, a 
smooth curve resulted. Too large values of the incre¬ 
ment would reverse the direction of the curve. 

The integral curves were tested from the relation¬ 
ship 


£ B (1 - f)dx 


3 

2K t K 2 ' 


(17) 


As shown later, this integral is the area above the 
curve of / vs x up to saturation. 

Figures 1 and 2 show some typical integral curves 
for point and line sources for several different atmos¬ 
pheric conditions, source strengths, and particle 
sizes. It is evident that, for the conditions chosen, the 
clouds are saturated only very near the source unless 
the drop size is below 1 micron. Drops as large as 24 
or 48 microns evaporate slowly and cause the cloud 
to persist for considerable distances even for the 
small source strengths chosen. For higher “R” values 
or greater source strengths, the integral curves are 
shifted upward toward the saturation line and the 
boundary curve is displaced farther to the right. 


30.4.3 The Boundary Curves 

The curves on the right in Figures 1 and 2 show the 
distance from the generator at which the particles 
from a homogeneous aerosol of pure mustard gas 
would disappear. They represent also the total con¬ 
centration of mustard gas, as vapor plus aerosol, at 
any point in the cloud. As such, they do not end at a 
fraction of saturation of unity but could be extended 


to the source position, through the region in which 
the aerosol cloud would exist regardless of the size 
of the droplets. 

The boundary curves, representing as they do the 
concentration of matter in a cloud, could be calcu¬ 
lated by means of the concentration range slide rule. 
As derived from equations (13) and (15), they were 
obtained by equating the terms (1 — K 2 fx m ) l/3 and 
(1 — K 2 fx m/2 ) 1/3 to zero and solving for/ as a function 
of x. Thus they serve as a check on the accuracy of 
the simplifying assumptions described above. From 
equations (8) and (9), it may be seen that these terms 
represent the fraction of the original particle diame¬ 
ter of the droplet existing at any point. 

The boundary curves can be represented by straight 
lines on log-log paper. The position of the lines de¬ 
pends on the value of the meteorological constant m 
(or “R”), the saturation concentration W s , and the 
parameter u/Q. For constant source strength and 
meteorological conditions (i.e., turbulence and wind 
velocity) the logarithmic lines for different tempera¬ 
tures are parallel. The actual concentration, equal to 
fW s , along the boundary curve, however, is essen¬ 
tially independent of the temperature of the air. 

30.4.4 Maximum Drop Size to Maintain 

Essentially Saturated Clouds 

The integral curves for small droplets, lying near 
the saturation ordinate, are practically linear up to 
the boundary curve. 

Equation (13) may be written in the form 

- d(l - K 2 fx"'?' 1 = (1 - f)dx ■ (18) 

The left side of this equation represents the decrease 
of the fraction of the original surface of a drop in the 
distance dx. In the distance from x = 0 to x = xb 
where the drop disappears, this quantity is equal to 
unity, or 

f d( 1 - K 2 fx") !/l = 1 . (19) 

Jx = 0 

Therefore 

C x = x r 3 

L o (20) 

The value of this integral depends upon the path of 
(1 — /) vs x. Let us assume that the cloud is essen¬ 
tially saturated throughout its life, provided that it 
is at least 90% saturated when it disappears, that is, 


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418 


THERMAL GENERATOR MUNITIONS 


/ = 0.9 when x = x B . Then, from the area under 
the curve, 


C X ~*B 0.1 

(1 - f)dx ^ — x B ■ 

J x = 0 l 

(21) 

But xb is determined by 


(1 - K i f B x’S)' h = 0 . 

(22) 

Substituting from equation (20), 


^ _30(0.9) 1/m 
^ 1 — K 2 m ~ 

(23) 


Again substituting the values of Ki and K 2 from 
equation (14) 


I) 2 ~ 


12k 


30(0.9A) 1/m \ Pl 




(m — 1 ) jm s\l/m, 

„ f (m + 1 )/m ’ (^4) 


which gives the maximum original drop diameter 
that will keep the cloud from a point source better 
than 90% saturated throughout its life. 

A similar treatment for a line source gives 

12 k Q 2/m 

m — 30(0.9B) 2/m \pi/ u ( ”* +2,/ “ ( > 


It may be noted that the value of D m is not so sensi¬ 
tive to decreasing the value of fn as it is to increasing 
it. That is, the maximum drop diameter could be ap¬ 
proximately 40% greater if it were assumed that the 
cloud is only 80% saturated at the point of disap¬ 
pearance. On the other hand, the permissible size 
would decrease considerably if it were desired to keep 
the cloud 99% saturated, or better. 


30.4.5 Effect of Nonvolatile Impurities 


When a nonvolatile impurity is present and if the 
vapor pressure follows Raoult’s law, as it does in the 
case of Levinstein mustard, 4 equation (13) becomes 


£- 7 - a ~ 



The mole fraction of the solvent Na may be ex¬ 
pressed in terms of z, the original concentration of 
the impurity, and the quantity K 2 fx m , so that equa¬ 
tion (26) for a point source becomes 




(• 


(1 - z) - 

- z + ^?) - 

PA / 



mf 

x 


(27) 


The corresponding equation for a line source is 


df = 

dx x m/2 


(1 


K‘ 2 fx m,2 )' / ‘ . 


(1 - z) - Kjfxjii 

1 - z + —- K'Jx m/2 


mf 
2x ’ 


(28) 


These equations can be integrated in a step-wise 
manner similar to that described for equations (13) 
and (15). 

The approximations made in these mathematical 
derivations leave much to be desired before the actual 
concentration of vapor in a mustard gas aerosol cloud 
can be estimated. Such clouds, of course, would not 
be uniform in particle size, and this would add a 
complication not considered here. Furthermore, the 
deposition of droplets greater than 5 microns in 
diameter on horizontal and vertical surfaces probably 
proceeds at a finite rate comparable with the rate of 
vaporization, so that the calculated concentration 
for aerosols of large droplets is too great. Neverthe¬ 
less, it appears fairly certain that aerosol clouds made 
up of droplets of pure mustard gas less than 1 micron 
in diameter would always be saturated as long as the 
cloud persists. On the other hand, fine sprays and 
mists from explosive bursts 20 are by no means satu¬ 
rated, and atomizing nozzles would be of little use in 
a munition designed to generate high concentrations 
of vapor. 


Nomenclature for Section 30.4 

A Gustiness factor for point source = 0.34. 

B Gustiness factor for line source = 0.31. 
c Axial concentration in gas or aerosol cloud. 
d Drop diameter at distance x. 

D Initial drop diameter in a homogeneous cloud 
at the source. 

D m Maximum initial drop diameter to maintain 
the cloud essentially saturated. 

/ Fraction of saturation, p/p s . 

Jb Fraction of saturation at the point of disap¬ 
pearance of the aerosol cloud. 
k Molecular diffusivity. 
k g Molar mass transfer coefficient. 

K h K 2 , K'i, K 2 Parameters. 
m Meteorological constant. 

M Molecular weight. 

M Viscosity of gas (air). 
n Moles of agent in the air as a vapor. 


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MUSTARD GAS FROM THERMAL GENERATORS 


419 


WATERPROOF MEMBRANE 



8.282 


•ELECTRIC SQUIB 

Figure 8. The F7A thermal generator. 



Figure 7. The F7A thermal generator pot. 

N Source strength of aerosol cloud expressed as 
number of droplets/time for a point source; or 
number/(time) (length) for a line source. 

Na Mole fraction of solvent in a binary liquid 
agent. 

Nu Dimensionless group = RTk g d/k. 
p Partial pressure of vapor in air. 
p s Saturation vapor pressure of pure agent. 

Q Source strength expressed as volume/time for 
a point source; or volume./(time) (length) for 
a line source. 
p g Density of gas (air). 

Pi Density of liquid agent. 
pa , ps Molar liquid densities. 

“R” Ratio of wind velocity at 2 m to that at 1 m. 

R Gas constant. 

Re Dimensionless group, Reynolds’ number, 

dVPg/p. 

S Surface area of drop. 

Sc Dimensionless group, p/pgk. 

T Absolute temperature, K. 


t Time. 

u Wind velocity. 

v Interfacial velocity of drop in air. 

V Volume of air associated with a drop. 

W s Saturation concentration of vapor. 

x Distance downwind. 

Xb Distance from source to point of disappear¬ 
ance of cloud. 

z Initial volume fraction of impurity in binary 
liquid mixture. 

Note: The units used in the derivation of the 
British diffusion equation are uniformly in the cgs 
system. Because of the exponential factors, conver¬ 
sion of the equations to the English system cannot be 
made conveniently. The integrations were therefore 
performed in the cgs system and the concentrations 
and distances, etc., then expressed in the units com¬ 
monly in use. 

30.5 MUSTARD GAS FROM THERMAL 
GENERATORS 

30.5.1 Thermal Generator Pots 

The improved thermal generator is well illustrated 
by the experimental pot 6 known as the F-7A shown 
in Figures 7 and 8. This pot is a practical munition 
for hand carrying in field use. It has been produced 
by production methods in a small quantity of ap¬ 
proximately 2,000 units. The pot has not been recom- 


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420 


THERMAL GENERATOR MUNITIONS 


mended for adoption as a standard munition because 
of the general conclusion that gas cloud attacks from 
hand-placed generators are no longer practical in 
modern warfare. The small quantity of pots was 
produced for use in testing the tactical advantages of 
mustard vapor clouds from thermal generators. 5 The 
application of this general design to aerial bombs is 
practical in modern warfare and such a bomb will be 
described later. 

Description of the F-7A Thermal Generator 
Mustard Pot 

This pot consists of a fuel block and agent in 
separate compartments. The liquid agent is fed into 
the hot gas stream from the fuel block in a high- 
velocity Venturi vaporizer. The high-velocity gases 
atomize the liquid agent, and the atomized liquid 
evaporates rapidly into the high-velocity hot gases. 
The feed rate is so adjusted that all but a small frac¬ 
tion of the atomized agent is evaporated in one pass 
through the vaporizer. This small fraction which is 
not vaporized is emitted with the vapor-gas mixture 
as a fine spray. 

The pot is 7 in. in diameter and approximately 
8J4 in. high. It is made up of two major assemblies 
which are crimped together. These are (1) the agent 
compartment assembly, and (2) the fuel container 
assembly. With the exception of the machined parts, 
the munition is fabricated throughout from 20 gauge 
sheet steel of deep drawing quality. 

The fuel mixture is pressed into the fuel container 
under a dead load of about 1,000 psi. The composi¬ 
tion of this mixture is as follows. 


Slow base mixture, 1,000 g 

NH4NO3 

80.7% 


Charcoal 

13.1% 


NH4CI 

3.2% 


Linseed oil 

3.0% 

Fast base mixture, 400 g 

NH4NO3 

83.5% 

Charcoal 

13.5% 


Linseed oil 

3.0% 

Starter mixture, 20 g 

KNO3 

53.0% 


Silicon 

39.2% 


Charcoal 

5.8% 


Linseed oil 

2.0% 

The surface of the block is sprayed with 

a pyroxylin 


lacquer for protection against moisture. The fuel is 
ignited by a one-delay electric squib held in place on 
the surface of the block by a metal clip. The tip of the 
electric squib is coated with a 34% aluminum/66% 
potassium perchlorate mixture to insure ignition of 
the fuel block. The details of making these fuel 
blocks are described in Chapter 31. 


The agent container assembly is made up of five 
parts, as follows: (1) agent container top, (2) agent 
container bottom, (3) Venturi tube, (4) Venturi 
throat, and (5) filler cap sleeve. These are joined in 
one operation by copper-brazing all joints simultane¬ 
ously in a special furnace. Prior to crimping this as¬ 
sembly to the fuel can, the feed holes (No. 30 tap 
drill size — 0.1285 in. diameter) and the vent hole 
located near the top of the Venturi are soldered 
closed with Wood’s metal alloy. A pressure test for 
leaks is specified with air at 35 psi. The lugs for the 
carrying handle are then soldered to the outside of 
the container. The diffuser cap is crimped onto the 
flanged end of the Venturi tube which projects above 
the top of the unit. A waterproof membrane of 
0.010-in. thick aluminum foil placed over the end 
of the Venturi tube prevents moisture from reaching 
the fuel. 

The unit, charged with distilled mustard gas, 
ready for functioning, weighs approximately 13 lb. 
This weight is distributed as follows: distilled mus¬ 
tard gas, 6.5 lb; fuel, 3.12 lb; metal components, 
3.38 lb. 

30.5.2 Operation of Unit 

The F-7A thermal generator charged with 6.5 lb 
distilled mustard gas functions from 33^ to 4 min, 
emitting a dense mustard gas aerosol which evapo¬ 
rates downwind of the generator to form mustard gas 
vapor. To ignite the unit, an electric current is ap¬ 
plied to the squib, and the spit from this ignites the 
fuel block. The initial pressure surge from the fuel 
gases fractures the waterproof membrane. The hot 
gases pass upward through the Venturi, causing the 
fusible plugs in the two feed holes and the vent hole 
to melt. The liquid agent then feeds into the Venturi 
throat, entering the high-velocity hot gas stream at 
right angles. The agent feed rate is controlled by the 
size of the two feed orifices and the pressure differ¬ 
ential between the agent compartment and the Ven¬ 
turi throat. The agent is broken up by the velocity 
of the gas stream and partial vaporization of the 
agent takes place in the throat section. The contact 
time of the agent with the hot gases is extremely 
short, being of the order of several thousandths of a 
second. Further vaporization takes place as the hot 
gas-vapor-droplet mixture passes through the 
divergent section of the Venturi. The mixture issues 
to the atmosphere from the top of the munition 
through the diffuser cap, which contains eight No. 2 


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MUSTARD GAS FROM THERMAL GENERATORS 


421 


holes, 0.2210 in. diameter, at an angle of 223 ^° above 
the horizontal. These holes are designed to avoid 
flaming of the vapor, by rapid cooling with entrained 
air. The vapor condenses to form an aerosol upon 
being cooled by dilution with the air. A small frac¬ 
tion of the agent is deposited in the vicinity of the 
munition as droplets of unvaporized agent. 

30.5.3 Development of the Pots 

The development of these pots is of importance 
because a major part of the work on the improved 
thermal generators was done with them. Field tests 


VAPOR GAS EXIT 



VAPOR GAS EXIT 



Figure 9. Thermal generator experimental pots. 


with these pots provided the basis for interest in the 
use of thermally generated clouds of concentrated 
mustard gas vapor. This interest lent support to the 
development of the 10-lb, E29R1 thermal generator 
bomb described in the following text. In addition 
to the 13-lb size pot, units weighing 25, 35, and 125 
lb were also built. 51 The last held 80 lb of mustard 
gas which could be dispersed in 10 to 12 min. 

The F-7A thermal generator pot was the last of a 
series of experimental models and the only one which 
was manufactured by production methods. Some of 
the earlier models were built in lots of a few hundred 
by hand-welding methods and were used for field 


tests. Outline sketches of these various designs are 
shown in Figure 9, and significant comments on some 
of the designs will be made. 

The early work 10 ’ 11 was directed toward an improved 
generator for solid agents which melt at a tempera¬ 
ture above normal atmospheric temperature. These 
early models (C-8, D-10, and F-6) make no pro¬ 
vision for sealing the agent in a closed compartment 
as would be necessary with a liquid agent. It was also 
believed at that time that the agent could not with¬ 
stand direct contact with the hot fuel block gases 
without serious decomposition. The first pots were, 
therefore, designed to cool the fuel gases by entrain¬ 
ing outside air before the gases came in direct contact 
with the agent. A series of experiments were carried 
out to provide a basis for the design of the air en¬ 
trainment feature. 9 It was realized that using part 
of the heat from the fuel to heat the entrained air 
reduced the amount of agent that could be vaporized 
by a given amount of fuel. The quantitative relation 
between the amount of agent that can be vaporized 
and the ratio of entrained air to fuel gases was pre¬ 
dicted. 9 

The development of the Venturi vaporizer re¬ 
sulted in such extremely short times of exposure that 
direct contact of agent and hot gases was possible 
and the air entrainment feature was eliminated in 
later models (see F-6 and F-7). The C-8, D-10, 
and F-6 models were provided with a baffle above 
the vaporizer. This separated unevaporated liquid 
drops from the gas stream and returned the liquid to 
the agent compartment for recycling through the 
vaporizer. The feed orifice at the throat of the Ven¬ 
turi was then designed to feed the agent at a higher 
rate than it could be evaporated. This recycling 
feature could not be readily incorporated in a unit 
with a sealed agent compartment for liquid agents, 
and it has not been included in the F-7 design. The 
agent feed orifice must then be of the proper size to 
feed the agent at such a rate that it will nearly all be 
evaporated in one pass through the vaporizer. This 
was accomplished satisfactorily. 

C-8 Design. This was the original Venturi vapori¬ 
zer design. 7 The fuel gases passed through an ex¬ 
ternal tube and entered the entrance to a Venturi in 
a jet. This jet entrained air and the mixture passed 
through the Venturi. The lowest static pressure and 
the highest gas velocity are attained in the throat of 
the Venturi and this point was chosen for the intro¬ 
duction of the agent. A contact chamber downstream 
from the Venturi was provided, but this was later 


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422 


THERMAL GENERATOR MUNITIONS 


found to be unnecessary because of the extremely 
good contact between the liquid and gas in the Ven¬ 
turi itself. This pot evaporated from 600 to 700 g of 
liquid Glaurin (diethylene glycol monolaurate) or 
solid paraffin wax in 3 to 4 min with 1,190 g of fuel 
block. The liquid temperature in the agent compart¬ 
ment ranged up to 240 F and the contact time of the 
agent with the hot gases was of the order of 0.01 sec. 
These agents have estimated average boiling points 
of 700 to 800 F. 

D-10 Design. This is a more compact arrangement 
of the C- 8 . The model D-10, with air entrainment, 
has been found to disperse DM, Cyan DA, CN, 
sulfur, paraffin wax, Glaurin (diethylene glycol 
monolaurate) and tertiary butyl stearate. It is 
recommended for toxic smoke agents which are too 
thermally unstable to be used in the simpler pots 
without air entrainment. This candle is 8^2 in- high 
by 7 in. in diameter and the experimental model 
weighs 11 lb when charged with 2 lb of agent and 
3Ke lb of fuel. The burning time averages 33^ to 4 
min and the particle size of the smoke is probably 
between 0.2 and 0.3 micron radius. 

The features of the candle include an air entrain¬ 
ment device, a means of spraying the liquid agent 
into the hot gas stream, and a special baffle to re¬ 
move liquid droplets from the gas stream. The candle 
dispersed 84.4% of the DM charged, as undecom¬ 
posed smoke in one test, and averaged 67.9% in two 
other tests. This compared with 56.1% dispersed by 
two DM irritant smoke M-2 candles. The D-10 
candle also dispersed Cyan DA with 91% of this 
agent appearing in the smoke undecomposed. Earlier 
tests with tertiary butyl stearate 12 as a simulating 
compound, indicated that the D-10 model would 
disperse 89% of this material as smoke undecom¬ 
posed, compared Avith 53% dispersed by the M-2 
candle. The D-10 model is not adapted to field use 
with agents which may be liquid at times. Other 
modifications 8 of this design were tested briefly and 
ratios of entrained air to fuel gas as high as 6/1 were 
attained. Attention was then directed to the design 
of a pot without air entrainment. 

F-6 Design. In this design the upper compart¬ 
ment contains the agent. A Venturi-shaped tube con¬ 
nects the fuel compartment with the agent compart¬ 
ment and the hot gases pass through the Venturi at a 
velocity of about 700 fps. The agent compartment, 
up to the top of the Venturi, has a total capacity of 
somewhat over 2,500 cc. The bottom of the agent 
compartment is slightly conical, allowing the liquid 


to drain to the throat of the Venturi. Two feed holes 
(0.024 in. diameter) are provided in the throat. The 
liquid flows through these holes from the agent com¬ 
partment into the hot gases passing through the 
Venturi tube. This flow is caused by the pressure in 
the agent compartment (about 20 to 30 in. of water) 
plus the liquid head, and is aided by the vacuum in 
the throat of the Venturi. The liquid enters at right 
angles to the high velocity hot gas stream, and is 
broken up into fine droplets which evaporate rapidly 
in the turbulent gases in the diverging section of the 
Venturi. This cools the hot gases quickly. The agent 
is thus exposed for a very short time to the high 
temperatures. The mixture of gas, vapor, and liquid 
particles then impinges on a baffle where the 
unevaporated particles are thrown out and allowed 
to drain back into the agent compartment. The va¬ 
pors then pass around the baffle and are emitted 
to the air through three J^-in. holes. On mixing with 
the cooler air they cool rapidly and partially con¬ 
dense to an aerosol. Temperatures in a pot similar 
to the F -6 are shown in Figure 10. 



Figure 10. Temperature of agent in agent compart¬ 
ment of thermal generator. 


30.6 RESULTS OF EXPERIMENTS 

30.6.1 Composition of Vapor from the Pot 

An attempt was made to determine the extent of 
decomposition of Levinstein mustard in the pot . 8 The 
pot was connected directly to a suitable air-cooled 
condenser followed by a water-cooled condenser. A 
relatively large amount of aerosol passed through the 
apparatus uncondensed and it was not possible to 
account for more than 50% of the agent charged in 
the condensate. The purity of the condensate was 
determined by three independent methods. 


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RESULTS OF EXPERIMENTS 


423 


1. Melting points and mixed melting points were 
measured. 

2. A sample of the condensate was tested on the 
same men for vesicant action in comparison with 
Levinstein redistilled mustard. 

3. A method of determining the purity of mustard 
by means of the rate of evaporation of small drop¬ 
lets 4 was used. 

All these methods indicated that the condensate 
had a higher mustard content than the agent charged. 
A Cottrell-type electrostatic precipitator was then 
designed and used later to recover as condensate 80% 
of the agent charged to a thermal generator bomb. 

30.6.2 Field Test on the Thermal Gener¬ 
ator at Suffield Experimental Station 

The F-6 design was used in a field test at the Ex¬ 
perimental Station, Suffield, Alberta, in October 
1943. 15 In this test 96 pots were tried. They were 
charged with 5 lb of stripped mustard (90% pure) 
and placed in a straight line at 1 J^-yd intervals. The 
meteorological conditions were as follows. 

Air temperature, F 74 

Ground temperature, F 84 

Relative humidity, % 25 

Sky Clear 

Time 12:37 to 12:42 p.m. 

Wind velocity 24 fps, 16 mph 

“R ” value 1.12 

Gustiness, G y 0.61 

G z 0.35 

On a line 50 yd downwind, 6 yd long, and opposite 
the center of the line of generators, four observers 
Avere seated on chairs at 2-yd intervals. Immediately 
up\A r ind from each observer was a chemical sampler 
3 ft abcwe the ground. The observers Avere completely 
protected by masks and impregnated clothes, except 
for a spot 2x2 in. on each upper arm. 

At 75 yd doAAmAvind, chemical samplers Avere placed 
on a line 300 yd long at 15-yd intervals, except at the 
center Avhere they Avere at 5-yd intervals. An observer 


dressed in battle dress Avith impregnated underpants 
and Avearing a gas mask Avas stationed at each of 
these center samplers. 

On a line 150 yd doAvnAvind, four observers dressed 
in the same way as those on the 75-yd line Avere sta¬ 
tioned at 24-yd intervals, and carried portable 
sampling apparatus. 

Of the 96 pots, 5 did not fire. Five bleAv the lids 
loose and tAventy more blew the lids completely off. 
The vapors from one ignited near the end of the run. 
These lids Avere applied Avith a pressed fit, and they 
could easily have been fastened on more securely if 
the need for this had been anticipated. As it Avas, the 
lids that Avere bloAvn off remained in position in most 
cases during a large part of the burning time and 
apparently did not seriously affect the functioning 
of the candles. 

A summary of the analytical results and the 
physiological effects reported from Suffield is given 
in the table beloAv. 

These results are in reasonable agreement with the 
doses predicted from the British diffusion equation, 
as shoAvn in the table. All men exposed on the 75-yd 
line shoAved effects which Avould correspond to a Ct 
betAveen 300 and 400 mg-min per cu m. It is possible 
from these results that the pot dispersed from 75 to 
100% of the mustard gas charged as mustard gas 
vapor. Of six men exposed on the 75-yd line, three 
became true casualties Avithin ten days after the trial, 
due to lesions in the armpits. One casualty developed 
out of the four men on the 150-yd line. The estimate 
is therefore probably not greatly in error since the 
temperature Avas only 74 F. It Avas estimated that a 
20 to 40% increase in concentration Avould have re¬ 
sulted in a large proportion of casualties, Avhich pro¬ 
portion Avould have been markedly increased if no 
impregnated underpants had been provided. 

The high Avind velocity and Ioav “R” value during 
the test are unfavorable for obtaining casualties with 
a small expenditure of agent. They Avere chosen here 
because they gave conditions Avhich could be pre- 


Predicted 

dosages Dosages from 

Position Analyzed dosages mg-min/cu m (diffusion physiological results 

downwind Iodoplatinate Chloramine-T Pyridine theory)* (estimated) 

50 yd 450 Not done Not done 750 Not reported 

75 yd 380 350 420 535 3 casualties out of 6 men 

300-400 

150 yd 350 Not done Not done 350 1 casualty 

2 definite lesions 
1 negligible 

* These dosages were based on a purity of 90% in the charge. 


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424 


THERMAL GENERATOR MUNITIONS 


dieted with considerable certainty at the positions 
of the human observers used for assaying the physio¬ 
logical effects of the cloud. 

F-7 Design. The F-7 A thermal generator shown 
in Figures 7 and 8 is the production model of the F—7 
type shown in Figure 9. The latter was developed as 
an improvement over the F-6 model w 7 hich was quite 
efficient in operation, but could not be transported 
once it was charged with liquid mustard gas. The 
agent was not confined to a sealed compartment and 
could slop over through the vaporizer tube, and 
thence onto the surface of the fuel block, if handled 
roughly after loading. In the F-7 the agent was com¬ 
pletely sealed in the agent compartment resulting in 
a practical pot for field use. There was no provision 
for recycling unevaporated agent and it was therefore 
necessary to obtain a proper balance between the 
agent feed-hole size, the diameter of the vapor exit 
orifices, and the weight of fuel and agent charged. 
The agent vapor issued horizontally over an angle of 
approximately 120° from five x % 4 -in. diameter holes. 
Vertical discharge through a F 2 -in. diameter hole w 7 as 
also tried, and, under neutral conditions at low wind 
velocity, the aerosol cloud rose to a height of about 
20 ft and was considerably diluted before it reached 
the ground. The horizontal discharge placed the 
aerosol along the ground. 

Field Tests 

Six field tests with F-6 and F-7 thermal generator 
pots were carried out at Bushnell, Florida, in January 
and February 1944. 13 The first tw 7 o trials w 7 ere for the 
purpose of determining the functioning character¬ 
istics of the F-7 generators w hen charged with either 
Levinstein or distilled mustard. These tests indicated 
that Levinstein mustard is unsuitable for use in these 
thermal generators because of flaming of the agent. 
It is also anticipated that storage of Levinstein 
mustard in the generators w 7 ould frequently result in 
deposition of solids w hich would interfere with proper 
operation by plugging the feed holes. Distilled mus¬ 
tard is relatively free from these tw 7 o disadvantages 
and is recommended for use in the generators. In the 
other four trials, two of which w r ere in the open 
meadow 7 and two in the forest, vapor sampling data 
were obtained. Physiological data w 7 ere obtained in 
one of the meadow^ trials with the aid of human 
observers. 

The official report of these trials 13 states: 

On the basis of the rather limited data obtained . . . the 
thermal generator is capable, under proper conditions, of 


setting up in a short time at some distance from the source 
dosages of mustard vapor which will produce a high per¬ 
centage of casualties in troops protected only by gas masks. 

There was a difference in the behavior of the cloud 
in the meadow and in the forest. Under inversion 
conditions in the meadow, the cloud remained in a 
compact mass, close to the ground, moving down¬ 
wind. Under the same meteorological conditions, in 
the forest, the cloud tended to rise at first to treetop 
level and then slowly diffused downward to the 
ground. 

No large-scale tests have been carried out with the 
F-7 type thermal generator since the Florida trials. 
However, several small-scale experiments have been 
reported at Dugw 7 ay Proving Ground using the F-7 A, 
charged with distilled mustard. 21-23 In one of the 
tests, an F-7A pot w r as functioned 10 ft in front of 
the entrance to a cave. Although most of the visible 
cloud w r as seen to flow past the opening, total dosages 
at all stations within the cave w r ere in excess of 
2,000 mg-min per cu m. 

An F-7 A w 7 as functioned at the bottom of an old 
mine shaft. 23 The mine tunnels extended for a total 
of 818 ft in different directions and had a volume of 
approximately 25,000 cu ft. Observed dosages were 
between 20,000 and 40,000 mg-min per cu m ob¬ 
tained over a 20-hr period. 

Two small-scale tests with the F-7 A have been 
carried out at the Suffield Experimental Station 49 at 
35 and 26 F, respectively. The generators functioned 
satisfactorily at these temperatures but only 65% of 
the distilled mustard gas charging was emitted. The 
approximate composition of the agent in the cloud 
produced w r as 60% as mustard gas vapor, 10% 
mustard gas droplets with a MMD of 30 to 40 mi¬ 
crons, and 30% mustard gas droplets of less than 
3 microns diameter. There was no evidence of decom¬ 
position products of mustard gas, and the fall out 
close to the point of emission w r as small. The effects 
on physiological observers exposed to the cloud were 
greater than would have been anticipated for the 
dosages to w r hich they were subjected. This may have 
been due to the droplets in the cloud. 

30.7 CONCLUSIONS 

The following conclusions can be drawn from the 
tests on the F-7 A. 

1. The F-7 A thermal generator, charged with dis¬ 
tilled mustard gas, is a practical hand-carry mimition 
for use in the field. 


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THERMAL GENERATOR BOMBS 


425 


2. No tactical requirement for a hand-carry pot 
exists or is anticipated. 

3. The pot described disperses distilled mustard 
gas as an aerosol which evaporates to form mustard 
gas vapor having a physiological activity at least as 
great as that of pure mustard gas vapor. 

4. This thermal generator is capable of setting up 
concentrations of mustard gas vapor of physiological 
importance in a fraction of the time required by 
bursting-type munitions. 

5. The F-7A type thermal generator does not func¬ 
tion satisfactorily when charged with Levinstein 
mustard, due to flaming of the vapor as it issues from 
the generator. When charged with distilled mustard 
gas, functioning is satisfactory. 

30.8 THERMAL GENERATOR BOMBS 

30.8.1 Introduction 

Field tests with mustard gas in the thermal genera¬ 
tor pots indicated that the chief characteristics of the 
thermal generator are: 

1. It produces high concentrations of vapor that 
are effective against masked men and these effective 
concentrations are set up in from 2 to 10 min. This is 
to be compared with 30 min to 4 hr for bursting muni¬ 
tions which disperse the liquid on the ground. 

2. It disperses mustard vapor as a nonpersistent 
gas. This leaves a minimum of residual contamina¬ 
tion on the target area and the target may therefore 
be occupied by friendly troops shortly after the con¬ 
clusion of an attack. 

3. In open terrain with a moderate breeze the 
dosages will be comparable to those from an equal 
amount of nonpersistent agent. 

4. In the forest or in open terrain at low wind 
velocities, the dosages are comparable to those de¬ 
veloped in a longer time by an equivalent amount of 
liquid mustard dispersed on the ground. They are 
less than the dosages from a typical nonpersistent 
agent because the thermal generator does not set up 
self-inversion as do the nonpersistent agents. 

Designing a bomb to function as a thermal genera¬ 
tor involves several innovations. Unlike high-ex¬ 
plosive bombs, this bomb must remain in good 
mechanical working condition after impact. It must 
then function as an evaporator for several minutes, 
and vaporize a liquid without appreciably decom¬ 
posing it. The liquid is somewhat unstable, and, if 
boiled at its atmospheric boiling point, an appreciable 


part decomposes. The vaporization of this liquid by 
the most modern industrial equipment would require 
several times the volume of space allotted to this 
operation in the bomb. 

After these requirements had been provided for in 
the design of the bomb, the center of gravity was 
found to be farther back from the nose than in any 
other bomb. To operate properly it must not land 
flat. This meant that a new and more effective tail 

i 

had to be developed. A new\fuse and ignition system 
were necessary. Even the standard procedure for 
applying a protective coating inside the agent space 
could not be used. The present design is successful in 
meeting these problems. It has not yet been pro¬ 
duced or used in large quantities and, since the design 
is so new, it is to be expected that additional minor 
faults will become apparent from time to time. 

The bomb must land upright and penetrate into 
the ground a short distance so that the agent can be 
completely discharged. It is realized that perfect 
functioning is not to be expected on hard surfaces. 

30.8.2 Description of 10-lb, E29R1 
Thermal Generator Bomb 

An assembly drawing of the bomb 14 is shown in 
Figure 11 and a picture of an assembled bomb is 
shown in Figure 12. The overall dimensions of the 
cylindrical bomb are 2% in. in diameter by 19^ in. 
long. It is composed of two pieces, the main body 
of the bomb and the streamer tail unit which screws 
onto the body. Approximately 5,000 of these bomb 
bodies and 2,000 of the streamer tail units were fabri¬ 
cated and assembled by production methods. 

The Bomb Body 

The body consists essentially of an impact nose, a 
fuel compartment, an agent compartment, and a 
Venturi vaporizer passing through the center of the 
agent compartment. The agent compartment is 
separated from the fuel compartment by a steel cup 
which also houses the Venturi vaporizer. The vapor¬ 
izer consists of a Venturi and a vapor mixing tube. 
The Venturi includes a rounded inlet, a short straight 
section at the Venturi throat, and a diverging section. 
It is screwed into a Venturi sleeve brazed into the 
agent compartment bottom. There are two shoulders 
on the Venturi which seat against the Venturi sleeve. 
These seats are sealed with copper-clad asbestos 
gaskets. The Venturi sleeve contains eight liquid 


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THERMAL GENERATOR MUNITIONS 



VENTURI VAPORIZER 


CLOTH STREAMER TAIL- 


AGENT 

Figure 11. E29R1 - 10-lb thermal generator bomb. 



Figure 12. E29R1 - 10-lb thermal generator bomb. 


feed holes which allow the agent to flow into the 
annular space between the Venturi gaskets. The main 
feed hole in the Venturi throat is sealed with a low 
melting solder. In operation, this solder melts out 
and allows the agent to feed into the Venturi throat. 

Below the entrance to the Venturi, is a circular 
baffle which keeps slag from the burning fuel out of 
the Venturi throat and liquid feed hole. 

The vapor mixing tube connects the Venturi sleeve 
with the agent compartment top. The agent com¬ 
partment top is threaded to receive the tail housing 
cup and also the fuze base. It also contains the filling 
hole and two index bosses with holes which are used 
to register the bomb in the filling apparatus. The 
filling hole is designed to avoid contamination of the 
threads. A shoulder is provided below the threads. 
The filling head seats on this shoulder, sealing the 
threads off from the agent. As an added precaution 
in filling the bomb, the agent compartment top con¬ 
tains an annular trough for decontaminating solu¬ 
tion. After filling, the hole is closed with a %-in. pipe 
plug. 

The inside of the agent compartment is coated with 
a bakelite-type resin to reduce the pressure caused by 
the reaction between steel and mustard. 


The Fuel Block 


The fuel block is pressed into a cylindrical steel can 
lined with heavy paper which is then inserted into the 
fuel compartment. The fuel consists of two layers and 
a starting layer with the following compositions: 


Bottom layer 


Top layer 


Weight of fuel 

Starting layer (or first fire) 


Total weight of fuel block 


243.5 g (84%) NH 4 N0 3 

5.9 g ( 2%) NH 4 CIO 4 

31.9 g (11%) Charcoal 
8-7 g ( 3%) Linseed oil 
290.0 g 

139.4 g (82%) NH 4 NO 3 

6.8 g ( 4%) KNOs 
18.7 g (11%) Charcoal 

5.1 g ( 3%) Linseed oil 
170.0 g 
460.0 g 

5.3 g (53%) KNOs 

3.9 g (39.1%) Silicon 
0.6 g ( 5.9%) Charcoal 
0.2 g ( 2%) Linseed oil 

10.0 g 

470.0 g 


In the production of the fuel blocks the percentages 
of ammonium perchlorate and potassium nitrate 
were varied slightly to compensate for variations in 
the burning characteristics of the charcoal. Blocks 
made with a batch of charcoal which burned too 
slowly were made to burn at the proper rate by in¬ 
creasing these percentages. Blocks made with a batch 
of charcoal which burned too fast were slowed down 
by decreasing these percentages. Several thousand of 
these fuel blocks were manufactured by the Unex¬ 
celled Manufacturing Company. The weight of the 
fuel block is limited by the space available in the 
bomb, and in about 15% of the production blocks, 
it was necessary to reduce the weight of fuel used to 
within the range 455 to 470 g because of variations 
in the density. 


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THERMAL GENERATOR BOMBS 


427 


The fuel block 26 is discussed at length in Chapter 
31 and only a few details will be mentioned here. The 
bottom layer is first pressed into the fuel can with 
a stepped ram. The top layer is added and smoothed 
with a flat ram but not pressed. The starting layer is 
added and these layers are then pressed in with a flat 
ram. A dead load of 8 tons is used in both these 
pressing operations. 

No. 1 Navy Quickmatch is inserted through the 
Venturi and vapor mixing tube. A doubled piece is 
used with the loop near the top of the tube, and two 
knots tied below the Venturi, one on either side of 
the baffle. The lower knot is coated with a small 
amount of primer powder. This powder contains 
65.8% potassium perchlorate and 34.2% finely pow¬ 
dered aluminum, and is mixed with a solution of 5% 
celluloid in acetone to a pasty consistency. When the 
bomb functions, the top of the Quickmatch is ignited 
by the flash of the powder in the fuze booster tube. 
The Quickmatch ignites the primer and the flash from 
this powder ignites the starting layer of the fuel 
block. 

A chipboard buffer ring separates the fuel con¬ 
tainer from the agent compartment bottom and acts 
as a cushion. Below the fuel container is a chipboard 
disk, a metal impact disk, and the nose cup. The nose 
cup contains two bosses with index holes to orient 
the bomb in the filling line. The nose cup is silver- 
soldered in place by induction heating after the fuel 
block has been placed in the bomb. In this operation 
a suitable jig is used, and water is sprayed around the 
case of the bomb to keep the fuel block below its 
ignition temperature. 

The Fuze 

The fuze shown in Figure 13 for use with the cloth 
streamer tail is an inertia impact fuze provided with 



Figure 13. Impact fuze for use with cloth streamer 
tails on the 104b — E29R1, thermal generator bomb. 


a safety arming pin which is pulled out by the cloth 
streamers after the bomb leaves the cluster. The fuze 
is mounted in the tail of the bomb and screws into the 
top of the agent compartment. It spits a flame into 
the vapor mixing tube. The fuze case is aluminum 
and consists of two parts, the base and the firing pin 


cylinder, which screw together. The firing pin is a 
cylindrical steel pellet with the striker at the lower 
end and the upper end, fitted with two safety balls in 
a radial hole. When the safety pin is in place, these 
balls are forced apart and engage a groove in the 
upper part of the fuze case preventing the firing pin 
from moving forward. When the safety pin is re¬ 
moved, the balls slip into the firing pin and the latter 
is free to move forward on impact and strike the 
primer. A small keeper-spring holds the firing pin 
away from the primer when the fuze is armed. 

The primer is an M-29 percussion cap mounted in 
the base of the fuze. The primer ignites a booster tube 
which is also mounted in the fuze base. This is a brass 
tube in. in diameter by % in. long, filled with 
powder, and with its lower end closed by a small wad 
of chipboard. The booster powder contains 65.8% 
potassium perchlorate and 34.2% grained aluminum. 
The mixture is grained with a 5% solution of cellu¬ 
loid in acetone. It should then pass a 40-mesh screen 
and be held on a 100-mesh screen. 

The Bomb Tail 

The cloth streamer tail is assembled as a separate 
unit which screws onto the bomb after the latter has 
been filled, and the fuze inserted. The tail consists of 
three cloth streamers 3 in. wide and 40 in. long. 
These are fastened to a shroud ring which is attached 
to the bottom of the tail housing by three nylon 
shroud lines 10 in. long. The streamers are packed 
into the tail-housing cup and held by a cover plate. 
The ends of the streamers are fastened to the cover 
plate by a spring clip. This plate pulls the streamers 
out during flight and then drops off. The cover plate 
is sealed by a fiber gasket and held in place against 
the tail-housing cup by a spring clip. When in the 
cluster, this clip is held in place by an adjacent bomb. 
When the bomb is released from the cluster the spring 
clip flies off and releases the housing cover. The safety 
pin in the fuze is attached to the streamer by a wire 
clip. When the streamers pull out, the fuze arms. In 
flight the cloth streamers are about 8 in. behind the 
bomb body and extend back to about 48 in. They are 
held in this position by the shroud ring which is in 
turn connected to the bomb body by the 10-in. long 
shroud lines. 

Metal Telescoping Tail for the E29R1 Bomb 

A metal telescoping tail has been developed 27 to 
replace the streamer tail described above. This tail 
causes the bomb to spin during its fall, reaching 3,500 


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428 


THERMAL GENERATOR MUNITIONS 



rpm when dropped from 2,500 ft. This spin stabilizes 
the flight and also makes it possible to use a centrif¬ 
ugal arming fuze which is easier to seal against 
moisture. 

The metal telescoping tail is shown in Figure 14. 
It is composed of a housing cup (this is the same 
housing cup used for the streamer tails, and the two 
tails appear identical when assembled on the bomb), 
a telescoping cup, and a telescoping hub with three 
folding vanes. The hub and telescoping cup are inside 
the housing cup when the bomb is clustered, and the 
housing cup cover is held in place in the same way 
as with the cloth streamer tail. When released from 
the cluster the telescoping cup and the hub spring 
out, and the vanes in the hub open out. 

A relatively small number of these tails have been 
built and tested. They gave excellent promise and 
it is recommended that a sufficient number be made 
to provide for adequate field testing, with a view to 
adopting this tail as standard for the E29R1 bomb. 

Centrifugal Arming Fuze for Use with the 
Telescoping Metal Tails 

The centrifugal arming fuze 14 for use with the 
above telescoping metal tail is shown in Figure 15 


and the component parts in Figure 16. The operation 
of the fuze is quite simple. The firing plunger shown 
in Figure 16D is held in place by two centrifugal arm¬ 
ing pins (Figure 16F), which fit into a continuous 
groove in the firing plunger. These make the fuze 
safe until sufficient centrifugal force pulls the pins 
away from the grooves in the firing plunger. This 
action can be regulated at any rpm by varying the 
strength of the arming springs (Figure 16G) behind 
the arming pins. A keeper spring (Figure 16C) is used 
to prevent the firing plunger from drifting onto the 
primer after the fuze is armed. The advantages of 
this fuze are its increased sensitivity after arming, 
complete sealing of the fuze mechanism from mois¬ 
ture, elimination of external safety pins, ease of as¬ 
sembly into the bomb, absolute safety during han¬ 
dling, and elimination of air bursts. 

Some two hundred fuzes of this type have been 
dropped. The arming rpm has been varied from 
1,750 to 3,200. A final rpm of 2,200 was used as an 
average operating speed. 

30.8.3 Chemical Efficiency of the Bomb 

A number of tests were made to determine the ex¬ 
tent of the decomposition of mustard gas in the E29 


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THERMAL GENERATOR BOMBS 


429 



Figure 15. Centrifugal arming fuze for use with tele¬ 
scoping metal tails. 


and E29R1 bombs. This was done by collecting the 
mustard issuing from the bomb and analyzing it. 

Two methods of recovering the mustard were used. 
One method consisted of passing the vapors from the 
bomb through an absorption column where the 
mustard gas was absorbed in butyl Cellosolve. This 
method was used on an earlier model E29 bomb. The 
efficiency of removal of the mustard gas from the hot 
gases by this method was open to question. The tests 
indicated however that approximately 80% of the 
mustard charged left the unit undecomposed. 

The method 14 used on the E29R1 bombs consisted 
Of cooling the hot gas-vapor mixture in a water- 
cooled condenser, where most of the mustard gas was 
condensed and collected as a liquid. The remainder of 
the mustard gas which did not deposit in the con¬ 
denser was present as an aerosol and was removed by 
a Cottrell electrostatic precipitator. These tests in¬ 
dicated that approximately 78% of the mustard 
charged was expelled from the bomb undecomposed. 

30.8.4 Choice of Size of Bomb 

The E29R1 is a small bomb compared to other 
chemical bombs. This raises the question of whether 
a larger size would be more generally effective. It 
may be desirable eventually to develop three or four 
sizes for a variety of atmospheric and tactical situa¬ 
tions. Further development of the bomb and addi¬ 
tional field tests will be needed to answer these ques¬ 
tions. Some information on this subject is available 
now and is discussed below. 


*4* 


B 


C 


«» !*■ 
D E 


Figure 16. Component parts of centrifugal arming 
fuze. (A) fuse base; (B) primer and booster tube as¬ 
sembly; (C) firing plunger creep spring; (D) firing 
plunger; (E) fuse head; (F) centrifugal arming pin (only 
one shown, two are used); (G) centrifugal arming pin 
spring. 

Single or widely scattered E29R1 mustard bombs 
impacting in open or wooded terrain are ineffective 
since personnel may easily move out of the cloud. 
The effective dosage area from a single bomb is not 
large. As the number of bombs dropped on an area 
increases, the effectiveness will begin to increase rap¬ 
idly when the effective dosage areas from adjacent 
bombs overlap, and it becomes impossible to escape 
from the cloud. 

The results expected from 64 bombs per artillery 
square have been calculated as a percentage of the 
target area covered with a given dosage under several 
meteorological conditions. These are given in Table 1. 


Table 1. Expected results from a density of 64 E29R1 
bombs per artillery square on a large target area. 



Wind °/ 
speed 

(mph) 

r c of target area covered with a given dosage 
Dosage, mg-min/sq m 

10,000 

4,000 

2,000 

1,000 

500 

Clear day 

2 



74 

92 

100 


4 




76 



8 




57 

81 

Neutral 

2 


82 

95 

99 + 

100 


4 



77 

92 

100 


8 




72 

89 

Clear night 2 

79 

97 

100 

100 

100 


4 



83 

95 

100 


The calculations should be confirmed by field trials. 
The table indicates that the bombs are large enough 
to set up effective dosages on the target. Under the 
best meteorological conditions, such as a clear night 
with a 2-mph wind, dosages of 10,000 mg-min per 
cu m are predicted over 79% of the target area. Un- 


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430 


THERMAL GENERATOR MUNITIONS 


der unfavorable conditions, as on a clear day with 
an 8-mph wind, dosages of 500 mg-min per cu m over 
81% of the target area may be expected. 


Derivation of Results Predicted in Table 1 

The following theoretical treatment is based on 
methods used by the Project Coordination Staff, 
CWS, which have been applicable to nonpersistent 
and persistent gas bombs, from data on a large 
number of field trials. 

Only the dosages in open level terrain have been 
calculated and no consideration has been given to 
possible pillaring of the cloud. 

The basic equation of the British diffusion theory is 

D = e ~W/*r , (29) 

7 rux m 


where D is the dosage developed at a point x,y,z in 
space, when a weight W of agent is released at a point 
with a wind speed of u, and turbulent meteorological 
conditions represented by k , j, and m. 


m 1 + (log “R ”)/(log “R” + log 2) ’ (30) 

where “R” is the ratio of wind velocity at 2 m to that 
at 1 m above the ground over a standard prepared 
area. 

The center line dosage near ground level can be 


given as 


D c 


Or/100r * 


(31) 


The integrated crosswind dosage near ground level is 
given by 


ICW = 


(32) 


(z/100) m/2 

and the half width of the cloud (defined as the dis¬ 
tance from the centerline of the cloud to the point 
at which the dosage is 0.1 of the centerline dosage) as 


Half width = 
where Kz = 0.9SK 2 /Ki. 



(33) 


The following table of “R” values represents aver¬ 
age values for the gross meteorological conditions 
shown. 


Table 2. Summary of “R” values to be used for 
meteorological combinations. 


Wind speed 
mph 

Clear 

day 

Neutral 

conditions 

Clear 

night 

2 

1.08 

1.14 

1.25 

4 

1.08 

1.14 

1.18 

8 

1.08 

1.14 



For “R” = 1.14 and u = 4 mph, the value of m is 
1.794. Several values of D c and ICW are read from 
the concentration range slide rule and values of Ki, 
K 2 , and Ks computed. Table 3 contains the values 


Table 3. Calculation of the numerical values of K h * 
K 2 , f and Kzt for neutral conditions, with wind speed of 
4 mph for a source strength of 1 lb of agent. 


X 

(yd) 

D c 

(mg-min/ 
cu m) 

(ioo) 

K x 

ICW 
(mg-min/ 
sq m) 

(ioo) 

m ft 

Kz 

100 

40 

1 

40 

780 

1 

780 

150 

18 

2.07 

37 

550 

1.438 

790 

200 

11 

3.47 

38 

420 

1.86 

780 

400 

3.5 

12 

42 

230 

3.47 

800 


* Average Ki = 39. 
t Average K>. = 790. 
t Average Kz = 18.7. 


thus calculated for a source strength of 1 lb of agent. 

By a series of such calculations, the values sum¬ 
marized in Table 4 were obtained. These values are 


Table 4. Summary of the numerical values of K h K 2 , 
Kz, m, and m/2 for various gross meteorological condi¬ 
tions for a point source of 2.34 lb of agent. 


Wind speed 
(mph) 

Constant 

Clear 

day 

Neutral 

conditions 

Clear 

night 

2 

K x 

32.2 

177 

550 


Ki 

1,710 

3,400 

6,450 


Kz 

49 

18 

11 


m 

1.818 

1.794 

1.610 


m/2 

0.909 

0.897 

0.805 

4 

K\ 

18.2 

92 

164 


Ki 

865 

1,850 

2,100 


Kz 

44 

18.7 

13 


m 

1.818 

1.794 

1.674 


m/2 

0.909 

0.897 

0.837 

8 

Ki 

11 

54 



Ki 

468 

1,000 



Kz 

40 

17.3 



m 

1.818 

1.794 



m/2 

0.909 

0.897 



for 2.34 lb of agent, which is the amount given off 
by the E29R1 bomb. 

The distribution of dosage across the width of the 
cloud is given by 

D = D c (34) 


where Y is the half width of the cloud. This is pre¬ 
sented graphically as curve A in Figure 17. For con¬ 
venience in the later mathematical treatment, this is 
replaced by the straight line marked B, whence 


1.17 X Half width — y 
G 1.17 X Half width 


(35) 


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THERMAL GENERATOR BOMBS 


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FRACTION OF HALF WIDTH OF CLOUD 

Figure 17. Variation of dosage across cloud. 


or 

Ki 1.17K a (x/m) m/2 - y 
Or/100)'” ‘ 1.17Ks(x/100) m/2 


(36) 


The values of y and x for D equal a constant (i.e., an 
isoline) and are given by 


y 


l AIK- 




(37) 


and the area enclosed by the isoline of dosage equal 
to D is 

A d = 2 ^ydx, (38) 

or 


Ad 


<Ki/D)V 




(39) 


or 

A D = 2.34AVvi'” + 2)/2 ’“ 

2 2 


f ---1 D -(rn + 2) /2m, ( 4 Q) 

Lm+2 Sm + 2J 


where Ad = area in hundreds of square yards. This 
can be written as 

A d = K<(,D)~ k ‘. (41) 

For the meteorological combinations given in Table 
2, the values of and K b are given in Table 5. This 
equation predicts the area enclosed by any isoline 
and the numerical value of the dosage on that isoline. 
This type of equation has been quite useful in cor¬ 
relating data from field experiments on mustard gas 
bombs. 



Figure 18. Area-dosage relation for a gas munition. 


Table 5. Summary of coefficients for the area-dosage 
equation (41) for a point source of 2.34 lb of agent. 


Wind speed 
(mph) 

Constant 

Clear 

day 

Neutral 

conditions 

Clear 

night 

2 

K, 

1,110 

2,530 

7,940 


k 5 

1.0501 

1.0574 

1.1211 

4 

K* 

554 

1,320 

2,130 


K b 

1.0501 

1.0574 

1.0974 

8 

Ki 

297 

690 



K, 

1.0501 

1.0574 



Let a quantity be defined that measures the ef¬ 
fectiveness of a munition in producing a dosage H. 
This is the quantity used by the Project Coordination 
Staff in computing munition expenditures. Graphi¬ 
cally it is defined as the cross-hatched area in Figure 
18. Mathematically it is given as 

Ad — L 

E h = HKiH~ K> + f DdA, (42) 

Ad = II 

or 

H 

E h = KiH' ~ K ' + J DKJCJ) 1 ~ K, dD, (43) 

L 

or 

E h = KJI'~ K ‘ ~ Ll_& ] • (44) 

In evaluating E H , L is chosen to be taken either as 
50 or as the centerline dosage 100 yd downwind from 
the source, whichever gives the larger value of Eh- 
This is, of course, somewhat arbitrary, but it con¬ 
forms to some extent with the procedure used by the 
Project Coordination Staff. 

If N bombs are dropped in a target area T, the 
fraction of the area covered with a dosage equal to, 
or greater than, H is given by 

/ = 1 _ri_^r ( 45) 

l H XT A 


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THERMAL GENERATOR MUNITIONS 



Figure 19. Preliminary model K-l of thermal gener¬ 
ator bomb. 


For the units used here, and for an impact density of 
64 E29R1 bombs per artillery square, which repre¬ 
sents approximately the maximum concentration of 
bombs that may be expected from aimable clusters, 
this becomes 



Using equations (46) and (44) and the values of 
Table 5, the expected results from a density of 64 
bombs per artillery square were computed. These 
are given in Table 1. 

30.9 A LARGER THERMAL GENERATOR 

CLUSTER BOMB 

Experimental work was also started on a larger 
thermal generator bomb of the type described above. 
This was designated the K model. It was 19% in. 
long with a hexagonal cross section 3.64 in. across the 
flat sides. A sketch of the experimental model is 
shown in Figure 19. It contained 1,500 g of fuel and 
had an agent capacity of 2,000 ml. Several successful 
static runs indicated that a thermal generator of this 
size and shape would function satisfactorily. The work 
was stopped to concentrate all effort on the smaller 
E29 size. This latter was a size and shape which 
Avould fit into existing cluster adaptors. The K model 
was not a suitable size to fit existing cluster adaptors, 
and development of this size cluster bomb would have 
required a new cluster adaptor. A better choice for a 
larger bomb would be a cylindrical bomb about 4.6 in. 
in diameter and 19% in. long. This size could proba¬ 
bly be clustered in existing 500-lb cluster adaptors 
with 14 bombs per cluster. 

30.10 A 50-LB NONCLUSTERING THER¬ 

MAL GENERATOR BOMB 

A 50-lb nonclustering thermal generator colored- 
smoke bomb for use in target identification has been 
developed for the Navy 28 and designated Mark 72 
Model 2. The bomb functions best in a horizontal 
position but is not critical as to functioning position. 
It is intended for use from low altitudes and employs 
a parachute to reduce its impact velocity. Tests have 
been made with mustard gas in this bomb, and 
promising results were obtained. 48 ’ 50 This bomb 
might prove especially useful for setting up high 
concentrations on local strong points, pill boxes, 
caves, etc. The bomb is described later in this 
chapter. 


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A 50-LB NONCLUSTERING THERMAL GENERATOR BOMB 


433 





Figure 20. Dimensions of Venturi sections. All Ven¬ 
turi throats are x /± inch in diameter length of parallel 
section as indicated: 

No. 1 — Rolled from sheet metal and welded 
No. 2 — Highly finished machined Venturi 
No. 3 — Roughly finished machined Venturi 
No. 4 — Machined and highly finished. 

30.10.1 Development of the E29R1 
Bomb 

The salient problems encountered in the develop¬ 
ment of the E29R1 bomb and the solutions to these 
problems will be discussed briefly. For further de¬ 
tails 14 as to the actual tests the original report 
should be consulted. 

Feeding the Agent to the Hot Gas Stream 
The development of the bomb was carried out con¬ 
currently with that of the pots (F-7 and F-7A) which 
incorporated a completely closed agent compartment. 


The problem of feeding the liquid agent into the 
high-velocity hot gas at the proper rate was therefore 
encountered. It was proposed to use the pressure 
from the fuel gases to feed the liquid by drilling a 
small hole in the agent compartment bottom and 
sealing this hole with a low-melting alloy. This design 
was unsatisfactory because variations in the fuel- 
block pressure, caused by irregularities in the burning- 
rate, allowed the liquid to flo,w into the fuel compart¬ 
ment and quench the fuel. This difficulty was 
eliminated by placing the vent hole near the top of 
the vapor mixing tube. The pressure difference be¬ 
tween the Venturi exit and the Venturi throat was 
then used to feed the liquid into the throat. The use 
of a tube connecting the fuel compartment with the 
void space above the agent, or a check valve to keep 
the agent from leaking into the fuel, were discarded 
because they would complicate the construction. 

The High-Velocity Vaporizer 

The results from a few early models made it evident 
that the design of the vaporizer would have a pro¬ 
nounced effect on the feeding of the agent. Tests were 
therefore made to study the effects of variation in 
this design. Two modifications of the Venturi, in¬ 
tended to simplify large-scale manufacture, were 
tried: (1) The 7° diverging section was replaced by a 
welded sheet metal 90° diverging section, and (2) the 
Venturi was machined in a separate piece which 
screwed into a Venturi sleeve. The first design of the 
separate Venturi contained a 90° divergent section. 
The 7° divergent section was omitted because it was 
thought difficult to manufacture. The Venturi was 
designed as a separate part because it would be diffi¬ 
cult to obtain access to the main feed hole for the 
soldering operation in production, if the Venturi was 
an integral part of the bottom of the agent compart¬ 
ment. The designs containing the 90° divergent sec¬ 
tion were unsatisfactory because the pressure dif¬ 
ferential between the vapor discharge tube and the 
throat was not sufficient to feed the liquid agent. 
Several tests were then made with air (but no liquid) 
flowing through various nozzles in which the pressure 
at the throat and the pressure in the vapor-mixing 
tube were measured. Figure 20 shows sketches of the 
nozzles which were tested. Figure 21 shows the pres¬ 
sure available for feeding liquid as a function of the 
air velocity for each nozzle. This pressure was nega¬ 
tive at any air rate when a 90° divergent section was 
used. When a 7° divergent Venturi section was used, 
the pressure available for feeding liquid increased to 


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THERMAL GENERATOR MUNITIONS 



Figure 21. The static pressure available to feed liquid. No liquid was fed (vent pressure — throat pressure). 


a maximum and then decreased with increasing air 
rate and became negative at high air rates. The 
Venturi used in the E29 was the same as No. 2 
(Figure 20), and was a separate piece. Additional 
qualitative tests indicated that the cylindrical section 
at the throat should be no longer than the throat 
diameter, and that the cylindrical throat and conical 
divergent section should be coaxial. A well-rounded 
inlet was used to minimize the fuel compartment 
pressure. 

Figure 22 shows the effect of gas rate (or fuel burn¬ 
ing rate) on the pressure available for feeding liquid 
as measured with no liquid flowing. Pressure taps 
were mounted on the bomb before assembling it with 
a fuel block in the regular way. With a fast-burning 
fuel block in the bomb, the pressure available for 
feeding the liquid increases to a maximum, then falls 
off and becomes negative for an instant as the fuel 


burns progressively faster. With a slower-burning 
block this pressure is positive throughout the run. 
The pressure reversal with fast blocks was responsible 
for failure of the liquid to feed during part of the run 
in some cases. The pressure available for feeding 
liquid is less than shown in the figures when liquid 
is actually being fed. 

Measurements of the feeding pressure in the bomb 
Venturi were made when water was being fed and 
comparable measurements were made with oil on a 
Venturi installed in an airplane smoke generator. 
Tests were also made with air floAving through the 
Venturi and water being forced through the feed hole 
with a pump. The fuel compartment pressure and 
agent compartment pressure were measured. The 
throat pressure was calculated for the same air rate 
by subtracting the pressure difference from the fuel 
compartment to the throat when no liquid was flow- 


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435 



Figure 22. Pressures in fuel compartment, Venturi throat, and vapor mixing tube of E29 bomb during burning of fast 
and slow fuel compositions. No liquids fed. 


ing from the measured fuel compartment pressure 
when liquid was being fed. By direct measurement in 
another apparatus it was found that within the range 
of flow rates used, this pressure difference is inde¬ 
pendent of the liquid feed rate. In Figures 23 and 24 
the rate of liquid feed at a given pressure drop across 
the feed orifice can be compared at several gas flow 
rates. The pressure required to feed the liquid (meas¬ 
ured pressure drop across the feed hole) and the 
pressure available in the bomb for feeding liquid (gas 
discharge pressure minus throat pressure) are given 
as functions of the liquid feed rate for three different 
air rates. The intersection of each of these pairs of 
lines gives the expected liquid feed rate in the bomb 
corresponding to a given air rate. For the narrow 
range of expected liquid feed rates covered by the 
data, these rates appear to be relatively constant and 
independent of the gas flow rate. This conclusion is 
not definitely established but both Figures 23 and 24 
indicate this. 

This conclusion must necessarily break down at 


the pressure reversal and probably at lower gas flow 
rates. 

Figure 25 shows the relation between the liquid 
feed rate and the pressure upstream from the 
Venturi. 

30.10.2 The E 29 Design 

The first design produced in any quantity by pro¬ 
duction methods was given the CWS designation 
E29. About 500 bomb bodies of this design were 
manufactured. These were hexagonal with a cylindri¬ 
cal tail cup. Tests in which this bomb was fired from 
a mortar against concrete indicated that the fuel 
would withstand such impact without breaking. 

Booster Tube Powder 

A problem was encountered in carrying the flash 
from the primer in the fuze down to the Quickmatch 
in the vapor mixing tube. A small booster tube was 
used below the primer. Several types of powder were 
tried in this booster tube. To avoid blowing back 


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THERMAL GENERATOR MUNITIONS 


0 0.25 CU FT PER SEC AIR (60F, 1 ATM) 

□ 0.21 CU FT PER SEC AIR (60F, 1 ATM) 

& 0.18 CU FT PER SEC AIR (60F, 1 ATM) 



Figure 23. Effect of air flow rate on rate of feeding 
water in an E29 Venturi, with 0.073-inch feed hole. 


through the primer, it was necessary that this powder 
should not pack tightly in the tube. A grained powder 
containing potassium perchlorate and grained alumi¬ 
num gave the best results. 

The Cloth Streamer Tail 

The E29 bomb was fitted with a cloth streamer 
tail attached to a ring in the tail cup. A number of 
drop tests were made with this bomb. These indi¬ 
cated that the bomb was not sufficiently stable in 
flight. Many of the bombs landed flat. The center of 
gravity of the thermal generator bomb is farther back 
from the nose than in the M-69 incendiary bomb. 
Therefore it requires a different tail design. 

These first production bombs functioned well 
enough to give promise that a satisfactory thermal 
generator bomb could be developed. Several faults 
were evident and a new design was made to eliminate 
these. 

30 . 10.3 The E29R1 Bomb 

Clustering Bands. When the hexagonal shape of 
the E29 bomb was changed to the cylindrical E29R1 
it was not certain that the latter could be held firmly 
in the cluster adaptors without shifting. Hexagonal 
bands were therefore provided at each end of the 


© 0.22 CU FT PER SEC AIR (60F,1 ATM) 
0 0.19 CU FT PER SEC AIR (60 F,1 ATM) 
A 0.17 CU FT PER SEC AIR (60 F,1 ATM) 



30 50 100 200 400 600 1000 


LIQUID FEED RATE 

Figure 24. Effect of air flow on rate of feeding water 

in E29 Venturi with 0.046-inch feed hole. 

bomb as an aid in clustering. The outside diameter 
of the bomb was made slightly smaller to allow room 
for these bands in the clusters. After several clusters 
had been assembled it was clear that the round bombs 
were no more difficult to cluster than hexagonal ones 
and that the bands were not needed. 29 

Agent Feed System. With the separate Venturi de¬ 
sign there is the problem of holding the agent in the 
agent compartment without leakage during storage 
and handling and at the same time providing for its 
easy flow during functioning. Several designs involv¬ 
ing gaskets and fusible seals were tested. 25 An excess 
of fusible metal in the feed channels must be avoided 
since this is often slow in melting and can solidify 
and block the channels when the cold agent flows 
over it. Intermittent feeding in a number of cases was 
traced to this cause. The latest design used in the 
bomb is satisfactory but could be simplified. 

Slag from the starter layer of the fuel block was 
frequently blown up into the Venturi and lodged in 
the feed hole. A baffle was provided to avoid this. 
This baffle is a disk of sheet iron, ^ in- below the 
entrance to the Venturi, held in place by three radial 
arms. Three stops are also provided above the baffle 
to prevent it from closing the entrance to the Venturi. 
The baffles first used did not have these stops and a 
number of bombs burst when the fuel block gases 
could not escape. 

Coating the Agent Compartment. A protective coat- 


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A 50-LB NONCLUSTERING THERMAL GENERATOR BOMB 


437 



Figure 25. Effect of feeding water on upstream air 
pressure, in E29 Venturi at constant mass rate of flow 
of air. 0.073-inch liquid feed hole. 


ing was applied to the inside of the agent compart¬ 
ment. In using thin-walled containers such as the 
agent compartment of the E29R1 bomb for storing 
mustard, it is important to keep the pressure de¬ 
veloped by the corrosive action of the mustard on the 
iron at a minimum. In the E29R1 bomb, it is also 
important to eliminate any formation of sludge which 
would clog the feed holes. A protective phenolic 
coating (specification CWS 196-131-207) has been 
used in other munitions for this purpose. Preliminary 
trials in which several E29 bombs were coated, indi¬ 
cated that the vapor-mixing tube which passes 
through the center of the agent compartment com¬ 
plicated the coating process. A special technique was 
required to insure complete coverage with the coat¬ 
ing. When the bomb was heated in the oven to bake 
the coating, the bomb case would heat first and the 
solvent would evaporate and condense on the vapor¬ 
mixing tube which was cooler. This condensed solvent 
would then flow down the tube and wash off the 
phenolic resin. This problem was solved by control¬ 
ling the amount of solvent used, the amount of resin 
solution applied, and the method of heating. 

Development of an Improved Tail 
Folding Metal Tail. The development of a metal 
tail for the E29R1 bomb was undertaken. Wind- 
tunnel tests showed that it was not possible to stabi¬ 
lize the bomb with simple cloth streamers of a practi¬ 
cal length when the center of gravity was back 
farther than about 8.5 in. from the nose. It was 
recommended that a folding tail similar to the AN- 
M52 tail be used. Preliminary results indicated that 
a proper design of such a tail would include six fins, 
so proportioned that the tail surface contained an 
area approximately equal to the nose area, set on 
bars at an angle of 45° with the bomb axis, and ex- 



Figure 26. Thermal generator bomb with folding vane 
tail. (A) Vanes folded for clustering. (B) Vanes in flight 
position. (C) Tail removed for loading bomb. 


tending 5 in. out from the bomb (measured normal 
to the bomb). With this tail, stability was attained in 
the wind tunnel when the center of gravity was as 
far as 9% in. from the nose. It was pointed out that 
to have a stabilizing effect, the fins should be far 
enough out from the bomb so as not to be in the 
turbulent wake from the nose. They should be out 
in the virgin air or region of undisturbed air. 

Several tails were constructed according to these 
recommendations. Pictures of this tail in the open 
and closed positions are shown in Figure 26. In the 
closed position, the tail lies within a hexagon, the 
size of the M-69 cross section. The length, width, 
and number of fins, and the angle between the bars 
and the bomb axis were varied. However, none of the 
tails tested gave the bomb stability when actually 
dropped from an airplane. An unexplained difference 
existed between the conditions in the wind tunnel 
and those in the atmosphere. The bombs yawed and 
landed flat when dropped. 

Streamer Tail with Shroud Lines. The improve¬ 
ment of the cloth streamer tail was undertaken. The 
mass center of the E29R1 is only slightly less than 


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THERMAL GENERATOR MUNITIONS 


ft 

A B C D E F G 

Figure 27. Types of metal tails used in drop tests. 
(A) Four-vane sheet metal tail (vanes fixed). 3)^-inch 
tail extension. (B) Three-vane sheet metal tail (vanes 
fixed). 7^-inch tail extension. (C) Three-vane sheet 
metal tail (vanes fixed). 5)^-inch tail extension. (D) 
Complete telescoping metal tail, three-vane. 5)^-inch 
tail extension with no baffle between vanes. (E) Com¬ 
plete telescoping metal tail fixed at acute ejection angle 
with baffle between vanes. 5)^-inch tail extension. (F) 
Complete telescoping metal tail, three-vane. 53^-inch 
tail extension with baffle between vanes. (G) Complete 
telescoping metal tail, three-vane. 3.6-inch tail exten¬ 
sion with baffle between vanes. 

8.5 in. from the nose, and the wind-tunnel tests in¬ 
dicated that this bomb might possibly be stabilized 
with cloth streamers. Preliminary tests showed that 
the stabilizing effect of the streamers could be in¬ 
creased by mounting them on a ring which was at¬ 
tached to the bomb body by several nylon cords or 
shroud lines. In flight, the ring trailed behind the 
bomb about 8 in. and allowed the air to pass through 
inside the streamers. This increased the drag surface 
of the tail and made possible the use of shorter 
streamers than would be possible if the streamers 
were attached directly to the bomb body. Since the 
available space into which the tails could be folded 
was limited, this is an important factor. 

Metal Telescoping Tail. The first work on this type 
of tail was done with 24-gauge sheet metal tails as 
shown in Figures 27A, B, and C. Work on the four- 
vane unit shown in Figure 27 A was soon discontinued 
because of poor ballistics caused by the relatively 
small vane diameter. The use of three vanes allows 
the vane surfaces to extend further radially from the 
bomb body than the four-vane unit. In the three- 
vane unit, the vanes extend radially 1.43 in. from 
the bomb body; the four-vane unit has an 0.98-in. 
radial extension. This extension is very important 
in obtaining good ballistics with this type of tail. 

The distance that the vanes should be extended 
longitudinally from the end of the bomb body was 
also important in the functioning of these tails. The 


first drop tests were made using the tail shown in 
Figure 27B. This unit had an extension length of 
73^ in. It gave good ballistics, but was objectionable 
because of its length, and tests were made with the 
shorter units shown in Figure 27C. The tail shown in 
Figure 27C has an extension length of 5.6 in. It also 
gave good ballistics. After impact with one of these 
tails on medium soft ground, the bomb penetrated 
20 in. The impact angle was approximately 86°. These 
tests established the vane profile and extension length 
necessary for good ballistics. 

A complete telescoping tail, as shown in Figure 
27D, was then made. Its total weight was 13 oz. Drop 
tests with this unit, however, proved that it had 
very poor ballistics. Further work indicated that 
baffles between the vanes, as shown in Figure 27F, 
were necessary. Fifty of these units were made using 
this baffle and a tapered type of joint between the 
telescoping sections. Tests using this tail at an acute 
ejection angle, shown in Figure 27E, were made. At 
this ejection angle the ballistics were still good. 

Forty-three of these metal tails were dropped at 
Edge wood Arsenal from a B-25 airplane in quick¬ 
opening and aimable clusters. 46 The results showed 
that 37 of the 43 tails failed at the tapered telescoping 
joint. Those which did not fail at these sections gave 
very good ballistics. 

A new design was then developed which used a 
square shoulder in place of the tapered joint. This 
design gave a much stronger joint and provided a 
positive means of preventing the telescoping parts of 
the unit from canting when these parts were ejected 
by the ejector spring. 

Further tests were made using a tail unit having 
one telescoping cup in place of two, as shown in 
Figure 27G. The vane assembly was modified to pro¬ 
vide a 34 _ in- longer radial vane extension from the 
body of the bomb. This unit consistently gave good 
ballistics when dropped singly from a slow plane. It 
was not tested in clusters from fast planes. This metal 
tail ready for assembly onto the bomb is shown in 
Figure 28. 

The production cost of this unit was materially 
reduced by eliminating the second telescoping cup. 
The costs of this metal tail and the streamer tails are 
very nearly the same. 

Considerable data on the rotative speed of the one- 
cup unit was obtained by the use of a centrifugally 
operated recording instrument. 27 This instrument 
uses a small, weighted, spring-loaded, recording 
stylus. The centrifugal force caused by the rotation 


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A 50-LB NONCLUSTERING THERMAL GENERATOR BOMB 


439 


r 



Figure 28. Complete metal telescoping tail ready for 

assembly onto bomb body. 

of the bomb causes the stylus to move outward from 
the center of the instrument against the spring ten¬ 
sion. The sensitivity of the instrument was changed 
by using different sizes of retaining springs. During 
flight the stylus records its path on waxed record 
paper. On impact, a small hole is punched into the 
record paper as a record of the impact rotational 
velocity. The average rpm recorded by this instru¬ 
ment for the one-cup tail was 3,500. 

Work was done to record the impact velocity of the 
bomb with the metal tail. The velocity recording 
instrument 27 used the ram effect of the air to move 
a piston and record the air velocity. Measurements 
with this instrument have recorded an impact veloc¬ 
ity of approximately 270 fps. However, these records 
were obtained from altitudes of 2,000 ft and do not 
represent the terminal velocity of the bomb. The 
terminal velocity of the bomb with this tail is 350 to 
375 fps. 

Sealing the Fuel and Ignition System. The fuel block 
used in the bomb and some of the powder in the 
ignition system are adversely affected by high 
humidity. Therefore, it is necessary to seal the in¬ 
terior of the bomb from the atmosphere. Several 
methods were tested. 

1. The use of waterproof paper over the exit holes 
was satisfactory for only short periods of time under 
relatively dry conditions but would not withstand 
tropical or cyclical temperature conditions. 

2. The whole bomb including the tail was hermeti¬ 
cally sealed with a thin (0.006 in.) brass diaphragm 
under the tail cover plate. Two methods of tearing 
open this diaphragm after the bomb broke away from 
the cluster were tried. In one, a cutter ring was used, 


and in the other, a tear wire was attached to the 
cover plate. Both were promising but not quite 
satisfactory because of difficulties with the tear 
features. 

3. The fuel and ignition system was sealed by ar¬ 
ranging the fuze as a solid plug in the end of the 
vapor-mixing tube with a Morse taper fit. The fuze 
was to be blown out by pressure from the fuel block 
after ignition. The design was objectionable because 
it was difficult to reproduce the pressure at which the 
fuze blew out. Some bombs blew up when the fuze 
failed to be expelled. 

Table 6. Static tests on E29R1 bombs, Brooksville 
Army Field, December 5, 1945; an average of 2.23 lb 
of distilled mustard was charged in each bomb. 


No. 

Burning 

time 

(min) 

End 
of agent 
emission 
(min) 

Amount 
of agent 
left 

(oz) Remarks 

1 

4.0 

3.0 

nil 


2 




Dud 

3 




Dud 

4 




Dud 

5 

4.9 

2.5 

nil 


6 

4.6 

4.3 

6 

Fair cloud 

7 

4.9 

4.9 

10 

Fair cloud 

8 




Dud 

9 

4.8 

4.3 

nil 

Very good cloud 

10 




Dud 

11 

4.8 

4.8 

nil 


12 

4.7 

3.1 

nil 


13 

5.5 

5.3 

13 

Erratic feeding, 3.9 to 5.3 





min 

14 

4.75 

4.75 

nil 

Did not feed, 4.0 to 4.3 min 

15 

5.2 

3.3 

10 

Probably plugged part of 





the time 

16 

5.0 

5.0 

19 

Erratic feeding 3.9 to 5.3 





min 

17 

5.0 

5.0 

18 

Poor cloud, 1.7 to 3.0 min 

18 

5.1 

5.0 

nil 

Poor after 3.3 min 

19 

5.1 

4.9 

4 

Fair cloud 

20 




Dud 

21 

4.75 

2.5 

nil 


22 

4.8 

4.9 

nil 


23 

4.8 

4.9 

17 

Poor at first 

24 

5.1 

3.6 

nil 

Very good cloud 

25 

5.1 

3.7 

nil 


26 

4.7 

4.7 

nil 


27 

5.2 

3.7 

11 

Probably plugged 

28 




Dud 

29 

4.5 

3.3 

nil 

Very good cloud 

30 

5.2 

5.1 

11 

Erratic 1.4 to 2.5 min 


4. The method finally adopted in the E29R1 bomb 
consists of a fusible diaphragm between the fuze base 
and the agent compartment top. This is made of a low 
melting alloy (50% bismuth, 31% lead, 19% tin) 
0.015 in. thick, with a reinforcing ring around the 
periphery. It is ruptured by the flash from the fuze 
and does not impair ignition. 


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THERMAL GENERATOR MUNITIONS 



Figure 29. Proposed modification of E29R1 bomb. 


30.10.4 Field Test of E 29 R 1 Bomb 

Tests were made in December 1945 at Brooksville, 
Florida, 14 on 30 bombs chosen at random from the 
production lot and charged with distilled mustard. 
These are listed in Table 6. A number of duds were 
caused by failure of the Quickmatch in the ignition 
system to burn completely. Twenty-three bombs 
functioned and were generally satisfactory. On the 
average these bombs discharged 85% of the agent 
charged to them. A few of these bombs apparently 
plugged either partially or completely during part 
of their functioning period. As a result of these tests, 
plans for field-sampling tests on statically fired 
bombs, and on large-scale drop tests have been made 
by the CWS. 

30.10.5 Recommendations for Improv¬ 

ing the E 29 R 1 Bomb 

During the manufacture and testing of the E29R1 
bomb it became apparent that a number of improve¬ 
ments could be made. 

1. The presence of the impact diaphragm in the 
nose structure is undesirable since on impact it 
flattens out and tends to push the case away from 
the nose cup at the silver-soldered joint. 

2. The operation of silver-soldering the nose cup 
alter the fuel block is in place has been carried out 
successfully, but it would be preferable to eliminate 
it if possible because of the hazard involved. 

3. The separate Venturi section is complicated and 
offers opportunity for leaks at the two gaskets. The 
Venturi should be made an integral part of the agent 


compartment bottom and a satisfactory method of 
sealing the feed hole devised. 

4. The outside diameter of the bomb should be in¬ 
creased to 2 1 Jki6 in. This will increase the filling 
capacity and will make the bomb almost the same 
diameter as the distance across the flat sides of the 
M-69 bomb. 

5. The cloth streamer tails are undesirable for the 
following reasons: 

a. They tend to cause flaming of the vapors. 

b. They cause the bomb to have too low an im¬ 
pact velocity to insure good functioning of 
an impact fuze when the latter conforms with 
military safety requirements on sensitivity. 

c. The hand work required in the assembly 
operations is complicated, and this increases 
the cost of the tail to a figure comparable 
with the cost of a metal tail. 

d. The tail is subject to tangling when released 
from the cluster. Twisting of the shroud lines 
makes the bomb unstable in flight. Improper 
packing of the streamers may result in failure 
of the tail to open. 

30.10.6 Proposed Improved Design 
of Thermal Generator Bomb 

A new design for a thermal generator bomb of the 
same size as the E29R1 has been partially prepared. 
An assembly drawing is shown in Figure 29. A bomb 
of this design has not yet been built. The entire im¬ 
pact nose structure of the E29R1 has been eliminated. 
The fuel block container serves as both the outer 


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OIL SMOKE POTS 


441 


case and the nose. It has a wall thickness approxi¬ 
mately equal to the combined thickness of the fuel 
container and bomb case of the E29R1 bomb. The 
large number of impact tests made on the E29 and 
E29R1 bombs indicated that the fuel block can with¬ 
stand impact without the protection of a special nose 
structure. By eliminating the void space in the nose, 
the capacity is increased and the mass center is 
nearer the nose. 

The Venturi is to be forged as an integral part of 
the agent compartment bottom. The fuel compart¬ 
ment is threaded to screw onto the agent compart¬ 
ment. The feed hole is readily accessible for soldering 
before assembling the fuel block to the bomb. The 
rest of the agent compartment is essentially the same 
as in the E29R1. The bomb is equipped with the 
metal tail described earlier and the centrifugal arm¬ 
ing fuze. 

The proposed design includes three separate as¬ 
semblies : the nose containing the fuel, the body con¬ 
taining the agent, and the tail. These assemblies fit 
together with screw threads and permit inspection 
and separate storage of the fuel, agent, fuze, and tail. 

30.11 OIL SMOKE POTS 

30.11.1 Floating Oil Smoke Pot, E-23 

A thermal generator floating oil smoke pot utilizing 
the high velocity vaporizer principle was developed 31 
to meet specifications set by the Naval Bureau of 
Ordnance. 30 These specifications were as follows: 

1 . It should be the thermal generator type. 

2. It should produce a nontoxic smoke. 

3. It should have a burning time of 10 to 15 min 
duration. 

4. It should produce a volume of smoke compara¬ 
ble to the M4A2 pot. 

5. It should be suitable for mass production from 
readily available materials. 

6 . It should not be subject to spontaneous ignition 
from the effects of moisture, water, or rough han¬ 
dling. 

7. When burned at night, it should not be visible 
from aircraft flying at an altitude of 1,000 ft or 
higher. 

8 . It should have a mechanical type of igniter, 
such as either a bouchon or scratcher igniter, and it 
should also be equipped for electrical ignition. 

9. It should occupy a space no greater than 13 3^ in. 
diameter by 133^ in. high. 


10. It should be completely waterproof and mois¬ 
ture proof, and should function in a satisfactory 
manner from OF to 120 F after being subjected to 
the standard Chemical Warfare Service desert, tropi¬ 
cal, and arctic surveillance tests for 90 days. 

11. It should function satisfactorily after being 
subjected to a drop of 40 ft into water from a station¬ 
ary position. It should also function satisfactorily 
after being subjected to a rough handling test simu¬ 
lating the handling normally encountered in ship¬ 
ping, storing and use. 

12. Satisfactory functioning is considered to be at 
least 90% functioning with normal volume of smoke. 

13. It is considered desirable to incorporate a 
feature in the floating smoke pot which will insure 
that it will sink within 45 min after the completion of 
burning so that ships dropping floating smoke pots at 
sea will not mark their course with them. This feature 
should be incorporated only if it will not interfere 
with or delay the fulfillment of the above require¬ 
ments. 

The pot was designated, Pot , Smoke , Oil , Floating , 
E-23 by the Chemical Warfare Service. Apparently 
it will meet the specifications set by the Navy, except 
that no provision has been made for the empty pot 
to sink within 45 min after functioning. This was a 
casual requirement and the final model was consid¬ 
ered to be satisfactory. 

Principle of Operation 

The principle of operation involves vaporizing a 
high-boiling petroleum oil in a high-velocity stream 
of hot gases. The vaporized oil-gas mixture leaving 
the unit is cooled by entrained air, and condensation 
of the oil vapor into small droplets forms a screening 
smoke. 

The unit consists of (1) a fuel block in one com¬ 
partment to produce hot gases, (2) the oil in a 
separate compartment, and (3) a high-velocity 
vaporizer tube in the form of a Venturi. Another tube 
connects the agent compartment and the fuel com¬ 
partment, and permits pressure from the fuel com¬ 
partment to force the oil through an orifice into the 
Venturi throat. Here the oil mixes with the hot gas 
stream flowing through the Venturi. The high gas 
velocity atomizes the incoming oil stream and the 
droplets are quickly vaporized. 

The rate of feeding is governed by the pressure 
differential between the agent compartment and the 
throat, the size of the feed orifice, and, to a minor 
extent, by the resistance to flow through the feed 


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THERMAL GENERATOR MUNITIONS 


0OUCHON FUSE 



tube. The ratio of agent to fuel is limited by the 
available heat in the fuel gases and the efficiency of 
the vaporization process. 

Description of the Floating Smoke Pot 

Figure 30 shows the design of the floating smoke 
pot. The completed unit weighs 36.5 + 0.2 lb. This 
includes 14.5 lb of SGF No. 1 oil and 12.16 lb of fuel. 
A bouchon fuze, modified to give a delay of 12 to 
22 sec, serves as the ignition system. The spit from 
the fuze ignites the Quickmatch on top of the fuel 
block; this in turn ignites the British starter. Hot 
gases from the fuel block immediately melt the 
fusible plugs, opening the feed orifice and the pressure 
tube. Oil is fed from the bottom of the annular space 
through a feed tube into the feed orifice at the throat 
of the Venturi, and the mixture of hot gases and oil 
vapor pass through the Venturi into the air chamber 
and then to the atmosphere through four Y^-vn. 
diameter exit ports in the cover. A 4-in. diameter 
“collar” in the air chamber prevents condensation 
from taking place at this point. 

Fuel Block. The fuel block is composed of three 


layers. Table 7 shows the compositions and weights 
of each of these layers. A complete discussion of the 
fuel is given in Chapter 4. 31 

The ammonium nitrate and ammonium chloride 
are placed in an edge runner mixer and the oil is 
slowly added over a 4-min period during mixing. 
Charcoal is then added and mixed for 16 min. Transi¬ 
tion mixtures are made by blending top and base 
compositions in the desired ratio for 3 to 4 min in the 
edge runner. 

These mixtures are pressed under a dead load of 
36 tons, or 1,380 psi in six increments. A wooden ram 
and a steel form are used during the pressing opera¬ 
tion. The pressure is held on each increment for about 
5 to 10 sec. Before pressing the final increment, 40 g 
of British starter is placed in a ring about 1 y 2 in. in 
from the edge of the can. The British starter has the 
following composition: 


Charcoal 

6 % 

Linseed oil 

2 % 

kno 3 

53% 

Silicon 

39% 


The block is allowed to cure for one day, and then 
two coats of a special pyroxylin base lacquer are ap¬ 
plied to the surface. Waterproof Navy Quickmatch 
is then fastened to the surface with tacks. The com¬ 
pleted block is stored for at least three weeks in a dry 
room (relative humidity below 50%) at a temperature 
below 85 F. During the curing period, the linseed 
oil polymerizes causing the block to harden and its 
burning rate to increase. The block, after curing, has 
a burning time of 12 min + 1.5 min when burned in 
the E-23 smoke pot. 

The fuel block described above was used in the later 
models of the E-23 and served for the completion 
of the design. It was realized that it had certain 
faults such as, (1) a tendency for the burning time to 
vary somewhat, (2) occasional fast burning periods, 
(3) information needed for the specification of the 
charcoal was incomplete, and (4) the pressing pro¬ 
cedure and the number of mixtures used could 
probably be simplified. Paper liners for the fuel block 


Table 7. Composition of fuel block for E-23 (expressed in weight per cent). 


Top 

Base 

Wtg 

NH4NO3 Charcoal 

Linseed 

oil 

Wt g 

NH4NO3 

Linseed 

Charcoal oil 

NH4CI 

Transition 

700 

86 11 

3 

3,000 

82 

7 3 

8 

1,800 g of two parts top 
mix to one part base 


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OIL SMOKE POTS 


443 


cans were used by others. These prevented the fuel 
from burning down the side and consequently gave a 
more uniformly burning block. 

Agent Compartment. The outside of the agent com¬ 
partment is formed by the standard outer can of the 
M4A2 pot. A flanged air partition serves as a top for 
this compartment and a sheet metal shell, which en¬ 
closes the fuel block and leaves an annular space for 
oil, is the agent compartment bottom. The agent 
specified is SGF No. 1, or fluid (oil), Fog No. 1 
(Standard Stock No. 7-F-500). A 5% void space is 
allowed when filled with oil. The Venturi vaporizer 
passes vertically through the center of the agent com¬ 
partment and contains a feed orifice 0.0890 in. in 
diameter (No. 43 drill) at the throat. The pressure 
tube is open to the fuel block at one end and extends 
above the oil level in the agent compartment. 

A 16-mesh wire screen is placed over the entrance 
to the feed tube to prevent foreign matter from 
reaching the feed orifice. The filler plug is placed 
directly above the feed tube and the weight of these 
two parts is off center and causes the unit to tilt to 
that side. The feed tube is thus able to discharge all 
but a very small amount of the oil charged. 

Buoyancy Chamber. The space between the top of 
the agent compartment and the can cover acts as a 
buoyancy chamber for the floating unit. A 4-in. 
diameter collar, placed around the exit of the Venturi 
and extending to the top of the chamber, prevents 
oil from condensing in this space. 

Cover. The cover has a lug-type seal. The center of 
the cover is dished in to house the bouchon fuze. The 
four exit holes are F 2 in. in diameter placed on a 
radius % in. from the center. These holes are covered 
by waterproof adhesive tape. A fuze adapter is 
welded in the center of the cover. An auxiliary cover 
with a ring-type seal is used to protect the bouchon 
fuze from moisture. 

Ignition System. The ignition system was de¬ 
veloped by the Technical Command, Chemical War¬ 
fare Service, and has been designated, Fuze, Igniting , 
E-10. Figure 31 is a drawing of this fuze. It has a 
delay of 12 to 22 sec and ignites the Quickmatch on 
the fuel block by “spitting” through the Venturi tube. 

Assembly. The outer can and the agent compart¬ 
ment form a complete unit assembly into which the 
fuel block is placed. The bottom of the unit is then 
double-seamed to the outer can and the unit is filled 
with oil. After the cover has been crimped in place, 
the bouchon fuze is screwed into the fuze adapter. 
White lead paste in oil is used to lute the threads of 



SIDE VIEW CROSS SECTION 

Figure 31. E-10 igniting fuze for E-23 floating oil 
smoke pot. 


the fuze adapter. The addition of the secondary fuze 
cover completes the assembly. 

Figure 32 shows a complete pot and one of the pots 
in operation. 

Development 

The E-23 floating smoke pot was developed from 
the thermal generator nonfloating oil smoke pot 
known as the E-20 described later. Problems common 
to all design stages during the development will be 
discussed in this section. For a description of the 
various designs, the individual problems encountered 
and their solution, as well as data on typical runs, the 
original report should be consulted. 31 

Control of Oil Feed Rate. It was necessary to bal¬ 
ance the heat and gas output of the fuel block against 
the feed rate of oil. A slow-burning fuel block usually 
produces gases at a low temperature and this reduces 
the amount of oil that can be vaporized. When this 
condition exists, the unvaporized oil is thrown out as 
spray and less oil is converted into smoke. If the feed 
orifice is too large, the oil feed rate is excessively high 
and the oil is exhausted early in the burning period. 
There is then insufficient heat for evaporation during 
this shorter discharge period and this also results in 
spraying. On the other hand, if the feed orifice is too 
small, the oil does not feed rapidly enough and the 
vapors issue at a high temperature. The resulting 
smoke is dry and oil may be left in the unit. The pot 
should use all its oil uniformly with a minimum of 
spraying. 

Flaming. Flaming at the start of functioning was 
eliminated by applying the British starter in the 


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THERMAL GENERATOR MUNITIONS 



Figure 32. E-23 oil smoke pots in operation. (A) The round and square can completely assembled. (B) 15 seconds after 
emission. (C) Cloud 6.1 minutes after emission. (D) Cloud 10 minutes after emission. The square can shown in upper 
left-hand picture is an alternative shape of experimental pot. 


shape of a ring. This removed the starter from directly 
below the Venturi throat and prevented the initial 
flash from igniting the oil. 

Terminal Surge. During the last few minutes of the 
burning period, the unit floats nearly horizontally in 
the water, and there was a tendency for the fuel block 
to come loose from the bottom and give a surge of gas 
at this time. When this happened, pressure sufficient to 
blow open the bottom seam was sometimes developed. 
Reinforcing wires were placed across the bottom of 
the fuel can to hold the block in place and prevent 
this difficulty. 

Functioning the Pot on Land. The floating smoke 
pot will function satisfactorily out of the water. A 
slightly shorter smoke emission time results. 


Effect of Temperature of Pot on Functioning. Pots 
were stored overnight at 0, 70, and 150 F and func¬ 
tioned shortly after being removed from storage. The 
pots at 70 and 150 F functioned satisfactorily except 
that the pot at the higher initial temperature gave a 
shorter smoke emission time. The pot at 0 F did not 
feed oil properly. It is evident that the fuel block 
does not readily heat the oil in the bottom of the pot 
near the feed tube inlet. The oil used in these tests 
had a pour point about 0 F, and consequently would 
not flow at this temperature. For satisfactory opera¬ 
tion at 0 F, an oil with a pour point below this 
temperature should be used. 

Toxicity. Tests on the toxicity of SGF No. 1 oil 
were made. 32 Monkeys were exposed for 30 min of 


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OIL SMOKE POTS 


445 


every hour for 100 consecutive days to a concentra¬ 
tion of 63 mg per cu m of SGF No. 1 oil in the air. 
The conclusion was drawn that similar exposure of 
men would be without serious pulmonary effects. 

Further tests on the toxicity of oil smoke were 
made in connection with the E-21 training smoke 
pot. 33 

Two chamber tests were made: in each, two goats, five 
rabbits, and five rats were exposed for one hour to the smoke 
and gases, and gas samples were taken from the chamber and 
analyzed. Two candles were burned. 

Three candles were burned to provide increased concen¬ 
tration of smoke and gases. 

In both cases, analysis showed no C0 2 , CO, saturates, un¬ 
saturates, or acidic constituents (percentages to the first 
decimal place) in the chamber atmosphere; the rats and 
rabbits showed no ill effect at any time, the goats were only 
very slightly affected — slight lung rales the next day, clear¬ 
ing up quickly, and a slight tendency toward diarrhea the sec¬ 
ond day after the test. 

Floating Stability. The initial problem with the 
floating pot was to design the pot to float and func¬ 
tion in a satisfactory manner. In the earlier pots for 
use on land, the oil was carried in a compartment 
above the fuel compartment. Since the weight of the 
oil is greater than the weight of the fuel, this made 
the pot top-heavy and caused it to turn over in the 
water. Buoyancy may be provided by simply in¬ 
creasing the void volume in the oil compartment, but 
this allows the oil to run to the top of the pot when 
the latter is inverted in the water. The pot would 
then be stable in this inverted position and would not 
right itself. The pot was thus designed to confine the 
oil as near the bottom as possible and to provide a 
separate buoyancy chamber at the top. About half 
the oil is carried in an annular space around the fuel 
block and the other half directly above the fuel com¬ 
partment. 

The next step was to provide for feeding the oil 
from the bottom of the pot up to the high-velocity 
vaporizer above the fuel. This could be arranged by 
leading a feed tube from the bottom to the feed 
orifice. However, the pot tends to float on its side and 
this tube would not feed oil if it happened to be on 
the high side with its inlet end out of the oil. This 
was overcome by weighting the pot eccentrically so 
the pot would float with the feed tube on the low side. 

Pressurized Feeding. With the arrangement just 
described the suction at the feed orifice was not 
enough to lift the oil and feed it uniformly. A pres¬ 
surizing tube was provided connecting the fuel com¬ 
partment with the upper part of the oil compartment. 



This raised the pressure in the oil compartment and 
forced the oil up through the feed tube and feed 
orifice. 

30.11.2 Nonfloating Oil Smoke Pot, E-20 

The E-20 thermal generator oil smoke pot for use 
on land or in boats is shown in Figure 33. The pot 
functioned on land for 6 min and weighs 21.5 lb. Ten 
pounds of fog oil in a separate agent compartment is 
used as the smoke-producing agent, while hot gases 
are supplied by a cast fuel block weighing 6 lb. The 
unit is ignited either electrically or manually. 

Tests were made on the E-20 pot at the Amphibi¬ 
ous Training Base, Little Creek, Virginia, in January 
1945. The following conclusions 34 were reached. 

1. That the volume of smoke produced from the E-20 
smoke pot is slightly greater than one-half that produced 
by the Mk-3 smoke pots. 

2. That the effective burning time of the E-20 smoke pot 
is slightly less than that of the Mk-3 smoke pot. 


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446 


THERMAL GENERATOR MUNITIONS 


3. That the short period of glow from the E-20 smoke 
pots will not pin-point the moving smoke boat at night. 

4. That when functioning properly the E-20 smoke pots 
are capable of producing a lengthy and an effective screen. 

The principle of operation of the E-20 pot is 
similar to that of the E-23 smoke float. Oil is sucked 
from a vented agent compartment through two feed 
holes into the Venturi throat. The agent compart¬ 
ment is not pressurized from the fuel compartment 
and all the agent is contained in a compartment above 
the fuel. 

30 . 11.3 Training Oil Smoke Pot, E-21 

A thermal generator pot, of the size of an M-8 
grenade, was developed. 35 This unit contains a small 
fuel block in a separate compartment and uses oil, 
such as “Diol 55,” or SGF 1, as a smoke agent. The 
pot operates best in a vertical position. A single pot 
fills a 13,000-cu ft room with smoke that totally 
obscures objects 4 to 6 ft away. The present CWS 
designation is Pot, Smoke, Oil, Training, E-21. The 
specifications 36 for the development were: 

1. The burning time should be from two to three minutes. 

2. The rate of emission of smoke should be approximately 
equal to that of the HC training candle M-2. 

3. The smoke produced should be non-corrosive to ma¬ 
terial and equipment, particularly delicate instruments aboard 
ship. 

4. No serious harmful effects should be experienced by 
unmasked personnel when exposed for sixty minutes to the 
smoke from two candles in a compartment of 5,000 cu ft. 

5. The size should be as small as possible consistent with 
the requirements of (1), (2), (3), and (4), but should not 
exceed 2x4x6 inches. 

The E-21 pot meets these specifications with the 
exception of the burning time. This is less than the 
2 to 3 min specified. 

Principle of Operation 

The principle of operation involves vaporizing a 
high-boiling petroleum oil by injecting it into a high- 
velocity stream of hot gases. The oil vapors thus 
formed are cooled rapidly when they mix with the air 
outside the unit and condense to small droplets. 
These condensed oil droplets form the screening 
smoke. 

The unit consists of (1) a fuel block in one com¬ 
partment to produce the hot gases, (2) the oil in an¬ 
other compartment, and (3) a high-velocity vaporizer 
tube. This latter is in the form of a Venturi and the 
low pressure at the throat is utilized to suck the oil 



into the hot gas stream. The high gas velocity 
atomizes the incoming oil stream and the small drop¬ 
lets are quickly vaporized. 

The rate of feeding oil is governed by the pressure 
differential between the oil compartment and the 
throat, as well as by the size of the feed orifice. The 
ratio of oil to fuel is limited by the available heat in 
the gases and the efficiency of the vaporization 
process. 

Description 

Figure 34 shows an assembly drawing of the E-21 
smoke pot and Figure 35, a photograph. * 

Oil and Oil Compartment. The oil compartment 
contains 107 g of SGF-1 oil or Navy Fog Oil No. 1. 
The Venturi tube, which serves as the high-velocity 
vaporizer, passes vertically through the center of the 
agent compartment and has a feed orifice 0.076 in. in 
diameter (drill size No. 48) drilled radially at the 
throat. Both the feed hole and the vent hole at the 


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OIL SMOKE POTS 


447 


a 



Figure 35. E-21 oil smoke pot (training). 

top of the Venturi tube are closed by fusible metal 
plugs. These plugs melt out immediately upon igni¬ 
tion of the fuel block and allow the unit to function. 
A 5% void space is left in the agent compartment. 

Fuel Blocks. The fuel block used in the E-21 has 
the following composition: 82% ammonium nitrate, 
11% charcoal, 4% potassium nitrate, and 3% boiled 
linseed oil. The dry ingredients, with the exception of 
the carbon, are weighed and placed in an edge 
runner. The linseed oil which serves as a binder is 
added slowly, and this is mixed for 4 min. Carbon is 
then added to the mixer and the mixing operation 
is continued for 16 min until the mixing time totals 

20 min. 

Each block consists of 95 g of the above mixture 
with 6 g of British starter placed on top. This is 
pressed into an M-8 grenade can held in a pressing 
form, under a load of 14,000 lb or a pressure of 3,500 
psi. The pressed blocks are stored in a room having 
a relative humidity below 50%, to cure for at least 

21 days before use. During the curing period, the 
linseed oil polymerizes causing the block to harden 
and also “speed up.” The block, after aging, has a 
burning time of 1.2 ± 0.25 min. 

British starter is a powdered mixture of 54% 


potassium nitrate, 40% silicon, and 6% carbon. Lin¬ 
seed oil is used as a binder for this mixture. 

Ignition System. The ignition system consists of a 
“fuze, igniting grenade, M-201.” This fuze “spits” 
through the Venturi and ignites the British starter 
on the surface of the fuel block. 

Assembly. The agent compartment is a complete 
unit assembly. After it is filled with oil it is placed 
into the M-8 grenade can, which already contains 
the pressed fuel block. A modified M-8 grenade can 
cover is then rolled on with a double seam. This 
modified cover contains three diameter exit 

holes instead of the four used in the standard cover. 
The bouchon fuze is screwed into the fuze sleeve. The 
threads of the sleeve are luted with white lead paste 
in oil. Waterproof adhesive tape is used to close the 
three exit holes in the grenade cover. 

Functioning. The pot functions best in an upright 
position. To ignite it, the arm of the bouchon fuze is 
held down, the safety ring is pulled out, the pot is 
set on a smooth surface, and the bouchon fuze arm 
is released. 

Burning Time. The specifications call for a burning 
time of 2 to 3 min. This has not been met since the 
fuel block and vaporizer tube in a unit of this small 
size are better adapted to a shorter burning time. 
The disadvantages of a longer burning time are: 

1 . At the lower gas rate it requires a very small 
vaporizer tube and oil feed orifice. These would have 
a greater tendency for plugging and malfunctioning. 

2. The slower burning fuel block generates less 
heat, and consequently less smoke, than the com¬ 
position now used. When used indoors the effective 
screening time of the smoke is not significantly in¬ 
fluenced by the emission time of the smoke pot. 

When the pots are burned in a closed room there 
is an initial flash from the British starter and an 
instantaneous generation of smoke. The jet of smoke 
rises to the ceiling and gradually diffuses down. In 
the course of a few minutes the whole room is ob¬ 
scured. A photograph of a unit functioning indoors is 
shown in Figure 36. 

Toxicity of the Smoke. The almost complete ab¬ 
sence of toxic effects from the oil smoke is described 
in the preceding text in connection with the E-23 
floating oil smoke pot. 

Inflammability. Tests were made on the inflamma¬ 
bility of oil smokes. 37 

These tests were carried out in a chamber 7 x 7 x 10 ft 
and also in the open. The smoke from the pots at various 
concentrations was subjected to a continuous 25 watt spark, 


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THERMAL GENERATOR MUNITIONS 



Figure 36. The E— 21 training oil smoke pot function¬ 
ing indoors. 


10,000 v, H in. spark gap, to a lighted kerosene torch, to 
the flash from 15 grams of guncotton, to an electric squib, 
and to the flame of a gasoline blowtorch. A number of these 
tests were repeated several times under various conditions, 
and no evidence of ignition or flaming of the oil smoke was 
encountered. 

Conclusions: It is concluded that oil smokes, made from 
Diol 55, of 0.35-0.45 micron radius, at all concentrations and 
in a confined space are safe from ignition in the presence of a 
spark, squib, lighted gasoline torch, and a flash of guncotton. 

It is further concluded that the E-21, Pot, Smoke, Oil, 
Training (Navy) which produces an oil smoke of about 0.40 
micron radius, at all concentrations and in a confined space 
is safe from ignition in the presence of a spark, squib, lighted 
gasoline torch and a flash of guncotton. 

The jet of smoke as it issues from the pot may be 
ignited with a torch placed within 6 in. of the top of 
the pot. The jet can be ignited from 6 to 12 in. but 
usually extinguishes itself. Above 12 in. the jet has 
cooled sufficiently so that it will not ignite. 38 No case 
of spontaneous ignition of the smoke jet from the 
design previously described was found and the smoke 
cloud itself was never ignited, exploded, nor gave any 
indication of toxic effect on personnel working in the 
chamber. 

30.11.4 Limited Persistence Smoke 

Control of the persistency of oil smoke especially 
for use with amphibious landings is desirable. Specifi¬ 
cations were set up for a bomb to be carried in 100-lb 
quick-opening clusters, and to function on land or 
water for a period of 6 to 10 min. The smoke was to 
dissipate completely at 100 yd at a temperature of 
75 F and a wind velocity of 5 to 10 knots. The screen 
should persist at 50 yd at even higher temperatures. 
Oils of different volatilities were tested in the F-7A 
pots. 52 The results indicated that a volatility about 


that of burning oil should be satisfactory. The design 
of a bomb based on the thermal generator principle 
which would float upright and also function on land 
was not successfully devised. It is suggested that a 
modification of the Mark 72 Model 2 bomb described 
in the following text may hold promise. 

Preliminary tests on an intimate mixture of a 
pyrotechnic fuel and diphenyl were promising. This 
agent has a melting point of 70 C and a volatility in 
the correct range. 

30.12 SULFUR SMOKE GENERATORS 

At least three continuous sulfur smoke generators 
have been built. Two of these were heavy fixed in¬ 
stallations while the third was suitable for modifica¬ 
tion as a mobile field unit. 

30.12.1 MIT-Freeport Sulfur Company 

Generator 

This generator 39 was in the form of a stainless steel 
tubular sulfur boiler fired with natural gas. Undiluted 
sulfur vapor passed from the boiler through a nozzle 
directly into the air where it was cooled by entrain¬ 
ment of the air and condensed to a cloud of sulfur 
particles which formed an obscuring smoke. Particle 
size determinations were made on this smoke. These 
indicated that the best covering smoke was produced 
using a %2-i n - diameter nozzle and a boiler pressure 
of 85 psia. These conditions yielded a particle size 
distribution curve with a peak at 0.23 micron radius. 
Sulfur rates as high as 275 lb per hour were achieved. 

It was found that above a nozzle pressure in the 
vicinity of 8 psi gauge, burning of the vapor neither 
occurred spontaneously nor could be it sustained by 
the application of a flame to the vapor jet. Below 
this pressure, however, the vapors always ignited 
spontaneously, and burned completely. Smokes of 
excellent covering power of an order of magnitude of 
1,000 lb per sq mile were produced. 

Prolonged exposure to the densest parts of the 
smoke cloud, a few feet from the source, caused minor 
irritation of the throat and lungs. In no case was this 
effect seriously uncomfortable. 

30.12.2 Texas Gulf Sulphur Company 

Generator 

This generator 40 was in the form of a unique direct- 
fired sulfur boiling pot in a firebrick setting. Steam 


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SULFUR SMOKE GENERATORS 


449 


was introduced into the pot and used to aid in the 
vaporization of the sulfur. A mixture of steam and 
sulfur vapor under pressures up to 12 psi passed from 
the pot through nozzles to the atmosphere where the 
sulfur condensed to an obscuring smoke. Sulfur and 
steam rates of the order of 600 and 250 lb per hour, 
respectively, were obtained. 

30.12.3 University of Illinois — Kim¬ 
berly Clark Corporation Generator 

This generator 41 was an experimental model in¬ 
tended as a step toward a relatively small, compact, 
mobile field unit. In this respect it was a competitor 
of the continuous oil smoke generators. The model 
was of intermediate capacity between the small 
smoke pots and the larger continuous oil smoke units 
for rear-area screening. The generator itself was de¬ 
signed for complete hand operation, and incorporated 
no powered unit such as motors, pumps, or fans. 
There were no moving parts of any kind except 
valves. The use of critical materials was kept to a 
minimum. The unit could be produced with the use 
of very little stainless steel and possibly without it. 

Briefly, it was a unit weighing 197 lb when un¬ 
charged, and standing 33^ ft high by 20 in. in di¬ 
ameter. One hundred twenty-five pounds per hour of 
sulfur was converted to smoke, while at the same 
time 10 lb of gasoline and 30 lb of water were con¬ 
sumed. The unit incorporated a Venturi high-velocity 
vaporizer for converting the molten sulfur to vapor. 
The combustion of gasoline was carried out in a space 
surrounded by a tangentially wound coil for gener¬ 
ating steam. This steam was used to provide draft 
through the unit by means of a steam injector nozzle. 

Certain disadvantages of the design were evident. 
First, the steam ejector proved to be an inefficient 
means of forcing the combustion gases through the 
unit. This resulted in a somewhat larger consumption 
of fuel and water than should be necessary on the 
basis of the smoke capacity. A more efficient steam 
ejector would make the design appear more favorable. 

Second, it is a characteristic of sulfur smoke that 
the size 1 of these smoke particles which give the most 
effective screen is somewhat smaller than that re¬ 
quired for oil smoke particles. These smaller particles 
were produced by the unit, but the design of the 
vapor dispenser is much more critical than with oil 
smokes. This is a disadvantage, since it means that 
the orifices or slots through which the sulfur vapor is 
emitted must be quite small, and therefore numerous 



Figure 37. Experimental continuous sulfur smoke gen¬ 
erator. 


or of considerable extent, in order to obtain the de¬ 
sired capacity. This is evident from the design of the 
wing jet smoke dispenser on the unit. 

Third, it is an inherent property of a sulfur smoke 
generator that a melting pot must be provided for the 
solid sulfur. This melting pot adds weight and bulk 
to the smoke generator over that required by a com¬ 
parable oil smoke generator. It seems unlikely that 
the preliminary melting and starting period can be 
reduced to less than 5 or 10 min. The melting pot 
also introduces the problem of disposing of its con¬ 
tents of molten sulfur when the unit is shut down. 
Probably the most convenient way of handling this 
would be to provide a drain for emptying this molten 
sulfur onto the ground. In any case, the sulfur melt¬ 
ing pot, with its somewhat longer starting time, its 
additional bulk and weight, and its content of hot 
liquid, makes the generator less mobile than an oil 
smoke generator. 

Description of the Generator 

The experimental generator is shown in Figure 37. 
It is producing sulfur smoke in Figure 38. The in¬ 
ternal construction of two of the principal parts is 
shown in Figure 39. Figure 40 is an assembly drawing 
of the generator (the hand-pressured gasoline and wa¬ 
ter tanks are not shown). 

The unit consists of a cylindrical angle iron frame 
which supports and encloses the four essential parts 
of the apparatus, namely, the burner, the boiler, the 
sulfur pot, and the sulfur vapor dispenser. The unit 
is constructed so that it can be easily disassembled 


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THERMAL GENERATOR MUNITIONS 



Figure 38. The sulfur smoke generator in operation. 


into the four essential parts by the removal of a few 
bolts. 

A standard design of gasoline or kerosene burner, 
modified for application to an enclosed combustion 
chamber and to burn the fuel completely in a small 
volume of combustion space, is attached at the bottom 
of the unit and is used for supplying heat. White 
gasoline is fed to the burner from two 4-gal hand- 
pressured tanks of commercial design. The combus¬ 
tion space is enclosed on the sides by a coil of steel 
tubing, which makes up the steam generating and 
super-heating surface of the boiler. The coil section 
is insulated from the atmosphere with a 2-in. thick 
Fiberglas blanket, which is, in turn, covered by light- 
gauge sheet iron for holding the insulation against the 
outside of the coils, and sealing the combustion 
chamber against excess air. The No. 16 BWG %-in. 
OD tubing from which the coils were made will with¬ 
stand over 300 psi. A convergent-divergent nozzle is 
affixed to the end of the tubing and directed through 
the entrance to the Venturi vaporizer in the bottom 
of the sulfur melting pot. The steam produced by the 
boiler passes through this nozzle. Water is fed to the 
boiler at the lower end of the coil by means of hand- 
pressure tanks of commercial design. 

A hinged covered hopper is provided for charging 
the raw solid sulfur to the sulfur melting pot. This 
pot forms the top section of the apparatus so that the 
bottom of the pot is the roof of the combustion 
chamber. The combustion gases sweep against this 
roof and are ejected through the Venturi vaporizer 
by means of the steam jet described above. Two 
valves control the flow of molten sulfur from the 
sulfur melting pot into the throat of the vaporizer. 



Figure 39. The two lower parts of the sulfur smoke 
generator. 


A sulfur vapor dispenser is provided on top of the 
unit. This is equipped with a baffle to remove un¬ 
vaporized liquid sulfur and return it to the melting 
pot. This dispenser consists of a partial cylinder 
divided into two sections by the baffle. Sulfur vapor 
passes to the upper section from the lower section, 
and liquid sulfur particles are retained in the lower 
section. The upper section of the dispenser is pro¬ 
vided with wing-type slotted jets through which the 
sulfur vapor is ejected into the atmosphere by the 
slight pressure inside. 

Operation of the Generator 

To operate the generator, solid lump sulfur is 
charged to the hopper on the melting pot and pres¬ 
sure is pumped up in the water and gasoline tanks. 
The burner is then lighted and the combustion gases 
are at first allowed to escape through a vent in the 
combustion chamber. With a bleeder valve in the 
upper end of the coil open, water is then admitted 
to the lower end. Dry steam will issue from the 
bleeder valve in a few minutes and this is then closed 
to allow pressure in the coil’to build up. The vent is 
likewise closed and the gases pass out through the 
vaporizer. As soon as the temperature at the top of 
the steam coil reaches the range 500 to 700 F and 
operation is steady, the sulfur control valve is opened 
and liquid sulfur flows from the melting pot to the 
vaporizer. Sulfur smoke is then produced immedi¬ 
ately. Additional sulfur is charged to the hopper from 
time to time, duplicate gasoline and water tanks are 
switched on, and the empty tanks recharged to main¬ 
tain continuous generation of sulfur smoke. 


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451 



Figure 40. Continuous sulfur smoke generator. 


30.13 COLORED SMOKE MUNITIONS 

30.13.1 Floating Colored Smoke Signal 

(DS-4) 

Specifications 

The development of an improved daytime floating- 
distress signal was requested at a conference with 
representatives of the Air-Sea Rescue Agency in 
September 1944. It was specified that the signal 


should conform to Coast Guard specifications which 
limited the size to 7 in. in diameter and 10 in. high. 
The signal was to give an orange smoke visible from 
5,000 ft altitude and two miles distance for a period 
of at least 4 min. 

Historical 

Colored smoke signals are commonly made of 
intimate mixtures of pyrotechnic fuels and volatile 


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452 


THERMAL GENERATOR MUNITIONS 


organic dyes (for example, mixtures of KC10 3 , 
lactose, NaHC0 3 and dyes). These mixtures require 
a fuel with a relatively low heat of combustion. There 
are also restrictions on the shape of the compressed 
block and on the burning rate. In general, the colored 
smoke clouds are small in volume and variable in 
color. 

Several commercial floating distress signals utiliz¬ 
ing the intimate mixture principle have been on the 
market for a number of years. It was felt that a signal 
utilizing the Venturi thermal generator principle 
could be developed that would be superior to these. 
This opinion was verified by tests made on several 
commercial signals compared with an experimental 
model of the thermal generator. 43 

A number of tests were made on different models. 
The results indicated that the Model F-6 thermal 
generator, in which there is a baffle over the Venturi 
tube, would disperse the pure dye efficiently and 
without decomposition. Several units of this type 
had been made up and demonstrated to repre¬ 
sentatives of the Coast Guard and the Air-Sea Rescue 
Agency on Long Island Sound in August 1944. The 
consensus was that the new signal 44 put out a greater 
volume and a better quality of smoke than the com¬ 
mercial signals. Some difficulty was experienced with 
the uniformity of the feeding of the dye, and it was 
recommended that further work be carried on to im¬ 
prove the signal and that its size be made to con¬ 
form with the specifications. 

Theoretical 

The Venturi thermal generator principle has been 
discussed in the preceding text. This principle was 
developed to produce a smoke cloud by atomizing a 
liquid agent in a high-velocity hot gas stream. Es¬ 
sentially, the generator consists of an agent compart¬ 
ment and a fuel compartment. The hot gases from 
the burning fuel pass through a Venturi vaporizer and 
the molten dye mixture from the agent compartment 
feeds into the hot gas stream at the throat section. 
The dye mixture is atomized and vaporized in the 
gases and this mixture is discharged to the atmos¬ 
phere. It issues in a vertical jet which is cooled by en¬ 
training air and the dye vapors are condensed to a 
colored smoke. 

The problem of developing a new type of daytime 
floating distress signal resolved itself into three 
phases. 

1 . Investigation of the properties of a number of 


dyes and dye mixtures and the choice of the most 
suitable for use in this unit. 

2. Design of the unit to obtain the desired heat 
transfer for melting the dye mixture. 

3. Design of the unit to obtain the desired floating 
characteristics. 

In the past, agents such as Diol 55, which remain 
liquid over most of the temperature range en¬ 
countered under field conditions, have been used as 
smoke agents in the thermal generator. The per¬ 
centages of dye compounds which can be dissolved 
in these agents, however, is insufficient to produce a 
smoke having the color intensity necessary for a 
signal. There are several organic dyes having melting 
points near 100 C which, when used in the thermal 
generator, can be melted by the heat of the fuel block 
and fed into the Venturi as liquid agents. 

Proposed dyes were divided into two categories, 
(1) those that do not melt but decompose with evolu¬ 
tion of gas in the neighborhood of the melting point, 
and (2) those which melt in the vicinity of 100 C and 
remain stable at temperatures above the melting 
point for at least 5 min. Dyes in group (1) are ob¬ 
viously unsuitable and were identified by a simple 
test tube heating test. Dyes in group (2), following 
the test tube test, were tried in the signal. Upon 
locating the most suitable dyes, an investigation of 
compatible organic diluents was carried out. The 
purpose of the diluents was to give a mixture having 
a melting point considerably below that of the pure 
dye. Such a mixture would facilitate melting and in¬ 
sure more uniform operation. 

The unit was designed with a maximum of the 
outer surface of the agent compartment exposed to 
the hot gases from the burning fuel. The greatest 
amount of heat to melt the dye is transferred by 
radiation from the surface of the fuel to the bottom 
of the agent compartment. An annular region be¬ 
tween the agent compartment and the outer case 
allows a certain amount of convection transfer of 
heat from the hot gases to the dye mixture. Further¬ 
more, this region serves to insulate the agent com¬ 
partment from the cold outer wall. 

The signal functions in any position from approxi¬ 
mately 10° above horizontal to the vertical. The 
weight of the unit is so distributed that it tilts near 
the end of the emission and floats with one side lower 
than the others. The entrance to the feed tube is 
located at the lowest point in the agent compartment 
in either the upright or tilted position. This design 
gives a higher loading efficiency than one in which 


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COLORED SMOKE MUNITIONS 


453 



Figure 41. Colored smoke floating distress signal, Model DS-4. 


vertical functioning only is possible. The latter de¬ 
sign requires the use of more ballast to keep the unit 
floating upright. 

Description of the Floating Colored Smoke 
Signal (DS-4) 

The proposed design 42 is shown in Figure 41. This 
is known as the floating distress signal , Model DS-4. 
Hand-fabricated units embodying the essential fea¬ 
tures of this model have been made and tested suc¬ 
cessfully. However, no units have as yet been con¬ 
structed precisely as shown in the drawing. 

The floating distress signal, Model DS-4, is 7 in. in 
diameter and 10 in. high. The complete unit including 
dye and fuel weighs about 12 lb. Of this, approxi¬ 
mately 5 lb are dye mixture and 3.3 lb are fuel. The 
assembly is composed of three subassemblies: the 
fuel container, the agent container, and the outer 
can or pot. 

The fuel mixture is pressed into the fuel container 
in one charge under a dead load of about 1,000 psi. 
The composition of this mixture is as follows: 


Slow base mix 

1,200 g 

NH4NO3 

86 % 

Charcoal 

9.9% 

Naphthalene 

1 -1% 

Boiled linseed oil 

3 % 

Fast base mix 

300 g 

NH4NO3 

86 % 

Charcoal 

11 % 

Boiled linseed oil 

3 % 

Starter composition 

20-24 g 

KNO3 

53 % 

Silicon 

39.2% 

Boiled linseed oil 

2 % 

Charcoal 

5.8% 


The top surface of the block is coated with a pyroxy¬ 
lin lacquer for moisture protection. A waterproof 
Quickmatch is then fastened to the block. This picks 
up the spit from the fuze and insures subsequent ig¬ 
nition of the fuel. 

The agent container is assembled from its com- 


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454 


THERMAL GENERATOR MUNITIONS 


ponent parts, and all joints are copper brazed. The 
feed hole and vent hole are soldered closed and the 
container tested for leaks. The agent container is 
then seam-welded onto the pot. The molten dye 
mixture composed of 50% Calco Oil Orange Y—293 
and 50% diphenylamine is charged through the filling 
hole and the plug inserted. 

The final assembly consists of registering the fuze 
assembly directly over the Venturi and crimping 
the top cover, then slipping the loaded fuel can in 
from the bottom and crimping the bottom cover. 

Operation of the Signal 

The first step in functioning the DS-4 signal is to 
remove the seal cup protecting the bouchon fuze. The 
cotter pin is then removed from the fuze, thereby 
initiating a 15-sec delay igniter composition. The 
spit from the fuze travels down the Venturi and is 
picked up by the Quickmatch on the surface of the 
block. The initial pressure surge from the burning 
fuel ruptures the fusible disks covering the exit holes. 
The heat from the fuel block melts the fusible plugs 
and the dye mixture. The liquid dye feeds into the 
Venturi due to the pressure from the fuel compart¬ 
ment vented into the agent compartment through a 
hole near the top of the annulus. The dye mixture is 
atomized and vaporized in the hot gases and this 
mixture is discharged to the atmosphere, where it 
condenses to form a colored smoke. 

Comments on the Proposed Design 

Although the design shown in Figure 41 has not 
been built, it is based on the experience from con¬ 
siderably more than a hundred tests on numerous 
experimental signals which were built and func¬ 
tioned. These tests indicated that the high-velocity 
thermal generator principle is a more efficient method 
of vaporizing dye for colored smokes than is the inti¬ 
mate mixture of dye and fuel. Since the design shown 
in Figure 41 has not been built and tested, certain 
dimensions and weights cannot be specified until this 
is done. 

The DS-4b model is the latest design that has been 
built and operated a limited number of times. The 
DS-4a model preceded it. The general arrangement 
of these designs together with several earlier ones is 
shown in Figure 42. 

The Model DS-4a depended on the suction in the 
Venturi throat to feed the molten dye and required 
up to 40 sec for smoke emission to start. It then 
generated an intensely colored orange smoke cloud 


having several times the volume of the cloud emitted 
by the best available commercial signals. After being 
cooled below 32 F it functioned satisfactorily in 
water at 32 F. 

The DS-4b utilized the pressure in the fuel com¬ 
partment to aid in feeding the molten dye. Smoke 
emission then began in a shorter time. 

The DS-4 can be expected to give smoke within 10 
to 15 sec after the fuel is ignited. 


Development 

The development proceeded along two parallel 
lines. On the one hand, it was necessary to find a suit¬ 
able colored smoke dye or dye mixture for use in the 
signal, and on the other, to design the unit to func¬ 
tion efficiently and to meet the requirements of the 
Air-Sea Rescue Group. 




2 F-7 



5 DS-la 




8 DS-40 















. 


3 F- 7A 








' 


6 DS-2 



9 DS-4b 


Figure 42. Outlines of several of the models tested in 
developing the floating distress signal. 


Open Dye Chamber. The initial work on the col¬ 
ored smoke signal was done with the F-6 type ther¬ 
mal generator shown in Figure 42. This functioned 
very well in a number of tests with Calco Y-293 dye 
but the emission time could not be extended to the 
required 4 min without frequent plugging of the feed 
holes and intermittent smoke emission. This design 
allowed free access to the dye chamber by the hot 


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COLORED SMOKE MUNITIONS 


455 



Figure 43. Smoke target identification bomb, Mk 72, Mod 2. 


gases from the vaporizer. This aided in melting the 
solid dye. Unevaporated dye from the vaporizer was 
returned to the dye chamber and recycled. 

Dyes. The following dyes were satisfactory in the 
F-6 pot: Calco Oil Orange Y-293, Calco Oil Green 
CG, duPont Oil Orange, and duPont Oil Yellow N. 

Addition Agents in the Dye. Addition agents, such 
as diphenyl oxide and diphenylamine, were used 
with the dye in amounts up to 50%. These were 
effective in lowering the melting point, diluting both 
the dye and decomposition products, avoiding the 
plugging of the feed holes, and giving a longer and 
more uniform smoke emission time. The low melting 
point of the dye mixture, however, made the open 
dye chamber unsuitable. 

Closed Dye Chamber. The work was then directed 
toward adapting the F-7 type thermal generator 
with its closed agent compartment for use as a signal. 
The hot gases from the vaporizer do not enter the dye 
chamber in this design, and no provision is made for 
recycling unvaporized dye. The rate of feed of dye 
must, therefore, be controlled more accurately to 
avoid spraying liquid dye from the signal. This design 
was carried over into the DS-3. Irregular smoke 
emission was encountered with the closed dye cham¬ 
ber. This was first attributed to a recurrence of the 
feed hole plugging difficulties noticed when pure dye 
was used in the open dye chamber design. It was later 
found that it was due to the slow rate at which the 
dye melted in the chamber. A considerable amount 
of solid dye was left on the cold outer walls of the 
hamber. 


Hot Gas Jacket for Dye Chamber. This led to the 
DS-4a with the dye chamber completely surrounded 
with hot gases from the fuel block. This greatly in¬ 
creased the melting rate of the dye and eliminated 
the difficulty from erratic smoke emission. This de¬ 
sign, modified by pressurizing the dye chamber and 
providing a feed tube for operation in a tilted posi¬ 
tion, resulted in the design proposed in Figure 41. 

30.13.2 Colored Smoke Target Identi¬ 
fication Bomb, Mk 72, Mod 2 

A colored smoke target identification bomb, 
equipped with a nylon parachute to be dropped 
from high-speed combat aircraft at low altitudes was 
developed 28 at the request of the Navy Bureau of 
Ordnance. The bomb, designated Bomb, Target 
Identification , Smoke, Mk 72, Mod 2 is shown in 
Figure 43. It weighs about 53 lb, consisting of: metal 
parts, 22.0 lb; fuel, 9.4 lb; dye, 18.7 lb; and parachute 
assembly, 3.4 l b. The bomb generates a dense colored 
smoke for 4.5 to 6.5 min. The colors now available are 
yellow, yellow orange, a bright orange, and red 
orange. The bomb functions on a thermal generator 
principle and contains fuel and dye in separate 
compartments. 

The original specifications indicated that the bomb 
was to be launched at about 200 ft altitude from a 
plane diving at 300 knots. It was to be equipped with 
a parachute which was to act only as a snubber. The 
fuze was to function when the parachute opened and 
have a delay of about 5 sec. The bomb was to emit a 


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456 


THERMAL GENERATOR MUNITIONS 


colored smoke for 5 min, 10 sec, ±40 sec. Orange and 
red smokes were preferred, but there was a definite 
interest in yellow, green and violet smokes. 

Colored smokes have generally been produced by 
burning intimate mixtures of dye and fuel. A typical 
mixture of this type contains the following: 22% 
KC10 3 , 9% sulfur, 24% NaHC0 3 , and 45% dye. 
These materials are thoroughly mixed and then 
pressed into the munition. The dye is vaporized by 
the burning fuel, and upon issuing from the generator, 
condenses to form a colored smoke. There are a 
number of limitations to this type of smoke munition. 
In general, the intimate mixtures are suitable for 
small units, such as colored smoke grenades, but are 
not so suitable for use in large munitions. The chief 
difficulties encountered in large colored smoke muni¬ 
tions is in controlling the burning rate of the fuel and 
the tendency toward decomposition or flaming of the 
issuing dye vapor when the fuel is too hot. The in¬ 
corporation of cooling agents such as sodium bicar¬ 
bonate to prevent undue decomposition of the dye 
decreases the thermal efficiency of the fuel. The dyes 
used are often expensive, especially the anthraquinone 
type, and certain mixtures have a tendency to explode 
when ignited. The maximum amount of dye that can 
be incorporated in a mixture is about 50% by weight. 

Preliminary tests indicated that a Venturi-type 
thermal generator described above was capable of 
generating a colored smoke cloud superior to that 
generated by the standard intimate mixture com¬ 
positions. 

The 12-lb F-7A experimental thermal generator 
pot was tried for this use. This was not designed for 
dropping from aircraft, and provision had to be made 
to retard its fall by means of a parachute. Tests with 
this unit were unsatisfactory, due to the tendency of 
the parachute to tip the munition over on its side. 
When in this position, the dye would not discharge 
completely. For this reason, the design of a thermal 
generator which would function in a horizontal as 
well as a vertical position was undertaken. 

Principle of Operation 

The design consisted of two compartments, one of 
which contained fuel and the other the dye in a solid 
cake. The dye compartment was surrounded by an 
annulus through which the hot gases passed. The dye 
fed into the annulus through several holes located 
at the base of the compartment. Vaporization took 
place in the annulus and the vapor issued through a 
single orifice in the top of th^ unit. The development 


of the target identification bomb was based on this 
principle. 

The fuel block consists of ammonium nitrate and 
carbon, and is pressed into a container in the nose 
end of the bomb. The dye is cast into a separate 
compartment above the fuel. Hot gases from the 
burning fuel block pass through orifices in the top of 
the fuel chamber into the annulus surrounding the 
dye compartment. Heat from these gases is trans¬ 
ferred through the walls of the dye compartment and 
melts the dye which then flows, through holes in the 
bottom of the dye compartment, into the annulus. 
Here the hot gases come in contact with the molten 
dye and vaporization takes place. A spiral baffle is 
used in the annulus to insure better contact between 
dye and gas. The fuel gas-dye vapor mixture issues 
from an orifice in the tail of the bomb. 

Description of the Target Identification Bomb 

The metal components of the bomb consist of three 
major assemblies: (1) the outer case, (2) the fuel 
compartment, and (3) the dye compartment. The 
fuel container and dye compartment are crimped and 
riveted together and constitute the inner assembly. 
This is slipped into the outer case and brazed in 
place. The parachute pack is located on the tail end 
of the bomb. 

The fuel block has the following composition: 


Base mixture 

3,000 g 

NH 4 NO 3 

86 % 

Boiled linseed oil 

3 % 

Charcoal 

8.3% 

Naphthalene 

2.7% 

Top mixture 

1,250 g 

NH 4 NO 3 

86 % 

Boiled linseed oil 

3 % 

Charcoal 

11 % 

Starter 

30 g 

KNO 3 

53.0% 

Silicon 

39.2% 

Charcoal 

5.8% 

Boiled linseed oil 

2 .0% 

The mixture is pressed in three increments into the 
fuel can under a dead load of 35 tons, or about 1,600 

psi. The surface of the block 

is sprayed with a 

pyroxylin lacquer for protection against moisture. A 


waterproof Navy Quickmatch is attached to the top 
of the block in a web-like pattern. This picks up the 


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COLORED SMOKE MUNITIONS 


457 


flash from the fuze and ignites the block uniformly 
over the surface. 

The flange which projects from the bottom of the 
agent compartment contains eight No. 2 holes for the 
hot fuel gases to pass through. It also forms the 
bottom of the annulus. Eight dye feed holes of the 
same size are provided opposite the holes for the fuel 
gas. These are closed with 50/50 solder before the 
dye is cast into the dye compartment. 

After the inner assembly is placed in the outer case, 
the top plate of the agent compartment is brazed to 
the outer case. A fusible diaphragm 0.10 in. thick is 
soldered over the vapor exit hole after the bomb is 
charged with dye. With the fuze assembly in place, 
complete protection from moisture is assured. 

The nylon parachute is a baseball type. Four 
steel cables, 34 in. in diameter, are attached to the 
shroud lines of the parachute and to load lugs on 
the tail plate of the bomb. A fifth cable, in. in 
diameter, is attached to the parachute and fastened 
to the arming plug of the fuze. The parachute case 
slips into the recess at the tail of the bomb and is 
bolted to the outer case. This parachute was manu¬ 
factured by General Textile Mills, Inc., New York. 

The fuze is a modification of the Navy submarine 
identification flare firing mechanism, Mk 10, and is 
actuated by the opening of the parachute. When the 
arming plug is pulled back by the opening of the 
parachute, it compresses a spring which acts on the 
firing pin. When the plug has been pulled far enough, 
it disengages the firing pin, and the latter strikes the 
primer which sets off the ignition mixture in the 
spitter tube. The flash travels down the fuze well and 
ignites the Quickmatch and then the fuel mixture. 

The bomb, completely assembled and ready for 
dropping, is approximately 37 in. long and has a 
diameter of 8% in. It weighs 5334 lb. 

Development 

The early experimental designs tested prior to the 
design described in the preceding text are omitted 
from this account. When the work reached a promis¬ 
ing stage 15 units were fabricated by hand. These in¬ 
corporated most of the principles of the later design. 
These functioned satisfactorily in static tests and one 
functioned when dropped from 45 ft in free fall onto 
concrete. Corrugations had been provided in the case 
and in the walls of the agent compartment to localize 
deformation on impact. These corrugations were ef¬ 
fective in this respect. Twelve of these bombs were 
fitted with rayon parachutes and delivered to the 


Naval Proving Grounds at Dahlgren, Virginia. There, 
11 were dropped from a Navy F-6-F fighter plane. 
They were released at an altitude of 75 to 125 ft and 
at a speed of from 270 to 300 knots. Five of the bombs 
were duds due to fuze failure. Five functioned satis¬ 
factorily for varying lengths of time until the issuing 
dye vapors flamed. Further tests showed that the 
rayon parachutes caught fire and ignited the dye 
vapor. One bomb functioned satisfactorily. 

Twenty-five bombs equipped with noninflammable 
nylon parachutes and improved fuzes were made and 
taken to Dahlgren for further drop tests. These were 
loaded with four different orange dye mixtures and a 
yellow dye. Twelve of these were dropped as before 
from an F-6-F plane. One fuze failure was en¬ 
countered, and two bombs flamed after emitting 
about one-half the dye. The remaining eight bombs 
functioned satisfactorily, giving a colored smoke 
emission time of about 534 min. 

To determine whether these bombs would present 
a hazard when exposed to enemy gunfire, three bombs 
were set up on a firing range. Single shots were fired 
into the bombs using a special .50-caliber incendiary 
bullet. When one of these bullets was fired into the 
nose of the bomb, the fuel was ignited in such a 
manner that the nose of the bomb was blown off. 
When the test was repeated later, after aging the fuel 
blocks, no ignition of the blocks could be obtained 
with incendiary bullets. 

One hundred twenty-nine additional target identi¬ 
fication bombs were delivered to the Navy Bureau 
of Ordnance for further tests. These were charged as 
follows: 

45 with Calco Oil Orange Y-293 
40 with duPont Oil Yellow N 
44 with Calco Oil Scarlet II with 15% 
diphenylamine, or National Oil Scarlet 
6 G with 15% diphenylamine. 

The parachutes on these bombs were of 234-oz 
nylon instead of the 4 oz used on the 25 bombs pre¬ 
viously delivered to Dahlgren. 

Control of Flaming. The chief difficulty has been 
with flaming of the dye vapor, usually as a result of 
the hot bomb case igniting either the parachute or 
dry grass in contact with the case. In 53 trials using 
bombs without parachutes or with nylon parachutes, 
five inflamed spontaneously or as a result of grass 
fires. Four were ignited intentionally to test flaming 
inhibitors. Out of eight trials with rayon parachutes 
attached, seven bombs inflamed. 


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458 


THERMAL GENERATOR MUNITIONS 


Tests were made using Calco Oil Orange Y-293 
mixed with hexachlorobutadiene and with Chlorpro- 
pane Wax 130, (the latter supplied by the Hooker 
Electrochemical Company, 85% octachloropropane, 
15% pentachloropropane). The purpose of these dil¬ 
uents was to inhibit flaming of the issuing dye vapor 
by raising the flash point. These agents had much the 
same effect as diphenylamine on the intensity of the 
color of the smoke. Insufficient data are available to 
draw any conclusions as to the merits of these agents 
as flame inhibitors. 

Ignition of the cloud has been prevented until near 
the end of the color emission, even in the presence of 
burning grass, by reducing the diameter of the vapor 
exit hole from 1% in. to % in. or by adding 25% 
Chlorpropane Wax to the dye. 

Effect of Position. The bomb was found to operate 
best with the long axis horizontal. However, it has 
operated successfully in a vertical position nose down; 
with the long axis at a 30° angle to the horizontal and 
the nose high; and in intermediate positions. In 
general, the dye emission time decreases as the bomb 
is changed from the horizontal to a vertical position. 

Dyes. The desirable properties for a dye suitable 
for use in colored smoke munitions of the thermal 
generator type munition having separate agent and 
dye compartments are as follows. 

1. The dye should preferably be a crystalline com¬ 
pound and have a melting point under 150 C, or a 
melting point of 100 C when mixed with a small pro¬ 
portion of a melting point depressant, such as di¬ 
phenylamine (less than 25% diphenylamine should 


be necessary). The dye should not undergo decom¬ 
position when heated to high temperatures for a 
short time. It is desirable for the dye to be stable for 
about 3 to 4 min at temperatures 50 to 100 C above 
the melting point. 

2. A rapid preliminary test may be run on a new 
dye by heating 5 g in a test tube and observing how 
it melts. If it melts and flows freely then 100 g should 
be tested in a small smoke generator. If this gives 
promising results the final and conclusive test is 
carried out in the full-scale munition. 

Four dye mixtures were found to give excellent 
smoke clouds: (1) Calco Oil Scarlet II, or National 
Oil Scarlet 6G with 15% diphenylamine (red orange 
cloud), (2) Calco Oil Orange Y-293 (bright orange 
cloud), (3) Calco Oil Orange 7078-V or duPont Oil 
Orange with 15% diphenylamine (yellow orange 
cloud), (4) duPont Oil YellowN (bright yellow cloud). 

These dyes are all common azo dyes made by 
simple coupling reactions and are readily available 
from several manufacturers. The addition of di¬ 
phenylamine generally lowers the melting point. If 
added in too large quantities, however, it dilutes the 
color of the cloud. The Oil Orange (Color Index No. 
24) dye is particularly sensitive to an excess of 
diphenylamine. 

The search for a satisfactory violet dye or a blue 
dye for mixing with red has so far been unsuccessful. 
The majority of blue and violet dyes are of the 
anthraquinone type and are less suitable than azo 
dyes. This is due to the high melting point char¬ 
acteristic of this class. 


SECRET 



Chapter 31 

FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 

By E. W. Comings 


31.1 INTRODUCTION 

number of the munitions described in Chapter 
30 function by vaporizing a liquid agent. This 
vaporization is carried out with a hot gas generated 
by a fuel block within the munition. The fuel block 
burns slowly and smoothly during the functioning 
time of the munition. It burns without using air or 
oxidizing agents other than those included in the 
block itself. In this way hot gases are generated under 
sufficient pressure to cause flow through the channels 
in the munition without using pumps or blowers. 4-8 
The latter would be needed if combustion with at¬ 
mospheric air were used to supply the hot gases. 

Fuel blocks giving satisfactory performance in a 
number of munitions ranging in size from a 1-lb 
training candle to a 125-lb generator have been 
made. 1 Blocks for two munitions were successfully 
carried through limited production. 

Blocks of two types were made, (1) pressed, and (2) 
cast. The pressed mixture consisted of NH 4 N0 3 , 
charcoal, a linseed oil binder, and an additive such as 
KN0 3 , NH 4 CIO 4 , or NH 4 CI to regulate the burning 
rate. This mixture was formed into blocks in a 
hydraulic press. Cast blocks consisted of NH 4 N0 3 , 
charcoal, 1.0M H 3 P0 4 , NH 4 C1, and an additive such 
as NaN0 3 or starch to regulate the burning rate. 
These were melted and poured into the fuel container 
at a temperature of around 115 C. 

The factors involved in the control of burning 
characteristics have been systematically studied. Of 
the ingredients used, charcoal is the least uniform 
and causes the greatest variation in block-burning 
characteristics. Treatment of charcoal with K 2 C0 3 
makes the block burn more rapidly; treatment with 
H 3 P0 4 reduces the block-burning rate. The block¬ 
burning rate can be changed by (1) varying the char¬ 
coal particle size, (2) modifying the charcoal surface 
properties as by treatment with K 2 C0 3 or H 3 P 04 , 
and (3) by formula variation. The latter was the 
method most commonly used. Substitution of KN0 3 , 
NaN0 3 , or NH 4 CIO 4 for part of the NH 4 N0 3 in¬ 
creased the burning rate. Addition of NH 4 CI to the 
mixture or substitution of naphthalene (or starch in 
the cast block) for charcoal decreased the burning 


rate. The method of changing charcoal surface 
properties has not been thoroughly investigated but 
offers promising possibilities. 

The conditions under which the block burns affect 
the burning characteristics. Increasing the initial 
block temperature, and increasing the gas pressure 
on the block during burning, increases the burning 
rate. For blocks pressed into metal cans, a cardboard 
or stencil board inner liner in the can between the 
block and the metal prevents burning down the side. 

A curious type of irregular and objectionable burn¬ 
ing known as surging has been observed in a few 
cases when these mixtures were burned under pres¬ 
sure. Data indicate that this is caused by two reduc¬ 
ing agents present in the mixture at the same time. 
These may be two different chemical compounds or 
the same compound (charcoal in this case) with 
different activities. 

A waterproof lacquer (Special 6C) was effective in 
waterproofing the exposed surface of a fuel block 
against tropical storage conditions for 15 days. 

Pressed NH 4 N0 3 -charcoal-linseed oil blocks show 
an increase in burning rate with age for the first three 
weeks after pressing. After three weeks no further 
change is observed. 

Gases from a surging and a smooth burning block 
have been analyzed and a surging mechanism 
postulated. 

All the fuel blocks used in the thermal generator 
munitions described in Chapter 30 have, up to the 
present time, included powdered hardwood charcoal 
as a major ingredient. Hardwood charcoal is not 
manufactured to specifications which will insure re¬ 
producible burning properties of the fuel blocks, but 
it is likely that it could be manufactured to such 
specifications. A fuel block which does not contain 
charcoal has also been carried through preliminary 
development, and offers much promise. 3 It contains 
guanidine nitrate. 

31.2 DESCRIPTION OF THE FUEL 
BLOCKS FOR THE THERMAL GEN¬ 
ERATOR MUNITIONS 

Many different sizes and shapes of thermal genera¬ 
tor munitions, ranging from a 1-lb training pot to a 



SECRET 


459 


460 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


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SECRET 


* Block height in normal production operations varies ±0.1 inch from values given, 
t Weight of starter mix not included, 
t DPA: diphenylamine. HD: distilled mustard gas. 

§ Block density calculated from weight and dimensions given. 














Table 2. Fuel block formulas for thermal generator munitions. 


PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


461 


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SECRET 


* Starter is poured on block as a thick slurry, 
t Not a Venturi unit. 
t 40% Si, 54% KN03, 6% charcoal. 











462 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


125-lb generator, have been made during the develop¬ 
ment work. Differences in size, shape, and required 
burning times of these munitions necessitated a wide 
range in the burning rate of the fuel. In Table 1, the 
physical characteristics of the more important ther¬ 
mal generator munitions are compared. In Table 2, 
the formulas of fuel mixtures for the munitions are 
listed. These formulas are varied as necessary to 
compensate for variations in the ingredients. 

Pressed blocks have been used much more ex¬ 
tensively than cast, and a major part of the work was 
done on mixtures that were pressed into E29 a and 
E29R1 a type fuel cans. 

Cast mixtures have been used for the slower burn¬ 
ing compositions of large diameter and low block 
height. Cast and pressed mixtures will be discussed 
separately because of the differences in their proper¬ 
ties and methods of manufacture. 

31.3 PRESSED FUEL MIXTURES CON¬ 
TAINING CHARCOAL 

These mixtures are composed of charcoal, NH 4 N0 3 , 
a linseed oil binder, and an additive such as KN0 3 or 
NH 4 CI to regulate the burning rate. 

31.3.1 Block Properties 

The volume of gas, reduced to a standard tem¬ 
perature of 60 F and a pressure of 760 mm of mer¬ 
cury, produced by a burning pressed block ranges 
from approximately 12.0 to 14.6 cu ft per lb of 
mixture (0.75 to 0.92 1 per g). The theoretical volume 
of gas measured under the same conditions for the 
reaction 

NH 4 NO 3 + C —^ CO + 2H 2 0 + N 2 

is 16.35 cu ft per lb of mixture (1.02 1 per g). For the 
reaction 

2 NH 4 NO 3 + C —^ C0 2 + 4H 2 0 + 2N 2 

the theoretical volume of gas is 15.4 cu ft per lb of 
mixture (0.96 1 per g). 

Analysis of the gases from a burning E29 block 
showed the following gas composition: 


h 2 o 

48.8% 

C0 2 

13.5% 

nh 3 

0.6 

CO 

5.2 

no 2 

0.0 

n 2 

26.1 

NO 

0.0 

h 2 

5.8 


a The E29 can is hexagonal, with the dimensions: 2.65 in. 
across flats, height 5 in., area 36.6 sq cm. The E29R1 can is 
round, with the dimensions: 2.52-in. diameter, height 5 in., 
area 32.3 sq cm. 


This corresponds roughly to the reaction 
6NH4NO3 + 4C 

11H 2 0 + CO + 3C0 2 + 6N 2 + H 2 

which gives 0.98 1 per g of mixture at 16 C and 
760 mm Hg. The calculated amount of heat evolved 
is 0.685 kcal per g of mixture. This compares with 0.72 
to 0.75 for black gunpowder. A fuel mixture contain¬ 
ing 5% charcoal instead of 11% will yield slightly 
more gas per gram of mixture but 17% less heat. 

By using the sodium “D” line reversal technique, 12 
the flame temperature 0.5 in. above the top of the 
fuel can was measured for an E29 block burning in 
the open. Values ranged from 2600 to 3000 F. Gas 
temperatures measured b by a shielded thermocouple 
placed about 8 in. above the enclosed burning mix¬ 
ture ranged from 1100 to 2100 F. In general, lower 
temperatures were associated with slower burning 
compositions. 

Burning rates for any composition in grams per 
minute are roughly proportional to the burning sur¬ 
face. This relation can be conveniently expressed as 
grams of mixture burned per minute per square centi¬ 
meter of burning surface. Rates from 1.2 to 4.8 g per 
min per sq cm have been obtained in pressed units 
burned in surroundings at 25 C and 1 atm pressure. 
This corresponds roughly to a gas evolution rate of 
from 1.08 to 4.3 1 (at 16 C and 760 mm Hg) per min 
per sq cm. 

The density of the block is 1.30 ± 0.20 and is in¬ 
fluenced by pressing technique, particle size, and 
nature of the ingredients. This density range corre¬ 
sponds to 24 ± 12% void space in the pressed block. 

The ignition temperature and nature of the de¬ 
composition of the mixture are dependent upon the 
rate and method of heating. The ignition temperature 
of the mixture used in the E29 fuel block, as deter¬ 
mined by heating the loosely packed powder in a No. 
8 brass detonator tube (0.218 in. diameter x 1.88 in. 
long) was 200 to 240 C. A complete E29 block heated 
in a Wood’s metal bath at a rate of 12 C per min 
ignited at 220 C. 

Heat conductivity of the pressed mixture is poor. 
A thermocouple, pressed in the center of an E29 
block about 134 in- from the edge, lagged a thermo¬ 
couple at the edge by 110C when a heating rate of 
12C per min was maintained at the edge. 

The pressed mixture, in the absence of moisture, 


b Measurements were made in a standard volume tester 
described in the following text. 


SECRET 





PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


463 



60 


50 


40 


x 

30 u. 
o 
2 
2 
Z 

20 “ 
Q. 
O 


10 


0 


-10 


Figure 1. Temperature and pressure of gases from 
burning E29Rl-tvpe fuel blocks. 


is not particularly corrosive to steel. Corrosion is 
serious when the mixture is moist. 

When properly made, blocks show good mechanical 
stability. E29 blocks are able to withstand impact on 
concrete at 300 fps without serious breakup. 


31.3.2 Manufacturing Procedure 

Salts such as ammonium nitrate, potassium nitrate, 
and ammonium chloride, were dried at 100 to 110C 
for 6 hr and stored at a relative humidity less than 
50%. Charcoal was blended into uniform lots by 
tumbling in a large mixer of about 13 cu ft capacity. 
Ingredients were mixed in a 2-ft diameter Simpson 
intensive mixer for 20 min in an air-conditioned room. 
British starter composition was mixed by hand on a 
glass plate. 

The mixture was pressed into cans in several incre¬ 
ments with a hydraulic press and the starter mixture 
was pressed on with the last increment. Steel retain¬ 
ing forms were used to prevent the cans from de¬ 
forming. The rams were made of wood and in some 
cases wooden rams were fitted with a brass face. 

After pressing, every effort was made to protect the 
blocks from moisture. Many were stored in metal 
cabinets containing CaCl 2 . Most of the blocks were 
coated with a special pyroxylin base lacquer desig¬ 
nated as Special 6C made by Pyroxylin Products Co., 
Chicago, Illinois. 


31.3.3 Testing Fuel Blocks 

The burning properties of the blocks were tested by 
burning them in four ways: (1) in their appropriate 



MINUTES 


Figure 2. Typical gas flow rate — time curves for an 
E29-type block. 


unit, (2) in the open, (3) in a special gas flowmeter 
known as the volume tester, and (4) in a unit known 
as the surge tester. 

The Volume Tester 

The volume tester is a flowmeter in which the gas 
is discharged through a sharp-edged orifice. The pres¬ 
sure drop across the orifice, along with the tempera¬ 
ture of the effluent gases, is measured and used to 
compute the instantaneous rate of gas flow at any 
time during a test. By graphical integration of the 
instantaneous flow rate over the burning time of the 
block, the total volume of gas produced is measured. 

From this apparatus two types of volume flow rate 
vs time curves may be obtained. In the first, the gas 



SECRET 











































































464 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 



Figure 4. Tester to measure volume and temperature 
of gases from E23 fuel block. 


volume under the conditions of temperature and 
pressure existing at the orifice is used. In the second, 
the gas volume is reduced to a standard temperature 
of 60 F (16 C) and 1 atm pressure. The latter volume 
rate is proportional to the mass flow rate, assuming 
that the gas has a constant molecular weight. Data 
for flow rates under actual conditions seem to show 
slightly better correlation with unit performance. 
Representative flow rate vs time curves of both types 
are shown in Figure 2 for an E29-type block. The gas 
pressure on the block inside the unit above that of the 
surroundings and the effluent gas temperature are 
shown in Figure 1. The volume testers used for the 
E29- and E23-size fuel blocks are shown in Figures 
3 and 4. 

The Surge Tester (for 0-100 psi) 

A surge tester for E29 blocks is shown in Figure 5. 
The surge tester permits variation of the pressure on 
a burning fuel block by increasing or decreasing the 
size of the gas exit orifice in a closed cylindrical vessel 
containing the block. For the E29 fuel block, the 
cylindrical vessel was made from 3-in. extra strong 
steel pipe. One end was welded shut with %-in. steel 



plate. The other end was threaded and was closed 
by a pipe cap which allowed insertion and removal 
of the fuel block. 

The gases of combustion are vented through a 
%-in. orifice drilled in the side of the pipe. The gas 
exit area is varied by moving a conical plug into or 
out of this orifice with the screw adjustment shown. 

A safety valve is incorporated in the equipment. 
The simple weighted orifice plug-type shown in the 
sketch has proven satisfactory. The area of this 
safety orifice should be at least 3^5 the area of the 
fuel block surface. The operator should be protected 
by a steel-covered or concrete shelter. The safety 
valve, set for the highest pressure to be reached, 
should be checked before each test to be sure it is not 
jammed. The pressure regulator threads should be 
oiled and free to turn easily. A test should not be 
started without this preparation. At the beginning 
of the run the exit orifice is completely open. The 
regulator plug is gradually screwed in, slowly in¬ 
creasing the pressure. If surging occurs it can be de¬ 
tected immediately both by the sound and by the 
characteristic rhythmic motion of the pressure gauge 
needle or manometer fluid. 


31.3.4 The Control of Pressed Block 
Characteristics 

The variables involved in the control of block 
characteristics may be grouped under four headings: 
(1) variables due to ingredients used, (2) variables 
due to njanufacturing procedure, (3) variables due to 
formula change, and (4) variables due to the condi- 


SECRET 























































PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


465 


5 

O 

O 

£ 3.0 

ui 

a. 

z 2.9 
2 
a: 

uj 2.8 

Q. 

? 2.7 

UJ 

2 2.6 
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1 ~ 3.30 3.40 3.50 

® SURFACE AREA IN SQ M 





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M 

r 


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/ 




' ^SURFACE 

, AREA 







5 10 15 20 

MASS MEDIAN PARTICLE DIAMETER IN MICRONS 


Figure 6. Burning rates of E29Rl-type blocks made from different bags of Flower City charcoal vs particle size and 
surface area of charcoal. 



SURFACE AREA IN SO M PERG 

Figure 7. Burning rate of E29Rl-type blocks as a 
function of the surface area of the charcoal. 


tions under which the block burns. Discussion follows. 

Variables Due to Ingredients 

Variables in Charcoal . The charcoal is a source of 
major variation in burning time. Rather pronounced 
differences in burning time for different bags of char¬ 
coal are obtained. 

Samples from each of five bags were examined to 
determine (1) particle size distribution by micro¬ 
scopic count, (2) per cent ash, (3) per cent volatile 
matter at 105 C, and (4) surface area by dye adsorp¬ 
tion. No definite correlation between burning rate 
and per cent ash or per cent volatile matter was ap¬ 
parent; however, a fairly good correlation between 
burning rate and particle size was observed, the 
burning rate increasing with a decrease in particle 
size. This is shown in Figure 6. 

1. Effect of charcoal particle size. In a systematic 
study of the effect of carbon particle size on burning 


K 3 

5 2 



MINUTES 


Figure 8. Gas flow rate vs time for E29R 1-type 
blocks made with different charcoal size fractions. 


characteristics, oak charcoal flour of airflow grade, 
which was supplied by the Tennessee Eastman Corp., 
was separated into four particle size fractions using 
an air classifier. E29R 1-type fuel blocks were made 
from each fraction and burned in the volume tester 
after predetermined periods of aging. Each charcoal 
fraction was analyzed for particle size distribution, 
per cent ash, volatile matter, and surface area as 
determined by methylene blue adsorption. The block 
burning rate is shown as a function of the charcoal 
surface area in Figure 7. The instantaneous gas flow 
rates under actual conditions for blocks from each 
charcoal size fraction are plotted against time in 
Figure 8. The block-burning rate is shown as a func¬ 
tion of the mass median charcoal particle diameter in 
Figure 9. The maximum gas temperature, maximum 
pressure differential, and block density are shown as 
functions of the mass median charcoal diameter in 
Figures 10, 11, and 12, respectively. The values given 
are the average of eight blocks from each charcoal 
fraction. The block ages range from 6 to 200 days. In 


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466 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 



0 10 20 30 40 50 60 70 


MASS MEDIAN 0IAMETER IN MICRONS 

Figure 9. Burning rate of E29R 1-type blocks as a 
function of mass median charcoal diameter. 


o 



Figure 10. Maximum gas temperature vs mass median 
diameter of charcoal. 


each figure the average value is represented by a dot; 
the range is indicated by the line. 

2. Alkali “activation” of charcoal. A number of in¬ 
vestigators have found K 2 C0 3 to be a catalyst in the 
oxidation of charcoal. 14-17 To extend these observa¬ 
tions to the burning characteristics of fuel blocks, the 
following solutions were made up: 1.5M H 3 P0 4 , 5% 
K 2 C0 3 , 10% K 2 C0 3 , 25% K 2 C0 3 , and water. To 
1,000 g of each of these solutions, 750 g of Flower City 
5CC charcoal was added. These slurries of charcoal 
were kept for 24 hr with occasional hand stirring. 
They were then vacuum dried at 85 C. After cooling, 
the solid masses were reground to pass a 48-mesh 
screen. Nine blocks of 500 g each were made with 
each treated charcoal as well as with an untreated 
charcoal. The composition used is given below. The 
weight of charcoal was corrected in each case for the 
weight of impregnant adsorbed on the surface so that 
the weight of actual charcoal was the same in each 
case. 

NH 4 N0 3 83 parts 

Oil 3 parts 

Charcoal 11 parts 

Block weight: 500 g 



Figure 11. Maximum pressure differential above fuel 
block vs mass median charcoal diameter. 



MASS MEDIAN DIAMETER IN MICRONS 

Figure 12. Block density vs mass median charcoal 
diameter. 


Blocks were pressed into E29R1 cans equipped with 
paper insulating liners, and were burned in the open 
and in the surge tester after aging three and nine 
days. These data are summarized in Table 3, and 
indicate that pretreatment of charcoal has a large 
effect on the burning rate of the block. A burning rate 
range of from 1.35 to 3.4 g per min per sq cm has been 
obtained in blocks of identical composition by con¬ 
trolling the charcoal activity through pretreatment 
with phosphoric acid or K 2 C0 3 . These data offer a 
reasonable explanation for the ability of KN0 3 to 
increase the burning rate. Since KN0 3 forms K 2 C0 3 
on burning with carbon, an alkali activator is sup¬ 
plied for the remaining charcoal. 

3. Other factors influencing the reactivity of charcoal. 
Charcoal properties such as degree of carbonization, 
volatile matter content, and other factors as yet un¬ 
defined, which are influenced by the type of material 
carbonized and the methods of carbonization, are no 
doubt also important. A complete study of the oxida¬ 
tion of charcoal should include detailed data on the 
source and type of wood used, on the methods of 
carbonization, and on the storage and handling of the 
charcoal before use. Such data are not available for 
commercial charcoal. Crude temperature and venti¬ 
lation controls in the retorts, poor timing control for 


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PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


467 


Table 3. Activation of charcoal with solutions of H 3 P0 4 and K 2 C0 3 . 


Solution 

for 

treating 

charcoal 

pH of* 
char¬ 
coal 

Age of 

block 

days 


Burning time 


Burning 

rate 

g/ 

min sq cm 

Surging 

Taper 

min 

Total 

min 

Effective 

min 

1.5 M H 3 P0 4 

1.70 

3 

11.6 

12.0 

11.8 

1.36 

None to 10 lb/sq in. = maxi¬ 



9 

11.5 

12.0 

11.7 

1.37 

mum obtainable 



9 

11.7 

11.8 

11.7 

1.37 


Water 

6.76 

3 

6.3 

6.5 

6.4 

2.51 

None to 50 lb/sq in. 



9 

5.6 

6.4 

6.0 

2.68 

1 



9 

5.6 

6.4 

6.0 

2.68 


Untreated 


3 

6.3 

6.5 

6.4 

2.51 

None to 50 lb/sq in. 



9 

6.2 

6.6 

6.4 

2.51 




9 

6.2 

6.4 

6.3 

2.55 


5% K 2 C0 3 

9.20 

3 

5.4 

5.6 

5.5 

2.92 

None to 50 lb/sq in. 



9 

5.1 

5.4 

5.3 

3.03 




9 

5.2 

5.4 

5.3 

3.03 


10% k 2 co 3 

9.44 

3 

5.1 

5.4 

5.3 

3.03 

None 



9 

5.2 

5.3 

5.2 

3.08 




9 

5.0 

5.2 

5.1 

3.15 


25% K 2 C0 3 

9.36 

3 

4.81 

5.1 

4.9 

3.28 

None 



9 

4.5 

4.9 

4.7 

3.41 




9 

4.5 

4.8 

4.7 

3.41 





Block 

composition — 500 g mix 




NH 4 NO 3 83 parts 

Linseed oil 3 parts 

Charcoal 11 parts 

Blocks in E29R1 cans with paper liners 

Block area: 31.1 sq cm 


* pH of slurry made with 10 g charcoal plus 10 g boiled distilled water. Addition of an extra 10 ml of water had no appreciable effect on pH values. 


the carbonization process, and division of manage¬ 
ment between processes, make control of the product 
difficult. 

Attempts to specify the properties of charcoal by 
laboratory tests have not as yet been successful. At 
the present time, the most practical method of char¬ 
coal characterization is by making a test fuel block. 

4. Variables in ammonium nitrate. The ammonium 
nitrate used in these investigations has been suf¬ 
ficiently uniform so that differences in block per¬ 
formance cannot be attributed to differences in this 
ingredient. Data taken from pilot plant production 
of fuel blocks have shown no consistent correlation 
between changes in burning time and changes in lots 
of ammonium nitrate. 

5. Particle size of ammonium nitrate. The am¬ 
monium nitrate in particle size ranges larger than 
20 mesh, between 20 to 35, and 35 to 60 mesh showed 
no consistent variation in burning rate. The fractions 
smaller than 60 mesh burned somewhat faster. That 
the burning rate is relatively independent of the 
particle size suggests that the ammonium nitrate 
either vaporizes or undergoes thermal decomposition 
before it reacts in the block. This seems much more 


probable than a solid-solid reaction between charcoal 
and ammonium nitrate. 

6. Moisture content of ammonium nitrate. Moisture 
in excess of 0.75% in the ammonium nitrate affects 
the burning properties of the block. The tendency 
of ammonium nitrate to corrode steel also increases 
with an increase in the moisture content. Detailed 
surveillance tests were not made at higher moisture 
contents. Burning tests only, made on blocks 17 days 
old, indicated that 0.5% moisture is a safe maximum 
limit for moisture content of ammonium nitrate as 
far as its effect on burning properties is concerned. 
Figure 13 shows the effect of moisture. This moisture 
content of 0.5% should not be considered as a final 
specification, since the effect of moisture on the stor¬ 
age and surveillance of the final munitions has not 
been thoroughly tested. In any such tests, the effect 
of moisture in the block on corrosion of the can 
should be noted. It has been reported 11 that moisture 
increases the powder breakup due to phase changes 
of NH4NO3. This may have to be considered also. 

It has been the practice of this laboratory to dry 
the ammonium nitrate until the moisture content, as 
determined by perchlorethylene extraction, is below 


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468 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


2 

o 

o 

</> 


UJ 

CL 

CD 


<r 

CD 


2.9 ---------- 

2.8 ----- 

2.7 - ---- 

"H HrtT: - 

2.5---- 

2 .4 -- 

2.3 -*—------- 

0 1.0 2.0 
























-<>- 

7 









J 

r 

'-J 

) 


























PER CENT WATER 


Figure 13. Burning rate of E29Rl-type fuel blocks as 
a function of the per cent water in NH 4 N0 3 . 



PRESSING PRESSURE IN PSI 


Figure 14. Specific gravity and burning rate of an 
E29-type block as a function of pressing pressure. 


0.01%. In the light of the above data, it might be 
possible to modify this specification to allow up to 
0.5% H 2 0 in the ammonium nitrate. 

7. Physical 'properties of ammonium nitrate. Am¬ 
monium nitrate is preferred over any other oxidizing 
agent because of the large volume of gas and heat 
produced in its decomposition. It has two rather 
serious limitations: (1) It is hygroscopic. (2) It exists 
in five different crystalline modifications, and the 
change in crystal volume which accompanies the 
change from one form to another has been reported 
to cause powder breakup. The phase modifications 
of ammonium nitrate are: 

169.6° _ 125.2° ___ 

Vapor Liquid Cubic I Tetragonal II 

\ [ 84.2° 

-18° 32.1° 

Tetragonal V IV Rhombic ^7 Monoclinic III 

The most troublesome transitions are those occur¬ 
ring at —18 C and 32.1 C. Powder breakup due to 
the change from III to IV has been one of the main 
objections to the use of ammonium nitrate in rocket 
mixtures. Wallerant 18 stabilized form V throughout 
the entire range —18° to 82° by adding isomorphous 
CsN 0 3 . Crystallization with small percentages (5 to 
20 %) of potassium nitrate together with very small 
amounts of magnesium nitrate hexahydratehave been 
useful in suppressing the 32° transition . 11 In fuel 
blocks with a boiled linseed oil binder, as described 
here, this transition has not appeared to be serious. 
The other objection to the use of ammonium nitrate, 
its hygroscopic nature, has been partially overcome 
by the use of an oil binder and by coating exposed 
surfaces with a waterproof lacquer. 


Variables Due to Manufacturing Procedure 

Mixing. Various mixers have been used success¬ 
fully for blending the ingredients. The product 
obtained should be uniformly blended and the oil 
should be worked into the composition thoroughly. 
All mixers give some grinding action. In some cases 
the amount of grinding was of major importance in 
determining the properties of the block produced. If, 
however, a mixer gives a uniform product with the 
proper particle size distribution, it should be satis¬ 
factory. Some changes in the preparation of the 
ingredients might be necessary with other types of 
mixers. In practice it is desirable to keep both mixing 
time and the size of the charge for a given mixer 
constant, since the extent of grinding is increased by 
an increase in the mixing time and decreased by an 
increase in the size of the charge. 

Pressing. The factors of major significance in the 
pressing of fuel blocks include the following . 19 

1. Pressing pressure. 

2. Distribution of the mixture in the can. 

3. Flow characteristics or fluidity of the mixture. 

a. Temperature of the mixture. 

b. Amount and fluidity of the binder. 

c. Particle size. 

d. Efficiency of coating of the mixture with the 
binder. 

e. Presence of wetting or flow agents. 

4. Pressing technique. 

a. Time and means allowed for the escape of air 
entrapped in the mixture. 

b. Time pressure is maintained in the mixture. 

c. Type of press, as single or double end pressing 
arrangements. 

d. Rate of pressure release. 


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PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


469 


2 

a. 

UJ 

a. 

o 


o 


z 

(E 

3 

CD 


* 9 


2.8 


1.8 

1.6 































X 

A 












A 



BLOCK COMPOSITION 

TOP BASE 

NH 4 N0 3 + CHARCOAL 93 94.5 

KN0 3 4 

NH 4 CI0 4 2.5 

OIL 3 3 

I80G295G 

BURNED IN OPEN 

AGE 20 DAYS 

BLOCK AREA = 31.1 SO CM (LINER) 



/ 






f 











1 






3 5 7 9 II 13 15 


PER CENT-CHARCOAL 


Figure 15. Burning rate of E29Rl-type block as a 
function of per cent charcoal in block. 


3.0 

Z 

- o 2.8 
uj w 

< £ 2.6 
cc °- 


2.2 

2.0 


BLOCK COMPOSITION 
NH 4 N0 3 +OIL 85.5% 

NH 4 CI0 4 3.5% 

CHARCOAL 11.0% 










475 G 











AT Cl 

JRING 

EQUILIBRI 

UM « 

54) D) 

YYS) 




















IMMEDIATELY AFTER PRESSING 













BURNED IN OPEN 

BLOCK AREA = 32.3 SO CM 


1.0 


2.0 

PER CENT-OIL 


3.0 


Figure 16. Burning rate of E29Rl-type block as a 
function of per cent linseed oil in block. 


Of these factors, only the first has been systemati¬ 
cally investigated in this laboratory. A series of E29- 
type blocks was made in which the pressing pressure 
ranged from 700 psi to 3,500 psi. After aging nine 
days at room temperature, the block dimensions 
were measured and they were burned in the open. 
The block density and burning rate are shown as 
functions of the pressing pressure in Figure 14. 

In connection with the remaining factors, only 
qualitative data are available. The fluidity of the 
mixture is increased by an increase in temperature 
and an increase in the amount of liquid binder. An 
increase in fluidity results in more uniform pressure 
distribution throughout the block. In mixtures of low 
fluidity it is essential that the mixture be evenly dis¬ 
tributed in the can before pressure is applied, and it 
is frequently desirable to press in several increments 
to insure uniform pressure distribution and block 
density. 

It has been found 19 that rocket fuel pellets could 
be pressed in large single increments by control of 
mixture fluidity and application of pressure over 
periods of time up to 10 to 12 min. Special techniques 
in the application of pressure were essential to allow 



PER CENT KN0 3 

Figure 17. Burning rate of E29Rl-type blocks as a 
function of per cent KNO3 in block. 



A 



0 12 3 4 5 6 7 

MINUTES 


B 

Figure 18. (A) Temperature of exit gases during burn¬ 
ing of E29R1 fuel blocks containing different amounts 
KN0 3 . (B) Gas flow rate under actual conditions for 
KNO3 series. 


the escape of air trapped in the block. In some cases 
double acting presses were used, thus applying pres¬ 
sure on both the top and the bottom of the pellet. 

In this work, fuel blocks have been pressed in 
increments. 

Lacquering. The exposed surfaces of all finished 
blocks are coated with a special pyroxylin base 
lacquer for protection against moisture. For best re- 


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470 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 



0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 


PER CENT NH 4 CI IN BLOCK 

Figure 19. Burning rates of F7- and E23-type fuel 

blocks as functions of the NH 4 C1 content of the block. 

suits the lacquer should be restricted to the surface 
of the block. Penetration into the interior should be 
avoided for two reasons. (1) There are some indica¬ 
tions that organic solvents promote surging with 
some charcoals. (2) An excess of lacquer tends to 
make the block ignite slowly. The best results and 
minimum penetration are achieved by spraying the 
lacquer at as high a viscosity as is practical. This is 
determined by the spray equipment available. Spray¬ 
ing is more satisfactory than brushing. The lacquer 
coat is less liable to crack at higher storage tempera¬ 
tures if the block is heated before the lacquer is 
applied. 

Formula Changes 

Required changes in block-burning rate have been 
achieved largely by formula variation. Ammonium 
nitrate has been the basic oxidizing agent in all mix¬ 
tures, charcoal has been the basic reducing agent, 
and boiled linseed oil has been the basic binder. To 
these ingredients certain additives such as KN0 3 
have been added to increase the burning rate and 
other additives such as NH 4 C1 have been used to 
lower the burning rate. 

Effect of Char coal-Ammonium Nitrate Ratio on the 
Burning Rates of E29-Type Blocks. A series of 
E29R1 fuel blocks was made in which the charcoal- 
ammonium nitrate ratio was systematically varied. 
These were pressed into cans with 0.025-in. paper 
inner liners, aged twenty days, and burned in the 
open in triplicate. Data are presented in Figure 15. 
The greater change in burning rate occurred for char¬ 
coal percentages below 7%. Blocks containing 5% 
charcoal surged even when burned in the open. This 
is discussed in detail later under surging. All burning 
rates are computed using effective time, which is the 



Figure 20. Burning rates of E29-type fuel blocks as a 
function of initial block temperature. 

arithmetical average of the total burning time and 
the time until the burning first begins to taper off. 

Effect of Linseed Oil-Ammonium Nitrate Ratio on 
Burning Rates of E29R1-Type Blocks. In Figure 16, 
data showing the variation in burning rate of a single 
composition E29Rl-type block as a function of per 
cent linseed oil binder are given. The increase in burn¬ 
ing rate on curing is very pronounced in blocks con¬ 
taining 1 to 3% linseed oil. Paper liners in the fuel 
cans were not used in these tests nor in those re¬ 
ported below, unless specifically mentioned. 

Effect of Potassium Nitrate-Ammonium Nitrate 
Ratio on Burning Rates of E29R1-Type Blocks. The 
effect of KN0 3 on block characteristics is shown in 
Figure 17 as burning rate vs per cent KN0 3 . Tem¬ 
perature vs time curves and the gas flow rate vs time 
curves are given in Figures 18A and 18B respectively. 

The volume of gas, corrected to 60 F and 1 atm, 
produced by blocks containing amounts of KN0 3 up 
to 12% was the same, within experimental error, as 
the volume produced by blocks containing no KN0 3 . 

Effect of Ammonium Chloride on the Burning Rates 
of E32- and F7-Type Blocks. Substitution of am¬ 
monium chloride for ammonium nitrate has been a 
satisfactory method for reducing the burning rate 
of fuel mixtures in the F7 and in the E23 units. In 
Figure 19, the burning rates of blocks for three dif¬ 
ferent munitions are shown as a function of per cent 
NH 4 C1. All these blocks contain a top layer to give 
more rapid starting. NH 4 C1 is added only to the base 
layer. 

A number of other modifications were made in the 
composition of the mixture. For the details of these, 
reference should be made to the original report. 1 

Variables Due to the Burning Conditions 
Block temperature, gas pressure on the block dur¬ 
ing burning, wall effects, etc., are of major significance 


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PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


471 



GAS PRESSURE ON BLOCK DURING BURNING 
IN CM OF HG 

Figure 21. Burning rate of E29Rl-type fuel block as 
a function of gas pressure on block during burning. 



THICKNESS OF PAPER LINER IN 
THOUSANDTHS OF AN INCH 


Figure 22. Effectiveness of paper liners in fuel can in 
retarding side burning in E29Rl-type blocks. 

in block performance. Not only do they influence the 
burning rate, but also temperature and pressure in¬ 
fluence the surging of fuel blocks during burning. 

Influence of Initial Block Temperature on Burning 
Rates of E29-Type Blocks. In Figure 20 the burning 
rate of E29 blocks is shown as a function of the initial 
block temperature. The blocks were in hexagonal E29 
cans and had been stored for one year in a dry room 
at about 25 C before these tests were made. 

Influence of Pressure During Burning. In Figure 21 
the burning rate of standard E29R1 blocks is shown 
as a function of the gas pressure on the block during 
burning. The block temperature was initially about 
25 C. 

Effect of a Paper Liner in the Fuel Can. Inspection 
of the instantaneous flow rate vs time curves for 
standard one-layer E29R1 blocks reveals a gradual 
increase in gas flow rate with time of burning. The 
most likely cause 19 is an increase in the burning sur¬ 
face due to burning down the sides of the block. 



Figure 23. Typical flow rate — time curve for a fuel 
block while surging. 



Figure 24. Typical temperature — time curve for a 
fuel block while surging. 


Since side burning is due largely to heat conduc¬ 
tion along the walls of the container, such burning 
can be decreased greatly by placing a nonconducting 
liner between the wall and the fuel mixtuie. In the 
E23 smoke generator, cardboard was used by the 
National Fireworks Co. as an insulator with good 
results. Such a liner aids in maintaining a more even 
gas flow rate and in decreasing the taper time. 

The results of tests to determine the minimum 
thickness of paper insulator necessary to prevent side 
burning in the E29R1 block are given in Figure 22. 

Since all blocks have the same composition, any 
decrease in burning time with a decrease in liner 
thickness indicates side burning. The minimum thick¬ 
ness of paper to prevent side burning completely is 
about 0.025 in. However, no center cone during 
burning was observed when paper 0.015 in. or over 
was used. A 0.015-in. liner of stencil board was used 
with good results in the E29R1. 

31.3.5 Surging in Fuel Blocks 

Description 

Surging of fuel blocks is an irregular type of com¬ 
bustion characterized by a rapid evolution of gas 


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160 

150 

140 

130 

120 

110 

100 

90 

80 

70 

60 

JRE 21 

k of i 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


\ 

\ 

\ 




l 



\ 

» 

l 

l 



i 

\ 














_ nh 4 no : 

CHARCC 

AQUE01 

nh 4 ci 

pH SERIES 

5 

)AL 

JS BINDER Si 

J_ 

82% _ 

12 % 

0LN 3 % 

3 % 

L_ 


5 6 7 


OH OF MIXTURE 

Effect of />H on surge pressure of fuel block. 
3.5 did not surge up to 220 cm Hg. 


followed by a sharp decline in burning rate. This re¬ 
peats itself many times in a regular cycle, giving a gas 
flow rate curve such as shown in Figure 23 and a 
temperature curve as in Figure 24. The length of time 
between successive crests (moments of maximum 
flow) is termed the period of the surge. This has 
ranged from 2 sec to 50 sec. Generally, an increase in 
the length of the period increases the violence of the 
surge. 

The time of appearance of surging is unpredictable. 
It has been observed at the start, the middle, and the 
end of the burning time, as well as throughout the 
entire burning time. It has appeared in units of all 
sizes, ranging from the smallest grenade up to the 
125-lb B model thermal generator, and appears to be 
very similar to “chuffing” in rockets. 10 Substitution 
of a boiled linseed oil binder for the cellulose nitrate- 
acetone binder decreased the frequency with which 
surging appeared in experimental fuel blocks. In 
fact, experimental work was conducted for several 
months before surging was observed with blocks con¬ 
taining an oil binder. On the other hand, cast blocks 
described later surged frequently in the early develop¬ 
ment. Hundreds of cast blocks and thousands of 
pressed blocks have been made which did not surge. 
Nevertheless, surging is not well understood. It 
causes the munition to malfunction and is occasion¬ 
ally dangerous to personnel, and should therefore be 
eliminated from the fuel blocks. 

A series of blocks was made in which aqueous 
alkali solutions and acid solutions of different con¬ 
centrations were used to replace the linseed oil as a 
binder in pressed compositions. The pH of each of 
these mixtures was determined, using a glass elec¬ 
trode. From this series a definite relationship between 
the pressure at which these blocks began to surge and 
the pH of the mixture was established. Data are 
given in Figure 25. The pressure at which surging 
began was quite characteristic and was taken as a 
semiquantitative measure of the surging tendencies. 

During the development of the 50-lb colored smoke 
Mk 72 Mod 2 bomb, blocks were made from a new 
batch of charcoal and burned in a test munition. A 
very violent surging occurred soon after ignition and 
blew the unit apart. Subsequent blocks from this same 
lot of charcoal gave similar performance when burned 
in a dummy unit. Other blocks were then made using 
the same lots of ingredients except that another batch 
of charcoal was used. These blocks did not surge. The 
evidence indicated that, in this particular case, surg¬ 
ing was related directly to the charcoal used. 


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PRESSED FUEL MIXTURES CONTAINING CHARCOAL 


473 


Laboratory Analysis of Charcoal Which 
Caused Surging 

The surge-producing and the smooth-burning char¬ 
coals were examined in some detail in the laboratory. 
Spectrographic analyses of the ash from both types 
showed no difference in their mineral composition. 
X-ray diffraction studies of the ash showed no dif¬ 
ference between the charcoals. 

Surface properties of the charcoals were next con¬ 
sidered. Variations in the performance of charcoal 
have been attributed to the presence or absence of 
oxides on the charcoal surface . 16 Such oxides increase 
the ability of the charcoal to remove alkali from solu¬ 
tion and decrease the ability to remove acid . 22 Char¬ 
coal, containing surface oxides, adsorbs polar mole¬ 
cules such as H 2 0 more rapidly than clean charcoal, 
and will thus settle much more rapidly in water . 22 

In order to establish the presence or absence of 
surface oxides, both the surge charcoal and good char¬ 
coal were floated on distilled water and the rate of 
settling of both samples was observed. The good char¬ 
coal wet easily and settled rapidly, thus indicating 
the presence of surface oxides. The surge charcoal 
failed to wet and was still floating after 24 hours. This 
indicated little surface oxide. Acid capacity was 
checked but differences in this test were too small to 
be significant. Thermal analysis of the two charcoals 
made according to the methods of Grim 23 showed 
no differences between the good and surge charcoals. 
Data on smooth-burning and surge charcoal are 


Table 4. Summary of tests on surging and nonsurging 
charcoals. 


Test 

No surge 

Surge 

% volatile matter 

5.6 

5.1 

% ash 

8.5 

7.2 

Mass median particle diameter (microns) 13.0 

12.0 

Charcoal surface area (sq m/g) 

3.3 

3.3 

pH initial — 10 g C + 20 cc water 

9.0 

9.2 

pH after adding 20 cc 0.22 N HC1 

6.0 

5.9 

pH as above after 24 hr 

6.9 

6.8 

Ease of wetting 

Very easy Very difficult 

Spectrographic analysis of ash 

No difference 

X-ray diffraction analysis of ash 

No difference 

Ignition temperature curves 

No consistent difference 


summarized in Table 4. The most significant differ¬ 
ence is the evidence of surface oxides on the smooth¬ 
burning charcoal, and the lack of such oxides on the 
surging charcoal. 

Surging in Fuel Blocks Containing Only Five 
Per Cent Charcoal 

Analysis of the Gases from a Surging Fuel Block Con¬ 


taining Only Five Per Cent Charcoal. Direct chemical 
evidence as to the reactions involved in surging was 
obtained by analyzing the gases. A block containing 
only 5% charcoal surged even when burned in the 
open. When burned under a pressure of 2 cm of 
mercury above atmospheric, surging was very pro¬ 
nounced, and it was possible to obtain gas samples 
at the trough of the surge (low -rate of gas evolution) 
and the crest of the surge (tygh rate of gas evolution). 
These data are summarized in Table 5. The charcoal 
used in the production of fuel blocks has been ana¬ 
lyzed for C, H, N, 0, and ash. From the analysis, the 
formula for the charcoal may be written as C 6 H 3 0 + 
10% ash. The following reactions for the trough and 
crest of the surge fit the analytical data with con¬ 
siderable precision. 

Charcoal C 6 H 3 0 + 10% ash 

Linseed oil C 57 H 90 O 6 

Ammonium nitrate NH 4 N0 3 

1. Reaction for crest: 

17NH 4 N0 3 + C 6 H 3 0 + 0.03C57H 90 O 6 —> 

33H 2 0 + N0 2 + N 2 0 + 6.3C0 2 

+ 3.8H 2 + 15.5N 2 + 0 2 + 1.5CO 

Overall block Composition of above 

composition reacting mixture 


nh 4 no 3 

92% 

nh 4 no 3 

91.6% 

Charcoal 

5% 

Charcoal 

6.6% 

Linseed oil 

3% 

Oil 

1.8% 


100 % 


100.0% 

2. Reaction for trough: 



17NH 4 N0 3 + 0.09C 6 H 3 0 + 0.06C 5 7H 9 o0 6 —^ 

36.8H 2 0 + 3N0 2 + 4C0 2 + 14.9N 2 

+ 0.6N 2 0 

Overall block 

Composition of above 

composition 


reacting 

mixture 

nh 4 no 3 

92% 

nh 4 no 3 

95 . 5 % 

Charcoal 

5% 

Charcoal 

0 . 7 % 

Linseed oil 

3% 

Oil 

3 . 6 % 


Discussion. From these data the course of the 
surge reaction in this particular block may be out¬ 
lined. During the crest of the surge, NH 4 N0 3 and the 
charcoal react according to reaction (1). It will be 
noticed, however, that the reacting mixture is richer 
in charcoal (6.6%) than the overall block composi¬ 
tion (5%), and thus a layer of NH 4 N0 3 containing 
some linseed oil but little charcoal is left on the im¬ 
mediate surface of the block. This layer burns 


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FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


Table 5. Summary of gas analysis data for surging blocks containing 5% charcoal and 11% charcoal. 

5% charcoal 11% charcoal 

Trough Crest Trough Crest 

Gas Observed Calculated* Observed Calculated* Observed Calculated* Observed! Calculated* 


H,0 

63.6 

62.1 

52.6 

52.5 

47.4 

48.2 

47.4 

47.4 

nh 3 

0.4 

0.0 

0.05 

0.0 

0.0 

0.0 

0.0 

0.0 

no 2 

5.03 

5.1 

1.6 

1.6 

0.0 

0.0 

0.0 

0.0 

C0 2 

6.4 

6.7 

10.4 

10.0 

11.5 

11.9 

13.7 

13.9 

CO 

0.4 

0.0 

2.5 

2.4 

4.9 

5.1 

2.5 

2.5 

h 2 

0.1 

0.0 

5.5 

6.0 

7.8 

7.8 

8.7 

8.6 

o 2 




1.6 

0.6 

1.3 

1.5 

1.4 

N 2 (residual) 

24.9 

25.1 

27.3 

24.6 

28.1 

25.7 

26.0 

26.2 

N 2 0 


1.0 


1.6 





Mol wt 

23.7 

23.9 

23.6 

23.5 

23.6 

23.2 

23.2 

23.3 


* Analysis calculated from equations given in the text, 
t Observed analysis was corrected for an air leak. 


through slowly according to the reaction given in the 
trough. The linseed oil is the chief reducing agent in 
the trough reaction, and it is known that linseed oil 
alone burns more slowly than charcoal. When the 
slow burning mixture has reacted, a normal surface 
is exposed and the charcoal again burns out rapidly 
in a crest reaction. Thus, the process is cyclic. It is 
probable that the linseed oil consumed in the crest 
reaction is present on the surface of the charcoal. 

This mechanism of surging in a block containing 
5% charcoal is supported by the following experi¬ 
mental data. 

1. Analysis of gases from the trough, crest, and an 
intermediate point in the surge cycle, has given 
definite and consistent experimental support for the 
reactions outlined. 

2. Blocks made at the same time with the same 
procedure from the same ingredients, but containing 
7, 9, 11, and 13% charcoal, did not surge under any 
pressure, since only 6.6% charcoal is necessary to 
maintain the crest reaction outlined in the preceding 
paragraph. 

3. Such a 5% charcoal block, when burned in the 
open, shows a mild form of surging which was ampli¬ 
fied by any restriction to the high gas flow. 

4. When the 5% block surges in the open, the 
crest of the surge and the crest only is marked by the 
evolution of a large number of sparks. The combus¬ 
tion of charcoal gives sparks while the combustion of 
linseed oil does not. 

Surging in Blocks Containing Eleven Per 
Cent Charcoal 

Analysis of Gases From Surging Block Containing 
Eleven Per Cent Charcoal. Several E29-type blocks 
which surged had the following composition. 



Top — 200 g 

Base — 300 

NH4NO3 

81% 

85% 

KN 0 3 

5% 

1% 

Charcoal 

11% 

11% 

Linseed oil 

3% 

3% 


They had been stored in a CaCl 2 dry box in an air- 
conditioned room for 14 months. Surging character¬ 
istics developed after about two or three weeks of 
storage. Gas samples were taken of a crest and trough. 
Analysis of the gas samples failed to show a large 
difference between trough and crest. This is in direct 
contrast to the block containing only 5% charcoal. 
Data are given in Table 5. The data for the crest fit 
the following equation with fair precision. 

1. Surge crest of E29-type block. 

I7.ONH4NO3 + O.8KNO3 + 1 . 67 C 6 H 3 0 

+O.O 33 C 57 H 90 O 6 —> 32.7H 2 0 + 8.1C0 2 + 3.5CO 
+5.3H 2 + 17.4N 2 + 0.9O 2 + 0.4K 2 CO 3 

The following equation fits the trough data. 

2. Surge trough of E29-type block. 

I7.ONH4NO3 + O.8KNO3 + 1.6C 6 H 3 0 

+ O.O 3 C 57 H 90 O 6 —*• 31.9H 2 0 + 9.2C0 2 + 1.7CO 
+ 5.8H 2 + 17.4N 2 + 1.0O 2 + 0.4K 2 CO 3 

This reaction is very similar to the crest reaction. 

The compositions of the reacting mixtures for the 
11% block, as calculated from the above equations, 
are as follows. 



Crest 

Trough 

Actual as 
prepared 

NH 4 NO 3 

83.1% 

83.5% 

81% 

KNO 3 

4.9% 

5.0% 

5% 

Charcoal 

10.2% 

9.8% 

11% 

Oil 

1.8% 

1-7% 

3% 


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475 


Compositions for the crest and trough are very 
close to the prepared compositions of the block. Con¬ 
siderable carbonaceous material was left in the fuel 
container. 

In summary, the following will be noted regarding 
the gas analysis of a surging block containing 11% 
charcoal. 

1. A large difference in composition between 
trough and crest samples was not observed. 

2. Somewhat more complete combustion occurs in 
the trough, producing more C0 2 and less CO. 

3. The data indicate conclusively that large dif¬ 
ferences between trough and crest such as were ob¬ 
served in the 5% charcoal block do not exist in the 
11% charcoal block. 

Discussion. An explanation of surging in the 11% 
charcoal block is suggested by the results from the 
5% charcoal block. If the charcoal in the 11% block 
were not of uniform activity, the more readily com¬ 
bustible material would burn out first to give the 
crest of the surge. The less active material would 
then burn more slowly in the trough. As soon as a 
fresh layer of the block was again exposed the more 
active charcoal would burn rapidly to give another 
crest, and this would be followed by a trough. Since 
charcoal would be burning in both cases (contrast 
with the block containing 5% charcoal), the reaction 
products should be the same in both cases except for 
somewhat more complete combustion where the char¬ 
coal is not as available. This is actually observed; the 
per cent C0 2 is slightly higher and CO is lower in the 
trough where charcoal is presumably less reactive. 
The more rapid combustion at the crest would ex¬ 
plain the maximum temperature found there. 

Mechanism of Surging 

When two reducing agents are present in a mixture 
containing sufficient oxidizing agent for both and 
when the oxidizing agent reacts in the gas or vapor 
phase, these two reducing agents tend to be oxidized 
simultaneously. However, one will usually react 
faster than the other and become depleted from the 
reacting layer. The oxidation of the second agent 
then proceeds at a slower rate until the burning layer 
reaches more of the first agent. This results in 
periodic changes in the burning rate and has been 
observed as surging in thermal generator fuels or 
chuffing in rocket fuels. For example, if both char¬ 
coal and sulfur were included in the same block with 
sufficient oxidizing agent for both, the mixture could 
be expected to burn with periodic fluctuations in the 


burning rate and also in the relative percentage of 
CO or C0 2 and S0 2 in the reaction gases. In this case 
the course of the two reactions could be easily fol¬ 
lowed in the analyses of gas samples taken at several 
times during a surge period. 

The results with 5% charcoal in the fuel represent 
a similar case with the linseed oil and charcoal serving 
as the two reducing agents. Here it is not so easy to 
trace the two reactions in tfye gas analysis, but it is 
possible, and this has been done. It is not necessary 
that the two reducing agents be different chemical 
compounds. If the same chemical compound is pres¬ 
ent in two different physical states such that one re¬ 
acts more readily than the other, the same periodic 
burning will result. In this case it will not be possible 
to trace the slow and fast reaction by the analysis 
of the reaction gases, since both result in the same 
gaseous products. This was the case with 11% char¬ 
coal in the block. 

It is not quite clear why the more reactive com¬ 
pound does not continue to react down through the 
block and leave the less reactive behind to burn later. 
It is an experimental fact, however, that this does not 
occur in these highly consolidated fuel blocks. The 
reaction proceeds regularly down through the block 
and completes itself in one layer before passing on to 
the next. 

In the case of charcoal used as the reducing agent, 
it is understandable that one part could be more re¬ 
active than another or that latent tendencies in that 
direction could be further developed in the course of 
processing or burning. This has been apparent in 
several tests. Surging resulted from the addition of 
water or alkali solutions to the charcoal. The water 
would tend to develop differences in wetability, and 
the alkali in alkali activation. Surging in the inter¬ 
mediate pressure range has been observed, but not 
at high pressures (500 to 1,000 psi). This may be due 
to differences in the adsorption of the oxidizing 
vapors, which are critical in this range. Low tem¬ 
peratures often augment surging tendencies, whereas 
linseed oil as a binder diminishes them. 

Charcoal oxidation is retarded by surface oxides 
and the catalytic action of alkali is due to its ability 
to remove those oxides and expose a clean reaction 
surface. 16 Clean charcoal without oxides on the sur¬ 
face would be more reactive than that heavily coated 
with the oxides. This clean charcoal burns very 
rapidly and produces a very violent and even ex¬ 
plosive surge. This was observed in connection with 
a charcoal which surged and blew up. Examination 


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476 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


of this charcoal gave evidence of very little surface 
oxide. Smooth-burning charcoal gave evidence of 
considerable surface oxide. 

Summary of Experiments on Surging 

The following are experimental facts regarding 
surging. 

1. Surging is related to the charcoal used in the 
block. 

a. Surging charcoals and nonsurging charcoals 
show no difference in ash composition. 

b. Surging charcoals give evidence of little sur¬ 
face oxide; nonsurging charcoals give evi¬ 
dence of surface oxides. 

2. Water and aqueous alkali binders promote surg¬ 
ing of charcoal fuels. Aqueous acid binders tend to 
retard surging. 

3. Surging of thermal generator fuels is promoted 
by pressure in the range 0 to 100 psi. Surging of 
rocket fuels takes place at comparatively low rocket 
pressures (300 to 400 psi) which are high compared 
to thermal generator pressures. At high pressures 
( 1,000 psi +) rocket fuels do not surge. 

4. Surging of both rocket and thermal generator 
fuels is promoted by low initial fuel temperatures. 

5. Surging tendencies increase with the age of char¬ 
coal blocks. 

6 . The simple geometry of the unit in which the 
block burns is apparently not related to the surging 
of a fuel block. 

7. Surging was observed in a block containing a 
low percentage of charcoal ( 5 %). 

8 . Analysis of the gases from a block containing 
5% charcoal which surged indicates that more char¬ 
coal burns at the crest of the surge. More linseed 
oil burns at the trough of the surge. 

9. Analysis of the gases from a block containing 
11 % charcoal shows no large difference in composi¬ 
tion between gases from the trough and crest of a 
surge. 

10 . The temperature of fuel gases rises from a 
minimum at the trough to a maximum at the crest 
of the surge. 

11 . No relationship between particle size of the 
ingredients and surging tendencies has been detected. 

Predictions Based on the Mechanism of Surging 

Predictions ( 1 ) and (3) have not been checked by 
actual experiment. They are given here as a guide for 
further work. 

1. The surging period is longer when small amounts 


of fast- or slow-burning charcoal are mixed with large 
amounts of slow or fast charcoal, respectively. 

2 . Two charcoals with different burning rates, but 
which do not surge when each is used alone, produce 
surging when used as a blend. (This has been experi¬ 
mentally verified in one case.) 

3. Charcoal from a single retort batch may be free 
from surging tendencies. When batches are blended, 
the probability of surging increases. 

It is to be noted that the nature and amount of 
binder used may introduce unexpected results in the 
NH 4 NO 3 -charcoal system. 

31.3.6 Storage of Fuel Blocks 

Two difficulties in particular are, to be anticipated 
in surveillance of munitions containing NH 4 NO 3 as an 
oxidizing agent. These are ( 1 ) moisture damage, and 
( 2 ) powder breakup due to phase changes of NH 4 NO 3 . 
Of these, the first has been the most serious problem. 
In munitions burning at the low pressures of the 
thermal generator, the effect of slight surface cracks 
from phase changes has not been so significant as in 
high-pressure powders such as gunpowder or rocket 
fuels. No completely satisfactory method of water¬ 
proofing the block itself has been found, and the 
blocks must, therefore, be used in sealed munitions. 
The linseed oil binder and pyroxylin lacquer coating 
have increased the moisture resistance so that blocks 
in sealed units can undergo surveillance tests satis¬ 
factorily. 

Change in Burning Properties of E29 Blocks 
with Age 

In Figure 26, the burning time of the hexagonal 
E29-type blocks is shown as a function of the age of 
the block. The blocks were stored at the three tem¬ 
peratures 25 C, 40 C, and 60 C and cooled to room 
temperature before being burned. 

The conclusions on curing E29-type blocks are 
summarized. 

1. A pronounced acceleration in burning rate (de¬ 
crease in burning time) occurs as the block cures, the 
most rapid change occurring during the first five 
days. This is followed by a more gradual change for 
16 to 20 days. The burning rate is then virtually con¬ 
stant for a given temperature of storage. 

In some cases equilibrium is reached before 20 
days, but, in general, no change in burning rate oc¬ 
curs after 20 days. Data are available for blocks as 
old as 563 days. 


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NONCARBON PRESSED FUEL MIXTURES 


477 



Figure 26. Effect of aging at different temperatures on the burning time of 500 g. Fuel blocks for E29 thermal generator. 


2. The time required to reach equilibrium at high 
storage temperatures is not significantly different from 
that required at lower temperatures. The equilibrium 
burning rate for the high temperature is slightly 
higher than that for lower temperature. The initial 
rate of change of burning rate with time is, however, 
more rapid at the higher temperature than at the 
lower. (Figure 26.) 

High-temperature storage at 60 C decreases the 
average burning time of E29 blocks by about 0.3 
±0.1 min as compared with the average of blocks 
stored at room temperature. Figure 26 shows a 
difference of about 0.4 min, but the overall averages 
for a large number of blocks was less. 

3. This behavior was general for all E29 mixtures. 

These changes during curing were at first attrib¬ 
uted to the polymerization or “drying” of the lin¬ 
seed oil used as a binder. If this were so, a com¬ 
mercial paint dryer in the formula should shorten the 
curing time. A paint dryer actually did not have any 
effect on the curing, although it did very markedly 
shorten the drying time of a thin film of linseed oil on 
glass. 

An ammonium picrate-ammonium nitrate-am¬ 
monium dichromate-linseed oil mixture showed an 
excessive increase in burning rate on curing (136% 
increase). On the other hand, NH 4 N 03 -(NH 4 ) 2 Cr 2 07 - 
linseed oil mixtures showed no change on curing. 
Simple polymerization of linseed oil in the block 
apparently does not account for the changes. The 
reducing agent, such as charcoal, ammonium picrate, 
or guanidine nitrate, appears to have a far greater 
effect. 


All NH4NO3 base blocks containing a linseed oil 
binder withstood cyclic surveillance and showed no 
breakup. Even blocks burned under 30 lb gas pres¬ 
sure after cyclic surveillance gave no evidence of in¬ 
creased burning rate due to internal cracking. 

31.4 NONCARBON PRESSED FUEL 
MIXTURES 

In view of the nonuniform properties of charcoal 
discussed in the preceding text, the preliminary de¬ 
velopment of a pressed fuel block which does not 
contain carbon was carried out, and excellent pros¬ 
pects of improved performance were obtained. 3 A 
survey of possible oxidizing and reducing agents for 
use in these fuels was made. Based on this survey, 
several promising mixtures were considered and these 
were given extensive preliminary tests in lined cans. 

A mixture composed of guanidine nitrate, am¬ 
monium nitrate, linseed oil, and ammonium dichro¬ 
mate showed more promise as a thermal generator 
fuel than any of the other new mixtures tested. 

31.4.1 Guanidine Nitrate-Ammonium 
Nitrate-Ammonium Dichromate- 
Linseed Oil 

Variation of Burning Rate and Other Block 
Properties with (NH 4 )2Cr 2 07 Content 

A basic mixture of NH4NO3 and guanidine nitrate 
was prepared in stoichiometric proportions for the 
reaction 

(NH 2 ) 2 CNH • HNO 3 + 2 NH 4 NO 3 —> 

4N 2 + 7H 2 0 + C0 2 . 


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478 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


BURNING RATE INGPER MIN PER SO CM 

— m w -byiO> >jco 

ooo o oooob 

BLOCK AREA = 11.4 SO CM 
BLOCK WT = 100 G MIX 

BLOCK DIA = 3.81 CM 

BLOCKHT = 70 MM 















BLOCK AGE = 0 DAYS 

BURNED IN OPEN 





















A 

r 


MIXTURE COMPOSITION 







0 ) BASE 

GUANIDINE NITRATE 42.2% 
NH 4 N0 3 55.8% 

BOILED LINSEED OIL 2.0% 

b)BLOCK 

BASE-MNH 4 ) 2 Cr 2 0 7 * 100% 
















0* 23456789 10 II 12 

PER CENT (NH 4 ) 2 Cr 2 0 7 


Variation of Burning Rate with Initial Block 
Temperature 

In Figure 29, the burning rates of blocks in the 
open are shown as a function of the initial block 
temperatures. The variation in burning rate with 
temperature for this mixture between 50 F and 
220 F was small. Blocks held at 220 F swelled some¬ 
what. This may account for the slight decrease in 
burning rate at the higher temperature. 

Variation of Burning Rate with Pressure 

In Figure 30, the burning rate is shown as a func- 


Figure 27. Burning rate of 100 g. Guanidine nitrate 
blocks as a function of per cent (NH 4 ) 2 Cr 2 07 . 


550 


< 500 


450 


z 400 


350 




















MIXTURE - SAME AS FIGURE 27 




















X 






10 II 


- 012345678 

PER CENT (NH 4 ) 2 Cr 2 0 7 

Figure 28. Ignition temperature for Guanidine ni¬ 
trate — NH4NO3 mixture with increasing amounts of 
(NH 4 ) 2 Cr 2 0 7 . 



6 AS PRESSURE ON BLOCK PSl ABOVE 1ATM 

Figure 30. Burning rate of block as a function of gas 
pressure during operation. 


This mixture contained 55.8% NH 4 NO 3 , 42.2% 
guanidine nitrate and 2% linseed oil binder. To this 
mixture were added increasing amounts of am¬ 
monium dichromate catalyst. Small test blocks were 
prepared from each composition and burned in the 
open (740 mm pressure) two to four hours after 
pressing. The initial block temperature was 20 to 
25 C. The burning rate is shown as a function of 
(NH 4 ) 2 Cr 2 07 content in Figure 27. The ignition point 
of each mixture is shown as a function of (NH 4 ) 2 Cr 2 0 7 
content in Figure 28. The ignition point decreases 
and the burning rate increases as the per cent 
(NH 4 ) 2 Cr 2 0 7 is increased. 



-60 -40 -20 


20 40 60 80 100 120 1*0 

TEMPERATURE IN DEGREES F 


160 180 200 220 


Figure 29. Burning rate of Guanidine nitrate -— 
NH 4 N0 3 mixture as a function of initial block tempera¬ 
ture. 


tion of gas pressure during burning. The blocks had 
the same composition as those used in the tempera¬ 
ture study. 

Variation of Burning Rate with Storage 
Temperature 

Representative blocks of the same composition as 
those used in the temperature study were stored for 
three weeks under the following conditions of tem¬ 
perature. 

1. Room temperature (about 70 to 80 F), low 
humidity. 

2. 150 F, low humidity (blocks were put in the 
oven after three days curing at room temperature). 

3. Cyclic temperatures. Blocks were held 12 to 72 
hr at low temperature (0 to 20 F); then transferred 
to 150 F storage and held for an equal period of time. 
This cycle was repeated eight to ten times. The 
temperature range includes two transition points for 
NH 4 N0 3 . Blocks were sealed against moisture. 

Data showing burning rates of guanidine nitrate- 
ammonium nitrate-linseed oil-ammonium dichro¬ 
mate blocks after storage under each of these condi¬ 
tions are shown in Table 6. All blocks were brought 
to 70 F before burning. 


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NONCARBON PRESSED FUEL MIXTURES 


479 


Table 6. Burning rate of guanidine nitrate-NH 4 N 03 - 0 il-(NH 4 )^Cr 2 07 blocks after storage at different temperatures. 


Check 

immediately after 
pressing 

Room temperature 
storage: 21 days at 

70 F; low RH 

150 F 

storage: 3 days 70 F; 

18 days 150 F; 1 day 70 F 


Cyclic 

0-150 F, 8 cycles 
low RH 

Burning 

time 

min 

Burning 

rate 

g/(min) sq cm 

Burning 

time 

min 

Burning 

rate 

g/(min) sq cm 

Burning 

time 

min 

Burning 

rate 

g/(min) sq cm Remarks 

Burning 

time 

min 

Burning 

rate 

g/(min) sq cm Remarks 

3.4 

2.58 

2.8 

3.13 

3.3 

2.65 


3.15 

2.78 

3.4 

2.58 

2.8 

3.13 

3.3 

2.65 


3.4 

2.58 

3.5 

2.50 

2.9 

3.02 

3.1 

2.82 


3.15 

2.78 No observable crack- 



2.9 

3.02 

3.0 

2.92 

No 

3.15 

2.78 ing. About 2% in- 



2.9 

3.02 

3.1 

2.82 

observable 

3.1 

2.82 crease in block 



3.0 

2.92 

3.1 

2.82 

swelling 

3.1 

2.82 height. 








3.3 

2.65 








3.3 

2.65 

Avg 









3.43 

2.55 

2.88 

3.04 

3.15 

2.78 


3.21 

2.73 





TIME IN MINUTES 

Figure 31. Gas temperature and pressure differential 
across exhaust orifice of volume tester during burning of 
block. 


Volume Tester Data 

E29Rl-type blocks were burned in the volume 
tester. Pressure-time curves and temperature-time 
curves during operation of the block are shown in 
Figure 31. Flow rate vs time curves giving the gas 
volume under actual conditions are shown in Figure 
32. Flow rate vs time curves for gas volume reduced 
to 60 F and 1 atm are shown in Figure 33. The rate 
of gas flow is remarkably uniform from this mixture. 

Tests in E29R1 

E29Rl-type blocks were burned in E29R1 units. 
Guanidine nitrate blocks gave excellent performance 
in the unit. 

31.4.2 Discussion of Noncarbon Mixtures 
Since composite propellants of guanidine nitrate 
have never shown chuffing in rocket fuels, this mix¬ 


ture offers promise of more complete control of surg¬ 
ing in thermal generator fuels. The most annoying 
feature of this mixture is the 19% increase in burning 
rate on curing. However, this increase is not ex¬ 
cessive. 

The importance of the reducing agent to the surg¬ 
ing problem is further emphasized by these tests. In 
blocks containing excess (NH^Ci^Oy but no reducing 


BLOCK WT * 4756 
BLOCK AGE * 34 DATS 



TIME IN MINUTES 

Figure 32. Gas flow rate — time curves for gas volume 
measured under actual conditions of temperature and 
pressure. 


BLOCK WT = 475G 
BLOCK AGE = 34 DAYS 
BLOCK AREA * 31.1 SQ CM 
BURNED IN VOL TESTER 



Figure 33. Gas flow rate — time curves for gas volume 
reduced to 60 F and 1 atmosphere pressure. 


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480 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


agent, surging was severe in the unit, the volume 
tester and the pressure tester. Blocks containing 
sulfur showed somewhat less tendency to surge, 
while those containing guanidine nitrate or am¬ 
monium picrate showed no surging tendencies. 

31.5 CAST FUEL COMPOSITIONS 

31.5.1 Comparison of Cast and Pressed 

Mixtures 

Cast fuel blocks differ from pressed blocks in that 
(1) the linseed oil binder of the pressed block is re¬ 
placed by 1.0 M or 0.75M H 3 P0 4 ; (2) the burning 
rate of cast mixtures is controlled by variation in the 
relative amounts of starch and charcoal present in 
the mixture; (3) the cast mixture is poured into cans 
while molten and allowed to solidify, whereas the 
pressed mixture is compacted under pressure. 

The basic chemistry in the combustion of the two 
blocks is very similar. A number of the basic princi¬ 
ples, such as the effect of the particle size of the char¬ 
coal and alkali catalysis of the burning, can be ap¬ 
plied to cast mixtures as well as to pressed. 

31.5.2 Properties of Cast Mixtures 

Cast mixtures are, in general, much slower burning 
than pressed mixtures. Burning rates range from 0.6 
to 1.8 g per min per sq cm. The volume of gas produced 
per gram of mixture, measured at 60 F and 1 atm, is 
about the same in cast and pressed mixtures (0.841). 
The temperature of the gases from a burning cast 
block is somewhat lower than from a pressed block; 
thus, the overall capacity of cast blocks for evaporat¬ 
ing other agents is less. 

Cast blocks are more difficult to ignite and have 
presented a much more serious surging problem. The 
ignition temperature of the loose mixture is compara¬ 
ble to that of loose mixture for pressed blocks (200 to 
240 C), but a block of cast mixture requires considera¬ 
ble hot slag from the starter to initiate combustion. 
Cast blocks ignited on the surface with a bunsen 
burner or blowtorch did not continue to burn after 
the torch was removed. Block density ranged from 
1.41 to 1.52 g per cu cm. 

Cast mixtures presented a rather serious corrosion 
problem in unprotected cans. A means for protecting 
the metal would have to be used or the composition 
of the mixture changed. The mechanical strength of 
the mixture was good. Units withstood transit and 


handling well. The cast mixture was never subjected 
to cyclic surveillance to check the action of NH 4 N0 3 
phase changes. 

31.5.3 Manufacturing Procedure 

Base Mixture 

The base mixture consisting of NH 4 N0 3 , charcoal, 
phosphoric acid, NH 4 C1, and starch was mixed in a 
Simpson intensive mixer for about 10 min, then 
melted in a deep steam-jacketed kettle supplied with 
steam at 50 psi. The molten mixture flowed into the 
container placed on a balance pan below the outlet 
of the kettle. The formulas used are given in Table 2. 
Melting temperatures ranged from 110 to 120 C. 

Top Mixture 

While the base mixture was cooling, a faster mix¬ 
ture consisting of ammonium nitrate, ammonium 
chloride, charcoal, sodium nitrate, and phosphoric 
acid was mixed by hand and melted in a smaller 
steam-jacketed kettle. This mixture was poured onto 
the top of the base layer and allowed to cool. 

Starter Mixture 

The starter mixture was 54% KN0 3 , 40% silicon, 
and 6% charcoal intimately mixed in the dry state 
and made into a slurry with a binder of 5% cellulose 
nitrate in acetone. This slurry was distributed over 
the surface of the block in a gridiron pattern. 

Safety Rating of the Process 
The product and process were examined by the 
Safety Section of the U.S. Bureau of Mines, and the 
process was classified as at least no more hazardous 
than the manufacture of black powder. The product 
is less hazardous than black powder. 

31.5.4 Factors in the Control of Cast 

Block Characteristics 

Variation of Ingredients 
As in pressed blocks, charcoal was the least uni¬ 
form ingredient. Conclusions concerning ingredients 
of pressed blocks are equally applicable to cast units. 

Variations in the Manufacturing Procedures 
A detailed study of the manufacturing procedure 
was not made. A standard procedure was established 
and followed as closely as possible. Mixing times, 
casting temperatures, and the like were maintained 


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CAST FUEL COMPOSITIONS 


481 


Table 7 


System 

Melting 
point C 

Mole % 

nh 4 no 3 

Mole % 
NaN0 3 

Mole % 
NH 4 C1 

Mole % 
Other 

a. 

Melting points and compositions ‘ 

!4 for eutectic salt mixtures. 


NH 4 N0 3 — NaN0 3 

120.8 

80.27 

19.73 



NH 4 N0 3 — NH 4 C1 

140.9 

82.92 


17.08 


NH 4 N0 3 — (NH 4 ) 2 S0 4 No eutectic 




NH 4 N0 3 — NaN0 3 

— NH 4 C1 112.5 

74.76 

17.71 

7.53 


NH 4 N0 3 — NH 4 C1 

- KN0 3 134.5 

76.54 

13.92 


KN0 3 9.54 

nh 4 no 3 — NH 4 C1 

— LiN0 3 113.6 

76.73 


14.10 

' LiN0 3 9.17 


b. Effect of water on f reezing point of NH 4 N0 3 . 


| 

wt % h 2 o 

0 1.05 

2.01 

3.20 4.39 

,6.24 8.76 10.04 


Freezing point, degrees C 169 157 


146 


133 


122 


112 


99 


95 



Figure 34. The system NH 4 N0 3 — NaN0 3 — NH 4 C1. 

fairly constant. Several problems appeared in the 
casting process which were troublesome. 

Evolution of Gas. Some mixtures gave off NH 3 on 
heating. This caused swelling and produced holes in 
the block. NH 3 evolution was minimized by the addi¬ 
tion of H 3 P (>4 solution to the mixture. 

Lowering of the Melting Point. This was accom¬ 
plished by formula variation. 

Corrosion of Casting Kettle. This was minimized by 
using H 3 P0 4 instead of other acids to retard the 
NH 3 evolution. 

Formula Variation 

Burning rates and melting points of cast mixtures 
have been largely controlled by formula variation. 
Phase diagrams of NH 4 N0 3 systems were studied to 
obtain a low melting mixture of oxidizing salts. Varia¬ 
tion of the reducing agent was used to control the 
burning rate. 

Phase Diagrams. Phase diagrams and melting point 
information for a number of pertinent systems 24 from 
the literature are summarized in Table 7. 



Figure 35. The system NH 4 N0 3 — NaN0 3 — NH 4 C1. 

Table 7b indicates that water is very effective in 
lowering the freezing point of NH 4 N0 3 . 

These data were supplemented by additional phase 
investigations. Samples were melted in a small test 
tube suspended in an oil bath. Cooling curves were 
obtained for each mixture. Analytical or crystallo¬ 
graphic studies were not made on any of the phases. 

Data for a part of the ternary system NH 4 N0 3 - 
NH 4 Cl-NaN0 3 are given in Figures 34 and 35. Data 
for the ternary system NH 4 N0 3 -NH 4 C1-H 2 0 are 
given in Figure 37, and for the quaternary system 
NH 4 N0 3 -NH 4 Cl-NaN0 3 -H 2 0 in Figure 36. The 
melting point of ammonium nitrate and the data in 
Figures 36 and 37 indicate that the NH 4 N0 3 used in 
these experiments was not absolutely dry even after 
drying for 16 hr at 100 C. This nitrate apparently 
contains about 0.25% water, but this water is re¬ 
moved with great difficulty and is not detectable by 
heating at 70 C or by perchlorethylene extraction. 
Thus, this nitrate would be reported as 0% moisture 
if checked by the technique given in the specifications 
for NH 4 N0 3 , and would be considered “dry” in 
regular production work. 

The eutectic mixture of NH 4 N0 3 -NH 4 Cl-NaN0 3 
appeared promising, but blocks made from this oxi¬ 
dizing mixture with charcoal as the reducing agent 


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FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 



Figure 36. The system NH 4 NO 3 — NaNOs — NH 4 C1 
— H 2 0. 


surged violently and burned too rapidly. It seemed 
desirable to eliminate the NaN0 3 , and, since this 
resulted in a rise in the melting point, water was 
added as suggested by Figure 36. These blocks 
showed a tendency to swell on cooling and also 
surged when burned. 

Addition of 1.0 M H 3 P0 4 minimized the evolution 
of NH 3 and also aided in the control of surging. From 
tests with a variety of compositions, the following 
formula was evolved. 

NH 4 N0 3 83% 

1.0M H 3 P0 4 3% 

NH 4 C1 3% 

Charcoal) — 

Starch J /o 


The burning rate was controlled by variation of the 
starch-charcoal ratio. 



Figure 37. The system NH 4 NO 3 — NH 4 C1 — H 2 0. 


Effect of Starch on the Burning Rate. Variation of 
burning rate as a function of per cent starch in the 
block is shown in Figure 38. Percentages of starch up 
to 2.5% have little effect on the burning rate, but 
percentages in the range 2.7 to 4.0 influence the 
burning rate markedly. 


Effect of pH of the Mixture. A series of cast blocks 
was made containing different concentrations of acid. 
The acid strength had a very marked influence on 
surging. Blocks containing 0.75 M H 3 P0 4 showed no 
tendency to surge, while blocks containing 0.25M 
H 3 P0 4 surged so violently that seams of the fuel cans 
were split. Conditions other than acid concentration 
were identical in both sets of blocks. In a few later 
cases, increasing the acid concentration did not com¬ 
pletely eliminate surging. Although the acid had a 
definite effect in controlling surging, it was not en¬ 
tirely satisfactory. 

Storage of Cast Blocks 

. Cast blocks show no change in burning rate on 
curing; however, blocks with mild surging charac¬ 
teristics developed much more violent surging prop¬ 
erties after storage. Storage at elevated temperatures 
appeared to cause a greater tendency to surge than 
storage at room temperature. 

Cast blocks poured into noninsulated light gauge 
cans corroded through from the inside after about 
50 to 75 days in either tropical or desert storage. 

31.5.5 Suggestions for Improving Cast 
Mixtures 

Casting a fuel block, rather than pressing it, should 
have a considerable advantage, especially for large- 
scale production. A number of the difficulties en¬ 
countered with cast blocks might be overcome. Based 
on the present knowledge, certain principles now seem 
apparent which should serve as a guide for further 
development. First, a single reducing agent should be 
used to control surging. This agent could be charcoal, 
carefully prepared, and meeting rather exact specifi¬ 
cations, or a pure compound such as guanidine 
nitrate or ammonium picrate. Second, the use of 
water or acid solutions should be avoided. 

31.6 OTHER FUELS FOR THERMAL 
GENERATORS 

The development work described in the preceding 
text was done on mixtures of two or more principal in¬ 
gredients either pressed or cast into a solid block of 
fuel. At the time, these were believed to hold the best 
promise for satisfactory application in the thermal 
generator munitions. The results achieved apparently 
justify this belief. Nevertheless, it is recognized that 
other fuels have merit and deserve consideration. 
These may be classed as other solid fuels and liquid 
fuels. 


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OTHER FUELS FOR THERMAL GENERATORS 


483 


31 . 6.1 Other Solid Fuels 

Smokeless powder has been developed and used as 
a rocket propellant. Although rocket fuels burn under 
an entirely different set of conditions than do thermal 
generator fuels, a good many of the problems of pro¬ 
duction and operation are similar, and mixtures suit¬ 
able for rockets can be modified in many cases to give 
satisfactory fuels for thermal generators. Smokeless 
powder is the most common rocket propellant, 
though during World War II a number of composite 
propellants such as intimate mixtures of ammonium 
picrate and sodium or potassium nitrate were de¬ 
veloped. The advantages and disadvantages of smoke¬ 
less powder and composite propellants for rockets 
have been compared 10 and the following advantages 
and disadvantages are pertinent to fuel block per¬ 
formance for thermal generators. 

Advantages of Smokeless Powder Fuels 

1. The composition and properties of smokeless 
powders are familiar through their use as gun pro¬ 
pellants. 

2. They can be manufactured with equipment on 
hand, by known processes. This is perhaps their 
greatest advantage. 

Disadvantages of Smokeless Powder Fuels 

1. The burning rate of smokeless powder is sensi¬ 
tive to changes in the gas pressure. 

2. The burning rate is sensitive to changes in the 
initial powder temperature. 

3. At very high and very low temperatures the 
mechanical properties of the powder show failure. 

4. Chuffing, an irregular burning similar to surging 
in fuel blocks, is encountered at low temperatures. 

5. Production of thick grains is difficult; the sol¬ 
ventless process makes such grains possible, but 
equipment for the production of solventless powder 
is limited. 

Advantages of Composite Fuels of Ammonium 
Picrate and Sodium Nitrate 

Composite propellants vary with their composi¬ 
tion. For a mixture of ammonium picrate and sodium 
or potassium nitrate compounded with a suitable 
binder, the following is pertinent. 

1. The burning rate is much less sensitive to 
changes in equilibrium pressure or area of burning 
surfaces than are those of smokeless powders. 

















l \ 






M 

\o 










\ 










N 




EACH 0.1% STARCH ABOVE 2.75% 
DECREASES BURNING RATE 

0.08 G PER MIN PER SQ CM 

\ 



■ \ 

\ 

. 

\ 

V 










\ 

\ 



PER CENT STARCH 


Figure 38. Burning rate of cast fuel blocks as a func¬ 
tion of per cent starch in block. 


2. The dependence of burning rate on the initial 
powder temperature is about one-fifth that of a 
typical smokeless powder. 

3. No chuffing phenomena appear at any pressure. 

4. Material can be produced in a wide range of 
block sizes. 

5. A wide range of absolute burning rates is avail¬ 
able due to the dependence of the burning rates on 
the particle size of the basic ingredients as well as the 
mixture composition. 


Disadvantages of Composite Ammonium Picrate- 
Sodium Nitrate Fuels 

1. Its preparation is not suited to conventional 
powder manufacturing equipment. 

2. Mechanical strength is somewhat low. 

Advantages of Charcoal-KN0 3 or KCIO4 and 
Binder Composite Fuels 

For a mixture of charcoal, potassium nitrate or 
potassium perchlorate, and a cellulose nitrate binder, 
the following is pertinent. 

1. The burning rate is much less pressure sensitive 
than that for smokeless powder. 

2. The dependence of burning rate on initial 
powder temperature is one-sixth to one-half that of 
a typical smokeless powder. 

3. Chuffing phenomena are encountered only at 
very low pressures (probably several hundred pounds 
per square inch in most rockets). 

4. The powder shows increased mechanical strength 


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484 


FUEL BLOCKS FOR THERMAL GENERATOR MUNITIONS 


at high temperatures, as compared with double base 
powder. 

5. There is a wide range of absolute burning rates. 

6. Densities are 10 to 25% above conventional 
double base powders. 

From this summary of the burning characteristics 
of rocket fuels it appears that composite propellants 
and related powders are more suited to the burning 
conditions and the wide range of burning rates re¬ 
quired in the thermal generator than smokeless 
powders. 


31.6.2 Liquid Fuels 

Liquids such as hydrogen peroxide have been used 
successfully as a source of hot gas under pressure. 
They offer the desirable feature of a controlled rate 
of gas generation. The design of storage space and 
the means for controlling the rate of generation 
within the munition must be necessarily quite simple 
for these small munitions. It is questionable whether 
this restriction could be met with liquid fuels at the 
present time. 


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Chapter 32 

NEW SCREENING SMOKE MIXTURES 

By E. W. Comings 


32.1 THE CHANGING REQUIREMENTS 
FOR SMOKE POTS 

B oth the tactical and production requirements 
for smoke pots varied considerably during 
World War II. At first, the available smoke muni¬ 
tions consisted of burning pots generating smoke of 
metal chlorides such as zinc chloride, bursting muni¬ 
tions containing white phosphorus or sulfur trioxide- 
chlorosulfonic acid mixture, and airplane spray tanks 
using the latter mixture or titanium tetrachloride. 
The need for screening large areas from attack from 
the air required greatly increased production of the 
smoke pots. This need was soon largely filled by the 
development of the continuous oil smoke generator. 
These were especially useful where smoke protection 
was required for an appreciable percentage of the 
time. However, there were not enough generators 
available nor could their use be justified in areas re¬ 
quiring very infrequent screens or hastily established 
screens. Smoke pots were well suited for these latter 
purposes as well as for some of the screens set up 
under fire both over land and over water. Somewhat 
unpredictable changes in the course of the war were 
reflected in large variations in the demand for the 
type and quantity of smoke pots. 

32 . 1.1 Need for Substitute Smoke 
Mixture Specifications 

These periods of large demand occurred at times 
when the supply of one or more of the ingredients in 
the mixture was short. Thus, at one time it was 
anticipated that sufficient chlorine could not be 
made available for the organic chlorides used in the 
mixture. Zinc and aluminum (early in the war) were 
possible limitations on the supply. Changes in the 
tactical use of the pots also revealed the need for 
revised specifications. When used for short periods 
of time the HC pots did not produce serious toxic 
effects, but where they were used for longer periods 
of time or when the concentration of smoke was high, 
objectionable toxic effects (from the zinc chloride 
smoke) were noticed. 

The problem of eliminating the fire and explosion 
hazard from the HC-type mixture was ever present. 
This was apparently solved in the laboratory, but 


continued to recur with pots from the production 
line. All these problems indicated the need for im¬ 
proved smoke mixtures but especially for substitute 
mixtures or specifications which could be used to meet 
special production or tactical situations. 

32.1.2 Use of Smoke Pots to Replace 
Continuous Smoke Generators 

The continuous oil smoke generators developed 
during World War II must be supplied with both fog 
oil and fuel. If a simple expendable smoke generator 
could be built which would serve as the container for 
its own smoke agent and fuel, this might well be more 
advantageous than the continuous generators. The 
generator would then always be available with the 
smoke agent. This is essentially the description of a 
smoke pot, except that the smoke mixture has in the 
past been more expensive and less available than fog 
oil and gasoline. A plentiful and inexpensive smoke 
mixture for use in expendable pots would be prefer¬ 
able in many situations to the continuous oil smoke 
generators. Such pots could be emplaced in or around 
an area and fired selectively or in rotation from a 
central control. In an emergency, they could be 
ignited and rolled off the tail board of a truck. A 
single vehicle could thus supply many point sources 
over a line of considerable length. 

32.1.3 Features Desired in a Smoke 

Mixture 

The features especially desirable in a smoke mix¬ 
ture are: (1) all the ingredients should be available in 
sufficient quantities for large-scale production of the 
mixture; (2) a maximum of screening power should 
be obtained per unit weight of mixture; (3) the smoke 
should be nontoxic and also nonirritating to the eyes, 
throat, and skin, and noncorrosive to materiel; (4) 
the mixture should be suitable for large scale manu¬ 
facture, storage, and transportation without hazard 
or deterioration. 

No one mixture is likely to excel in all four of these 
features and some compromise must usually be made. 
These features will be discussed at greater length as a 
criterion for evaluating a smoke mixture. 


SECRET 


485 


486 


NEW SCREENING SMOKE MIXTURES 


Availability of Ingredients 

Production of the mixture has been considered in 
terms of approximately 50,000 to 100,000 tons a year. 
If it had been necessary to protect large areas in 
continental United States from air attack, this figure 
would have been multiplied several fold. The availa¬ 
bility of an ingredient is a relative term and depends 
upon many other often unpredictable factors, such as 
the demand for material necessary for its manu¬ 
facture, the possible stoppage of raw material sources 
in wartime, and even the destruction of facilities for 
manufacture by enemy action or otherwise. Provi¬ 
sion for substitute ingredients and substitute mixtures 
is a foresighted policy. The common materials gener¬ 
ated by the smoke mixtures, and forming the basis of 
the actual smoke particles, and available in sufficient 
quantities to warrant consideration are: (1) metal 
chlorides of zinc, magnesium, aluminum, and iron, 
(2) phosphorus, (3) oleum, (4) sulfur trioxide and 
chlorosulf'onic acid mixtures, (5) fog oil, (6) sulfur, 
and (7) possibly carbon. 

In the mixtures based on the metal chlorides the 
metals were incorporated into the mixture either in 
the metallic form or as oxides, and the chlorine was 
supplied by organic chlorides such as hexachlore- 
thane or carbon tetrachloride. Other oxidizing or re¬ 
ducing agents, such as perchlorates or calcium silicide, 
were used to supply heat or reduce the oxides. Sub¬ 
stitute ingredients and mixtures for producing iron 
chloride smokes will be discussed below. Phosphorus, 
as used in the past, produced a large puff of smoke 
of short duration and was not suitable for use on 
friendly areas. A means of generating phosphorus 
smoke uniformly over a relatively long period of time, 
and of confining combustion within or near the smoke 
pot, would make this material more suitable for use 
in a smoke pot. The use of oleum or the sulfur tri- 
oxide-chlorosulfonic acid mixture both require a uni¬ 
form rate of vaporization or generation throughout 
the functioning time of the pot. The development of 
smoke pots for generating fog oil and sulfur smokes 
will be described in this chapter. 

Maximum Screening Power 

The screening power per unit weight of mixture de¬ 
pends first on the weight of actual material available 
for forming the smoke particles, whether this is 
originally present in the mixture itself or is contrib¬ 
uted from the air. Second, it depends on the effi¬ 
ciency with which this actual smoke material is used 
to form smoke particles with the greatest light scat¬ 


tering or obscuring ability. It is easily possible for a 
mixture to yield the largest amount of actual smoke 
material and yet produce a smoke cloud with a lower 
obscuring power, because the material is wasted in 
particles of a size which do not obscure efficiently. 

Weight of Smoke Agent per Unit Weight of Smoke 
Mixture. The metal chlorides, phosphorus, oleum, 
and sulfur trioxide all have the advantage of remov¬ 
ing water vapor from the air to augment the smoke 
material present in the mixture. The material, which 
actually forms the smoke particles, is a water solution 
of the salts or acid produced by the mixture. This ad¬ 
vantage is greater in relatively humid atmospheres 
than it is in dry ones. Phosphorus has the added ad¬ 
vantage that it increases the amount of smoke ma¬ 
terial by removing oxygen as well as water vapor 
from the air and yields an exceptionally high ratio of 
smoke material per unit weight of phosphorus. A 
comparison of the three metal chlorides and phos¬ 
phorus is given in Table l. 1 


Table 1. 

Smoke forming aqueous solution* produced 

by various agents in air at 75% relative humidity. 



Water 

Water 


Total g 



vapor 

vapor 


smoke 



combining absorbed 

Total 

solution 


Oxygen 

with 

as 

g 

per g 


from 

the 

hygroscopic smoke- 

chlorine 


air 

agent 

water 

forming 

in 

Agent 

g 

g 

g 

solution 

agent 

Phosphorus 

Aluminum 

1.29 

0.87 

3.95 

7.11 


chloride 

Ferric 

0 

0 

4.0 

5.0 

18.8 

chloride 

Zinc 

0 

0 

2.1 

3.1 

14.2 

chloride 

0 

0 

1.5 

2.5 

9.6 

Fog oilf 

0 

0 

0 

1.0 


Sulfurf 

0 

0 

0 

1.0 



* The figures are based on 1 g of agent shown in first column (except 
for the last column). 

t These do not form aqueous solutions but are used in their original 
form. 

It is evident from the table that for the agents com¬ 
pared, white phosphorus yields the greatest weight of 
aqueous solution in equilibrium with air at 75% rela¬ 
tive humidity per unit weight of the agent. The smoke 
particles are composed of this aqueous solution. 
Aluminum chloride, ferric chloride, and zinc chloride 
yield decreasing amounts of solution in that order. 
This ratio of aqueous smoke-forming solution to 
smoke agent varies from 7.11 to 2.5 for these four 
agents. The same ratio for fog oil or sulfur is unity 
(1.0) since these agents are not hygroscopic and only 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


487 



0 V . ----1- 

0)2 3 4 5 


WATER CONTENT 

Figure 1. The variation in water content of smoke 

forming aqueous solutions with relative humidity. 

the agent itself is available to form the smoke par¬ 
ticles. The table does not take into account ingre¬ 
dients in the smoke mixture which remain behind as 
residue or otherwise contribute little to the obscuring 
power. This comparison will vary with the relative 
humidity of the air but changes very little with air 
temperature at any one valu6 of the relative humid¬ 
ity. This is shown by Figure 1. These data have been 
taken from the literature except in the case of ferric 
chloride where the necessary measurements were 
made. 1 The re-examination of these data with addi¬ 
tional experimental determinations is recommended. 

Effect of Smoke Particle Size. Considerable infor¬ 
mation was developed during World War II on the 
effect of smoke particle size on obscuring power. 2 - 3 
The relative light-scattering effectiveness per unit 
weight of smoke agent as it varies with the smoke 
particle radius is shown in Figure 2. The hygroscopic 
agents forming aqueous solutions are represented ap¬ 
proximately by the curve for water. This curve indi¬ 
cates a somewhat lower light-scattering power than 
for oil or sulfur with an optimum particle size of 
about 0.4 micron radius. The curve is quite flat, how¬ 
ever, and the reduction in light-scattering power from 
the maximum is not great in the range from 0.25 to 
0.6 or 0.7 micron radius. The screening power of a 
unit weight of water solution is roughly 60% of that 
of a unit weight of oil when both are compared near 
their optimum particle size. The optimum size (which 
was discussed in Chapter 22 of this volume) for oil 
particles is about 0.3 micron radius although the 
scattering power does not drop below 75% of the 
maximum in the range 0.2 to 0.45 micron radius. 
Sulfur shows an optimum at 0.13 micron that is 25% 



Figure 2. Scattering of light by smokes of sulfur, tri- 
cresyl phosphate (oils), and water. Watts of light scat¬ 
tered by one microgram of particles from a beam of one 
watt per cm 2 of wavelength. X = 0.55 microns (green). 
(Based on calculations furnished by Dr. A. Lowan.) 

greater than oil, but this occurs in such a narrow 
particle size range and at such a small size that it is 
difficult to realize this advantage. The reduction in 
screening power due to variation from this optimum 
particle size is relatively great in the case of sulfur, a 
decrease of 0.03 micron in radius from the optimum 
resulting in about a 60% decrease in screening power. 
In general, all the agents show a more rapid decrease 
in screening power as the smoke particle size is re¬ 
duced below the optimum than when it is made larger. 
This may not be so important from the practical 
point of view since it is doubtlessly easier to waste 
smoke agent in particles that are too large than in 
ones that are too small. 

Volatility and Dilution. A screening smoke in the 
atmosphere eventually loses its obscuring power. The 
common mechanisms by which this occurs are by the 
evaporation of the particles or by dilution until the 
particle density is too low to obscure. The steam from 
a locomotive disappears by evaporation whereas a 
cloud of very small dust particles is eventually di¬ 
luted since the particles are nonvolatile. The maxi¬ 
mum area that can be obscured per unit weight of 
agent increases as the volatility of the agent decreases 
if the cloud disappears by evaporation. When the 
volatility of the agent is low enough that the smoke 
cloud loses its obscuring power by dilution, further 
decrease in the volatility will not increase the area 
obscured. There is not a clean cut distinction between 
the high and low volatility agents. Thus, both fog 
oil and sulfur smokes may disappear by evaporation, 


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488 


NEW SCREENING SMOKE MIXTURES 


but it is unlikely that the area obscured per unit 
weight of each would be increased by more than 
several per cent if they did not evaporate at all. A 
comparison of the weight of sulfur vapor and Diol 55 
vapor required to saturate a cubic mile of air is of 
interest in this connection. 

The vapor pressure curve for sulfur (solid) extra¬ 
polates to about 8 X 10~ 6 mm at 20 C. The calcu¬ 
lated amount of sulfur vapor (S 8 ) required to saturate 
1 cubic mile of air is as follows: 

Degrees C 10 20 30 

Pounds per cubic mile 330 1,000 3,100 

A single figure at each temperature for Diol 55 can¬ 
not be given to compare with these since the Diol 
is not a pure compound. The amount of Diol 55 re¬ 
quired to saturate 1 cubic mile varies depending on 
the initial amount of Diol introduced into the air. 2a 
When this is from 70 to 7,000 lb per cubic mile, the 
weight required to saturate the air would range from 
28 to 147 lb at 10 C, 56 to 390 lb at 20 C, and 70 to 
1,060 lb at 30 C. Although these figures may not be 
very accurate, they indicate that, from the stand¬ 
point of vapor pressure, sulfur and Diol 55 are in the 
same class with a slight edge in favor of the Diol. 

These figures may be compared with the estimated 
quantities of these agents required to screen a square 
mile of area. Under severe conditions 1,400 lb Diol 55 
per square mile will give obscuration. The figure for 
sulfur is at least as large (possibly a little larger) and 
the required weight of HC mixture is of the same 
order. 

The particles of aqueous solution formed by the 
hygroscopic agents are in equilibrium with the air 
surrounding them and will not evaporate even when 
the cloud is diluted. Such clouds lose their obscuring 
power by dilution. 

Toxicity and Irritancy 

Of all the smokes mentioned under “Availability 
of Ingredients,” zinc chloride is probably the most 
toxic to personnel. When the dosage of this smoke is 
kept low, either by infrequent and short time ex¬ 
posure, or by keeping the clouds very dilute, no ill 
effects have been noted. However, when the screens 
are used for considerable periods of time or in high 
concentrations, personnel are adversely affected. 
None of the other smoke agents listed are toxic when 
in a smoke cloud. The hygroscopic agents are ir¬ 
ritating while they are absorbing moisture from the 
air, but at a short distance from the smoke pot are 


quite innocuous. Fog oil is completely nonirritating. 
Some of the fuels used to vaporize it contain black 
powder or sawdust, and these produce fumes which 
are irritating to some extent. Sulfur smoke is slightly 
irritating to the eyes, but no health hazards have been 
observed among the workmen at the sulfur wells who 
are exposed continuously to sulfur fumes. Phosphorus 
in the elemental state is poisonous and it, as well as 
oleum and sulfur trioxide mixture, will produce 
serious burns if scattered about on personnel. The 
latter two are corrosive to materiel. 

Stability in Manufacture, Transportation, and 
Storage 

The HC mixture based on zinc chloride is, at best, 
on the border line between being safe and hazardous 
for handling. Rather serious consequences can ensu 3 
from a lack of close adherence to specifications. This 
may and has resulted in explosion or fire, either in 
manufacture, transportation, or storage. Neverthe¬ 
less, large quantities of this mixture have been pro¬ 
duced and handled satisfactorily. Other mixtures 
based on the Rietal chlorides are not hazardous but 
may possibly deteriorate on storage unless handled 
properly. The pots based on fog oil as a smoke agent 
are probably the least hazardous once the oil is in¬ 
corporated in the mixture. The other components, 
essentially black powder or sawdust-chlorate mixture, 
are hazardous when dry. The latter is probably ruled 
out as far as practical use is concerned because of its 
extreme sensitivity. The sulfur nitrate mixtures have 
always been suspected of being hazardous especially 
in manufacture, but no evidence of this was found 
during extensive experimental work with them. 
Phosphorus, oleum, and the sulfur trioxide mixtures 
are not susceptible to spontaneous explosion, but 
leaky containers in storage or shipment or in tactical 
use must be avoided. 

New screening smoke mixtures developed to meet 
some of these requirements better are described in 
the following text. 

32.1.4 New Chlorine Carriers for Metal 
Chloride Screening Smoke Mixtures 

Introduction 

Aerosols of the hygroscopic metallic chlorides have 
been extensively used as screening smokes for a 
number of years. The hygroscopic nature of these 
aerosol particles permits them to pick up moisture 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


489 


from the air immediately after discharge from the 
smoke pot, thus increasing the amount of material 
available for forming smoke. 

One of the earliest of the metal chloride smokes was 
produced from the Berger mixture which consisted of 
Zn, CC1 4 , ZnO, and kieselguhr, the last two constit¬ 
uents serving to absorb the CC1 4 and slow down the 
rate of reaction during smoke evolution. The smoke 
evolved was light gray in color and consisted largely 
of ZnCl 2 with some colloidal carbon. This pot had 
numerous limitations, chief among them being that 
the CCI 4 was a volatile liquid, thus making the pot 
subject to deterioration on storage and difficult to 
manufacture. Kendrick 6 at Edgewood Arsenal sug¬ 
gested solid hexachloroethane (C 2 Cl6) as a chlorine 
carrier to eliminate the inherent difficulties of liquid 
CCI 4 . This compound has been used extensively since 
that time and is now the most widely used chlorine 
carrier for screening smokes. 

Lawrence 7 reports the early work in the develop¬ 
ment of the hexachlorethane mixture, while Conk- 
ling 8 reviews the basic requirements of such a pot 
and summarizes the later developments. He sug¬ 
gested a mixture of 

36% Zn 
44% C 2 C1 6 
10 % NH 4 CIO 4 
10 % NH 4 CI. 

This was adopted and used with some modification 
until 1940. Limited supplies of NH 4 CIO 4 led to at¬ 
tempts to substitute KN0 3 as the oxidizing agent. 
These mixtures ignited spontaneously during storage. 
Smith and Hormats 9 attributed the difficulty largely 
to heating due to water picked up during manufacture 
and to the low ignition temperature of the mixture 
containing KN0 3 . They found that KCIO 4 could be 
satisfactorily substituted for NH 4 CIO 4 and the mix¬ 
ture had a higher ignition temperature than the 
nitrate mixture (249 to 269 C as compared with 110 
to 140 C). 

A mixture containing CaSi 2 -ZnO-C 2 Cl6 has been 
widely used. The sensitivity of CaSi 2 to water and the 
difficulty of obtaining it led Finkelstein and Becker 10 
and Barnard 11 to suggest a mixture of 

5.50% A1 
47.25% ZnO 
47.25% C 2 C1 6 . 

This mixture is stable to water and has an ignition 
temperature of 775 to 800 C. 12 The smoke produced 
is excellent. 


Hexachlorethane is made from acetylene and 
chlorine by a rather involved process. The supply is 
therefore limited by the amounts of chlorine and 
acetylene available as well as by the processing equip¬ 
ment on hand. A more readily available chlorine 
carrier is needed. To find such a compound a system¬ 
atic survey of the periodic table has been made. The 
results are discussed in the following text. 

Development of Mixtures 

A large number of mixtures that produce a metal 
chloride screening smoke was investigated. The 
principal object was to find a mixture, comparable 
with the present HC mixture, that could be manu¬ 
factured in large quantities in case the production of 
the HC mixture became limited by the supply of 
chlorine or acetylene, or by the processing equipment 
available for its manufacture. The mixtures tried 
were those based on: 

1. The simple inorganic chlorides FeCl 3 , ZnCl 2 , 
and PbCl 2 reacting with Al. 

2. The ferric chloride complexes, including those in 
which FeCl 3 is associated with KC1, NH 4 C1, NaCl, 
and CaCl 2 , as well as the ammines in which it is 
associated with NH 3 . 

3. Mixtures of high efficiency containing FeCl 3 , 
and also hexachloroethane in which all but about 5% 
of the mixture makes smoke. 

4. A few mixtures in which Chlorpropane Wax 
(approximately octachloropropane) is substituted for 
hexachloroethane. 

The following composition gives an excellent smoke 
comparable to the HC mixture. 

A. 88% anhydrous FeCl 3 

12% Al 

This mixture is highly sensitive to moisture before it 
is pressed and is hazardous in manufacture unless 
special precautions are taken to handle it in a dry 
atmosphere. After pressing it is damaged by exposure 
to moist air or water but single units were not made 
dangerous by such exposure. 

It is questionable whether a large production of 
anhydrous ferric chloride can be secured in a short 
time without using elemental chlorine to supply all 
three chlorine atoms. Several such processes have 
been suggested, but inquiries into each reveal tech¬ 
nical difficulties that have not been satisfactorily 
overcome. Therefore, each is in the developmental 
stage with little certainty as to the time required to 
reach a satisfactory design. The chief difficulty is 


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490 


NEW SCREENING SMOKE MIXTURES 


that it is not practical to dehydrate ferric chloride 
from a solution made by the action of hydrochloric 
acid (and some chlorine) on iron or iron oxide. A 
hexahydrate is formed which breaks down when 
heated and gives off HC1 rather than water. 

This difficulty led to the investigation of ferric 
chloride complexes. If one mole of KC1 is mixed with 
one mole of FeCl 3 *6H 2 0 and heated, a complex is 
formed and the water can be driven off below 205 C 
without decomposition, giving a compound KFeCl 4 . 
This complex in the mixture 

B. 8.0% A1 
30.0% ZnO 

2.2% NaN0 3 

59.8% KFeCl 4 , 

gives a smoke of ZnCl 2 , KFeCU, and FeCl 3 which is 
slightly inferior to and has a shorter burning time 
than the HC mixtures. It should be relatively easy to 
produce in quantity. It is less hygroscopic than the 
FeCl 3 and is much easier to handle in the mixing and 
pressing operations. The ignition temperature of the 
mixture is of the order of 335 to 350 C. 

The efficiency of this mixture can be increased and 
the burning time lengthened by adding small percent¬ 
ages of hexachloroethane. A mixture of the following 
composition 

C. 7.3% A1 
27.2% ZnO 

4.5% NaN0 3 
52.0% KFeCl 4 
9.0% C 2 C1 6 , 

burned noticeably longer and gave a smoke slightly 
superior to the mixture with straight complex. This 
mixture is preferable to that with the complex alone 
if limited amounts of hexachloroethane are obtain¬ 
able. 

The use of the complex KFeCl 4 in smoke mixtures 
has the advantages that (1) it is easy to manufacture 
from available raw materials; (2) it is easy and safe 
to incorporate into a mixture, press, and store; and 
(3) it gives a good screening smoke, although not 
quite as good as the HC mixtures. It has the disad¬ 
vantage of leaving a relatively high percentage of 
bulky residue in the pot. 

It is recommended that the above two mixtures, 
B and C, be considered for the larger size smoke pots 
and floats in case the supply of organic chlorine 
carriers is not adequate. The choice between mixtures 
B and C will be dependent upon the supply of 
hexachloroethane available. 


The high-efficiency mixture contains 

D. 51.6% FeCl 3 

38.3% C 2 C1 6 
8.8% A1 
1.3% NaN0 3 . 

About 95% of the mixture is converted to smoke¬ 
forming products. It produces an excellent smoke 
with little residue, but contains both FeCl 3 and 
C 2 C1 6 . It is sensitive to moisture in the same way as 
the FeCl 3 -Al mixture. 

Chlorpropane Wax, which was tested briefly, gives 
indication of having certain advantages over hexa¬ 
chloroethane as an organic chlorine carrier. It is man¬ 
ufactured by a relatively simple two-step process of 
chlorinating propane. Its vapor pressure is lower than 
C 2 C1 6 . On the other hand, its chlorine efficiency from 
elemental chlorine to smoke is not so good. 

A mixture similar to the HC mixture, in which 
hexachloroethane was replaced by octachloropropane, 
gave a smoke comparable to the present HC mixture. 
This mixture had the following composition: 

E. ' 6.25% A1 

46.15% ZnO 
47.60% C 3 C1 8 . 

If it is found that octachloropropane can be manu¬ 
factured more readily than hexachloroethane, it is 
recommended that mixture E be tested to replace or 
supplement the present HC mixture using hexachloro¬ 
ethane. 

Possible Chlorine Carriers 

The physical properties of the more available 
simple chlorides were tabulated. 13 The chlorides of 
the metallic elements such as Ni, Cu, Cr, Hg, which 
are scarce during wartime, have not been considered. 

The solid chlorides include TiCl 3 , PC1 5 , BiCl 3 , SbCl 3 , 
SeCl 4 , TeCl 4 , ZnCl 2 , FeCl 2 , FeCl 3 , CdCl 2 , PbCl 2 , the 
chlorides of the alkaline earths (Be, Ca, Mg, Sr, Ba), 
and the chlorides of the alkali metals (Na, K, NH 4 ). 
With the exception of CdCl 2 , PbCl 2 , NaCl, and KC1, 
all these solids are deliquescent and give off con¬ 
siderable heat during hydration. 

A comparison of the heats of reaction and free 
energies for reaction of these solid chlorides with A1 
is given in the original report. 13 Aluminum was 
chosen as the reducing metal since it stands high in 
the electromotive series, its chloride volatilizes at a 
comparatively low temperature, and secondary grades 
of powdered metal can be obtained in considerable 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


491 


quantity. 11 The reduction of the alkali and alkaline 
earth chlorides is strongly endothermic (AH and A F 
are positive); therefore, the use of these simple 
chlorides is not practical. The reduction of both 
ZnCl 2 and PbCl 2 is slightly exothermic. The reduc¬ 
tion of ferric chloride is more markedly exothermic. 
Since FeCl 3 , ZnCl 2 , and PbCl 2 are somewhat easier to 
obtain than the other chlorides, these were used in 
preliminary trials. 

Smoke Mixtures from the Simple Chlorides 

The Ferric Chloride and Aluminum Mixture. Theo¬ 
retically, the reaction of A1 with anhydrous FeCl 3 
proceeds according to the equation: 

A1 FeCl 3 —> A1C1 3 ~\- Fe 36.6 kcal. (1) 
The stoichiometric mixture for this reaction contains 
14.7% A1 and 83.3% FeCl 3 . The smoke produced 
from such a mixture is excellent, being entirely com¬ 
parable to that from the best of the HC mixtures. 
This mixture has several limitations, however, be¬ 
cause of the extremely hygroscopic nature of the 
anhydrous FeCl 3 . These limitations will be treated in 
more detail later. 

The smoke from the mixture is red when it first 
leaves the pot, and gradually changes to buff, then to 
white. This suggested that FeCl 3 was being vaporized 
directly and the smoke was a mixture of iron and 
aluminum chlorides. Variation of the percentage of 
aluminum in the mixture and analysis of the resulting 
residues for aluminum and iron confirmed this obser¬ 
vation. The most efficient mixture contains 12% A1 
and 88% FeCl 3 . The percentage of aluminum can be 
varied over a wide range with little difference in 
performance. 

Stability of Mixture. The hydration of FeCl 3 is 
accompanied by the evolution of considerable heat 
and HC1. The loose smoke mixture reacts vigorously 
with water to give HC1 and sufficient heat to ignite 
the mixture. Under the low and moderate indoor hu¬ 
midities of winter and spring, it was found possible 
to mix and press successfully small batches of up to 
5 lb. It was necessary to set the mixtures aside in air¬ 
tight containers for as much as 24 hr after mixing and 
before pressing. This allowed the heat of hydration 
of the moisture picked up from the air during mixing 
to be dissipated before pressing. In two cases where 
pressing was carried out shortly after mixing, spon¬ 
taneous ignition took place soon after pressing. In the 
high humidity of summer (70% humidity or higher) 
it was almost impossible to carry out the mixing and 
pressing operations in the laboratory. On one oc¬ 


casion about 20 lb of mixture were made up and set 
aside in screw-top glass bottles. One of these blew off 
the top and scattered hot mixture over the rest. 
They all ignited subsequently over a period of a few 
minutes and scattered glass and mixture over the 
laboratory. Another 10-lb mixture of the aluminum 
and FeCl 3 type was successfully mixed and stored but 
began to heat during pressing. The pressing operation 
was discontinued and some minutes later the mixture 
ignited. Apparently spontaneous ignition took place 
within the cake and blew it apart. Mixtures of FeCl 3 
and aluminum are therefore quite sensitive to mois¬ 
ture and have to be handled in a dry atmosphere. If 
kept dry and then pressed, the cakes give every 
indication of being safe to store and handle. 

After pressing, the mixture picked up moisture on 
top and could not be ignited until this hydrated layer 
was removed; however, no case of spontaneous igni¬ 
tion was ever observed after a mixture had been 
successfully pressed without overheating. Water can 
be poured directly on the pressed surface without 
vigorous reaction. Penetration of water into the 
pressed mass is sufficiently slow to allow dissipation 
of the heat of hydration of the FeCl 3 . 

Ignition Temperature of the Mixture. These values 
were obtained by slowly heating the loose mixture in 
a crucible and measuring the ignition temperature 
with a thermocouple in the mixture. Some smoking is 
first observed at 105 to 110 C. Ignition does not occur 
if the heat is removed at this point. Definite ignition 
occurs at 150 to 160 C. 

Burning Time. The burning time for a 600-g pot is 
generally around 3 min. The 5-lb pots (can size — 
53^-in- diameter, 4 in. high) ranged in burning time 
from 3 min 45 sec to 5 min 15 sec. The amount of 
hydration during mixing may have some influence on 
the rate of burning. 

Manufacture of Anhydrous Ferric Chloride. The 
successful commercial processes for the manufacture 
of anhydrous ferric chloride on a limited scale use 
elemental chlorine to supply the three chlorine atoms 
needed. This is done because it is not practical to 
dehydrate the ferric chloride formed in solution by 
the action of hydrochloric acid (and some chlorine) 
on iron or iron oxide. The ferric chloride forms a 
hexahydrate and, on heating, this gives up HC1 
rather than water. Elemental chlorine could be used 
for either increasing the production of hexachlorethane 
or ferric chloride. A large increase in demand for 
chlorine carriers would call for other sources of supply 
that do not depend on elemental chlorine. Work has 


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492 


NEW SCREENING SMOKE MIXTURES 


been done on several processes designed to avoid 
using elemental chlorine to supply two or all three of 
the chlorine atoms in anhydrous ferric chloride. 
Further developmental work is needed on all these 
processes. Some of them are outlined below and the 
engineering problems involved are pointed out. 

1. Scrap iron or iron oxide can be treated with 
hydrochloric acid to produce ferrous chloride. The 
ferrous chloride is crystallized from solution, de¬ 
hydrated probably under reduced pressure, and con¬ 
verted to the anhydrous ferric chloride. The latter 
step would probably be done with chlorine. 

2. The reaction of sodium or calcium chloride, iron 
sulfide, and air has been suggested. Evidence exists 14 
to indicate that the separation of anhydrous ferric 
chloride from the resulting mixture with sodium or 
calcium sulfate is difficult. It must be vaporized from 
the mixture, and its vapor pressure is very much less 
from the mixture than when pure. Possibly reduced 
pressure or an inert carrier gas and a high temperature 
would effect a separation. 

3. The reaction of iron sulfate and calcium chloride 
is in the same class as paragraph 2. 

4. Dehydration of the FeCl3-6H 2 0 in a stream of 
hot dry HC1 would require specially designed equip¬ 
ment. 

5. The reaction between iron oxide (roasted py¬ 
rites) and dry HC1 proceeds with the formation of 
three moles of water per mole of FeCl 3 . By proper con¬ 
trol of the temperature of the condensing surfaces it 
may be possible to condense anhydrous ferric chloride 
from the hot gas stream. 

Chloride Complexes 

Anhydrous ferric chloride has several disadvan¬ 
tages as a chlorine carrier, chief among which are its 
extreme hygroscopicity and the limitations in its 
manufacture which were discussed previously. Com¬ 
plex salts of ferric chloride have been investigated 
to avoid these difficulties. 

Ammonium Ferric Chloride Complexes. Several 
complexes of NH 4 Cl-FeCl3-H 2 0 are reported in the 
literature 15> 16 including salts of the composition 
NH 4 FeCl 4 and (NH 4 ) 2 FeCl 5 -H 2 0. The former sub¬ 
stance is obtained by fusion of equimolecular amounts 
of NH 4 C1 and FeCl 3 -6H 2 0. The water is removed by 
evaporation. A boiling point of 386 C has been re¬ 
ported. The (NH 4 ) 2 FeCl 5 • H 2 0 is obtained by crystal¬ 
lization from a solution of the mixed chlorides. Be¬ 
cause of its high percentage of NH 4 C1 and its water of 
crystallization, this compound is of little interest here. 


Theoretically the reduction of NH 4 FeCl 4 with A1 
proceeds according to the equation 

A1 + NH 4 FeCl 4 —> A1C1„ f + NH 4 C1 f + Fe. (2) 

The stoichiometric mixture for this equation burned 
very slowly, giving a poor smoke over a long period 
of time. 

Various heating mixtures were tried with the above 
stoichiometric smoke mixture for the complex 
NH 4 FeCl 4 . No completely satisfactory heating mix¬ 
ture was found which could be used in connection 
with the above reaction. Complexes of KC1 showed 
much less cooling action than complexes of NH 4 C1. 
For this reason KC1 complexes were more desirable. 

Potassium Ferric Chloride Complexes. The only salt 
of FeCl 3 and KC1 found in the literature had the 
composition K 2 FeCl 5 • H 2 0. 17 

1. K 2 FeCl 5 -H 2 0, an orange-yellow complex, was 
prepared by evaporating water from a fused mixture 
of FeCl3*6H 2 0 and 2KC1. The extra molecule of 
water was driven off to give a complex of the com¬ 
position K 2 FeCl 5 . Mixtures made from this compound 
gave a very poor smoke with a high residue. 

2. KFeCl 4 . This complex was not found in the 
literature, but since ionic radii of NHt and K + are 
reasonably close to the same value, and salts of the 
two ions are isomorphous in many cases, the exist¬ 
ence of this salt was suspected. The salt was pre¬ 
pared by evaporation of a mixture of FeCl 3 -6H 2 0 
and KC1. Two lots were prepared and analyzed. In 
making lot No. 1 the heat was removed as soon as 
the liquid water was gone. The massive product was 
a deep brownish-red but became bright yellow when 
ground. The color changed to reddish-orange when 
moisture was picked up. Lot No. 2 was fused after 
the liquid water was gone and the odor of chlorine 
could be detected coming from the mass. This mas¬ 
sive product was a deeper brownish-red and remained 
red-brown after grinding. The analyses of the two 
products showed the following compositions. 

Observed Theoretical Observed Theoretical 
% Cl % Cl % Fe % Fe 

Lot 1 59.53 59.94 24.41 23.66 

Lot 2 57.75 59.94 25.62 23.66 

Excessive heating appears to have driven off 
chlorine to form some of the ferrous complex. 

3. Mixtures from KFeCl 4 . Mixtures of this com¬ 
plex combined with aluminum and zinc oxide to 
supply heat were made. A good smoke was produced 
which had a characteristic orange color as it left the 
pot. This color persisted longer than that with the 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


493 


FeCl 3 mixture, gradually fading to white. The 
principal objections to this mixture were its com¬ 
paratively short burning time and its relatively high 
percentage of residue (50%). The reaction 

2A1 + 3ZnO + 2KFeCl 4 —> 

A1 2 0 3 + 2ZnCl 2 + 2KC1 + Fe 

indicates a theoretical efficiency of 52.5% if no KC1 is 
volatilized, and 71.5% if all of the KC1 is volatilized. 
Analysis of the residues for potassium revealed that 
from 46 to 92% of the KC1 was volatilized, de¬ 
pendent upon the amount of KN0 3 in the mixture. 

The amount of residue was reduced by adding 
sufficient C 2 C1 6 to react with the Fe formed by the 
reaction. A mixture of 

6.2% A1 
23.2% ZnO 
22.6% C 2 C1 6 
43.5% KFeCl 4 
4.5% KN0 3 or NaN0 3 

gave a very good smoke, with about 30% residue. 
The smoke produced was tan, gradually fading to 
white. In volume and screening power it was not 
quite equal to the Al-ZnO-C 2 Cl 6 mixture. 

The hexachloroethane serves to improve the smoke 
but the quality is not markedly affected by con¬ 
siderable variation in the percentage. A mixture of 
the following composition is recommended if C 2 Cl6 is 
available. 

52.0% KFeCU 
27.2% ZnO 
9.0% C 2 C1 6 
7.3% A1 
4.5% NaN0 3 . 

If C 2 C1 6 is not available, a mixture containing 

8.0% A1 
30.0% ZnO 
2.2% NaN0 3 
59.8% KFeCl 4 

gives a good smoke for a shorter period of time. 

The mixture is not nearly so sensitive to water as 
the FeCl 3 mixtures. However, if the loose mass is 
triturated with water, the KFeCU will hydrate giving 
off HC1, evolving heat, and swelling markedly. The 
evolution of heat was never sufficient to ignite the 
mixture. The KFeCl 4 is definitely hygroscopic but 
less so than FeCl 3 . The completed mixtures were very 
convenient to press and handle. The ignition tem¬ 
perature for this mixture was determined by the 


same technique as that used for the Al-FeCl 3 candle. 
Values of 335 to 350 C were obtained. KFeCl 4 ap¬ 
pears very promising to supplement hexachloroethane. 
The complex should be easily manufactured from 
KC1 and hydrated FeCl 3 . 

4. Manufacture of anhydrous FeCl 3 • KC1 complex. 
It is evident that the manufacture of ferric chloride 
hexahydrate is much easier than that of the anhy¬ 
drous material, especially if both products are made 
without the use of elemental chlorine. It should be 
possible to produce readily large quantities of the 
hexahydrate using hydrochloric acid and iron or iron 
oxide with no more than one atom of chlorine being 
supplied from elemental chlorine. The hexahydrate 
can be melted and mixed with an equal number of 
moles of KC1. The complex KFeCl 4 then forms and 
allows the dehydration to take place readily by heat¬ 
ing to 205 C. 

High-Efficiency Smoke Mixtures 

In the reduction of ferric chloride by aluminum in 
the Al-FeCl 3 mixture, elemental iron is left as the 
principal constituent of the residue. Addition of 
enough C 2 C1 6 to remove the iron as FeCl 3 increases 
the theoretical efficiency of the mixture considerably, 
leaving the carbon of the hexachloroethane as the only 
element not used in smoke production. The reaction 
should proceed as follows: 

2A1 + 2FeCI 3 2A1C1 3 + 2Fe 
2Fe + C 2 C1 6 —> 2FeCl 3 + 2C 
or in the following manner: 

2A1 + C,C1 6 —> 2A1CU f + 2C + heat 
FeCl 3 (solid) + heat —> FeCl 3 f (vapor). 

The end result is the same in both cases. Probably 
both reactions are involved. 

The stoichiometric mixture for these reactions 
gives a theoretical efficiency of 96%. The mixture 
has the following composition: 

8.8% A1 
52.6% FeCl 3 
38.6% C 2 C1 6 . 

The above mixture gave actual residues of from 3 to 
5% of the original mixture, but the burning rate was 
too slow and the resulting rate of smoke evolution 
was correspondingly slow. Small amounts of NaN0 3 
were added to increase the burning rate. This per¬ 
centage is rather critical, Very small differences 
having a marked effect upon the burning time. 

A smoke cloud superior to that produced by the 


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494 


NEW SCREENING SMOKE MIXTURES 


HC mixture of Al-ZnO-C 2 Cl 6 was produced by a 
mixture of the following composition: 

8.8% A1 
51.6% FeCls 
38.3% C 2 C1 6 
1.3% NaN0 3 . 

This mixture burned noticeably faster than the 
standard Al-ZnO-C 2 Cl 6 mixture in M-l pots. 

Large percentages of both FeCl 3 and C 2 C1 6 are 
used in this type of mixture, but an extremely dense 
smoke cloud is produced. A mixture of this type may 
have application where a high-efficiency mixture is 
desired. Because of the FeCl 3 content it is sensitive 
to water before pressing, evolving HC1 and heat. 
After pressing, the candle is damaged by water but 
the reaction is not vigorous. The mixture should be 
protected by a watertight container. 

Chlorpropane Wax 

Chlorpropane Wax produced on a pilot plant scale 
was investigated as a possible chlorine carrier. 
The product corresponded approximately to the 
formula C 3 C1 8 . This material was substituted for 
hexachloroethane in the standard HC mixture of 
Al-ZnO-C 2 Cl 6 . 

The reactions are probably very smiliar to those 
for the standard HC candle. 

2A1 + 3ZnO —► A1 2 0 3 + 3Zn 
4Zn -f- C 3 C1 8 ^ 4ZnCl 2 ^ 3C 

C + ZnO —> Zn + CO. 

The reaction 

8A1 + 3C 3 C1 8 —► 8A1C1 3 f + 9C 

undoubtedly occurs to some extent in conjunction 
with the above. The burning time was regulated by 
adjusting the per cent of Al. 

A mixture with a smoke volume and burning time 
comparable to the standard HC mixture was pro¬ 
duced. This had the composition: 

Al = 6.25% ' 

ZnO = 46.15% 

C 3 C1 8 = 47.60%. 

32.1.5 Sulfur-Nitrate Screening Smoke 
Mixtures 

Summary 

Mixtures containing essentially a nitrate, charcoal, 
and sulfur have been investigated as a source of 
screening smoke. 24 These mixtures are placed in a 


metal can with a perforated cover. The nitrate and 
charcoal and some of the sulfur react, giving off heat 
which vaporizes the remaining sulfur. The mixture of 
reaction gases and elemental sulfur vapor is emitted 
with some velocity through the perforations. Each jet 
entrains air and cools the sulfur vapor, condensing it 
to form minute smoke particles. This smoke is white 
and shows little of the yellow color of sulfur. 

Sodium, potassium, or ammonium nitrate may be 
used. The former is available in the largest quantities 
while the latter gives a greater amount of diluting 
gases. The chief advantage of the mixture is that all 
the ingredients are available in large quantities. 
Weight for weight they are in the order of 50% as 
efficient as HC smoke mixtures. 

The mixtures appear to be safe to handle and 
store. No evidence to the contrary has been found 
during the rather extensive experimental work. As a 
conservative precaution, however, it is recommended 
that adequate steps be taken to protect property and 
personnel from fire or explosion during the mixing 
and pressing operations. 

Methods of Producing Sulfur Smoke 

Sulfur smoke as discussed here refers to small par¬ 
ticles of elemental sulfur suspended in the air. Such 
a smoke has been set up in a number of ways. A 
continuous sulfur boiler fired by a gasoline burner 
was described 19 in Chapter 30. This produced up to 
500 lb per hr of sulfur smoke by forcing a mixture of 
sulfur vapor and superheated steam through nozzles 
under a pressure of several pounds per square inch. 

A sulfur smoke was also produced on a small scale 
in three units housed in a greenhouse. 20 These pro¬ 
duced sulfur smoke by (1) forcing a mixture of steam 
and sulfur vapor through nozzles, (2) using a steam- 
powered atomizer to spray liquid sulfur (containing 
0.2% iodine) into a heated iron tube, (3) allowing 
molten sulfur to run into the exhaust of an automo¬ 
bile engine operating at 15 hp. 

A stainless steel tubular sulfur boiler was built and 
operated. 21 This unit produced up to 275 lb per hr of 
sulfur smoke by forcing pure sulfur vapor through a 
nozzle at pressures up to 70 psi. 

Sulfur smoke was also produced by a small two- 
compartment thermal generator pot. 22 A fuel block 
of ammonium nitrate and charcoal was placed in the 
lower compartment and lump sulfur in the upper. The 
hot gases from the fuel block passed to the upper 
compartment through a Venturi-shaped tube and the 
molten sulfur was drawn into the throat of the Ven- 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


495 


turi through a hole. The mixture of sulfur vapor and 
fuel gases issuing from the top of the Venturi passed 
around a baffle and out through holes in the top of 
the upper compartment. Cooling of the vapor by air 
entrainment formed smoke. 

A continuous portable sulfur smoke generator us¬ 
ing the hot gases supplied by a gasoline burner and 
with molten sulfur sprayed into these through a hole 
in the throat of a Venturi tube was built and operated 
successfully. 23 The flow of hot gases through the 
Venturi and of the sulfur vapor-combustion gas 
mixture through the exit holes was induced by a 
steam entrainment jet. 

The SN Mixture — Factors Affecting its Per¬ 
formance 

This sulfur smoke mixture is composed of sulfur 
intimately mixed with a suitable fuel. When this 
mixture is ignited in a closed container with holes 
through which the resulting sulfur vapor-gas mixture 
can escape, a smoke of elemental sulfur particles is 
formed. The fuel used contained a nitrate as oxidizing 
agent and hence the mixtures have been designated 
sulfur-nitrate or SN mixtures. 

Mixtures have been made which contain principally 
sulfur, sodium nitrate, and charcoal; sulfur, am¬ 
monium nitrate, and charcoal; and sulfur, potassium 
nitrate, and charcoal. The sulfur is present in con¬ 
siderable excess over that in black gunpowder and its 
latent heat of fusion and vaporization absorbs the 
heat of reaction and slows the burning rate. The rate 
of burning is influenced by the percentage of sulfur. 

The mixtures can be made by blending and press¬ 
ing the dry screened ingredients or by mixing the 
nitrate (except NH 4 N0 3 ) and charcoal into the 
molten sulfur. Better results have been obtained by 
dry mixing and pressing since this method results in a 
greater percentage of the mixture being evolved as 
sulfur smoke. These dry mixtures must be pressed to 
insure a compact block and uniform burning. The 
minimum load to produce a satisfactory cake is of the 
order of 600 to 800 psi. Some of the sulfur reacts dur¬ 
ing the burning to form sulfides and sulfates which 
are left in the residue. This does not occur when am¬ 
monium nitrate is used, and apparently all the sulfur 
is then converted to smoke. In any case, the burning 
fuel does not produce S0 2 in the container. The per¬ 
centage of sulfur which reacts during the burning, and 
the rate of burning depend to some extent on the 
particle size of the sulfur in the mixture. The ideal 
condition is an intimate mixture of nitrate and char¬ 


coal which transfers its heat of reaction to the sulfur 
without reacting with it. This situation can be ap¬ 
proached by using a larger particle size for the sulfur 
than for the other ingredients. If the sulfur particle 
size is too large, however, some of the sulfur is not 
evaporated and the efficiency drops off. The rate of 
burning also increases because the sulfur is not so 
effective as a cooler. When the mixture is made by 
melting the sulfur, it is intiipately mixed with the 
fuel and, on burning, a part is oxidized to S0 2 with 
the result that a thin smoke is produced. 

The fuel gas-sulfdr vapor mixture is hot as it comes 
from the burning block and will readily ignite and 
burn to form S0 2 if mixed with air. If, however, this 
mixing with air is carried out rapidly, the sulfur 
vapor is cooled below its ignition point before it 
ignites. Rapid dilution and cooling is also required to 
form the proper size sulfur particles (about 0.15 
micron radius) for an effective screening smoke. This 
rapid cooling and dilution with air is accomplished by 
forcing the hot gases through a number of small 
orifices in the container out into the air. Orifices about 
%2 in- in diameter have been used. The number of 
orifices must be balanced against the burning rate. 
If too few orifices are used, excessive pressure will 
develop and rupture the container. At low pressures 
the rate of flow through the orifices increases in pro¬ 
portion to the square root of the pressure in the con¬ 
tainer. This will adjust the flow rate automatically for 
small changes in the burning rate. At pressures above 
about 12 psi, the rate of flow increases much less with 
pressure. A sufficient number of orifices should be 
used to insure against the pressure rising higher than 
this. There will be no need then to build the con¬ 
tainers to withstand a higher pressure. Inert gases, 
such as C0 2 or N 2 , evolved by the fuel and mixed 
with the sulfur vapor, help to prevent flaming and 
give a smaller particle size in the smoke. 

The amounts of heat and the volumes of gas 
generated by a number of possible fuel reactions are 
shown in Table 2. Of the possible reactions of char¬ 
coal with NH 4 NO 3 , NaN0 3 , or KN0 3 , the first gives 
the largest amount of heat and gas, and the others 
fall in the order named. This is based on the assump¬ 
tion that the carbon is oxidized to C0 2 [see equations 
(2), (4), (6), Table 2]. At 600 C the sodium nitrate 
produces 60% as much heat and 43% as much gas as 
the ammonium nitrate per unit weight of fuel mix¬ 
ture. If the sulfur enters the reaction [equation (9)] 
the amount of heat produced per unit weight of 
carbon plus nitrate is increased and in the case of 


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NEW SCREENING SMOKE MIXTURES 


Table 2. The heat evolved and the volume of inert gases furnished by several fuel mixtures based 
on an assumed reaction is tabulated below. 



Reaction 

kcal/g 

20C 

mix 

600 C 

Liters gas 
(STP, 0 C, 1 atm) 

(1) 

C + NH 4 NO 3 = CO + N 2 + 2H 2 0 (g) 

0.588 

0.384 

0.975 

(2) 

h C + NH 4 NO 3 = h C0 2 + N 2 + 2 H 2 0 (g) 

0.87 

0.667 

0.910 

(3) 

§ C + NaNOa = f CO + h N 2 + h Na 2 0 

0.029 


0.578 

(4) 

f C + NaNOa = f C0 2 4- i N 2 + i Na 2 0 

0.55 

0.400 

0.392 

(5) 

f C + KNO 3 = £ CO + 4 N 2 + | K 2 0 

-0.065 


0.515 

(6) 

1 C + KNO 3 = 1 C0 2 + h N 2 + 1 K 2 0 

0.365 

0.256 

0.338 

(7) 

§ P + NH 4 NO 3 = l P 2 0 5 + N 2 + 2H 2 0 (g) 

1.09 

0.799 

0.725 

(8) 

P 4- NaNOa = h P 2 O 5 4- i N 2 + i Na 2 0 

0.975 

0.805 

0.0963 

(9) 

C + NaNOa 4- i S = 1 C0 2 + i N 2 + l Na 2 S 

0.715 

0.580 

0.378 

(10) 

2A1 4- C 2 C1 6 = C + 2AlCla 

0.838 

0.679 

0.000 


(Note: The heat required to heat and vaporize sulfur (18 to 600 C) amounts to 0.216 kcal/g.) 


sodium nitrate it is 87% of that with ammonium 
nitrate. 

Description of SN Mixtures 

The compositions of typical SN mixtures are shown 
in Table 3. These mixtures all produced excellent 
smoke in several tests although all gave somewhat 
variable performance. 

Suggestions for Improving the Mixtures 

These mixtures were never completely developed to 
give reliable and reproducible results. The chief diffi¬ 
culty arose from nonuniform and nonreproducible 
rates of burning which resulted in flaming of the 
vapors in some cases. Work on these mixtures was 
discontinued in order to concentrate effort on the 
black powder-oil gel mixtures described below. The 
final results from the latter, however, were not en¬ 
tirely satisfactory. The two-compartment oil smoke 
generator (see Chapter 30) resulted in a satisfactory 
smoke pot, which meets the requirements for oil 
smoke pots in spite of its more complicated internal 
construction. The improvements developed for the 
fuel block for this latter pot and other thermal 
generators, and described in Chapter 31, could very 
likely be applied to the SN mixtures to give a satis¬ 
factory sulfur smoke pot of the intimate mixture 
type. Specifically the improvements suggested are: 

1. The use of linseed oil binder instead of celluloid 
in acetone. 

2. The use of a heavy paper liner for the cans to 
prevent burning down the sides of the mixture. 

3. Pretreat the charcoal and develop specifications 
for its manufacture. 

4. As an alternative for 3, the use of a noncarbon 
pyrotechnic fuel for mixing with the sulfur. All 
ingredients of such a fuel would be subject to rigid 
manufacturing control. 


The Screening Power of Sulfur Smoke 

The screening power of sulfur smoke has not been 
measured in tests on a relatively large scale in com¬ 
parison with other types of smoke. In tests on a con¬ 
tinuous sulfur smoke generator, producing as high 
as 275 lb per hr with an average particle size of 0.23 
micron, it was estimated that in the order of 1,000 lb 
sulfur per square mile was required for a good screen 
in winds from 7 to 17 mph. This is approximately the 
same amount as for Diol and also HC mixture. 

A visual comparison was made at Edgewood 
Arsenal of the M-l HC smoke pots containing about 
12 lb of HC mixture with SN pots containing about 
5p2 lb of mixture. The volume of smoke near the pots 
compared favorably, but the sulfur smoke was some¬ 
what less persistent. The sulfur pots generate ap¬ 
proximately 50% of the weight of the mixture as 
smoke, whereas the HC mixture gives in the order of 
75% of its weight as ZnCl 2 . The latter weight of 
smoke is augmented by taking water vapor from the 
air to hydrate the ZnCl 2 . 

A rough estimate of the cost of area screening by 
SN mixture can be made, although this is not based 
on adequate field tests and may be inaccurate. A 
figure of 1,400 lb per square mile required for screen¬ 
ing is taken as a basis. In a 10-mph wind this would 
require 14,000 lb per hr of sulfur smoke or 28,000 lb 
per hr of SN mixture. With sodium nitrate at $1.35 
per 100 lb, and sulfur about one cent per pound or 
less, the cost of the mixture prepared and loaded into 
containers should be in the order of 3 to 5 cents per 
lb. (Note. Diol itself costs from 3 to 4 cents per lb.) 
This would indicate a cost of $800 to $1,400 per hr 
per square mile for SN pots alone, exclusive of the 
labor to place and operate them. 

Safety Precautions 

Mixtures of the type consisting essentially of 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


497 


Table 3. Compositions of typical SN smoke mixtures. 


Sulfur-N aN O 3 -C harcoal 

1,500 g mixture used with a surface area of 22.7sq in.; 
binder, 5% celluloid in acetone; 75 g of starter, 32.0% 
NaN0 3 , 8% charcoal, 60% sulfur. 


NaN0 3 , wt % 

31.47 

34.0 

Charcoal, wt % 

5.53 

6.0 

Sulfur, wt % 

63.0 

60.0 

Binder, cc 

140.0 

150.0 

Burning time, min 

2-2 j 

4-4f 

Sulfur, mesh size 

14-28 

28-35 

Per cent of mixture as smoke 47-50 

46 

Orifice size, in. 

Number of orifices 

£ to A 

_ 3 _ 

32 

12-14 

14 

Sulfur-NHiN O 3 -C harcoal 


1,250 g mixture with 

a surface area of 38.5 

sq in.; 

binder, 5% celluloid 

in acetone; sulfur, commercial 

flowers; 20 g British 

starter (40% Si, 54% 

kno 3 , 

6% C) compressed into I x 2-in. diameter pellets; 

pressed in three layers. 




Bottom Middle 

Top layer 

NH 4 N0 3 , wt % 

45 55 

86 

Charcoal, wt % 

9 11 

14 

Sulfur, wt % 

Binder, cc 

Weight of layers, g 

46 34 

200 60 

20 

1,000 200 

50 


NHiN O a -KN Os-Charcoal-Sulfur 
2,500 g mixture was used with a surface area of 50 sq in. 
The mixture was in three layers of 270 g, A; 1,750 g, B; 
then 270 g, A. A hard core of 270 g A compressed under 
10 tons/sq in. was arranged to pass through the center 
of the other three layers; 20 g of C was used as starter 
and the whole pressed under 600 lb /sq in. 



A 

B 

C 

Charcoal, wt % 

6.3 

3.1 

15.0 

NH 4 N0 3 , wt % 

19.9 



KN0 3 , wt % 

27.8 

32.2 

75.0 

Sulfur, wt % 

46.0 

64.7 

10.0 

Binder, cc/100 g 

30.5 

14.2 

25.0 


sodium nitrate, charcoal, and sulfur have been mixed 
and pressed in amounts up to 3 lb and mixtures of 
potassium nitrate, charcoal, and sulfur in amounts up 
to h }/2 lb. During this experimental work, there was 
no incident to indicate that these mixtures were 
sensitive or dangerous to handle by the methods of 
mixing and pressing employed. During burning of 
the completed experimental smoke pots in the field, 
there was a number of tests in which the mixture 
burned too rapidly for the gases to escape through 
the perforations in the cover; the cover was blown 
off and the contents scattered over a radius of several 
yards. 

It was found possible to ignite small samples of the 
mixtures by impact. Samples fired on a type of 


machine that afforded some confinement for the 
mixture were found to give only a small amount of 
smoke upon the impact of a 2-kg weight dropped 
70 to 75 cm. Under identical conditions, an explosive 
considered to be moderately sensitive gives complete 
detonations at 40 to 45 cm. On the other hand, TNT 
fails to fire at 100 cm. Under conditions which af¬ 
forded very little confinement, samples gave a small 
amount of smoke, but no ignitions or detonations at 
200 cm. The moderately sensitive explosive fires at 
approximately 25 cm. Therefore, the samples were 
apparently not very sensitive to impact. In all cases 
it was necessary for the operator to watch very closely 
for the small wisp of smoke which indicated that some 
decomposition had taken place. 

A small pile of the mixture could not be ignited 
with an ordinary match. Black gunpowder is known 
as an unpredictable composition, and extreme care, 
practically amounting to distrust, should be exercised 
in processing it. Experience indicates that the cooling 
effect of the large excess of sulfur in these mixtures 
makes them much less sensitive to ignition by sparks 
and much slower burning when ignited than black 
powder. In view of the limited experience with the 
mixtures, however, it is advisable to handle them 
with the same precautions as black gunpowder. 


32 . 1.6 Diol-Sawdust-Chlorate Smoke 
Mixtures 

Summary 

An intimate mixture of Diol and a fuel was par¬ 
tially developed into a smoke pot of promising per¬ 
formance. 25, 25 The fuel consisted of a mixture of saw¬ 
dust and charcoal, impregnated with a solution of 
potassium chlorate which was subsequently dried. 
The Diol was jelled with 2^ to 3% Ivory soap flakes. 
The chief drawback of this smoke mixture is the 
extreme hazard incurred in handling the impregnated 
sawdust, especially when dry, before the Diol is 
added. Once the Diol has been blended into the fuel 
the mixture is quite stable. This pot weighed about 
45 lb, contained 39 lb of smoke mixture, and burned 
about 20 min. 

Theory of Operation 

The fuel used in this mixture is bulky. The oxidiz¬ 
ing agent, which may be potassium chlorate or sodium 
nitrate, is deposited from solution in the pores and on 
the surface of the sawdust. It is very reactive in this 
condition and when the mixture is dry, combustion 


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498 


NEW SCREENING SMOKE MIXTURES 


will flash through the mixture very rapidly. If Diol 
is added and thoroughly mixed in so that the saw¬ 
dust is oil soaked but not submerged in oil, the burn¬ 
ing rate is slowed down considerably but the combus¬ 
tion may still pass throughout the mixture quickly 
and even fail to vaporize some of the oil. If the fuel is 
submerged in oil the combustion does not take place 
below the oil level, and burning takes place regularly 
and progressively down through the mixture vola¬ 
tilizing the oil as it goes. This latter is the principle on 
which the pot functions. 

Description of the Smoke Pot 


The arrangement of the smoke pot is shown in 
Figure 3. 



Figure 3. Experimental pot for Diol-sawdust-chlorate 
smoke mixture. 


Smoke Mixture. A fairly satisfactory mixture con¬ 
sisted of 24.8% sodium chlorate, 10.1% charcoal, 
10.1% sawdust, and 55% Diol. A mixture with a 
higher Diol content could probably be developed but 
the work did not continue far enough to establish 
the limits in this respect. The mixture was prepared 
by soaking the sawdust in a water solution of potas¬ 
sium chlorate and then drying this sawdust to re¬ 
move the water. The treated dried sawdust was ex¬ 
tremely hazardous to handle. The sawdust thus pre¬ 


pared was then mixed with a suspension of charcoal 
and additional chlorate in Diol. The Diol used was 
prepared by dissolving 23^ to 3% Ivory soap flakes 
in it at 230 F with continuous stirring during the 
cooling of the mixture. The cooling should take place 
at a moderate rate. 

In addition to this main mixture, a transition mix¬ 
ture and a starting mixture were employed. About 
35 lb of the main mixture with 3 lb of the transition 
mixture and 1 Yi lb of the starting mixture were used. 
The transition mixture contained 18% sodium chlo¬ 
rate, 5.6% charcoal, 21.9% sawdust, and 54.5% Diol 
and the starting mixture contained 13.5% sodium 
chlorate, 32.5% sawdust, and 54% Diol. In each case 
the ingredients were 24-mesh yellow pine sawdust, 
150-mesh charcoal powder and Diol 55. 

Container. The smoke mixture was placed in the 
bottom of a 12-in. diameter by 15-in. high steel can 
closed with a tight cover. The oil vapor and combus¬ 
tion gases issued from a single 1-in. diameter orifice 
in the center of the cover. A spark filter consisting of 
an arrangement of baffles was placed between the 
smoke mixture and the cover. The pot was well suited 
for use as a smoke float. The smoke mixture ignites 
when a strong acid comes in contact with it. This 
was the method used to ignite the pots. A glass vial 
of sulfuric acid was placed in a metal case and in¬ 
serted in the starting layer of smoke mixture. The 
metal case contained a cocked firing pin actuated by 
a spring. The pin was held by a rod extending up 
through the cover of the pot. When the firing rod was 
pulled, the cocked pin was released and broke the 
acid vial igniting the smoke mixture. 

The screening power of the smoke was entirely 
comparable to the oil smoke produced by the con¬ 
tinuous oil smoke generators, except that the pot 
generated it at a much lower rate. The burned saw¬ 
dust gave the smoke the acrid smell of burning wood 
which was somewhat irritating near the pot but was 
diluted sufficiently a short distance away. 

Development 

Smoke Mixture. Some of the salient features of the 
development work will be mentioned especially where 
they convey ideas for the improvement of this or 
similar mixtures. 

The charcoal was added to increase the heat avail¬ 
able to vaporize oil since charcoal has a significantly 
higher heat of combustion than wood. This resulted 
in complications due to a decreased burning rate. 

The burning rate is affected by the ingredients used 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


499 


in the mixture, their proportions, and method of 
preparation as well as the conditions of operation. 
The ideal mixture 26 will oxidize all the sawdust and 
charcoal and none of the oil. A theoretical mixture 
should be possible containing 17.5% sodium chlorate, 
1.4% charcoal, 2.9% sawdust, and 78.2% Diol. Heat 
losses from the pot and incomplete combustion re¬ 
duce the per cent Diol below this theoretical figure. 
It should be possible to incorporate a considerably 
larger percentage of Diol than the 55% used in the 
pots. The mixture was not very sensitive to the tem¬ 
perature of the mixture at the time of ignition. Two 
identical pots were prepared and stored, one at 110 F 
and the other at 10 F for 72 hr, and then burned 
immediately. The higher temperature pot burned in 
18 min while the cold one burned in 21 min. 

The oil was jelled to improve the performance at 
the higher temperatures (110 F). There was a tend¬ 
ency for a layer of oil to separate at these tempera¬ 
tures and interfere with the ignition. Various jelling 
agents were tested. These included aluminum stea¬ 
rate, oleate (titer number 10-12) flakes, amber flakes 
(titer number 42), and both Ivory and Swift soap 
flakes (both have a titer number of approximately 
32). The oleate flakes were mainly sodium oleate; 
Ivory flakes are about half and half sodium oleate 
and sodium stearate; and the amber flakes, mainly 
sodium stearate. The oleate flakes formed a poor jell. 
The Ivory and amber flakes were about equal in jell¬ 
forming properties, with the Ivory flakes possibly a 
little superior. Of several greases tested, Nakta 8-F 
(Standard Oil Co. of Pennsylvania) gave the best 
results. 

Sodium nitrate may possibly be substituted wholly 
or in part for the potassium chlorate. This may be 
found desirable due to a shortage of potassium 
chlorate or to the reduced hazard from sodium ni¬ 
trate, although both chemicals are considered hazard¬ 
ous. Black gunpowder can be used for the fuel in 
place of the mixtures described. A smoke mixture 
with black gunpowder is described in the next sec¬ 
tion. The oil in the mixture depresses the burning 
rate and eliminates the hazards normally associated 
with black powder itself. 

The Container. Several sizes of containers were 
tried in addition to the one described above. These 
were 12 in. in diameter by 8 in. high, 6 in. in diameter 
by 7 in. high, and \ x /± in. in diameter by 4 in. high. A 
5-gal paint or oil can would no doubt be the most 
suitable. This would compare with the M4A2-HC 
smoke float. 


The smoke exit orifice is of great importance since 
it controls the flaming tendency of the mixture, the 
particle size of the smoke, and hence its screening 
power, and the pressure within the pot. In the pot 
described, this orifice might well be reduced to a 
single %-in. diameter hole or several smaller orifices 
of the same total area. 

The partially burned sawdust and charcoal showed 
a tendency to be blown from the pot in a shower of 
sparks. If the exit smoke velocity was low, these 
sparks ignited the oil vapors before they had time to 
condense to smoke* particles, and flaming from the 
orifice resulted. Various forms of spark filters were 
tried over the smoke mixture. Those which consisted 
of an actual filtering material, such as a wire mesh or 
steel wool, were not satisfactory due to plugging of 
the filter. A baffle arranged as shown in Figure 3 was 
found to be quite satisfactory. The gases rose to the 
top of the pot around the periphery and then re¬ 
versed their direction down into a centrally located 
ash trap and then reversed direction a second time to 
reach the exit orifice. This flow removed the ash 
and sparks without obstructing the flow of gases and 
vapors. 

The trigger should be centrally located in the 
starting layer so that the flame will spread out radially 
in all directions equally. 

32.1.7 Jelled Oil-Black Gunpowder 
Smoke Mixture 

Requirements and Preliminary Work 

The principle involved in these pots consists of 
vaporizing a high-boiling mineral oil by a fuel inti¬ 
mately mixed with the oil, followed by expulsion of 
the oil vapors and combustion gases from the fuel 
through an orifice or orifices and subsequent con¬ 
densation of the oil vapor into oil droplets of about 
0.3 micron radius. Oil droplets of this size have 
optimum screening powers. 

Specifications called for the filling mixture (1) to 
be composed of noncritical materials; (2) to be chemi¬ 
cally stable and capable of withstanding the effects 
of prolonged storage at temperatures up to 150 F; 
(3) to produce a thick, persistent, nontoxic smoke for 
10 to 15 min; (4) to produce smoke at a maximum 
rate within a few seconds after ignition, the rate to 
be about the same at 0 F as at 150 F; and (5) the 
combined weight of filling and container to be 35 lb 
or less. 

It was decided to develop a filling mixture similar 


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500 


NEW SCREENING SMOKE MIXTURES 


to the KC103-sawdust-oil mixtures. The use of chlo¬ 
rates was prohibited due to the great hazards in¬ 
volved in handling these salts. The possibility of 
utilizing black powder as fuel to vaporize the Diol 
was given primary consideration. Since a prerequisite 
of the fuel was its availability in large quantities, it 
was decided to confine the major portion of the work 
to sodium nitrate base (B) black powder. The A 
powder is more expensive and its base, potassium 
nitrate, is much more critical in supply than sodium 
nitrate. The A black powder is a trifle stronger, some¬ 
what quicker, resists moisture better, and will keep 
in good condition longer than B blasting powder. 

The best base charge developed was composed 
of 48% B black powder, 1 % 4 -mesh; 2% coarse 
sawdust; 8% treated AL wood pulp; and 42% Diol 
55 jelled with 13^% sodium stearate. The best tran¬ 
sition mixture was composed of 43% B black pow¬ 
der, i^-mesh; 6% treated AL wood pulp; 21% 
coarse sodium nitrate; and 30% Diol 55 jelled with 
1 y 2 % sodium stearate. Although both mixtures func¬ 
tioned reasonably well from —40 to 150 F and pro¬ 
duced a good smoke cloud, neither was stable when 
stored at 150 F for prolonged periods. Syneresis of the 
Diol jell occurred at this temperature, resulting in 
the formation of a layer of free oil on top of the 
charge that destroyed the proper functioning of both 
mixtures. The manufacturing process for both mix¬ 
tures was simple, short, and practical, and required 
no elaborate equipment. 

A number of oils, greases, jells, and absorbents 
were tested in an effort to produce a mixture which 
would be stable at 150 F and would perform satis¬ 
factorily at all temperatures from —40 to 150 F. An 
outstanding characteristic of the oil-smoke mixture 
was the effect produced by varying the amount of 
jelling agent. When the amount of the latter was 
sufficient to stabilize the resultant jell at 150 F, a 
high percentage of fuel was required to maintain 
combustion. This resulted in a much higher tem¬ 
perature than was necessary to vaporize the unjelled 
oil. Consequently, the oil vapors were cracked and 
the smoke cloud was thin, nonpersistent, yellowish 
brown in color, and of very small particle size. 

The various phases of the work will be described 
under separate headings. 

General Experimental Tests 

A total of 1590 oil-black gunpowder smoke mix¬ 
tures were tested. 28 They were burned in containers 
ranging from 3 in. to 12 in. in diameter, and from 


7 Y 4 in. to 24 in. in height. The container used most ef¬ 
fectively was a 5-gal, 24-gauge, lug-covered, straight¬ 
sided shipping container equipped with six 1 ^-in- 
diameter side orifices. The pot was ignited by an 
electric squib and primed with a mixture of Pb 3 0 4 , 
Al, and FeSi contained in a quick-melting zinc cup. 
The cup was soldered in a 3 3^-in. hole in a sheet metal 
diaphragm which was utilized to hold the charge 
securely in place. A cork gasket resting on a flat bead 
rolled in the side of the container formed a seal with 
the diaphragm. The filling mixture was composed of a 
fast-burning transition layer weighing 4 lb and a 
base charge weighing 24 lb. The entire unit weighed 
35 lb. 

The following conclusions were drawn: 

1. A primer composed of red lead, aluminum, and 
ferrosilicon was entirely satisfactory. 

2. From 2 to 4 lb of transition mixture were neces¬ 
sary to produce rapid, positive, and uniform ignition 
of the base charge. 

3. Standard 5-gal paint pails were entirely suitable 
for use as containers. 

4. No baffles or spark filters were required to pre¬ 
vent flaming when the smoke issued through small- 
diameter orifices. 

5. No base charge was produced which proved 
satisfactory under all conditions to which smoke pots 
are exposed. 

6. When sufficient jelling agent was added to oil to 
prevent separation of fuel from the oil and free oil 
from the jell at elevated temperatures, an excessive 
amount of black powder was required to maintain 
combustion. 

7. Attempts to prevent separation of the fuel from 
the oil by the use of absorbent materials produced 
charges which burned at excessive rates due to the 
porosity of the charges. 

8. Charges formulated with reduced amounts of 
jelling agent, supplemented by absorbent material, 
exhibited syneresis at elevated temperatures. 

9. Potassium nitrate black powder was a much 
more efficient fuel than sodium nitrate black powder. 

Experimental Development 

Basic Mixture. The basic mixture which made up 
the major part of the charge to the smoke pot was 
compounded of a wide variety of ingredients con¬ 
sisting principally of various grades and types of 
black powder; oils such as Diol 55, Diol 55 with 
jelling agents, vaseline; bulky fillers such as wood 
pulp, ground newsprint, and sawdust; and sodium 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


501 


nitrate. The Diol jell was prepared by heating Diol 
55 with Ivory soap flakes to 240 C accompanied by 
considerable agitation and followed by cooling slowly 
in air without further agitation. Although a fair 
amount of smoke was produced by some of the initial 
filling mixture compositions, considerable trouble was 
encountered from flaming and uneven burning rates. 

Decreasing the orifice diameter increased the veloc¬ 
ity of the smoke vapors and decreased the particle size 
of the smoke. For example, smoke issuingfrom a J^-in. 
diameter orifice was much finer and more persistent 
than if it had passed through a 1 -in. diameter orifice. 
Subsequent tests were made in pots equipped with a 
medium-size single orifice, or a number of relatively 
small diameter orifices. 

Numerous jelled-oil, vapor-producing materials 
were tested. Included in this group were: Diol 55 
jelled with 3% sodium stearate; kerosene jelled with 
3 and 5% sodium stearate; 969 oil jelled with 3, 8 , 
and 23% sodium stearate and with 15% aluminum 
stearate. Base charges containing the relatively high 
stearate-content greases (15% aluminum stearate 
and 23% sodium stearate) and 4FB or 3FB black 
powder burned very slowly and produced very little 
smoke. In general, the charges containing the lower 
stearate-content jells burned faster, but still were 
slower and produced a thinner smoke than those con¬ 
taining unjelled oils. The extent to which the rate 
was retarded was proportional to the stearate con¬ 
tent of the jell. 

To circumvent the objectionable features of the 
jelled oils, and produce a filling mixture whose in¬ 
gredients would not segregate at 150 F, a large 
number of base charges were formulated with B 
blasting powder, highly absorbent carbonaceous ma¬ 
terial, and either Diol 55 or vaseline. At least 7% of 
absorbent material was required to prevent the black 
powder from settling out of a 50-50 mixture of powder 
with vaseline or Diol 55 at 150 F. As a rule, these 
charges burned at a high nonuniform rate and pro¬ 
duced a good volume of fairly white, persistent 
smoke. 

A group of base charges, which contained a rela¬ 
tively fine granulation of KN0 3 -base black powder, 
exhibited excellent smoke-producing properties. A 
charge which was representative of the group was 
composed of 37% 3FG sporting powder, 13% am¬ 
monia dope, and 50% Diol jell ( 1 % sodium stearate). 
It was believed that the excellent properties pos¬ 
sessed by this group of charges was due either to the 
fine granulation, the 4-hr milling time, or the KN0 3 


base of the 3FG sporting powder. A supply of B 
blasting powder having the same granulation, i.e., 
2 ^ 6 -mesh silk was procured. Charges containing 
this powder and having the same percentage com¬ 
position as the one containing 3FG powder were very 
slow burning. 

Charges containing 43% 3FG sporting powder, 5% 
T-14 wood pulp, 5% sawdust impregnated with 50% 
NaN0 3 , and 47% Diol jell ( 1 % sodium stearate) 
burned at a satisfactory uniform rate, and produced 
a good volume of fairly persistent smoke. The nitrate- 
impregnated sawdust, as well as the sporting powder 
fuel, apparently influenced the functioning of these 
charges. Charges in which a mechanical mixture of 
coarse sawdust and coarse sodium nitrate was substi¬ 
tuted for the impregnated sawdust functioned prac¬ 
tically as well as those just described. Substituting 
3FG sporting powder which had been milled 1 % hr, 
instead of the usual 4 hr, in these formulations had 
very little effect on their performance. Sporting 
powder milled for iy> hr would be a much cheaper 
product than the regular 4-hr milled powder. 

B blasting powder, 2 % 6 -mesh, which had been 
milled for 3 or 4 hr did not improve the performance 
of charges similar in formulation to those containing 
B blasting powder, 2 ^e-mesh which had been milled 
for iy hr. B blasting powder, which was manufac¬ 
tured with sporting powder pulverize (charcoal-sul¬ 
fur mixture), possessed none of the desirable burn¬ 
ing characteristics of sporting powder. Therefore, in 
view of the fact that B blasting powder of the same 
granulation as 3FG sporting powder, milled for the 
same period as sporting powder, or containing the 
same pulverize as the A powder did not equal the lat¬ 
ter in performance, it is apparent that the excellent 
properties of sporting powder were due primarily to 
its base, potassium nitrate. 

In order to secure more uniform distribution of the 
fuel in the filling mixture, B blasting powder, x % 4 ~ 
mesh (considerably finer than 4FB blasting powder) 
was tested in base charges having the following com¬ 
position: 48% B blasting powder, 1 % 4 -mesh; 3% 
coarse sawdust; 5% T-14 wood pulp; and 44% Diol 
jell (1% sodium stearate). These charges burned at a 
fairly uniform rate and produced a good cloud of 
smoke. The -mesh granulation of B powder was 
of normal composition. It was used in the majority 
of the charges tested during the latter part of the 
investigation. The 3% coarse sawdust in the above 
charges apparently maintained a thicker burning 
layer, thereby producing a uniform rate of smoke 


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502 


NEW SCREENING SMOKE MIXTURES 


production. The fact that these charges were dense, 
soft, and wet (oily) probably had a great effect on 
the burning. In practically all cases in which the 
charge was low in density, dry, and porous, the burn¬ 
ing rate was uneven and uncontrollable. 

The first few attempts to burn charges at initial 
temperatures greater than 120 F resulted in blowing 
the covers from the pots within a few moments after 
ignition. The fact that the charges were mixed at room 
temperature and then heated to 120 F or higher 
seemed significant. Mixing at 120 F under atmos¬ 
pheric pressure, or mixing at room temperature under 
4 to 5 psia, resulted in charges which burned at a 
normal rate when ignited at 120 F. The excessive 
burning rates were evidently due to air entrapped 
during mixing at room temperature (sometimes as 
high as 22 % of the volume occupied by the charge), 
which expanded when the charge was heated to 120 F 
and made the mixture porous. The viscosity of the 
Diol jell at 120 F was much less than at room tem¬ 
perature, and, consequently, less air was entrapped. 
Mixing under reduced pressure also reduced the 
amount of air entrapped. Although these two 
methods produced charges containing much less air 
than previously, a considerable amount of air still 
remained. An effective but impractical method of re¬ 
moving substantially all of the air, consisted of 
jouncing the pots at 150 F. This method was im¬ 
proved later by jouncing under reduced pressure. 
Subsequently, a simple, practical method was de¬ 
vised for removing most of the entrained air. It con¬ 
sisted of drawing the hot, freshly mixed charge into 
the smoke pot through a in. diameter orifice under 
a fairly high vacuum. 

When the last mentioned charge (48% B powder, 
3% sawdust, 5% T-14 pulp, 44% Diol jell) was 
heated to 150 F and subjected to a test simulating 
the vibrations which might be encountered during 
shipping, the black powder settled to the bottom of 
the pot, leaving a 134 -in. top layer consisting only of 
oil and carbonaceous material. To prevent settling of 
the black powder under these conditions, the per¬ 
centage of absorbent materials and the amount of 
sodium stearate in the Diol jell were increased, and 
more highly absorbent wood pulp was substituted for 
T-14 pulp. The resultant charge was composed of 
48% B blasting powder, 1 % 4 -mesh; 2% coarse saw¬ 
dust; 8 % treated AL pulp; and 42% Diol jell (134% 
sodium stearate). This charge performed very satis¬ 
factorily at all temperatures between 0 F and 150 F, 
and produced a good cloud of white, fairly persistent 


smoke for about 10 min. However, during hot storage 
at 150 F, the jell broke down to an extent depending 
on length of storage, causing the formation of an oil 
layer on top of the charge. Upon ignition of these 
pots after hot storage, the oil layer either quenched 
the primer or caused the charge to burn very slowly 
for several minutes. As soon as the oil layer was 
vaporized the remainder of the charge, which was 
now rich in fuel, burned at a high rate and in some 
cases the cover was blown from the pot. 

Diol 55 in combination with Diol jelled with 6 % 
sodium stearate resulted in charges which were quite 
stable at 150 F. This jell, when tested by itself at 
150 F for one month, showed very little tendency to 
break. A typical charge was composed of 50% B 
blasting powder, 1 % 4 -mesh, 2 % coarse sawdust, 8 % 
treated AL pulp, 28% Diol 55, and 12% Diol jell 
( 6 % sodium stearate). This type of charge did not 
burn at a uniform rate, and its smoke was thin, yel¬ 
lowish white in color, and lacked persistency due to 
its high fuel-to-oil ratio. Although 1 part of black 
powder should vaporize 2 parts of oil, this charge 
required 234 parts of fuel per 2 parts of oil. 

Non-Jelled Mixture. A group of charges containing 
B blasting powder, shredded asbestos, and/or kiesel- 
guhr, Diol 55, and in some cases a few per cent of 
coarse sawdust were tested. A typical charge was 
composed of 40% B blasting powder, 1 % 4 -mesh, 14% 
shredded asbestos, and 46% Diol 55. This was the 
most efficient smoke charge tested. Only 1% parts of 
fuel were needed to vaporize 2 parts of oil. Since the 
oil contained no jelling agent, the problem of syneresis 
at 150 F did not exist. Another advantage of this type 
mixture was that very little air was entrained in it 
during mixing and, therefore, it required no de-airing. 
The smoke produced by this charge was very white, 
dense, and persistent, and possessed excellent screen¬ 
ing qualities. The charge was very dense, koft, and 
oily. It surged considerably throughout its burn¬ 
ing time. Much additional work would have to be 
done in order to perfect this particular type of 
mixture. 

Other Tests. An oil-smoke mixture, composed of 
48% B blasting powder, 8 % AL pulp, 2% coarse 
sawdust, and 42% Diol jell (1 34% sodium stearate), 
had no corrosive or other deleterious action on the 
various materials contained in a smoke pot such as 
the lacquer-coated steel container, the zinc primer 
cup, the galvanized sheet-metal diaphragm, and the 
cork gasket. 

An 1134-in. pot containing 25 lb of charge of this 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


503 


composition performed very well when thrown in a 
pool of water. 

Numerous tests on charges of various compositions 
at — 40 F indicated that this temperature had a very 
considerable slowing effect on the burning rate. 

Transition Mixtures. Transition mixtures were 
employed to produce rapid, uniform, and positive 
ignition of the base charge. It was also desirable 
(1) that they give off sufficient heat to warm the 
upper portion of the smoke pot in a relatively short 
time, thus minimizing the condensation of oil vapors 
on the inner walls of the container; (2) that they 
generate a good cloud of smoke themselves; (3) that 
they cause combustion to transfer smoothly to the 
base charge so that there would be no sag, in the 
production of smoke vapors, which would interrupt 
the continuity of the smoke cloud; (4) that they 
ignite over their entire surface within a few seconds; 
(5) that they perform the same at — 40 F as at 150 F; 
and (6) that they have the same oil-to-absorbent ratio 
as the base charge, to prevent migration of the oil. 

A layer Yi in. deep, weighing 1,000 g, was employed 
in a number of 12-in. pots. However, a 1-in. layer, 
weighing 2,000 g, proved much more effective in pre¬ 
heating the sides of the relatively heavy 12-in. pot, 
and in effecting more uniform ignition of the base 
charge. The formulation contained 10% of coarse 
NaN0 3 for the express purpose of securing a higher 
degree of oxidation, and thereby producing a greater 
amount of heat. 

Some sag in smoke production between transition 
mixture and base charge occurred. In an effort to 
overcome this characteristic, annular rings, % in. 
deep and 1 in. wide, were formed in the surface of 
the base charge before adding the transition mixture. 
It was thought that the transition mixture in the de¬ 
pressions in the base charge would still be burning 
after the ridges of base charge had been ignited. The 
idea did not prove effective. A method for preventing 
sagging, which did prove satisfactory, consisted of 
blending about Y of the transition mixture with the 
upper portion of the base charge. The remaining por¬ 
tion of the transition mixture was then added as a 
separate layer. 

The transition mixtures developed contained: 


B black powder, 1 5'24-mesh 

48 

50 

Treated AL pulp 

8 

8 

Pellet NaN0 3 

10 

10 

Diol 55 

23 

22 

Diol jell (6% sodium stearate) 

11 

10 


They were used together; 3 lb of the first mixture 
was placed on top of the base charge and then 1 lb of 
the second mixture, which was faster, was added. In 
actual operation, the top layer of transition mixture 
burned in a few seconds, igniting the second slower 
layer and, at the same time, blowing off the tapes 
which covered the orifices. Very little sagging oc¬ 
curred between the second transition mixture and 
the base charge. Both of these transition mixtures 
proved to be quite stable when stored at 150 F. In 
fact, the combination of Diol 55 jelled with 6% 
sodium stearate and Diol 55 absorbed by a carbo¬ 
naceous material proved to be more stable at 150 F 
than any of the other vapor-producing materials 
tested in transition mixtures. 

Containers. The container should be so designed 
that it could be manufactured easily and, if possible, 
be a currently manufactured, standard-size article. 
Tests were made in pots 6-in. diameter by 7J4 in., 
12-in. diameter by 15 in., and in standard 5-gal round 
cans. 

At first, the 6-in. pots were equipped with a single 
1-in. diameter orifice. Later it was observed that a 
decrease in the diameter of the orifice changed the 
smoke particle size from coarse (blue sun’s disk) to 
fine (magenta sun’s disk). 8 A number of tests were 
then performed with pots equipped with a device 
which permitted the orifice diameter to be changed 
gradually from %-in. to %-in., while the pots were 
functioning. 

Some of the first tests were made in pots which 
contained no baffles or spark filters. Even though 
glowing particles were carried out of the pot by the 
smoke stream, the tendency of the oil vapors to ignite 
from the sparks was only slight. Decreasing the orifice 
size and thereby increasing the velocity of the oil 
vapors minimized any tendency toward flaming. 
When the smoke velocity was greater than the rate of 
flame travel, flaming which did occur was only 
momentary. 

A number of tests were made with 6-in. pots which 
contained a baffle arrangement to reduce the large 
number of sparks thrown out by certain types of 
charges. The baffle-type spark filter reduced the 
flaming tendencies of all base charges with which it 
was tried. Very coarse mesh screens, tested in an at¬ 
tempt to filter out sparks, quickly became clogged 
with residue, restricting the passage of the smoke 


a The latter smoke particles were of 0.3 micron radius, which 
size is most desirable for maximum screening effect. 


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504 


NEW SCREENING SMOKE MIXTURES 


vapors. Consequently, very little work was done with 
screen-type spark filters. 

Six-inch pots equipped with a number of equally 
spaced diameter orifices, drilled in the side 

of the lid, possessed numerous advantages over those 
with the single, large orifice in the top of the lid. The 
smoke from the multiple-side orifices was whiter, 
denser, of smaller particle size, and more persistent 
than smoke emitted through the single large orifice. 
Ejecting the smoke parallel to the ground through 
these small, side orifices also reduced the tendency of 
the smoke to rise, which was quite marked when the 
smoke issued in a column perpendicular to the 
ground. The smoke vapors from pots having a 
number of small orifices also showed little tend¬ 
ency to flame even when the pot was not equipped 
with a spark filter or baffles. Figure 4 shows a 
6-in. pot equipped with fifteen %6-in. side orifices. 
Twelve-inch pots equipped with fifty diame¬ 

ter side orifices were tested and found to have the 
same features as the multiple, side-orifice, 6-in. pots. 
The % 6 -in. diameter orifices possessed one undesir¬ 
able characteristic in that they frequently became 
clogged with residue. As a result, the pressure in the 
containers would rise and cause the filling mixture to 
burn unevenly. This condition was remedied by in¬ 
creasing the orifice diameter to % in. and at the same 
time reducing the number of orifices to two for the 
6-in. pot and to eight for the 12-in. pot. 

Standard 5-gal containers similar to HC smoke 
floats were found to be quite satisfactory. These con¬ 
tainers were equipped with eight %-in. side orifices 
for the first tests. The velocity of the smoke after 
passing through these orifices was lower than normal, 
and the number of orifices was reduced to seven. In 
order to have an even number of orifices and to ob¬ 
tain the advantages of slightly larger orifices, the 
number was decreased to six and their diameter was 
increased to 1 %2 in- This number and size of orifices 
was tested extensively. The pot is shown in Figure 5. 

A fairly satisfactory method for sealing the charges 
in the pot was developed. An 18-gauge, flanged, sheet- 
metal diaphragm which fits tightly against the walls 
of the pot was forced down against a cork gasket 
% in. thick, which in turn rested on a %- in. deep 
bead rolled into the side of the container. After the 
diaphragm was in place, it was secured by means of a 
second bead, }/% in. deep, rolled immediately above 
the flange of the diaphragm. A better oil seal between 
the diaphragm and pot was secured by replacing the 
flanged diaphragm with a flat one and then rolling a 



Figure 4. Six-inch diameter experimental smoke pot 
for jelled oil-black powder mixtures. 


bead, similar to the lower bead, immediately above 
the diaphragm. As the bead was formed, a downward 
pressure was exerted against the diaphragm resulting 
in a positive oil seal. 

The diaphragm shown in Figure 5 had a 3 3^-in. 
diameter hole in its center. A flanged 3-in. diameter 
x %-in. deep zinc primer cup was soldered to the 
edges of this hole. A zinc cover to confine the primer 
and to prevent moisture from coming in contact with 
it was soldered to the flange of the primer cup. Addi¬ 
tional fittings containing an electric squib were at¬ 
tached to the lid of the primer cup. In operation, an 
electric current was applied to the Fahnestock clips 
on the pot cover which set off the squib. The primer 
was ignited by the squib, and, in turn, melted the 
zinc cup and its lid and ignited the transition mixture. 
The combustion gases and oil vapors escaped through 
the hole in the diaphragm, blew off the tapes, which 
covered the orifices, and then passed out into the 
atmosphere. 

Two 5-gal pots were packed in separate wooden 


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THE CHANGING REQUIREMENTS FOR SMOKE POTS 


505 



FAHNESTOCK CLIPS 


ORIFICES C0VERE0 WITH TAPE EQUALLY SPACEO 
-ZINC COVER O.OIO" THICK 
-OPEN-TYPE ELECTRIC SQUIB 

ZINC PRIMER CUP 
-BEAD TO SECURE DIAPHRAGM 
18 GA DIAPHRAGM WITH J FLANGE 
>ASKET 

-BEAD AS SEAT FOR GASKET 
-A-15 PRIMER 
■5 GALLON STEEL PAIL 
-TRANSITION MIXTURE 
-BASE CHARGE 


Figure 5. Experimental smoke pot in 5-gallon oil can. Jelled oil-black powder mixture. 


boxes. Each box was subjected to rough usage tests 
which included vibrating on each face for 20 min, 
followed by dropping on each face and on two 
diametrically opposite corners from a height of 4 ft. 
The pots were then examined and found to be in 
excellent condition. Only a few minor dents were 
noted. Both pots functioned normally when burned. 

Temperatures in the Smoke Pot. The maximum 
temperature of burning mixtures ranged from 560 to 
1210 F. The maximum temperatures of smoke vapor 
ranged from 790 to 1010 F. Almost without excep¬ 
tion, the charges in which the ratio of fuel to oil was 
greater than 1 exhibited the highest maximum 
temperatures. 

The oil of charges whose maximum temperature 
was considerably greater than 800 F, evidently was 
cracked to a certain extent. The smoke from these 
charges was usually yellowish brown in color, thin, 
and lacking in persistency; whereas the smoke from 
charges whose maximum temperature was less than 
800 F was fairly white, dense, and persistent. 

Internal Pressure Measurements. The internal pres¬ 
sures of a number of 12-in. smoke pots were measured. 
All tests were performed with pots which were 


equipped with multiple side orifices. During one of 
the tests, the pressures at which the smoke particles 
produced a change in color of the sun’s disk were 
noted. These pressures were as follows: 

0 to 0.1 psi, blue sun’s disk (coarse particles); 

0.1 to 0.9 psi, permanganate sun’s disk; 

0.9 to 1.1 psi, magenta sun’s disk (optimum par¬ 
ticle size); 

1.1+ psi, orange sun’s disk (fine particles). 

Note. This pressure, sun’s disk relationship, is valid 
only during the first few minutes of the burning time. 
After this initial period, changes within the pot 
(temperatures, depth of residue, and so forth) and 
partial clogging of the orifices, produce entirely dif¬ 
ferent relationships. For example, when the charge is 
practically consumed, the pressure might drop to 
0.5 psi, yet the color of the sun’s disk would be orange 
instead of permanganate. 

Improvements in mixing and packing procedure 
and in composition resulted in charges whose average 
pressure was 0.75 psi, and whose maximum pressure 
was around 2 psi. Pots equipped with %-in. orifices 
developed lower pressures than those with J 16 -in. 


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506 


NEW SCREENING SMOKE MIXTURES 


orifices (of equivalent total cross-sectional area). This 
was because the larger orifices did not become 
plugged with residue as readily as the smaller ones. 

Since pressures no greater than 2 psi would be 
generated by an oil-smoke mixture which functioned 
satisfactorily, standard, lightweight shipping con¬ 
tainers, such as 5-gal, 24-gauge, lug-cover, steel pails 
(used in the manufacture of HC floats), could be em¬ 
ployed safely as oil-smoke pots. 

Primers. In general, the method of priming con¬ 


sisted of placing the primer in a wax paper or zinc 
container imbedded centrally in the surface of the 
filling mixture, and igniting it by a black powder 
fuze or an electric squib. It was necessary to use an 
oil-proof container for the primer, as it would not 
ignite when wet with oil. 

Twenty grams of primer were usually employed in 
6-in. pots, and from 75 to 100 grams in 1134-in. and 
12-in. pots. The method of priming as finally de¬ 
veloped for the 35-lb pot is shown in Figure 5. 


SECRET 



Chapter 33 

EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 

By H. F. Johnstone 


33.1 INTRODUCTION 

T he possibility of using the sensible heat of ex¬ 
haust gases for the evaporation of oil for laying- 
smoke was considered early in the war. In 1942, the 
DeVilbiss Company of Toledo, Ohio, undertook the 
design of exhaust-type smoke generators for small 
naval craft. A background existed of previous use of 
the principle in sky-writing, in the dissemination of 
fumigating chemicals, and (it is said) by rum runners 
off the Louisiana coast for screening purposes. The 
early efforts of DeVilbiss resulted in the production 
of prototype equipment for Hall-Scott gasoline 
marine engines and Grey diesel engines, both in the 
175- to 250-hp class. The gasoline engine generator 
was the more satisfactory; it vaporized about l}/£ lb 
of fog oil per hp-hour actual output. A few sets of this 
equipment were procured, but its adoption was not 
general. 

An NDRC contract was later placed with the De¬ 
Vilbiss Company for the development of large sta¬ 
tionary smoke installations for protecting airfields 
and carriers. The completed prototype unit, in sta¬ 
tionary mounting on a 550-hp Pratt and Whitney 
Wasp, Jr., aircraft engine, compared favorably in 
effectiveness of dispersal with the M-l oil smoke 
generator. 1 No field of usefulness was envisaged for 
the device, however, and the last formal demonstra¬ 
tion took place in November 1942. 

Early in 1943, representatives of NDRC and the 
DeVilbiss Company conferred with the CWS Liaison 
Officer at Wright Field, and through him made ar¬ 
rangements for a joint AAF-NDRC (DeVilbiss) at¬ 
tempt to develop exhaust smoke generating equip¬ 
ment for the B-26 bomber. The trial installation was 
fairly effective, and the plane was flown several 
times at Wright Field, at Edgewood Arsenal, and later 
before the AAF Board at Orlando, Florida. Evapora¬ 
tion rates of about 0.4 gal per hp-hour were obtained 
when diesel lubricating oil was dispersed. In Sep¬ 
tember 1943, the Board decided to equip six single¬ 
engine planes with exhaust generators. The B-26 was 
returned to standard, and was not used for this pur¬ 
pose beyond that date. 

After a delay of several months, during which time 
the DeVilbiss Company ceased to be active as an 


NDRC contractor, Division 10 attempted to renew 
the subject by means of a memorandum to the Navy 
Coordinator of Research and Development, giving a 
critical estimate of the possibilities of the develop¬ 
ment. The response was immediate, and at a meeting 
of the Navy Smoke Committee, in January 1944, the 
Bureau of Aeronautics was directed to equip three 
SB2A or SB2C aircraft with smoke generators, with 
assistance from Division 10. For this purpose, the 
Naval Aircraft Factory at the Philadelphia Navy 
Yard undertook the design and construction of six 
generators incorporating the B-26 experience. The 
units consisted of large cylindrical tanks into which 
the oil was injected through spray nozzles concurrent 
with the exhaust gases. The contact time was pre¬ 
sumed to be sufficient to evaporate completely the 
droplets of oil. Two of these units were completed at 
NAF and installed on an SB2A. The plane was 
tested at the Amphibious Training Base, Fort 
Pierce, Florida, in June 1944. The smoke production 
compared favorably with that of the B-26, but the 
aerodynamic characteristics of the plane were ad¬ 
versely affected and mechanical failure of the units 
occurred. 

In the meantime, the Munitions Development 
Laboratory [MDL] at the University of Illinois had 
been requested to analyze the entire smoke produc¬ 
tion process with a view to submitting an improved 
final design, since the earlier engineering had been 
on a strictly empirical basis. After the SB2A tests, 
MDL proposed a new design incorporating the Ven¬ 
turi atomization principle described in Chapter 29, 
and drastically reducing the diameter of the genera¬ 
tor. Two of these generators were built under MDL 
direction by the Solar Aircraft Company of San 
Diego, California, between July 10 and July 17,1944. 
These were installed on a TBM-1C plane at NAS, 
Patuxent, the following week, and the equipment was 
demonstrated at Fort Pierce on July-28. The per¬ 
formance and the further design modifications of this 
equipment will be described. 

33.2 THEORETICAL CONSIDERATIONS 

It has been shown that the maximum obscuration 
is obtained with an oil screening smoke when the 


SECRET 


507 


508 


EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 


droplets are between 0.4 and 0.8 micron diameter. 
Since there is no practical means of subdividing a 
liquid into such small drops, it is necessary that the 
droplets be formed by condensation. The theory of 
oil smokes has been discussed in Chapter 27. It has 
been shown that the size of the droplets, which de¬ 
termines the amount of scattering of the light in the 
smoke cloud, depends, in part, on the rate of cooling 
of the saturated vapors. 3 - 4 For practical reasons a 
spectrum of drop sizes is always obtained, and it is 
necessary only to chill the mixture of oil vapor and 
inert gases by emission into the cold air in order to 
obtain a screening smoke. The capacity of the smoke 
generator, therefore, is determined by the amount of 
heat available for evaporating the oil and by the size 
of the equipment used to effect the required heat 
transfer from the gases. 


33.2.1 Evaporation Capacity of 
Exhaust Gases 

The amount of oil that can be evaporated per 
pound of exhaust gas : is determined by the initial 
temperature of the gas, the vapor pressure of the oil, 
and the specific and latent heats of the oil. The tem¬ 
perature of the mixture of oil vapor and exhaust gases 
that results, when the maximum amount of oil is 
evaporated, is called the equilibrium saturation 
temperature. 



O 200 400 600 800 1000 1200 1400 1600 

TEMPERATURE IN DEGREES F 

Figure 1 . Determination of equilibrium saturation 
temperature. 


The equilibrium saturation temperature and com¬ 
position may be calculated from heat and material 
balances on the saturated gases. Either a graphical or 
trial-and-error calculation is necessary. The former is 
illustrated in Figure 1. The temperature and cor¬ 
responding oil content of the saturated vapors are 
determined by the intersection of two curves, (I) a 


vapor composition-temperature curve showing the 
pounds of oil per pound of exhaust gases at satura¬ 
tion, and (2) a curve showing the temperature of the 
gas-oil vapor mixture as a function of the amount of 
oil evaporated per pound of gas. The latter curve 
depends, of course, on the initial temperature of the 
exhaust gases, whereas the former is independent of 
the initial temperature. It is evident from the shape 
of the curves that the initial gas temperature does not 
greatly affect the equilibrium saturation temperature, 
but a slight increase in the latter may greatly increase 
the amount of oil evaporated per pound of exhaust 
gases. Likewise, for any given initial temperature, the 
use of a slightly more volatile oil will lower the equi¬ 
librium saturation temperature somewhat, and will 
increase the amount of oil vapor present at equilib¬ 
rium. Both of these points have a significant bearing 
on the present problem. 

The saturation vapor concentration curve for the 
mixture of oil vapor and exhaust gases is determined 
from the vapor pressure of the oil by applying Dal¬ 
ton’s law. The vapor pressure data for Diol 40 and 
Diol 55 were obtained from curves prepared by the 
Standard Oil Development Company. 5 The average 
molecular weights for these oils are 320 and 385, re¬ 
spectively. The latter corresponds to Navy Fog Oil 
No. 1 (also known in the Army as SGF No. 1). Diol 
40 is a lighter, more volatile fog oil which corresponds 
to Navy Symbol 2075, which was recommended for 
use under cold weather conditions. 

The weight of oil per pound of exhaust gases W\ is 
given by the equation 


w, = — ■ ——- 

M g 760 — po 


( 1 ) 


where M 0 is the molecular weight of the oil; 

M g is the molecular weight of the gas (= 25.6); 
Po is the saturation vapor pressure of the oil 
in mm mercury. 


The following values were computed. 


Temperature 

Po mm Hg 

Wi lb oil/lb gas 

°F 

Diol 40 

Diol 55 

Diol 40 

Diol 55 

550 

14 

5 

0.235 

0.088 

600 

40 

20 

0.694 

0.360 

650 

100 

45 

1.90 

0.835 


The calculation of the heat balance for the mixture 
of oil vapor and gases requires a knowledge of the 
specific heat of the gases and of the oil, and the 
enthalpy of vaporization as a function of temperature. 


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INSTALLATION OF VENTURI UNIT ON TBM PLANE 


509 


The composition of the exhaust gases for an air-fuel 
ratio of 0.101 is as follows: 

C0 2 4.96% 

H 2 8.11 

CO 13.50 

CH 4 0.20 

N 2 63.30 

H 2 0 9.91 

The mean specific heat of the exhaust gases was 
calculated from the mean specific heats of the 
components. The enthalpy of the liquid oil and the 
enthalpy of vaporization are given by the equations: 6 

h t = - (0.388* + 0.000225* 2 - 12.65), (2) 

P 

h fg = - (110.9 - 0.09*), (3) 

P 

where h fg = enthalpy of vaporization; 

h t = enthalpy of liquid oil in Btu per pound 
(h = Oat 32 F); 

p = specific gravity of oil at 60 F; 

* = temperature in degrees F. 

The heat balance on the basis of 1 lb of gas is given 
by the following equation: 

W 2 [_(h t — h 7 o) + h/ a ~] = h'uoo — h t (4) 

where h' is the enthalpy of the gas above 32 F. 

The calculations show that for an initial gas tem¬ 
perature of 1400 F and with Diol 55, the equilibrium 
saturation temperature is 630 F at which 0.61 lb of 
oil per lb of gas would be evaporated. This would 
require the transfer of 240 Btu per lb of gas. For the 
TBM-1 plane the maximum evaporation capacity is 
1,070 gal of oil per hr, or a heat transfer of 3,168,000 
Btu per hr, for the engine operating at 2,400 rpm and 
42 in. manifold pressure. While complete equilibrium 
saturation cannot be reached, it is desirable to ap¬ 
proach this condition as closely as possible in order to 
get the maximum capacity from the smoke generator. 

33.2.2 Atomization and Rate of Heat 
Transfer 

The most rapid transfer of heat from the gas to the 
oil is obtained when the largest amount of surface is 
available for the transfer, and when there is an inti¬ 
mate mixture of the oil and the hot gases. In order to 
make the evaporator as small as possible and to re¬ 
duce the time of contact between the oil and gases to 
avoid decomposition or cracking, it is desirable to 


atomize the fog oil into the smallest droplets possible 
as it comes into contact with the gases. 

As shown in Chapter 29, a convenient way for 
atomizing liquids into extremely small droplets by 
means of a low-pressure gas stream, is by injecting 
the liquid into a gas moving at high velocity through 
a Venturi throat. In this way, it is possible to atomize 
oil into droplets uniformly below 100 microns diame¬ 
ter and having an area of over 6,000 sq ft per gal. 
The conditions prevailing in the exhaust gases from 
an internal combustion engine are ideal for this type 
of atomization, especially since intimate contact and 
uniform dispersion of the droplets in the gas are 
desirable for the evaporation. 

33.3 INSTALLATION OF VENTURI UNIT ON 
TBM PLANE 7 

Installation of the exhaust smoke generator was 
made first on two Grumman Avenger airplanes, types 
TBM-1C and TBM-3C. These planes differ only in 
the size of the engine used. The former has a Wright 
R2600-8 engine, with a normal rating of 1,500 hp 
when operating at 2,400 rpm and 39 in. mercury abso¬ 
lute manifold pressure [MAP]. The TBM-3C plane 
uses a Wright R2600-20 engine with a normal rating 
of 1,800 hp at 2,600 rpm and 47 in. MAP. The greater 
power and higher speed of this engine represents an 
increase of about 10% in the gasoline consumption 
and in the volume of exhaust gases over that of the 
R2600-8 engine under the conditions used during 
smoke generation. This, of course, provides a greater 
capacity for laying smoke. Both of these engines have 
14 cylinders, with split exhaust collector rings, so 
that seven cylinders discharge the exhaust gases to 
ports on either side of the engine nacelle. 

The design of the TBM-type airplane is quite suit¬ 
able for adaptation of the exhaust smoke generator. 
The Venturi atomizer and a length of stack, sufficient 
to provide the necessary contact for evaporation of 
the oil, can be attached under the wing to the fuselage 
of the plane. Space is available between the fuselage 
and the landing gear wells for a stack about 8 in. in 
diameter. The length of the generator, however, is 
limited by the landing flaps to about 12 ft. In order 
to provide a contact time of approximately 0.05 sec, 
which was estimated to be the time required to 
supply the heat to evaporate the largest droplets, the 
size of the stacks was chosen as 6% in. OD. This was 
a convenient diameter because it was the same as 
that of the original exhaust port on the engine. 


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33.3.1 Design of Venturi Section 

The Venturi sections were designed in accordance 
with standard practice, with 30° convergent and 7° 
divergent sections. The throat diameter was found 
by calculation of the area to give the acoustic velocity 
of the exhaust gases when the engine was operating 
under takeoff power, assuming an allowable back¬ 
pressure of 6 to 8 in. mercury under these conditions. 



Figure 2. Air and fuel consumption data for R2600-8 
engine part throttle — sea level. 

Figure 2 shows the air and fuel consumption for 
R2600-8 engines. From these curves the amount of 
exhaust gas for any engine setting can be estimated. 
Assuming that the exhaust gas is equally divided 
between the two ports, it was estimated that at 
maximum power the flow of gas to each generator is 
approximately 6,600 lb per hr and that the tempera¬ 
ture of the gas at the collector ring was 1400 F. 
Under these conditions, the perfect gas laws may be 
applied, so that the acoustic velocity is given by the 
equation 



where k = ratio of the specific heats, C p /C v , 1-36 

g c = dimensional constant, 32.2 (lb mass) (ft) 
per (lb force) (sec) 2 

R = gas constant, 1,544 ft lb per (lb mole) (de¬ 
grees R) 

M g = molecular weight of the gas, 25.6 
T t = absolute temperature at the throat 

Assuming first that the flow of gases in the Venturi 
throat is frictionless and adiabatic, the relationship 


between the throat temperature and the temperature 
in the collector ring is given by the formula: 

(k-i)/k 


■ - 40 


( 6 ) 


The subscript 1 refers to the conditions in the ex¬ 
haust manifold. At the acoustic velocity 

k/(le — 1) 

= 0.536. (7) 


Thus 


©-GttJ 

( P \ (k — 1) /k 
0 - 


V s = \/(1.36) (32.2) (63.1) (1860) (0.848) 
= 2,085 ft/sec. 


The specific volume of the gas at the throat is 
likewise related to the upstream pressure by the 
adiabatic formula: 

l/k 


cu in./lb. (8) 



2.14 X 10 5 


The required area of the throat is then 


A t 


6.600 2.14 X 10 5 188 . 

3.600 X 2,085 Pi ~ p t sqln - 


(9) 


A Venturi with a throat diameter of 3.34 in. cor¬ 
responding to an area of 8.7 sq in. and a pressure of 
21.7 psia was chosen for convenience in manufacture. 
The maximum back pressure on the exhaust mani¬ 
fold during takeoff was not expected to exceed 7 lb 
above atmospheric pressure at sea level, when no oil 
was being injected into the Venturi throat. Injection 
of oil into the Venturi throat would tend to increase 
the back pressure, but since this would not occur 
when the engine was operating under takeoff power 
the actual back pressure should never be as great as 
that calculated for the acoustic velocity. 


33.3.2 Smoke Generators 

The generators were constructed of stainless steel 
and consisted of an adapting elbow, a ball joint, a a 
Venturi throat, two lengths of 6^-in. OD tubing, 
4 ft long, and a 45° elbow at the end. The entire 
equipment was constructed by the Solar Aircraft 


a On later installations the ball joint was replaced with stain¬ 
less steel flexible tubing. 


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INSTALLATION OF VENTURI UNIT ON TBM PLANE 


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Figure 3. Exhaust smoke generator installed on TBM-3 plane. (Official Navy Photo.) 


Company, San Diego, California. The adapting el¬ 
bows replaced the exhaust port extensions, or flame 
dampeners, on the ship. The ball joints connected the 
elbow to the stack and permitted some movement of 
the engine without producing strain on the rest of the 
system attached to the fuselage. The short 45° elbow 
was installed at the end of the stack to divert the 
exhaust gases away from the fuselage. A 5-in. diame¬ 
ter orifice was attached to the end of the elbow to 
give an emission velocity of approximately 600 fps to 
the exhaust gases. 

The generator was attached to the fuselage by 
means of clamps and hangers bolted to two aluminum 
angles which were in turn secured to the frame and 
skin in the ship. Figure 3 is a photograph of the first 
exhaust smoke generator installed on a TBM-3C 
plane. 

33.3.3 The Hydraulic System 

The fog oil was carried in the 270-gal bomb bay 
tank. In the original installation, two Pesco positive 
pressure fuel pumps, Model 1-E-754A, with capaci¬ 
ties of about 17 gal per min at 160 psi, were used to 


pump the oil to the nozzle. One and one-quarter inch 
seamless flared aluminum tubing was used from the 
bottom of the tank to the suction side of the pumps, 
and 1-in. tubing was used from the pumps to the 
nozzles. By-pass lines with control valves in the radio 
operator’s compartment were used to regulate the 
flow of oil to the two generators. 

The nozzles used for injecting the oil into the 
Venturi throats were oil burner nozzles, made by the 
Todd Shipyards Corporation, with Mayflower plates 
size 28-10 and with 0.140-in. orifices. These nozzles 
produce a coarse hollow cone spray. They were con¬ 
nected to the oil supply manifold block with F£-in. 
aluminum tubing. 

The Pesco pumps were motor-driven and were 
controlled by the pilot. Individual control switches 
were conveniently located in the cockpit, one for each 
pump. Since the power required by the motor ex¬ 
ceeded that available from the standard 24-v 200- 
amp d-c generator, this was replaced by a 300-amp 
generator. 

The total additional weight of the equipment on 
the plane, exclusive of the oil reservoir, was 210 lb. 


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0 10 20 30 40 50 60 70 80 90 

OIL FLOW IN LB PER MIN (STARBOARD SIDE ONLY) 

Figure 4. Smoke generator performance; oil flow, smoke temperature characteristic. 


0.7 


0.6 


0.5 


0.4 


0.3 


0.2 


0.1 


0 


v> 

< 


33.3.4 Performance of Equipment 

A project was established by the Bureau of Aero¬ 
nautics at the Tactical Test Unit, Patuxent River 
Naval Air Station, to determine the operating condi¬ 
tions of the equipment which gave the best smoke 
production, to evaluate the tactical usefulness of the 
Venturi smoke generator, and to determine the effect 
of the installation on the flight characteristics of the 
airplane. Personnel of the NDRC Munitions De¬ 
velopment Laboratory participated in all of the tests 
and assisted in making modification of the equipment 
when necessary. 8 - 9 

Evaporation Capacity 

The capacity of the units for evaporating fog oil, as 
affected by various operating conditions, was de¬ 
termined by measuring the temperature of the ex¬ 
haust gas-vapor mixture and by observing the wet¬ 
ness of the smoke as the oil flow was increased. If the 
evaporation of the oil was not complete because of 
insufficient time or area of contact, the gas tempera¬ 
tures for any given rate of oil flow would be higher 
than those calculated from the heat balance. Such 
temperature curves, supplemented by observation of 


the wetness of the smoke (determined by waving 
glass slides to determine if large droplets remain un¬ 
evaporated), indicated the efficiency of the equip¬ 
ment and served as a basis of the comparison between 
operating variables. 

Tests were run with the two fog oils, Diol 40 and 
Diol 55, and with two types of nozzles, the Todd 
nozzles described in the preceding section, and a 
nozzle designed by the Naval Aircraft Factory. The 
performance of the installations on the two TBM 
planes was also compared. 

The temperature curves for the starboard gener¬ 
ators are shown in Figure 4. It is evident that for the 
same operating conditions for the engine on the 
TBM-1 plane, the Todd nozzles and the Venturi give 
lower temperatures than the NAF nozzles. The use 
of the Todd nozzles without the Venturi, i.e., inject¬ 
ing the oil into a low-velocity gas stream, gives much 
higher temperatures. These results are interpreted as 
indicating that a combination of the Todd nozzles 
and the Venturi gives the best atomization of the oil, 
resulting in the most nearly complete evaporation in 
the time and contact available in the exhaust stack. 
The dotted curve in Figure 4 shows the theoretical 


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INSTALLATION OF VENTURI UNIT ON TBM PLANE 


513 


temperature when Diol 55 is injected into gases at 
1188 F. It is evident that the actual temperature 
curve obtained when the Todd nozzles were used in 
the Venturi approached very closely to the ideal, 
thus indicating the high efficiency of the evaporation. 
The curve at the bottom of Figure 4 shows the calcu¬ 
lated oil vapor content of the gas as a function of the 
rate of oil flow for ideal transfer. The sharp maximum 
at the equilibrium saturation is of interest since it 
indicates a decided decrease in smoke efficiency if too 
much oil is pumped. The lower temperature obtained 
with Diol 40, as compared with Diol 55, is consistent 
with that expected when using a more volatile oil. 
The higher temperatures obtained on the TBM-3C 
plane, as compared with those on the TBM-1C plane, 
are caused by the higher initial temperatures of the 
exhaust gases, and indicate the greater evaporation 
capacity of the generator on this plane. 

It was concluded from these tests that approxi¬ 
mately 54 lb per min of Diol 55 could be evaporated 
in each generator on the TBM-1C plane, correspond¬ 
ing to a total capacity of approximately 840 gal per hr 
when the engine is operated at 2,400 rpm and 42 in. 
manifold absolute pressure. About 10% more Diol 40 
could be evaporated under the same engine condi¬ 
tions. For the TBM-3C plane, the corresponding 
figures were 67 lb, or 1,050 gal per hr. These represent 
an evaporation efficiency of approximately 85% of 
the theoretical, and indicate the extremely high rate 
of heat transfer in this type of equipment. 

Effect of Equipment on Performance of Engine 
and Airplane 

Flight tests were made to determine the drag 
created by the installation of the equipment on the 
plane. The results indicated that, at full speed under 
military power, the reduction in speed due to the 
drag was from 3 to 5 knots. The installation had no 
noticeable effect on the stability of the plane or on 
the stalling speed, nor did it affect the center of 
gravity of the plane. The back pressure on the engine 
under normal operating conditions, when the genera¬ 
tor was not in use, was less than 1 psi. When the oil 
was being injected into the Venturi throat, however, 
the back pressure increased to about 5 psi (9 in. 
mercury). This caused no noticeable effect on the 
engine operation and performance, however, and ap¬ 
parently did not decrease the power output seriously 
or cause overheating or damage to the engine. After 
55.6 hr of flight with the equipment on the TBM-3C 
plane, the engine was overhauled and examined and 


no excessive wear was found. Excepting the periodic 
cleaning of the nozzles which was necessary because 
of the collection of carbon after every few hours of 
operation, there was no failure or damage to any part 
of the smoke generating equipment. 

Effectiveness of Smoke Screens 

Visual evaluation of the smoke screens from the 
exhaust generator equipment was made in the course 
of tactical tests carried out with the Amphibious Re¬ 
search and Development Group at Fort Pierce, 
Florida. The observations were made by flying the 
planes between an amphibious vessel on which the 
observers were stationed and a landing craft LCM, 
which was stationed about 150 yd away. The smoke 
screens were laid with the planes flying into the wind 
and at an altitude of 50 to 75 ft. The screens were 
evaluated as to their density, uniformity, rapidity of 
contact with the water surface, persistence, length of 
time of obscuration, and the completeness with which 
the oil was evaporated. 

It was concluded from these tests that the equip¬ 
ment was tactically suitable for the formation of 
smoke screens when used on a TBM-3 plane, pro¬ 
vided the air was thermally stable and the wind not 
over 15 knots. Under these conditions the planes 
could be flown at 200 knots with flaps up and with 
the engine set at military power (2,600 rpm, 44.5 in. 
manifold absolute pressure). It was recommended 
that fog oil No. 1 be used when the oil temperatures 
were above 60 F and that the lighter oil, Navy 
Symbol 2075, should be used below 60 F and above 
5 F. 

In amphibious operations from ship to shore, this 
equipment was satisfactory for laying frontal screens 
under all wind conditions, except when there was an 
off-shore wind above 15 knots or a wind above 20 
knots from any other direction. An example of the 
proposed use of the equipment for this type of opera¬ 
tion is shown in Figure 5. Under calm conditions, a 
single plane could lay a satisfactor}^ smoke screen 
which persisted for 3 to 4 min, but under less favor¬ 
able conditions, it was necessary to reinforce the 
screen at much shorter intervals or, even better, to 
have another plane follow the lead plane so as to lay 
a denser smoke screen. 

On the basis of the tests made by the Tactical Test 
Unit, the equipment for 12 planes was produced and 
sent to the Pacific Fleet for further evaluation. The 
units were installed on TBM-3C planes at Pearl 
Harbor NAS and tests were made for comparison 


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EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 



Figure 5. Aerial views of smoke screen from TBM-1 plane showing tactical use in amphibious operation. Airplane opera¬ 
tion; 110 knots, flaps down, 2,400 rpm, 42 in. MAP; Diol 55 used at the rate of 840 gal per hr. (Official Navy Photo.) 


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DEVELOPMENT OF EXHAUST COMBUSTION SMOKE GENERATOR 


515 


between the oil exhaust smoke generator and the 
standard FS smoke tank. Consideration was given to 
the vulnerability of the plane laying the smoke screen 
over enemy positions, the number of planes required, 
the training of the crew, the ship stowage, the air¬ 
plane installation and maintenance, and the reliabil¬ 
ity of the equipment. 

It was concluded from these tests that the density 
of the smoke screen from the exhaust generator was 
not sufficient to compete with the smoke from the FS 
tank, in spite of the longer emission time and the ad¬ 
vantages of handling a noncorrosive material. For 
satisfactory smoke screens under the atmospheric 
conditions likely to prevail, it was felt that three of 
the oil smoke planes would be required, and these 
would have to fly at a low elevation with flaps down 
in order to get the obscuration desired. This, of 
course, increased the vulnerability of the planes to a 
point where it was no longer practical to use the 
equipment. It was recommended that the equipment 
be improved to increase the evaporation capacity so 
as to put out a denser screen, and also that it be 
simplified in installation so that it could be attached 
to an airplane on board a combat carrier in less than 
one hour. 

33.3.5 Methods of Increasing Smoke 
Output 

Consideration had already been given to possible 
methods of increasing the output of the exhaust 
smoke generator so as to secure denser smoke screens. 
It was realized that the limitation to the capacity of 
the generator was the amount of heat available from 
the exhaust gases. Three ways of overcoming this 
were suggested. 

1. Use of more volatile fog oil. Although this should 
lower the equilibrium saturation temperature and in¬ 
crease the rate of output, it had the disadvantage 
that the smoke was less persistent in hot weather, 
since a larger amount of oil would be required to 
saturate the air in the screen. No great advantage was 
found in using Diol 40 rather than Diol 55 in the tests 
at Fort Pierce. However, if an organic compound 
with a higher temperature coefficient of the vapor 
pressure were available, it might be more suitable 
than the hydrocarbon oils. 

2. Preheating the oil either before it is charged to the 
bomb bay tanks, or by means of a heat exchanger with 
the exhaust gases while the plane is in flight, before 
laying smoke. This method seemed to have some 


possibilities and exhaust preheaters were obtained 
for one plane. It can be seen from equations (2) and 
(3) that, if the equilibrium saturation temperature is 
600 F with exhaust gases at 1400 F, nearly 80% of 
the heat required to evaporate Diol 55 from 70 F 
goes to raising the temperature of the oil, while the 
other 20% is used for the latent heat of evaporation. 
Consequently, if it were possible to preheat the oil to 
400 F, which is just below ,the flash point, nearly 
twice as much oil could be evaporated from the heat 
available in the exhaust gases. This method was 
abandoned when it appeared that it would complicate 
the equipment too much, and when the results on the 
third method gave assurance of success. 

3. Increase the heat content of the exhaust gases. 
Several methods were considered by which, with 
reasonable adaptation to the limitations of the tail 
pipe, this might be accomplished. 

a. Burning the combustible constituents of the 
exhaust in the tail pipe. 

b. Burning a mixture of fuel and air in an ex¬ 
ternal heater and combining the resulting 
gases with the exhaust gas in the tail pipe. 

c. Burning gasoline vapors led from the super¬ 
charger into the tail pipe. 

The first method is the desirable one, since the 
gases are already available for combustion in large 
enough quantities to supply the necessary heat. 
Furthermore, the high gas temperatures and sea level 
pressures are factors favorable to good combustion. 
For an engine operating under military power at a 
fuel-air ratio of 0.10, the combustion efficiency is ap¬ 
proximately 60%. With the R2600-20 engine this 
means that about 11,500,000 Btu per hr additional 
heat would be available, as compared to the 6,500,000 
Btu per hr available before combustion. 

The encouraging aspects of burning the exhaust 
gases, although not entirely free of difficulties, ap¬ 
peared to justify an investigation. Accordingly, the 
Solar Aircraft Company of San Diego, California, 
was engaged on a NDRC contract to develop the 
prototype unit. 

33.4 DEVELOPMENT OF THE EXHAUST 
COMBUSTION SMOKE GENERATOR 10 

33.4.1 Theoretical Considerations 

The composition of exhaust gases from internal 
combustion engines burning gasoline fuels depends on 
the fuel-air ratio. 11 ’ 12 The average composition is 


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EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 



0 2 4 6 8 10 12 14 16 

PER CENT BY VOLUME 


Figure 6. Average exhaust gas constituents vs fuel/air 
ratio of normal combustion processes. All percentages 
except for H 2 0 are based on dry volume. Methane (CH 4 ) 
is assumed to be 22% for all F/A. 


shown in Figure 6. The specific heat was calculated 
from the average specific heat and the weight propor¬ 
tions of the constituents. It was assumed that 95% 
of the combustibles could be burned with no excess 
air. For the R2600-20 engine operating under mili¬ 
tary power, the following quantities were estimated 
for 100% combustion efficiency. 


Initial exhaust temperature 
Initial exhaust flow 
Heat in exhaust 
Heat from combustion 
Total heat available 
Smoke temperature 
Oil evaporation 


1400 F 

15,600 lb per hr 
6.51 X 10 6 Btu per hr 
11.61 X 10 6 Btu per hr 
18.12 X 10 6 Btu per hr 
700 F 
70 gpm 


The primary problem in the development of the 
unit was to accomplish good combustion in the short¬ 
est possible distance, since only a limited length of 
tail pipe could be provided to evaporate the fog oil 
after the combustion process was completed. The fac¬ 
tors contributing to the efficiency of the combustion 
within a short space are: moderate gas velocities, 
high initial gas temperatures, high static pressure, 
turbulence for rapid mixing, and good flame propaga¬ 
tion. Since it is necessary to introduce the air for 
combustion by means of the ram effect, it was feared 
that the combustion efficiency might be affected by 
the attitude of the plane in flight, and that a diving 
attitude might disrupt the combustion or destroy the 
flame propagation if too high an air flow were pro¬ 
vided. Another consideration, which subsequently 
proved to be unfounded, was the danger of burning 
of the oil during combustion of the gases, thus using 


CE 

X 


z 


</> 

3 

CD 


3 

O 

o 



1000 1200 1400 1600 1800 2000 

ENGINE BRAKE HORSEPOWER 


Figure 7. Secondary air required for combustion of 
exhaust gas constituents. 


up the excess air. Previous experience with burning- 
exhaust gas had indicated the difficulty in maintain¬ 
ing proper combustion within a small restricted area 
because of the unstable flame propagation and high 
ignition temperature of the hydrogen and methane. 
If sufficient air is mixed with exhaust gases at 1400 F 
to oxidize the combustibles, the gases in general will 
not ignite spontaneously since they are cooled below 
the ignition temperature. In order to assure depend¬ 
able operation it was decided to use a pilot flame in a 
vapor-burning chamber. For this, purpose, gasoline 
vapor was led from the supercharger case into a 
plenum chamber. 

The calculated quantity of secondary air required 
for combustion is shown in Figure 7. 

33.4.2 Development of Exhaust Com¬ 
bustion Units 

The initial development of the combustion genera¬ 
tor was carried out in an engine test cell in which 


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DEVELOPMENT OF EXHAUST COMBUSTION SMOKE GENERATOR 


517 



Figure 8. Diagram of test cell installation showing the tail pipe configuration and some of the instrumentation. 


the units were operated with a Wright R2600-8 en¬ 
gine. This engine is essentially the same as the 
R2600-20 on the TBM-3C, except that the military 
power rating is 100 hp less. The test installation, 
which is shown in Figure 8, consisted of an exhaust 
duct leading from the right-hand collector ring to 
which was attached the combustion unit and a tail 
pipe comparable to that used on the airplane. Second¬ 
ary air for combustion was furnished from a blower. 
Air flow measurements were taken with a calibrated 
Venturi, and the air flow was controlled with a but¬ 
terfly-type valve. In most cases, high temperature 
measurements were made with quadruple-shielded 
thermocouples and potentiometer. Temperatures 
were taken of the initial exhaust gas upstream of the 
burner unit, at the point where the oil is sprayed into 
the tail pipe after combustion, and at the end of the 
tail pipe where the exhaust gas is ejected into the 
atmosphere. Since the gases were often in excess of 
2200 F, and sometimes of a highly reducing or oxi¬ 
dizing nature, the temperature measurements did 
not have a high degree of accuracy. The installation 
in the test cell provided an accurate measurement of 
the air and fuel consumption from which exhaust 
flow data were obtained. 

Several different designs of the combustion unit 
were built in order to improve the efficiency and 
stability of the combustion process. Typical of all 
designs was the introduction of the secondary air in 
such a manner as to cool the vapor plenum chamber 
and prevent overheating of the inter-air nozzle. These 
are shown in Figures 9A, B, C, D, and E. 

Figure 9A shows the first combustion unit. In this 
design, the secondary air passages were too small to 
introduce sufficient air to support complete combus¬ 
tion. The gas temperature was approximately 1800 F 


and the exhaust heat was increased by a ratio of 1.38. 
Figure 9B incorporated such modified features as an 
exhaust nozzle to assist in the injection and mixing of 
combustion air, shortening of the combustion space of 
the pilot burner, and enlarging the tail pipe diameter 
from 6^8 to 7% in. The tests on the first unit had 
shown that the gas velocity in the tail pipe was too 
high for complete combustion within a short length. 
The larger burner gave an exhaust temperature in 
excess of 2000 F and an increase in the heat content 
of the gases by the ratio of 2.4. The flame front, how¬ 
ever, was observed to be too close to the exhaust 
nozzle causing the inner surface of the plenum cham¬ 
ber to overheat to such an extent that the fuel vapor 
was ignited within the plenum chamber. Figure 9C 
represents an attempt to overcome this difficulty by 
eliminating the holes in the air shroud and extending 
the exhaust nozzle. With this arrangement, the heat 
ratio was brought up to 2.6 and the final exhaust 
temperature to about 2200 F. In this unit, ignition 
was obtained from a spark plug, which proved to be 
more reliable than a gas jet extending into the pilot 
burner. 

Figure 9D represents a further improvement in 
preventing overheating of the plenum chamber by 
attaching a small collar to reduce the diameter of the 
air nozzle. This feature had the effect of reducing the 
static pressure on the pilot flame which assisted in 
relieving the blocking effect on the flame. This burner 
gave a temperature in excess of 2200 F and a heat 
ratio of about 2.6. Combustion was quite smooth for 
normal air flows but, with high rates of secondary 
air, violent intermittent explosions occurred in the 
tail pipe. Figure 9E represents an attempt to reduce 
the back pressures of the combustion generator by 
means of a diffuser shroud. It was believed that some 


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EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 




Figure 9. (A) First experimental combustion generator utilizing supercharger fuel/air vapors to stabilize combustion. 
(B) Experimental exhaust burner. (C) Exhaust burner with extended exhaust nozzle and large diameter air nozzle. 
(D) Exhaust burner with air nozzle reduced in diameter. (E) Exhaust burner with short exhaust nozzle and modified 
air nozzle using diffuser outlet. (F) Exhaust burner with mixer in exhaust nozzle. 


pressure might be recovered without interfering with 
the combustion process. Tests proved, however, that 
this was not the case as the heat ratio dropped to 
below 2.1. It appeared that the turbulence was ma¬ 
terially affected, resulting in poor mixing of the 
secondary air. 


Figure 9F represents the final design of the com¬ 
bustion unit which was used as the prototype for the 
installations later made on the airplane. In this de¬ 
sign, the hollow streamlined section was incorporated 
in the exhaust nozzle through which holes were 
drilled in the area of negative pressure. Air entrained 


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DEVELOPMENT OF EXHAUST COMBUSTION SMOKE GENERATOR 


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I 1 

CONTROL PANEL PILOTS COMPARTMENT 


IGNITOR 
VAPOR 

FWD PUMP 
RH GENERATOR 
AFT PUMP 
LH GENERATOR 



-PRESSURE SWITCH-SET FOR OPEN 

CIRCUIT BELOW 6" HG DIFFERENTIAL 
PRESSURE WITH ANPHENOL CONNECTION 



Figure 10. Schematic installation diagram smoke generator. 


through the holes assured rapid diffusion into the 
center of the exhaust jet. There was evidence that this 
materially assisted in the combustion processes. The 
heat ratio was increased to between 2.6 and 2.7 and 
temperatures above 2200 F were obtained. 

Data taken from the more advanced configurations 
of the combustion generator are shown in Tables 1 
and 2. These indicate that it is possible to generate 
2.6 to 2.7 times the original heat in the exhaust from 
the engine, which represents a combustion efficiency 
of about 90%, depending upon the air flow. All tests 
were conducted with a tail pipe of the length finally 
installed in the actual airplane. The heat values, as 
listed, were calculated from the gas temperatures 
taken at the spray nozzle section at a distance of 
about 38 in. from the combustion generator. It is 
probable that these temperatures were somewhat 
affected by local flame temperatures, but radiation 
losses tended to offset this effect. 

The operation of the combustion generator is 
simple, necessitating only turning on the vapor and 
ignition switch, after which combustion immediately 
takes place and the gases come up to full heat in 
about 30 sec. No difficulty is experienced with flaming 
of the fog oil at the exhaust outlet unless the flow 
rate is extremely small, e.g., less than 1 gal per min at 


which time a yellow torching flame appears. An in¬ 
crease in oil flow rate extinguishes the flame immedi¬ 
ately. When operated with the proper quantity of air 
(not more than 140%), combustion is smooth and 
virtually noiseless, with only a slight purr discernible 
above the noise of the engine. With excessive second¬ 
ary air flow, intermittent backfiring occurs with loud 
reports. Combustion is easily extinguished with 
normal air flows by simply turning off the vapor 
switch; however, if the air flows are low (less than 
100%), combustion may continue for a period of 
time. With still smaller air flows, combustion is some¬ 
times spontaneous and can be maintained indefi¬ 
nitely, especially once the generator is heated. 

While the burner is in operation, the surface of the 
tail pipe attains a high temperature. A temperature 
as high as 1450 F has been observed in the test cell. 
In order to investigate the possible effects of the hot 
tail pipe on the skin and structure of the airplane, an 
aluminum panel was placed approximately 4^ in. 
from the pipe surface. With the hottest conditions, 
the maximum temperature of the panel was 210 F. 
The actual airplane installation runs much cooler 
than that in the test cell because the air flow rate 
in the slip stream is much greater. 

One of the interesting things that was noticed in 


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520 EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 




Table 1A. Test cell performance of exhaust burner with large exhaust nozzle.* 



Run 

Engine condition 

MAP 

RPM Hg (in.) HP 

Spray 
section 
surface 
temp F 

Carburetor 

air 

lb/hr temp F 

Fuel 

flow 

lb/hr 

Initial exhaust 
condition 
lb/hr temp F 

Back 
pressure 
Hg (in.) 

1 

2,400 

42.0 

1,496 

1345 

10,745 

75 

1,099 

5,922 

1360 

3.55 

2 

2,400 

42.0 

1,488 

1350 

10,633 

75 

1,090 

5,808 

1360 

3.55 

3 

2,400 

42.0 

1,488 

1390 

10,633 

75 

1,090 

5,808 

1360 

3.80 

4 

2,400 

42.0 

1,488 

1395 

10,633 

75 

1,090 

5,808 

1355 

3.95 

5 

2,400 

42.0 

1,488 

1370 

10,633 

75 

1,090 

5,808 

1355 

4.15 

6 

2,400 

42.0 

1,488 

1370 

10,633 

75 

1,090 

5,808 

1355 

4.10 

7 

2,400 

42.0 

1,488 

1375 

10,633 

75 

1,090 

5,808 

1350 

4.10 

8 

2,600 

44.4 

1,638 

1360 

12,248 

80 

1,270 

6,699 

1415 

4.10 

9 

2,600 

44.4 

1,610 

1370 

12,192 

80 

1,270 

6,671 

1400 

. • . 

10 

2,600 

44.4 

1,610 

1370 

12,192 

80 

1,270 

6,671 

1400 

4.8 

11 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

2.65 

12 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

2.82 

13 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

2.95 

14 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

3.05 

15 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

3.10 

16 

2,400 

42.0 

1,508 


10,633 

85 

1,099 

5,871 

1360 

. . . 

17 

2,600 

44.4 

1,635 

1355 

12,164 

85 

1,270 

6,657 

1410 

4.40 

18 

2,600 

44.4 

1,635 

1385 

12,164 

85 

1,270 

6,657 

1410 

4.75 

19 

2,600 

44.4 

1,635 

1395 

12,164 

85 

1,270 

6,657 

1410 

4.95 

* Original unit with production exhaust nozzle and tail pipe assembly 


Table IB 

Run 

Fuel/ 

air 

Spray 
section 
temp Ff 

Tail 
pipe 
temp Ff 

Secondary air 
Pressure Flow 

H 2 0 (in.) lb/hr 

Final exhaust 
gas condition 
lb/hr temp F* 

Heat content of exhaust 
Btu/hr 

Initial X 10 6 Final X 10 6 

1 

0.102 

2150 

2068 

.92 

2,280 

8,202 

2150 

2.339 

5.167 

2 

0.102 

2140 

2082 

1.00 

2,375 

8,183 

2135 

2.294 

5.114 

3 

0.102 

2207 

2150 

1.65 

3,095 

8,903 

2230 

2.294 

5.831 

4 

0.102 

2195 

2140 

2.20 

3,615 

9,423 

2230 

2.283 

6.172 

5 

0.102 

2175 

2155 

2.80 

4,125 

9,933 

2215 

2.283 

6.456 

6 

0.102 

2155 

2135 

2.80 

4,125 

10,010 

2215 

2.283 

6.507 

7 

0.102 

2170 

2170 

2.80 

4,125 

10,002 

2215 

2.271 

6.501 

8 

0.104 

2058 

2058 

1.05 

2,440 

9,208 

2032 

2.760 

5.451 

9 

0.104 

2180 

2165 

1.90 

3,335 

10,071 

2185 

2.722 

6.466 

10 

0.104 

2210 

2130 

3.20 

4,455 

11,187 

2232 

2.722 

7.327 

11 

0.103 



.20 

1,050 

6,921 


2.319 


12 

0.103 



.95 

2,305 

8,176 


2.319 

.... 

13 

0.103 



2.33 

3,730 

9,601 


2.319 


14 

0.103 



3.75 

4,860 

10,731 


2.319 


15 

0.103 



5.00 

5,660 

11,531 


2.319 


16 

0.103 







2.319 


17 

0.104 

2165 


1.40 

2,835 

9,492 

2160 

2.736 

6.008 

18 

0.104 

2225 


2.20 

3,615 

10,272 

2240 

2.736 

6.749 

19 

0.104 

2217 


3.25 

4,495 

11,152 

2240 

2.736 

7.327 


* Shielded thermocouple at spray section, 
t Nonshielded thermocouple at spray section, 
t Nonshielded thermocouple at end of tail pipe. 


these tests and which gave some difficulty in the 
later installations was that there was a considerable 
difference in the composition of the gases and per¬ 
formance of the unit when attached to the right- and 
left-hand exhaust ports on the engine. This discrep¬ 
ancy was attributed to the distribution of the fuel-air 


mixtures in the induction system of the engine. The 
manufacturers of the engines, Wright Aeronautical 
Corporation, stated that this phenomenon was char¬ 
acteristic of the R2600 series engines. It was also 
discovered during the test on the combustion genera¬ 
tor that the condition of the spark plugs in the engine 


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INSTALLATION OF COMBUSTION UNIT ON TBM-3 PLANE 


521 


had a considerable bearing on the quantitative rela¬ 
tionship of the exhaust gas components. In several 
instances it was noted that the combustion was very 
poor, and that the flame did not fully propagate until 
it was some distance down the tail pipe from the 
burner. In every case, abnormally low initial exhaust 
temperatures were coincident with this condition. 
Low exhaust temperatures were almost always caused 
by dirty spark plugs. When these were replaced, the 
condition was immediately rectified and the burner 
operated normally. 

33.5 INSTALLATION OF COMBUSTION 
UNIT ON TBM-3 PLANE 

The general scheme of the combustion generator 
installation is illustrated in Figure 10. Two generators 
were installed, one on either side of the airplane, ex¬ 
tending from the exhaust collector outlet parallel to 
the line of thrust below the wing, to a point approxi¬ 
mately 3 ft from the trailing edge of the wing. The 
overall length of the tail pipe, including the combus¬ 
tion unit, was about 11 ft. The generators and tail 
pipe were held by brackets attached to an aluminum 
channel bolted to the side of the fuselage with a 4-in. 
space between the skin and the tail pipe. The genera¬ 
tor assembly was connected to the manifold by means 
of a flexible hose and an elbow clamped to the mani¬ 
fold which was originally provided with a clamp at¬ 
tachment for flame dampeners. The position of the 
scoops on the experimental installation was above the 
generators, and was such that there was little or no 
air flow interference by the engine cowl flaps. Gaso¬ 
line vapor was drawn from taps on either side of the 
supercharger to the common inlet of an electrically 
operated solenoid valve, from which it was again 
divided into a line for each generator. Automatic 
safety switches were provided to prevent the exhaust 
gas from being drawn into the supercharger case at 
negative pressures. 

It should be noted that in this installation no 
Venturi section was used to atomize the oil, since 
this would have interfered with the operation of the 
burner which depended upon having little or no back 
pressure in order to permit the air for combustion to 
be introduced by the ram effect. Because of the addi¬ 
tional volume of gas resulting from secondary air and 
the extremely high temperatures, the velocity through 
the 7%-in. tail pipe was approximately 600 fps. While 
this was less than the throat velocity in the first ex¬ 
haust smoke generator and resulted in poorer atomi¬ 


zation of the oil, it was in part compensated for by 
the higher temperatures which resulted in a faster 
rate of heat transfer. Nevertheless, the high heat 
efficiencies were never attained on this generator as 
they were on the first model and further improve¬ 
ments along this line should be sought. The spray 
nozzles which were used to inject the oil directly into 
the hot gases after combustion were the Todd 
nozzles with Mayflower 20-10 plates. 

A preliminary program of flight testing was carried 
on at San Diego to regulate the combustion unit to 
give the maximum generation of heat. This was 
mainly accomplished by varying the scoop size to 
control the flow of secondary air. The position of the 
spray section was also altered, with respect to the 
burner, to give the optimum proportioning of com¬ 
bustion and evaporation space. The flight tests 
showed that the injection of secondary air by the ex¬ 
haust nozzle was satisfactory at all flight altitudes or 
speeds of the plane. 

It was again noticed that the port generator gave 
somewhat poorer performance than the starboard 
generator. The amount of oil evaporated in each 
generator was, respectively, 18.5 and 22.5 gal per min 
with the engine operating at 2,600 rpm and 47 in. 
MAP. Under these conditions a dense curtain of smoke 
could be laid, which had a duration of 4 to 5 min 
when the plane flew downwind and 2 min when the 
plane flew crosswind of a 12-knot wind. This perform¬ 
ance was about 2 times as good as that of the simple 
exhaust generator. Further tests were carried out on 
the plane by the Tactical Test Unit at Patuxent 
River Naval Air Station. 13 These verified the con¬ 
clusions reached by the Solar Aircraft Company and 
demonstrated additional uses to which a squadron of 
planes equipped with the combustion exhaust smoke 
generator could be put for laying area screens. 

On the basis of these tests the equipment was 
standardized as the Aircraft Oil Fog Generator, Mark 
3. Procurement of 72 ship sets was immediately 
started with high priority. Actually, only 24 planes 
were equipped before the end of the war. In these, a 
simplified hydraulic system was used in order to 
eliminate the necessity of substituting the 300-amp 
generator for the standard 200-amp generator on the 
TBM-3C plane. The electric pump system was re¬ 
placed with a hydraulic drive for pumping the fog oil. 

The 24 planes equipped with the Mark 3 generator 
were delivered to the Fleet Operational Training 
Command, U. S. Atlantic Fleet, Norfolk, Virginia, 
just at the end of the war. During September and 


SECRET 



522 


EXHAUST SMOKE GENERATOR FOR AIRPLANE ENGINES 


October 1945, a series of operational and tactical 
tests were made on the equipment by Squadron 
VC-6 under the direction of the Research and De¬ 
velopment Center. In order to improve and simplify 
the installation and to hasten procurement, several 
modifications were suggested in the hydraulic system 
and in the method of attaching the generators to the 
planes. These changes were accepted in the standardi¬ 
zation of the modified equipment as the Aircraft Oil 
Fog Generator, Mark 4. 14 

During the course of the operational and tactical 
tests the 24 aircraft were operated for a total of 
966.7 hr. The maximum time put on any single plane 
was 58.2 hr. A total of 77,500 gal of fog oil was used, 
and this amounted to approximately 33.3 plane hours 
of smoke generation with a maximum of 190 min for 
any individual plane. During these tests the planes 
were operated at military power (2,600 rpm, 47 in. 
MAP) for a total of approximately 66.7 hr with a 
maximum for a single plane of 5.1 hr. In some cases 
the planes flew continuously at this power for more 
than 10 min. In the course of these tests no engine 
trouble occurred on any of the planes that could be 
attributed to the smoke equipment. 

33.6 TACTICAL USES OF AIRCRAFT 
OIL FOG GENERATOR 15 

The development of the oil fog generator for air¬ 
craft suggested several new tactical uses which could 
not be fulfilled by the older methods of dispersing 
smoke. It was now possible to lay a dense smoke 
curtain from a single plane flying at a speed of better 
than 200 knots and emitting smoke for a period of 
6 min, or a swath 20 miles long and 100 yd wide in 
a single flight. It was estimated that a squadron of 
planes prepared for take-off could screen an anchorage 
of 8 square miles within 10 min from the receipt of 
the warning of the approach of enemy planes. In the 
tests carried out at Norfolk after the war, this 
tactical problem was worked out and demonstrated. 
Consideration was given also to the possibility of 
screening a task force under way and of screening an 
individual ship, especially when in a crippled condi¬ 
tion. 

33.6.1 Area Screening of an Anchorage 

It was recommended that these screens be laid at 
an altitude of 400 ft since this would prevent any 
successful change in point of aim of an enemy plane 


that dived through the screen, and would take full 
advantage of a possible thermal inversion cap or 
existing air stability below 400 ft which would pre¬ 
vent the screen from falling to the surface of the 
water. With planes flying at 100-yd intervals, ap¬ 
proximately 200 gal of fog oil will be emitted per 
square mile of screen. This appears to be adequate on 
the basis of the best information that can be obtained 
from experiments with surface equipment. 

As the result of the Norfolk tests, it was concluded 
that area screens could be laid with the oil fog 
generator either in a dead calm or in a brisk breeze 
with turbulent air. The speed with which the screens 
could be laid is unaffected by the wind speed or 
direction, or by sea conditions. It was thought that 
the screens were as good as those laid by surface craft 
and usually better. The method has the advantage 
also of being more certain. On the other hand, the air 
screen cannot be laid at night without exceedingly 
hazardous operations. Furthermore, the presence of 
friendly airplanes over the ships means a loss of fire 
power to the ships which in some cases would be 
serious. 

33.6.2 Screening a Task Force Under 
Way 

While the tactics for this operation have not been 
tested at the time of writing of this report, it is be¬ 
lieved that a squadron of TBM-3 planes, equipped 
with the smoke generator, could screen a task force 
covering an area approximately 5,000 yd x 5,000 yd 
by flying in formation with 200-yd spacing at an 
altitude of 300 to 400 ft along a course determined by 
the vector difference between the velocities of the 
moving task force and the wind. Complete coverage 
will be obtained within 4 to 5 min. The time for which 
the smoke will remain over the task force from a single 
maneuver is determined by the following equation: 


W(tf - w ) 

where d is the distance the screen is laid beyond the 
ships (about 2 miles), and V(tf-w) is the vector dif¬ 
ference between the task force velocity and the wind 
velocity in knots. When the ships are moving with 
the wind, it may be necessary to renew the screen 
before it clears the task force since the smoke may 
have been weakened by diffusion. Table 2 is the esti¬ 
mated protection time obtainable for different wind 
and task force velocities. Shortly before the screen 


SECRET 




EXHAUST SMOKE GENERATOR FOR HIGH-SPEED PLANES 


523 


Table 2. Protection of a task force by aircraft oil smoke screens. 


Vector Protection time (min) 

Task force velocity Wind velocity difference Total from 

Speed Speed V(t f-w) Plane Single 1 flight of 

(knots) Direction (knots) Direction (knots) course maneuver aircraft 

15 000° 10 000° 25 000° 5 15 

15 000° 10 180° 5 000° 24* 72* 

15 000° 10 90° 18 027° 8 l A 25 

* The smoke may have been diffused prior to this time so that renewal would be required in 15 min thus giving a total time of only 45 
min per flight. 


becomes ineffective the planes should extend the 
screens by repeating the initial maneuver. Each 
plane should have sufficient fog oil to continue the 
screen in this manner at least twice in a single flight. 

The total protection time will be at a minimum 
when the task force is proceeding upwind, and a 
maximum when proceeding downwind at the speed 
of the wind. Thus, when the task force is merely 
taking evasive action and its course is not predeter¬ 
mined by other factors, best results will be obtained 
if the ships steam downwind. 

33.6.3 Screening of an Individual Ship 

This appears to be one of the most useful applica¬ 
tions of the aircraft oil fog generator, because surface 
methods of laying smoke screens are seldom available, 
especially to protect a crippled ship that has lost a 
portion of its fire power or maneuverability. 

In one test at Norfolk, a blanket screen was main¬ 
tained by means of three smoke planes over a 
destroyer under way, for approximately 30 min. This 
screen could have been maintained even longer. In 
this test, the wind conditions were quite unfavorable 
as the air was turbulent and the wind speed was 20 
knots. It was necessary for the ship to vary its speed 
as well as its direction to stay under the cover. It was 
concluded that three smoke planes can protect a 
single ship which is able to move downwind with the 
smoke, but it would require more than three planes 


if the ship were moving crosswind at a speed relative 
to the wind greater than 5 knots. 

33.7 DEVELOPMENT OF EXHAUST 
SMOKE GENERATOR FOR HIGH¬ 
SPEED PLANES 

It is evident that if the aircraft oil smoke generator 
is to maintain a useful position in naval warfare, its 
development must be continued and extended to jet 
propulsion and rocket planes. Some thought was 
given to this, since it was contemplated that if the 
installation were successful on the TBM-3 plane, it 
would next be installed on the PV-2 plane. Some 
rough calculations showed that the quantity of heat 
available for evaporating the oil was approximately 
proportional to the speed of the planes. Although no 
consideration was given to the method of introducing 
the oil into the hot gas stream, it seemed apparent 
that higher pressures of the gas and, therefore, higher 
velocities would be available for atomizing the oil 
and evaporating the droplets. 

It has been recommended that the Navy include 
in its fundamental research program, a study of the 
mixing of fluid streams, including atomization, mo¬ 
mentum and energy balances, turbulence, nozzle 
design, high-speed combustion, and other aspects 
which underlie the development of the oil fog genera¬ 
tor and other devices of military importance. 


SECRET 







Chapter 34 

MUNITIONS FOR THE DISPERSAL OF LIQUID DROPLETS 

By H. F. Johnstone 


34.1 INTRODUCTION 

he importance of dispersing chemical warfare 
agents and insecticides as very small droplets to 
obtain maximum effectiveness was frequently demon- 
strated in field tests carried on during the war. This 
was not only true of the solid toxic agents which must 
penetrate to the lungs, but applied equally well to the 
liquid agents when it was desired to set up an im¬ 
mediate high concentration of vapor in the initial 
cloud in order to produce casualties before the gas 
mask could be adjusted. This concept of the use of 
liquid chemical agents was held by the Germans who 
designed many of their shells and bombs with ex¬ 
tremely heavy bursters in order to convert the entire 
charging into aerosols. The American Army did not 
have any munition for setting up aerosols in this way, 
nor was there any completely successful method of 
dispersing small solid particulates. 

The British and Canadians reported some work on 
HE chemical shells and bombs for the dispersion of 
liquids, including small-caliber armor-piercing shells 
and Bofors shells with RDX bursters. The results 
indicated that fragmentation of a liquid from heavy- 
wall projectiles is incomplete, and much of the charg¬ 
ing remains as drops above 50 microns diameter. 
Thin-wall munitions, either projectiles or bombs, are 
suitable for dispersing a charging of a mobile liquid as 
small droplets. The violence of the explosion with the 
HE burster is often sufficient to give the cloud con¬ 
siderable vertical height. 

34.2 LIGHT PLASTIC BOMB 1 

The work of the NDRC on munitions of this type 
was undertaken primarily to devise an aerial bomb 
for dispersing DDT solutions to exterminate mos¬ 
quitoes in a region prior to a landing operation. The 
bomb was to be used for atomizing a liquid to give 
low concentrations of a finely divided aerosol, much 
in the same way that a chemical warfare agent might 
be used if it were highly toxic. It was desirable that 
the bomb provide uniform contamination of the 
vegetation by droplets in the range from 10 to 100 
microns diameter. For this reason a small bomb was 
chosen so that wide dispersion from a single cluster 


could be obtained. Good ballistics of the bomb were 
not necessary since large areas would be treated at a 
single time. In order to make use of existing standard 
cluster adapters, it was decided to make the bomb 
the same size and shape as the AN-M50 4-lb mag¬ 
nesium incendiary bomb. The bomb was provided 
with an all-way fuze which would function on impact 
with soft ground, water, etc., when dropped from an 
airplane either at low or high altitudes. 

The development work on the bomb was done in 
three parts, as follows: 

1. A study of the atomization of liquids with high 
explosives to determine the limits of the drop size 
distribution. 

2. A study of the effect of the shape and dimen¬ 
sions of the bomb and the thickness of the walls on 
the degree of atomization. 

3. The development of a design suitable for pro¬ 
duction followed by procurement of sufficient quan¬ 
tities of the finished munition for testing. 

34.2.1 Atomization of Liquids by 
Explosive Bursts 

The first experiments were made by bursting vari¬ 
ous small containers, such as cans, flasks, and tubes, 
containing DDT solutions in a mobile solvent, by 
means of various types of bursters, such as blasting 
caps, Primacord, tetryl, and black powder. The con¬ 
tainers were burst about 4 ft above the floor in a 
large room and the aerosol samples were collected by 
impactors located at a height of about 2 ft above the 
ground and along a radius from the burst. A paper 
was placed on the ground under the burst to show 
any ground loss. The slides from the impactors were 
examined under a microscope immediately after the 
burst. The results indicated that atomization of the 
mobile liquids to droplets below 50 microns diameter 
is quite possible. For best results, the solvents should 
be of low viscosity. The shape of the bomb is an im¬ 
portant factor in fixing the optimum ratio of the ex¬ 
plosive to charge and, apparently, limits the size of 
the munition. 

In a second series of experiments, liquids of dif¬ 
ferent viscosities were dispersed from containers of 



524 


SECRET 


LIGHT PLASTIC BOMB 


525 


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SECRET 


The drop size data were obtained in chamber tests where the aerosol cloud was allowed to settle on glass slides for hour. 












526 


MUNITIONS FOR THE DISPERSAL OF LIQUID DROPLETS 




O* 





M/VJmiw O ® o 1=°^ 


Figure 1. Disassembled parts of plastic bomb. 


different sizes and diameters. An axial burster in a 
bomb of small diameter with a thin wall gave a 
better break up of the solution than a bomb of larger 
diameter with the same amount of liquid. There is a 
minimum average drop size obtainable for any given 
solution regardless of the size of burster and the 
diameter of the container. The drop diameter in¬ 
creases rapidly as the viscosity of the liquid in¬ 
creases. 

The results of a series of tests using plastic tubes 
made of bonded Kraft paper are shown in Table 1. 
Here the amount of explosive was not so critical in 
determining the drop size as in the case of the metal 
and glass tubes, nor was the diameter of the bomb so 
critical as with the other tubes. The thickness of the 
plastic case was not important since the case was 
completely pulverized by the explosion. Either plas¬ 
tic or metal tubes were used for the burster-well with 
equally good results. Best results were obtained using 
solvents of low viscosity, high surface tension, and 
high density. Dilute solutions were atomized more 
easily than concentrated solutions. For DDT, it was 
recommended that a 10% solution in carbon tetra¬ 
chloride be used, and that the solution contain an 
equal percentage of a high-boiling oil, such as dibutyl 
phthalate or methyl naphthalene. 


34.2.2 Design and Manufacture of the 
Plastic Bomb 

On the basis of these results, a design was made of a 
bomb which could be fabricated from phenol form¬ 
aldehyde bonded Kraft paper. This was selected 
because of its rigidity, strength, and frangibility. The 
parts of the bomb are shown in Figure 1. An all-way 
fuze of conventional design, provides the extreme 
sensitivity required for functioning the bomb on 
light surfaces, such as small branches, and on 
water. The axial burster consists of reconsolidated 
tetryl pellets in a ^g-in. brass tube. The fuze con¬ 
tains an M-26 primer cap which functions the M-17 
detonator in the end of the tetryl tube. The fuze is 
armed by the removal of a pin which is held in place 
by the sealing cup. This, in turn, is maintained in 
position by a spring clip which flies off when the bomb 
leaves the cluster. An arming spring forces the sealing 
cup out of position and arms the fuze. 

The bomb is not stabilized in flight and falls at 
random to give the maximum dispersion pattern. The 
capacity of the bomb is approximately 400 cc, cor¬ 
responding in the case of the 10% carbon tetrachlo¬ 
ride solution to approximately 68 g of DDT. It is 
estimated that, for the control of mosquitoes, about 


SECRET 








EJECTION AIR-BURST BOMB 


527 


2,400 of these bombs would be required per square 
mile. This should give a dosage of about 0.5 lb DDT 
per acre. Each bomb would have to contaminate an 
area about 35 yd square. 

The plastic components for 3,500 bombs were ob¬ 
tained from the Formica Insulating Company of 
Cincinnati, Ohio. These were sent to the J. V. Pilcher 
Company, Louisville, Kentucky, where they were 
assembled. There was some difficulty in getting good 
seals before the proper gluing technique was de¬ 
veloped. All parts were matched with a clearance of 
0.003 in. The binding surfaces of the component 
parts were roughened by sanding, or by cutting 
helical or parallel 60° grooves 0.015 in. deep. The 
end plug and fuze holder were cut from laminated 
sheets with the laminations perpendicular to the axis 
of the pieces. 

A number of cements for sealing the joints were 
tested. The best cement found was Chrysler Cycle- 
Weld, Code CB-2. This produced a bond stronger 
than the plastic itself and had a short curing time. It 
formed a satisfactory joint when cured at room 
temperature for 24 to 48 hr. The best reproducible 
results were obtained when the cement was applied 
to the parts before assembly rather than by forcing 
the glue into the joints under pressure. It was neces¬ 
sary that the cement be made up fresh, and never 
used after it was more than 2 hr old. It was also 
recommended that the grooving, or roughening of the 
surfaces be done within 24 hr prior to gluing. 

After the assembly of the bombs and curing of the 
joints, each bomb was tested for leakage under water 
by applying air pressure at 30 psi. The percentage of 
failures in the later lots, after the gluing procedure 
had been worked out, was not more than 3%. After 
delivery, the bombs were again tested for leakage by 
filling with carbon tetrachloride containing a green 
dye. Here the percentage of failures amounted to 17%. 
Several of the bombs containing the carbon tetra¬ 
chloride solution were placed in tropical surveillance 
for several weeks. No leaks developed during this 
time. 

34.3 EJECTION AIR-BURST BOMB 2 

Vesicant agents are effective when impinged as 
droplets on personnel. Contamination of terrain and 
buildings is another use. The common dispersal 
methods for these agents are by artillery shell, air¬ 
plane sprays, and bombs. Shells are not always 
practical because of low-loading efficiency, high- 



Figure 2. Cross section of EK-3 bomb. 


SECRET 




















528 


MUNITIONS FOR THE DISPERSAL OF LIQUID DROPLETS 


Table 2. Comparison of capacities and burster charges of ejection air-burst bombs. 



M-69* 

EK-1 

EK-3 

EK-4 

Maximum capacity, cc 

1,650 

1,350 

1,270 

1,125 

Wt of HD filling, 10% void, g 

1,870 

1,530 

1,440 

1,275 

Wt of empty bomb and parts, g 

1,550 

2,450 

2,530 

2,885 

Grams of powder in bursterf 

0 

6 

6 

9 

Grams of powder for ejectionJ 

6 

30 

20 

20 

Total weight of bomb, g 

3,426 

4,016 

3,996 

4,189 

Loading efficiency, % 

54.6 

38.2 

36.0 

30.4 

Lb HD per 14- bomb cluster 

57.6 

47.2 

44.4 

39.3 


* Oil incendiary bomb. 

t Including g of black powder; remainder is 37-mm smokeless ball powder, 
t Grade A, No. 4 black powder. 


crater loss, and nonuniformity of contamination. 
High-altitude airplane spray is difficult to aim and 
produces a fight concentration over a large area. Low- 
altitude spray is effective, but such tactics are not 
always practical. The most effective bombs are those 
that are air-burst by means of a barometric, time, or 
proximity fuze. Such bombs disperse the filling more 
uniformly than ground-burst bombs and without 
crater loss. Inaccuracies and high costs of these fuzes, 
especially when used for small bombs, which are es¬ 
sential to obtain uniform coverage, are objections to 
this method. An equivalent to the bomb with proxim¬ 
ity fuze is the base ejection air-burst bomb which, 
upon impact, ejects a canister containing the vesicant 
that bursts 100 to 300 ft above the ground. 

Several attempts to develop an air-burst bomb of 
this type have been made in the past. A 30-lb bomb 
holding about 3 1 of vesicant agent was tested at 
Edgewood Arsenal in 1930. 3 In this case, the ex¬ 
plosive was contained in the nose section of the bomb 
and the entire tail section was blown into the air 
where it burst from 1 to 60 ft above the ground. 
During the war a modified version of the M-67 
chemical bomb was proposed for the dispersion of 
mustard gas. 4 This consisted of a hexagonal canister 
of 1,350 cc capacity fitted into the standard hexago¬ 
nal incendiary bomb, which was already provided 
with an impact fuze and powder chamber for ejecting 
the contents. The blast from the powder chamber 
simultaneously ignited a match train which initiated 
the powder burster in the inner canister so that it 
would burst in the air at an altitude of 100 to 250 ft. 
Tests on this bomb showed that the area, covered 
with drops larger than 1.5-mm diameter with a con¬ 
tamination greater than 0.5 g per sq m, was about 
four times that from the standard tail ejection chemi¬ 
cal bomb, i.e., either the 10-lb M-69 or M-74 bomb. 5 
With the bomb proposed, it was obvious that if im¬ 


pact occurred on rocks or hard surfaces, the case 
would be so badly deformed that the inner canister 
could not be ejected. 

Further development of the munition was under¬ 
taken at the Munitions Development Laboratory. 
This resulted in two designs which were constructed 
for test purposes. 

34.3.1 Hexagonal Bomb 

In order to study the impact forces on the bomb, 
25 units were assembled in M-69 incendiary bomb 
cases. These were fired from an inverted mortar to 
impact on clay, cinders, sand,and concrete at 240 fps. 
High-speed motion pictures of the bombs during im¬ 
pact were taken at 3,000 frames per sec. It was found 
that, on soft or hard soil, sand or cinders, the maxi¬ 
mum rate of deceleration occurred just after the 
initial impact. When the bomb penetrated 20 in. into 
the soil, the maximum deceleration was about 1,550 
times the acceleration of gravity. The average rate of 
deceleration was one-third to one-half of the maxi¬ 
mum. When the bomb impacted on concrete at 240 
fps, the tail section had an average rate of decelera¬ 
tion of more than 10,000 G, while the parts of the 
nose which collapsed averaged at least 10 times the 
deceleration rate of the tail section. The original 
design of the hexagonal bomb was known as the 
EK-1 bomb. 

A new design, making use of the hexagonal in¬ 
cendiary bomb outer case and known as the EK-3 
bomb, was produced. Changes were made to facilitate 
commercial manufacture and to strengthen the inner 
case. A stamped nose cup replaced the flat nose plate 
so that the assembly could be copper-brazed. The 
delay fuze was simplified by the use of a compressed 
powder delay train. A cross section of the EK-3 bomb 
is shown in Figure 2. One thousand of these bombs 


SECRET 











EJECTION AIK-BURST BOMB 


529 


were delivered to Edgewood Arsenal in September 
1944. The inner cases were filled with 3.18 lb of 
mustard or thickened mustard and then were as¬ 
sembled into M-69 bomb cases. Some trouble was 
encountered as the result of leakage through the soft 
solder joints at the inner tail cup. Furthermore, the 
cases did not stand the pressure test of 60 psi without 
some leaks showing up. Field tests on this munition 
were scheduled for Dugway Proving Ground at the 
end of the war. 

34.3.2 Round Bomb 

The round bomb was designated EK-4. It had 
two obvious advantages, (1) greater ease of manu¬ 
facture, and (2) greater strength and uniformity of 
deformation on severe impact. There was no standard 
round bomb in the 10-lb class and it was generally 
assumed that the hexagonal shape was necessary for 
clustering, although this was later proven to be un¬ 
true. The smaller agent capacity is a possible disad¬ 
vantage of the round bomb, but this is not as great 
as it may appear at first. A comparison of the 
capacities of the models considered and the ejection 
and burster charges for each is shoAvn in Table 2. 

Considerable attention was given to the design of 
the inner case. Since it was impractical to prevent 
severe deformation when the bomb landed on con¬ 
crete, a solution was found to the problem by con¬ 
trolling and directing the deformation so that it 
occurred at points which would not interfere with the 
ejection of the inner case. As a result of a series of 
firing tests, a bomb was finally designed which showed 
promise of proper functioning a large percentage of 
the time when striking concrete at a velocity of 
about 225 fps. 

A cross section of this bomb, which was called the 
EK-4, is shown in Figure 3. The inner case is made 
from 2%6-in. OD 20-gauge steel tubing. The nose end 
and the middle section are corrugated so that de¬ 
formation occurs inwardly, and the case is strength¬ 
ened so that it does not bulge from the hydraulic 
pressure of the liquid. The nose and tail cups of the 
inner case are copper-brazed. The latter has a circular 
groove stamped in it so that the thickness of the re¬ 
maining metal is slightly less than one-half of that 
of the wall. This insures that the agent is ejected 
through one end of the canister to provide large 
droplets. The outer case is made from 2 1 ^{q-iu. OD 
18-gauge steel tubing, 19% in. long. A 9% in. long, 
18-gauge sleeve was used to reinforce the nose end 



Figure 3. Cross section of EK-4 bomb. 


SECRET 



















530 


MUNITIONS FOR THE DISPERSAL OF LIQUID DROPLETS 


of the bomb. A dome-shaped diaphragm is used to 
absorb some of the impact of the inner case and to 
provide a chamber for the powder bags. The delay 
element is a compressed black powder train, which 
is ignited by a length of Quickmatch. This train is 
set for a delay time of 4.2 sec and can be made repro¬ 
ducible to ±0.2 sec. A new small inertia-type fuze 
was developed for the bomb. Cloth streamers similar 
to those used on the M-69 bomb are used to stabilize 
the bomb while falling. Good ballistics are obtained 
by attaching the streamers to a metal ring, which is 
fastened in turn to the bomb by means of nylon 
shroud lines 10 in. long. 

One thousand complete EK-4 bombs were manu¬ 
factured without difficulty and were delivered to 
Edgewood Arsenal in March 1945. The inner cases 
were filled with 2.8 lb of distilled mustard gas and 
thickened distilled mustard gas containing 0.5% oil 
red dye. The bombs were assembled, fuzed, and 
clustered, and sent to the Dugway Proving Ground 
Mobile Field Unit for field tests. The preliminary 
tests were started just before the end of the war. 
The static tests reported indicated that, when the 
bomb functioned properly, it distributed the filling 
fairly uniformly over a moderately large area which 
resulted in medium vapor dosages over that area. 6 
The bomb did not show any great advantage over 
other available munitions for dispersing liquid agents. 
In open terrain, it gave results similar to those from 
low-altitude spray; in wooded terrain the results were 
similar to those from the M47A2 bomb. It was ob¬ 
served that many of the canisters were ejected too 
high before they burst, and the results could have 
been improved if all of the canisters had burst below 
the tops of the trees. A large percentage of the bombs 
did not function satisfactorily and further develop¬ 
ment is necessary before definite assessment of this 
type of munition can be made. 

34.4 MUNITIONS CONTAINING LIQUIDS 
WITH DISSOLVED GASES UNDER 
PRESSURE 

Several attempts were made to develop a munition 
for dispersing liquid agents as aerosols by means of a 
gas dissolved under high pressure in the liquid. It 
was shown in Chapter 29 that no advantage is to be 
gained in the atomization of the liquid by explosives 
when the bomb is pressurized with C0 2 at 500 psi. 
There are several other methods, however, by which 
the pressurized liquid might be atomized. Two of 


these were suggested by A. R. Olson of the University 
of California. Neither of these were found to produce 
the desired results and both appear to be impractica¬ 
ble for a munition for field use. a The test results will 
be described here briefly as they may be useful to 
others seeking information on this subject. 

34.4.1 First Olson Bomb 8 

The first device proposed by Olson was a 100-lb 
bomb which was intended to impact and remain up¬ 
right, and then disperse its liquid contents as an 
aerosol by spraying through a small hydraulic 
atomizing nozzle. The liquid was to be maintained 
in the bomb under high pressure of carbon dioxide, 
or other suitable gas which was relatively soluble in 
the agent. It was contemplated that the presence of a 
dissolved gas in the liquid under pressure would im¬ 
prove the atomization. 

The solubilities of carbon dioxide in mustard gas 
and in butyl carbitol are shown in Tables 3 and 4. It 


Table 3... Solubility of C0 2 in mustard gas . 8 


Temperature 
degrees C 

Press 
C0 2 psi 

C0 2 g per 
100 g H 

AV 

Vo 

20 

200 

3.4 



250 


.062 


300 

6.7 

.082 


400 

10.1 

.130 


500 

13.1 

.190 


600 

18.5 

.285 


700 

27.4 

.475 

12 

200 

3.5 



250 


.090 


300 

7.0 

.120 


400 

11.3 

.165 


450 


.215 


500 

16.4 

.260 


600 

23.8 

.520 


was proposed that butyl carbitol be used as a simu¬ 
lant in the field tests because of the similarity of its 
properties to those of the vesicant agent. 

The difficulty of insuring that the bomb performs in 
the prescribed manner when dropped from an air- 


a It should be noted that this method of dispersing aerosols 
is indeed the basis of the aerosol bomb which was widely used 
for dispersing insecticides during the war. In this case, the 
gas used to pressurize the bomb was actually liquefied, and 
there was only a low concentration of the nonvolatile agent 
in the liquid vehicle. Furthermore, the rate of output of the 
bomb was much too low to be of use for field munitions. 
Particle size measurements on the aerosols generated from 
these bombs have been reported by LaMer. 7 


SECRET 









LIQUIDS WITH DISSOLVED GASES UNDER PRESSURE 


531 


Table 4. Solubility of C0 2 in butyl carbitol. 8 


Temperature 

Press 

C0 2 g per 100 g 

AV 

degrees C 

C0 2 psi 

butyl carbitol 

Vo 


22 

280 

7.7 

0.085 


470 

18.1 

0.180 


580 

29.8 

0.287 


670 

42.2 

0.409 


715 

51.0 

0.490 

19 

120 

2.23 

0.0189 


175 

5.26 

0.0396 


310 

11.3 

0.098 


530 

27.0 

0.226 


625 

46.0 

0.425 


775 

95.0 

0.91 


plane was recognized, and several methods of stabi¬ 
lizing the bomb in flight and making it land upright 
were suggested. One of these even conceived of having 
a parachute and a tripod which would hold the bomb 
in an upright position a few feet off the ground while 
it was dispersing its contents. A test on this device at 
Dugway Proving Ground in April 1943 showed that, 
under the best conditions, the atomization in no way 
produced a true aerosol, and much of the charging 
was dispersed as large droplets which settled out 
within a few feet of the bomb. 9 

Further tests on this device were made at the 
Munitions Development Laboratory in order to de¬ 
termine if an improvement could be made by using 
different orifices or nozzles. Table 5 shows the results 
obtained in atomizing butyl carbitol saturated with 
C0 2 at pressures of 600 psi at room temperature. It 
is evident that all the nozzles tested produced drop¬ 
lets considerably above the range of stable aerosols. 
Further tests were run in a settling chamber with the 
Olson bomb itself with results consistent with those 
reported here. 10 

34.4.2 Second Olson Device 11 

Another device, which might have been developed 
into a practical munition if the results had been more 
favorable, consisted of a bomb or shell filled with 
spray tubes. These tubes were thin-wall cylinders 
filled with the liquid agent and saturated with 
carbon dioxide at a high pressure. The tubes were to 
have several orifices on opposite sides at each end, so 
that upon burst of the munition, the tubes would 
spin end-for-end due to the recoil of the liquid leaving 
the tube. The spinning was to accomplish the follow¬ 
ing: (1) the centrifugal force would keep the liquid 
at the end of the tube so that it would empty com¬ 


Table 5. Atomization of butyl carbitol pressurized 
with carbon dioxide under 600 psi at room temper¬ 
ature. 


Nozzle Drop diameter 

No. Nozzle m 


1 

No. 27 hypodermic needle, .075 in. long, 



and beveled as received 

2 — 50 

2 

No. 27 hypodermic needle, .075 in. long, 



end ground square 

2 — 50 

3 

.0313 in. ID tube, 3 in. long 

5 — 75 

4 

Two tubes placed so thjit the streams 
would impinge on each other. Tubes 
were .0313 in. ID, .5000 in. long, and 
had an 0.014-in. diameter orifice in the 
end 



5 — 75 

5 

1-in. length of .0313in. ID tube, end square 

5 — 90 

6 

1-in. length of .0313 in. ID tube, end flared 



to .1250 in. at 20° 

5 — 90 

7 

Sharp-edged hole, .006-in. diameter, 



.0313 in. long 

5 — 90 

8 

Slit, .001-in. wide and .25 in. long 

5 — 90 

9 

Sharp-edged hole, .011-in. diameter, 



.0313 in. long 

8 — 100 

10 

Fan-type spray with a .025-in. diameter 



hole 

8— 100 

11 

Sharp-edged hole, .016 in. diameter, 



.0313 in. long 

10 — 125 

12 

Converging-diverging nozzle, divergence 
and size corresponding to a 5/0 dowel 



pin reamer 

20 — 300 


pletely; (2) there would be an increased shearing 
force with the air to atomize the liquid in addition 
to the atomization effect of the dissolved C0 2 ; (3) the 
aerosol would be so rapidly diluted at the source that 
agglomeration of the droplets would not take place. 

Preliminary tests 12 on this idea were made by 
ejecting a single tube 1% in. OD and 8 in. long from 
a bomb 1%6 in. ID and 16 in. long, filled with butyl 
carbitol under pressure of carbon dioxide. By means 
of a valve arrangement, the gas pressure could be in¬ 
creased until a frangible disk at the end of the bomb 
sheared at about 850 psi, releasing the tube and its 
contents. It was found that the tube actually spun 
end-for-end at a high velocity and was completely 
emptied in 3 to 5 sec. 

Further tests were made with a larger multiple- 
unit ejection bomb, 48 in. long and 5p6 in- OD. This 
bomb had a capacity of 21 spray tubes similar to that 
described above. The entire bomb was charged with 
14.3 lb of o-dichlorobenzene. Since the preliminary 
experiments showed that the bomb could not be used 
for setting up an aerosol, experiments were continued 
to determine if this device had any possibilities for 
dispersing mustard gas for antipersonnel purposes. 
Consequently, most of the tests were made with the 
simulant thickened with polymethyl methacrylate 


SECRET 











532 MUNITIONS FOR THE DISPERSAL OF LIQUID DROPLETS 


Table 6. Dispersion and distribution of o-dichlorobenzene from spinning tubes. 

Shoot No. 

1 

2 

3 

4 

5 

6 

Wind velocity (mph) 

7 

8 

10 

8.5 

2.5 

5 

Temperature (degrees C) 

4 

3 

0 

5 

5.5 

0 

Viscosity of simulant (poises) at 0 C 

1.25 

1.25 

1.25 

1.25 

1.70 

1.70 

CO 2 pressure, psia 

130 

110 

0 

• ••§ 

100 

70 

Wt of charging, g 

6,500 

6,500 

6,500 

6,500 

6,850 

6,500 

“Recovery” % 

79.2* 

89 

43.2J 

66.9|| 

92 

83.4** 

% of tube contents discharged 

100 

100 

0 

0 

100 

90 

Area contaminated 







>1.0 g/sq m and / , 

>1.0 mm diameter j s< * ^ 

450 

1,030 

135 

232 

355 

410 

Concentrations (g/sq m) 



Area contaminated sq yd 



>40 

0 

0 

0 

0 

46 

30 

>30 

25 

19 

2.5 

15 

72 

39 

>20 

70 

39 

16 

62 

136 

65 

>10 

160 

160 

70 

130 

205 

175 

>5 

395* 

295 

170 

215 

260 

320 

>2 

625* 

l,140f 

410 

550 

405 

440 

>1 

750* 

1,675 

560 

785 

740 

830 

>0.5 

860* 

2,370 

940 

1,185 

935 

109 

>0.25 





1,150 


Drop sizes (mm diameter) 



Wt per 

cent 



0 — 0.50 

22.7 

23.7 

37.7 

44.9 

24.2 

22.7 

0.50 — 0.75 

14.6 

15.2 

23.1 

23.8 

15.1 

14.3 

0.75 — 1.00 

22.9 

16.4 

22.3 

15.8 

16.5 

12.1 

1.00 — 1.20 

14.4 

12.1 

9.1 

6.4 

14.8 

16.4 

1.20 — 1.40 

10.4 

8.0 

4.8 - 

3.9 

5.3 

8.3 

1.40 — 1.60 

9.2 

7.6 

1.8 

2.6 

5.0 

10.9 

1.60 — 1.80 

2.1 

3.5 

0.6 

0.4 

7.8 

4.3 

1.80 — 2.00 

2.0 

5.1 

0.3 

0.1 

4.4 

1.9 

2.00 — 2.20 

0.6 

2.4 

0.3 

0.4 

2.2 

1.2 

2.20 — 2.38 

0.3 

3.4 


0.7 

2.6 

3.2 

2.38 — 2.53 

0.3 

1.4 


0.4 

1.0 

1.0 

>2.53 

0.6 

1.2 


0.5 

1.1 

3.8 


* These values are low since the contaminated area was not completely 
** Plus 3.1% remaining in the tubes bring this value to 86.5%. 

t Intermediate values were: 4 g per sq m 420 sq yd 
3 g per sq m 685 sq yd 

t Plus 29.6% remaining in the tubes bring this value to 72.8%. 

§ In this shoot the CO 2 was bubbled through the liquid on the outside < 
was in contact with the liquid for about 3^ min. 

|| Plus 29.6% remaining in the tubes bring this value to 96.5%. 

and dyed red with duPont Rhodamine. The liquid 
was saturated with carbon dioxide in an auxiliary 
bomb and transferred to the ejection bomb under 
pressure. The pressure was increased until the shear 
disk ruptured and the entire contents were thrown in 
the air to an altitude of 150 to 300 ft. The spray tubes 
were mostly discharged by the time they reached the 
peak of their flight. They were scattered over an area 
of 50 yd wide by 70 yd long. Two tests were made 
that varied from the above procedure. In one test the 
simulant was not saturated with carbon dioxide and, 
in the other, the simulant on the outside of the tubes 
was saturated with the gas after the tubes were filled. 
In both cases the tubes did not discharge the liquid 
contents. 


the tubes after they were filled. The final CO 2 pressure was 200 psi and 


The multiple-tube ejection bomb produced a spray 
from 100 microns to 3 mm in diameter, 75% of which 
was above 0.5 mm. More than 90% of the liquid dis¬ 
charged from the spray tubes was above 0.5 mm. The 
liquid between the tubes was atomized somewhat 
more, thus lowering the overall antipersonnel effi¬ 
ciency of the munition. A change of the simulant 
viscosity from 1.25 to 1.75 poises appeared to produce 
no change in the drop size; however, the lower the 
C0 2 pressure, the larger the drops came from the 
bomb. Table 6 shows the results of six tests run on 
this device. The degree of ground contamination and 
the area contaminated depended largely upon the 
wind velocity. Using 14.3 lb of simulant, in a 2.5- 
mph wind, 936 sq yd were contaminated with a 


SECRET 










LIQUIDS WITH DISSOLVED GASES UNDER PRESSURE 


533 


concentration greater than 0.5 g per sq m, and 410 
sq yd with a concentration greater than 1 g per sq m 
consisting of drops larger than 1.0 mm in diameter. 
In an 8-mph wind, the values were 1,675 sq yd and 
1,030 sq yd, respectively. The lowest C0 2 pressure 
which would completely discharge the spray tubes 
was about 85 psi at 0 C. 

It was concluded that the device is not effective 
for producing saturated aerosol clouds, but that it 
can be used to produce larger droplets that would 


have antipersonnel effects. The device is mechanically 
poor, and must be stored and transported while under 
high pressure. Once the munition is filled, the pres¬ 
sure varies greatly with the temperature. Therefore, 
the performance of a munition designed on this 
principle would also vary with the temperature. From 
a mechanical point of view, for antipersonnel effects 
and ground contamination, the airburst munition 
described in the previous section would have many 
advantages. 


SECRET 



Chapter 35 

MUNITIONS FOR THE DISPERSAL OF SOLID PARTICLES 

By H. F. Johnstone and H. C. Weingartner 


35.1 INTRODUCTION 

he existence of several solid chemical and 
bacteriological agents of extremely high toxicity 
suggests the use of these materials as warfare agents. 
Since the toxicity of these agents is greatest through 
pulmonary action, they are most effective when dis¬ 
persed as aerosols of particles sufficiently small to 
penetrate the nasal passages and reach and be re¬ 
tained by the alveoli of the lungs. These agents are, 
in general, odorless and difficult to detect in the 
dilute concentrations required to produce casualties. 
On the other hand, since the most effective particle 
sizes are easily removed by the gas mask filter, troops 
may have adequate protection by wearing the mask. 
The tactical use of these agents therefore requires 
instantaneous dispersion from a bomb or shell to set 
up an immediate dosage exceeding the lethal value 
before masks can be adjusted. The necessity for pro¬ 
viding a new munition designed specifically for the 
dispersion of these agents became apparent when it 
was found that the standard munitions for dispersing 
chemical agents were quite unsuitable. The dispersal 
of powdered agents from bursting or tail-ejection 
bombs and shells was ineffective because of the 
formation of large compacted particles. 1,2 Many of 
the agents are also subject to rapid detoxification 
even at moderate temperatures and, in some cases, 
it was found that an explosive shock would decrease 
or destroy the toxicity. These effects were present 
to a greater extent with aqueous solutions and sus¬ 
pensions than with dry powders. 

Laboratory techniques for the dispersal of these 
agents were developed while toxicities were being 
studied and compared. Best results were obtained by 
dispersing dilute solutions by means of a Benesh air- 
atomizing nozzle containing a baffle for removing the 
large droplets. 3 It was shown also that the dry pow¬ 
ders could be dispersed as essentially unitary par¬ 
ticles by means of a pneumatic nozzle. 4,5 Because of 
their complexity and the large quantities of air or gas 
required to effect the dispersion, these methods are 
unsuitable for incorporation into munitions for field 
use. From a practical standpoint, the objectives 
sought in the development of a suitable munition 
were: 


1. Development of a bursting munition for dis¬ 
persing dry powders by proper selection of the type 
and dimensions of the burster. 

2. Development of a base or tail-ejection bomb or 
shell which would exert little or no mechanical action 
on the dry powders. 

3. Development of a bursting munition for dis¬ 
persing solutions or suspensions of the agent without 
detoxification. 

The work in Division 10 NDRC was concerned 
mainly with the development of a munition for the 
dispersion of the protein agent designated as W. 
Early experiments indicated that this material was 
sensitive to heat and shock. Attention was given 
first, therefore, to a tail-ejection bomb using a com¬ 
pressed gas as propellant. In the field tests on this 
munition, comparisons were made with the dispersion 
obtained by high explosive. It was found that, with 
properly selected explosives, the detoxification of 
thick suspensions was not serious and that excellent 
dispersion could be obtained, suitable for field use 
because of the low concentration required at satura¬ 
tion. 

35.2 FUNDAMENTAL PRINCIPLES 

35 . 2.1 Impactability of Aerosol Particles 

The solid particles in an aerosol are made up largely 
of aggregates of smaller primary particles. A rela¬ 
tively small fraction of the mass of the material exists 
as unitary particles. The tendency of a particle to de¬ 
posit on a vertical surface depends on its diameter 
and density and the velocity with which it approaches 
the surface and on the size and shape of the surface. 
The measure of this tendency is called the im¬ 
pactability. 

Sell 6 has calculated the impactability of small dust 
particles on objects of various shapes and has found 
it to be a function of the dimensionless group. 


dup d 



where d is the diameter of the dust particle, p is its 
density, u is the velocity with which it approaches the 
object, D is a characteristic length of the object and p 



534 


SECRET 


FUNDAMENTAL PRINCIPLES 


535 


is the viscosity of air. Figure 1 shows Sell's curves for 
the impactability of particles on surfaces of various 
shapes. For small dust particles, the impactability 
is roughly proportional to the product of the density 
of the particle and the square of its diameter. It may 
be expected, therefore, that a large, loosely knit 
aggregate of low density and large diameter will be 
deposited to the same extent as a smaller and denser 
aggregate under the same conditions, as long as 
pid\ = pvd 2 2 . However, in passing through small chan¬ 
nels or through filters such as exist in the nasal pas¬ 
sages, the actual size of the particle is important in 



Figure 1 . The deposition of airborne particles on ver¬ 
tical surfaces. 


the removal and deposition from the air stream. 
Furthermore, the hygroscopicity of the particle must 
be a factor in the penetration of the nasal passages. 
Experiments at the University of Chicago Toxicity 
Laboratory show that approximately 50% of 6 mi¬ 
crons diameter droplets of oil will pass through the 
nose into the lungs when the breathing rate is 17 1pm. 
The penetration is less for aerosols of calcium phos¬ 
phate and sodium bicarbonate dust of the same size. 5 
The effect of flow rate is shown by the decreased 
penetration at 63 1pm which corresponds to rapid 
breathing. In this case 50% transmission is achieved 
only by 2-micron liquid droplets and by particles of 
less than 1 micron diameter in the case of sodium 
bicarbonate dust. The penetration decreases with in¬ 
creasing particle size until at 10 to 12 microns diame¬ 
ter the screening is complete. The density of the ag¬ 
gregates in these tests was in the range 1.0 to 1.4 
g per ml. 


The retention of dust particles by the lungs is also 
a function of the particle size and, at a breathing rate 
of 17 1pm, half of the 1.5 micron calcium phosphate 
dust particles was retained. There is an optimum par¬ 
ticle size, therefore, for penetration of the nasal pas¬ 
sages and retention by the lungs. It appears from 
these measurements that the desired range is between 
1.5 and 5 microns. 

35 . 2.2 Effective Toxicity of an Aerosol 

The effective toxicity of a particulate cloud depends 
upon the composition of the agent as well as upon the 
percentage of the material in the critical size range. 
The toxicity of the original charging is determined 
by the chemical and physical methods used in the 
preparation of the agent. The condition under which 
the agent is stored, the mode of functioning of the 
munition by which the agent is dispersed, and the 
behavior of the airborne particles from the point of 
burst are other important factors. 

The protein agent W was prepared by the Procter 
and Gamble Company by precipitation or by spray 
drying from aqueous solutions. The spray-dried ma¬ 
terial consisted of particles about 10 microns in 
diameter, which could be reduced to below 5 microns 
without detoxification by air micronizing. 7 

For the purpose of carrying out field tests on muni¬ 
tions, it was desirable to have a simulant which pos¬ 
sessed somewhat the same properties as the toxic 
protein. Egg albumin was most suitable, since it is 
also denatured by heating. Albumin powder with a 
mass median diameter [MMD] less than 4 microns 
was prepared by the duPont Company by ball¬ 
milling a suspension of the solid in organic liquids, or 
by micronizing in air. All of the ball-milled samples 
were seriously denatured as shown by the low solu¬ 
bility in water. Hammer-milling caused less dena- 
turation, but was unsuccessful in reducing the particle 
size below 15 microns MMD. 8 

35 . 2.3 Dispersibility of Powders 

It is well known that some powders are more easily 
dispersed than others. Experiments made at the 
Munitions Development Laboratory [MDL] using 
several types of very finely divided pigment powders 
showed that those materials, consisting of primary 
particles less than 0.1 micron diameter, could not be 
dispersed as unitary particles by any of the methods 
suggested above. The difficulty was apparently due 


SECRET 












536 


DISPERSAL OF SOLID PARTICLES 


to the high contact surface area which required more 
energy for dispersion than was available from an air 
jet or from an explosive charge. Good dispersibility 
is often associated with powders having a high poros¬ 
ity or free state. 9 The most easily dispersed albumin 
sample tested contained nearly uniform particles of 
about 6 microns and had a low bulk density. 2 It is of 
interest to note that the “dustiness” of a powder of 
this sort apparently bears no relationship to its 
dispersibility. 

Attempts were made to lower the cohesive forces 
between the particles by coating with surface active 
agents. 8 It was found that albumin and zinc oxide 
powders treated with diglycol laurate were more 
efficiently dispersed by small explosive munitions 
than the untreated powders. This treatment, how¬ 
ever, did not improve the dispersion of albumin 
powder by gas-ejection bombs, but actually decreased 
the dispersibility. There was some indication that 
treatment of the powder with soya lecithin improved 
the dispersion of zinc oxide but not that of albumin. 
Other surface active agents which affected the dis¬ 
persibilities were fatty acid esters, polyhydric alco¬ 
hols, octadecylamine hydrochloride, and micro silica 
dust. 

The dispersibilities of W and egg albumin powders 
were markedly influenced by their moisture contents. 
It appears necessary to maintain the moisture con¬ 
tent less than 1% in order to get the best dispersion. 10 
Since the protein material is hygroscopic, the humid¬ 
ity of the atmosphere in which it is prepared and into 
which it is dispersed is an important factor in deter¬ 
mining the ultimate nature of the aerosol particles. 

The existence of aggregates in the aerosol clouds 
depends upon the form of the agent in the munition 
as well as on the type of munition and, to some ex¬ 
tent, on the concentration of the initial cloud. Ag¬ 
gregates from the dispersal of dry powders are, in 
general, large and fleecy, whereas those from the dis¬ 
persal of thick suspensions of the powder in an inert 
liquid are apt to be smaller and more firmly bound. 
There is experimental evidence to show that aggre¬ 
gates exist due both to failure to separate the primary 
particles and to coagulation due to high initial con¬ 
centrations. 2 The agent compartment of a gas-ejec¬ 
tion bomb was divided into two compartments, one 
filled with dyed albumin and the other with undyed 
albumin powder. Examination of the airborne par¬ 
ticles after the dispersion showed aggregates com¬ 
posed solely of dyed and solely of undyed particles, 
as well as aggregates of mixed color. Furthermore, 


densely aggregated single-colored nuclei with fringes 
of lightly held particles of both colors were found. 


35 . 2.4 Concentration in Aerosol Clouds 11 

The travel of aerosol clouds in the air and the 
dosages downwind from the point of dispersion may 
be estimated by means of the British diffusion 
theory 12 corrected for losses by vertical and hori¬ 
zontal deposition. The concentration-time product F 
resulting from the passage of an aerosol cloud gener¬ 
ated at a line source in open country is given by the 
equation 


F = 


q ~f 


Fvdx 


( 1 ) 


Bux m/2 

where q is the source strength; 

v is the settling velocity of the particles; 
x is the distance downwind from the source; 

B and m are meteorological constants; 
u is the wind speed. 

After differentiation with respect to x and separa¬ 
tion of the variables this becomes 


dF _ / v | m \ 
~ Y ~ \Bux m/2 + 2x) 


dx 


Upon integration, equation (2) becomes 
K 


As d 


F = 


0, v 


- l /( Bux mli ) • (dx) /(I - m/2) 


m /2 


( 2 ) 


(3) 


—> 0, and 

-1 /( Burma ) . (dx) /(1 


m / 2 ) 


from which it is evident that 


K = 


Bu 

Let the aerosol dosage F be expressed by 

F = Ctf, (4) 

where Ct is the concentration-time product of a gas 
cloud of the same source emission as the aerosol cloud, 
and / is the fraction of the agent remaining airborne 
at any distance. Then f is given by 

j _ g — l /( Bux ml2 ) • (dx) /(1 — m / 2 ) ^ 

The term, 1/Bux m/2 , is equal to the gas cloud Ct for 
an emission of 1 g per cm of line source. The settling 
velocity of small aerosol particles in still air by 
Stokes’ law is 


pd 2 


3.40 X 10- 


(6) 


when all the quantities are in cgs units. 


SECRET 






TESTING OF MUNITIONS 


537 


If the quantities are expressed in the more familiar 
units for use with the gas concentration slide rule, 12 
equation (5) becomes 

j _ 3.25/10* *(p<i 2 )/(l — m/2) -Ct g x ^ 

where p = density of the aerosol material, g per cu m; 
d = drop or particle diameter, microns; 
x = distance downwind from the line source, 
yards; 

Ct g = gas cloud Ct for an emission from a line 
source of 1 lb per yd, mg-min per cu m; 
m = 2/[l + (log ft)/(log R + log 2)]; 

R = (u at 2 m )/{u at 1 m); 
u = wind speed. 

In equation (4), Ct may be used in any convenient 
units and F will be given in the same units since / is 
dimensionless. 

For aerosol particles larger than about 5 microns 
the evaluation of the constant K cannot be accom¬ 
plished in this simple manner. In actuality, the condi¬ 
tions deviate from the theoretical at a point near the 
source. In equation (7), as x — > 0, Ct g —>■ oo. The 
result is that the deposition within a short distance 
from the source, according to the equation, is rela¬ 
tively large but actually the aerosol cloud may not 
touch the ground until it is several yards from the 
source. In this work it has been assumed that the 
value of f at 10 yd is unity, and that the value of / at 
any distance x is that calculated from equation (7) 
divided by the value at 10 yd. This is somewhat 
arbitrary and may have to be modified when more 
information becomes available. 

The magnitude of the correction factor / has been 
determined for a liquid with a density of 1.0 g per 
cu m, drop diameters of 0.8, 8.0,12.0, and 24 microns, 
and for the atmospheric conditions corresponding to 
a sunny day (R = 1.05) with a moderate wind (u = 
5 mph), and a clear night (R = 1.25) with a low 
wind (u = 2 mph). 13 The values are given in Table 1. 


35.3 TESTING OF MUNITIONS 

35.3.1 Explosion Chamber 

It is frequently convenient to carry out tests on 
small aerosol munitions by functioning them inside 
a large closed room. Animals may be exposed within 
the room, and samples taken of the aerosol at various 
points to determine the variation of concentration 
and particle size with time. The concentration-time 
relationship may be obtained by drawing the aerosol 
through a suitable filter and determining the half- 
life of the aerosol. 



HALF LIFE IN MINUTES 


Figure 2. Limits of the half-life of a particulate cloud 
for settling in a closed room, in still air, and in turbulent 
air.. 

Another method of determining the settling rate, or 
the concentration-time relationship, is by means of 
pie plates exposed for fixed intervals of time during 
the settling. A differential pie plate settler was con¬ 
structed for this purpose in testing the munitions 
developed at the MDL. 14 

The MMD of equivalent spherical particles may be 
determined directly from the half-life of the aerosol. It 
makes no difference whether the air is still or if there 
are drafts or thermal currents, provided there is no 


Table 1 . Value of the correction factor/for deposition of aerosol clouds under two atmospheric conditions. 

(p = 1.0 g/cm 3 ) 


Distance 

downwind 

yd 

0.8 m 

II 

© 

Oi 

u = 5 mph 

24m 

0.8m 

R = 1.25, 

u = 2 mph 

24m 

Drop diameter 

8m 12m 

Drop diameter 

8m 12m 

100 

>0.99 

0.98 

0.96 

0.85 

>0.99 

0.89 

0.76 

0.32 

500 

>0.99 

0.96 

0.94 

0.78 

>0.99 

0.83 

0.64 

0.16 

1,000 

>0.99 

0.96 

0.93 

0.74 

>0.99 

0.78 

0.58 

0.11 

5,000 

>0.99 

0.95 

0.90 

0.65 

>0.99 

0.69 

0.42 

0.03 

10,000 

>0.99 

0.95 

0.88 

0.59 

>0.99 

0.63 

0.37 

0.02 


SECRET 





















































538 


DISPERSAL OF SOLID PARTICLES 


serious leakage of aerosol from the room. Figure 2 
shows the limits of the half-life of particulate clouds 
in which the particles have a density of 2, and for a 
room height of 15 ft. This chart may be used for 
rooms of different heights and for materials of dif¬ 
ferent densities by observing that the half-life of the 
cloud is proportional to the height of the room in 
which it is dispersed, and is inversely proportional 
to the density of the particles. The two lines show the 
variation in half-life caused by assuming both tur¬ 
bulent and quiescent settling and the extreme particle 
size distribution. Midway between the two lines lies 
the most probable case of normal particle distribution 
in turbulent settling. Although the density of the ag¬ 
gregates is often hard to evaluate to obtain an abso¬ 
lute answer, valid comparisons with the same filling 
dispersed in different ways are nevertheless possible. 

For a cloud of uniform particles the settling data 
plotted as the logarithm of the fraction of the ini¬ 
tial airborne charge against time is a straight line, 
of which the slope is proportional to the particle 
density and to the square of the particle diameter. 
It may be inferred, therefore, that a straight line 
settling curve implies the existence of particles of 
uniform deposition or impaction characteristics; 
whereas a curved line implies the existence of non- 
uniform particles. The smallest slope is associated 
with particles least likely to deposit by impaction. 

The characterization of aerosols by optical methods 
has been extensively studied at Columbia Univer¬ 
sity. 4 A statistical diameter suitable for comparison 
can be obtained from the scattering power of a de¬ 
posit of the aerosol which has been allowed to settle 
upon a clean glass slide. For use in the laboratory, 
this method yields information on the rate of settling, 
particle density, refractive index, and size distribu¬ 
tion of any aerosol. 

Some further indication of the impactability of 
aerosol particles is obtained by the use of the cascade 
impactor, a sampling device in which air is drawn 
through a series of four orifices of decreasing cross- 
sectional area; after each orifice the air impinges upon 
coated slides. 15 The larger particles impact upon the 
slide in the low-velocity chamber. As the impinging 
velocity is increased by decreasing the orifice size, 
the smaller particles are collected. A representative 
diameter may be determined by comparing a chemi¬ 
cal analysis of the mass of agent collected on each of 
the four slides with a calibration of the instrument. 
The calibration must be performed with a material 
having aggregate densities similar to those of the 


sample, otherwise the variation in aggregate density 
will obscure the true diameter determination. 

The average equivalent diameters determined from 
relative impactability measurements must be supple¬ 
mented by measurement of the actual dimensions of 
the airborne particles. This is done by microscopic 
examination of the cascade impactor slides, or sticky 
rods, slides, and other objects upon which the aerosol 
particles are collected. 2 The data are expressed as the 
distribution of mass within the limits of particle size. 
A sample may be characterized by its MMD. This 
diameter is usually approximated by the diameter 
corresponding to % 2 nd 3 . Refinements in this ap¬ 
proximation have been made at the University of 
Chicago Toxicity Laboratory in which corrections 
are made for nonsphericity and variations in density, 16 
Since the particles and aggregates found on an im¬ 
pactor slide are not spherical and are of varying 
density, the mean diameter from the summation may 
be plotted against the cumulative per cent of the 
mass determined analytically on each slide and the 
value corresponding to 50% of the mass is deter¬ 
mined. This is called the VMMD and is a closer ap¬ 
proach to the true MMD. 17 

The size distribution of a sample of agent, as 
charged to the munition, is found by the microscopic 
examination of the agent dispersed in a fluid and 
spread upon a slide. A small sample of the powder is 
dispersed in a mobile liquid (butanol) by stirring 
mechanically at a high speed. The dispersion is 
stabilized by the addition of a thickening agent such 
as Canada balsam, and a small amount of the suspen¬ 
sion is spread in a thin film between a clean slide and 
a cover glass. A representative area is then scanned 
to observe a sufficient number of particles (500 to 
5,000) to evaluate properly the median diameter. 
Because the mass of a single large particle may be 
equivalent to thousands of smaller ones, care must be 
taken to observe a truly representative group of 
particles. 14 

35.3.2 Field Assessment of Munitions 

In field trials, the relative impactability of the 
aerosol is determined from downwind total dosage 
samplers. These may be filters or impingers. The 
latter are samplers into which the aerosol is drawn 
through a horizontal tube facing upwind and trapped 
in a suitable inert liquid. The dosage is expressed as 
the concentration-time product [ Ct ]. The perform¬ 
ance of munitions in dispersing solid agents may be 


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DEVELOPMENT OF MUNITIONS 


539 


compared by the standard dispersal figure [SDF], 
which is the actual cross wind integrated Ct expressed 
as a percentage of the ideal gas cross wind integrated 
Ct as computed by means of the British gas slide rule. 
This figure is suitable only for similar field trials. 

The field assessment of particle size distribution is 
performed, as described above, by using cascade im- 
pactors and impinging surfaces for microscopic ex¬ 
amination. The sampling rates for cascade impactors, 
filters, and liquid impingers are adjusted as nearly as 
possible to provide isokinetic sampling conditions. 
The overall criterion in selecting an agent-munition 
combination is based upon the quantity of effectively 
dispersed active agent which can be applied by a 
single aircraft. This involves adjusting the dimen¬ 
sions of the munition to the munition performance 
and to the bomb-carrying equipment in the aircraft 
to get the maximum effective use of the aircraft as 
well as of the agent. 

35.4 DEVELOPMENT OF MUNITIONS 
35 . 4 .] British Work 

Most of the early work on the dispersion of solid 
powders as particulate aerosols was done by the 
British. 18 - 19 The bombs used were, for the most part, 
experimental modifications of the British 30-lb LC 
Mk 1 chemical bomb which had a 2-lb, 12-oz burster 
of 50/50 Amatol cast into the nose, and a capacity of 
22 1. The modifications of this bomb, made for dis¬ 
persing solutions and suspensions of the solid agents, 
were as follows. 

1. The Day bomb which contained a small axial 
TNT burster of the type used in the standard 250-lb 
LC bomb. The case for the 30-lb bomb was cut off to 
about one-half the original length so as to fit the 
length of the burster. The chemical charging was 
thus entirely in the annular space. 

2. The Double-Day bomb, forwhich the bursterwas 
twice the length of the standard burster for the 
250-lb LC bomb and was approximately as long as 
the 30-lb bomb itself. The burster contained 917 g of 
TNT. 

3. The Whytlaw-Gray bomb which contained a 
much heavier burster of 7 lb 12 oz TNT extending 
the full length of the 30-lb LC bomb, leaving only a 
small annular space for the chemical charging. 

No attempt was made to disperse solid powders 
with these high-explosive bombs. A series of field 
trials, made at Porton Experimental Station in 1942 


with aqueous solutions of W and suspensions in car¬ 
bon tetrachloride, showed that lethal dosages could 
be set up by a single small bomb. The dispersion 
efficiency, however, was quite low, amounting to 
about 20% when the HE/chemical ratio was 0.2, fall¬ 
ing to about 5% when the ratio was 0.5, and to 0.6% 
when the ratio was 1.5. The loss of activity with large 
amounts of explosives was partly due to the destruc¬ 
tion of the poison. Since it was noted that the initial 
explosion was followed by a secondary flash, it was 
presumed that at least part of the destruction of the 
agent was due to inflammation. 

35 . 4.2 Development of the Gas- 
Ejection Bomb 20 - 21 

The possibility of dispersing the dry powder by 
means of gas ejection, in order to avoid the mechani¬ 
cal shock and thermal detoxification of the most 
sensitive agents, was explored at the MDL. The gas- 
ejection principle involved the introduction of the 
gas from a suitable reservoir under high pressure 
into a compartment containing the powdered agent 
until sufficient pressure was built up to rupture a 
shear diaphragm, thus releasing the gas-agent mix¬ 
ture. The dimensions of the initial cloud could be 
controlled by the use of a suitable deflector on the 
tail of the bomb. Without a deflector, the bomb 
formed a cloud 30 to 40 ft high, whereas, with a de¬ 
flector, the initial cloud was not more than 12 to 15 ft 
high. 

In the early experiments on this type of bomb, the 
gas was introduced slowly into the agent compart¬ 
ment with the expectation that the solid would be¬ 
come aerated and thus more easily dispersed. Re¬ 
lease pressures below 400 to 500 psi gave poor dis¬ 
persions, while pressures about 600 psi gave excellent 
dispersions of egg albumin suspensions. 

This method of dispersing dry powders was also 
used for dispersing small quantities of toxic materials 
in the laboratory. 3 - 4 Here it was found that increas¬ 
ing the release pressure up to 1,500 psi would improve 
the results, but for practical purposes the limitations 
of the weight of metal for the gas reservoir limited the 
pressure to 600 psi. 

In later work at the MDL, the time of aeration of 
the solid was redrfced until finally a double-com¬ 
partment bomb was used in which the gas was re¬ 
leased instantaneously into the agent compartment 
by the rupture of another shear disk, separating the 
two compartments. This disk ruptured at a higher 


SECRET 



540 DISPERSAL OF SOLID PARTICLES 




Table 2. Chamber tests on munitions for dispersing solid particles. 



Run 

No. 

Albumin 

sample 

SP 

Weight 

of 

charge 

g 

Modification of bomb 

Ratio exit 

area to Release 

Diffuser area of pressure 

tube bomb Deflector lb/sq in. 

Cylinder 
pressure 
lb/sq in. 

Per 
5 min 

cent airborne* 

11 min 28 min 

C-39 

167DC 

390 

No 

1 

A C0> Bomb 

No 

600 


70 

40 

11 

038 


325 

Yes 

1 

No 

600 


86 

54 

19 

040 

170B 

255 

No 

1 

No 

600 


40 

30 

14 

042 

170B 

265 

No 

£2 

4 orifices 

600 


30 

19 

7 

044 

170C 

265 

No 

1 

No 

600 


53 

35 

13 

045 

170C 

280 

No 

1 

Conical 

60 


38 

26 

9 

047 

170C 

295 

No 

1 

No 

600 


50 

34 

11.5 

048 

170C 

325 

No 

1 

No 

20 


40 

29 

11.5 

049 

170C 

345 

No 

1 

8 

Pointed conical 

20 


43 

28 

16 

052 

170C 

355 

No 

1 

8 

Conical 

20 


26 

19 

6 

053 

170C 

310 

No 

1 

8 

Flat 

20 


40 

30 

11 

043 

172 (yeast) 195 

No 

1 

No 

600 


20 

11 

3 

059 

174 A 

342 

No 

1 

No 

600 


41 

20 

5.5 

060 

174B 

315 

Yes 

1 

No 

600 


48 

31 

13 

061 

174B 

325 

No 

1 

No 

600 


29 

15 

2.5 

062 

174 A 

300 

Yes 

1 

No 

600 


15 

7.5 

2.5 

063 

174 A 

330 

No 

1 

No 

600 


25 

18 

6 

064 

174 A 

330 

Yes 

1 

No 

600 


40 

30 

9 

065 

174B 

300 

Yes 

1 

No 

600 


50 

35 

14 

066 

174B 

330 

No 

1 

No 

600 


60 

36 

16 

067f 

174B 

290 

YesJ 

1 

No 

600 


60 

46 

20 

068 

174B 

290 

YesJ 

1 

No 

600 


65 

50 

21 

069 

174B 

320 

No 

1 

No 

600 


70 

50 

18 

070 

174B 

320 

No 

1 

No 

600 


70 

52 

20 

071 

174B 

140 

No 

1 

No 

600 


60 

40 

18 

072 

174B 

213 

No 

1 

No 

600 


75 

52 

23 

073 

175A 

320 

No 

1 

No 

600 


50 

36 

15 

074 

175B 

300 

No 

1 

No 

600 


30 

19 

12 

CA-3 

170 A 

210 


1 

B Air Bomb 

No 

405 

4,100 

35 

11 

2.5 

CA-4 

170 A 

210 


* 

No 

270 

2,100 

41 

14 

2 

CA-5 

170A 

210 


1 

8 

No 

135 

1,200 

17 

7 

2 

CA-7 

170 A 

240 


1 

4 orifices 

280 

2,100 

28 

18 

5 

CA-13 

170C 

215 


its 

Flat 

60 

3,000 

16 

12 

6.5 

CA-20 

170C 

268 


IS 

Pointed 

300 

3,500 

26 

11 

5 

CA-21 

170C 

270 


it 

No 

400 

3,500 

9.5 

5 

1 

CA-22 

170C 

267 


1 

8 

No 

400 

3,500 

24 

16 

5 

CA-23 

170C 

269 


1 

No 

600 

3,500 

19 

12 

4 

CA-24 

170C 

275 


1 

No 

800 

4,000 

25 

18 

6.5 

CA-30 

170C 

415 


1 

4 

Flat 

200 

3,200 

21 

16 

7 

CA-33 

174 A 

350 


1 

Perforated cap 

400 

4,000 

10.5 

14 

5.4 

CA-34 

174 A 

310 


1 

Perforated cap 

400 

4,000 

40 

27 

8.5 

CA-35 

174 A 

350 


1 

Perforated cap 

400 

4,000 

18 

12 

4.8 

CA-36 

174 A 

310 


1 

Perforated cap 

400 

5,000 

18 

14 

6.7 

CA-37 

174 A 

315 


i 

Perforated cap 

400 

5,000 

25 

21 

11.5 

CA-40 

174 A 

325 


i 

Perforated cap 

500 

4,400 

44 

25 

7.7 

CA-41 

174 A 

325 



Perforated cap 

500 

4,400 

16 

8 

2 

CA-42 

174 A 

320 


i 

Perforated cap 

500 

5,000 

45 

28 

8 

CA-43 

174 A 

320 


i 

Perforated cap 

500 

5,000 

25 

14 

5 

CA-44 

174 A 

330 


i 

Perforated cap 

500 

5,000 

38 

25 

11 

CA-45 

174B 

330 

v • • 

1 

Perforated cap 

500 

5,000 

37 

23 

8 


* From best curves (on log C vs t plot) drawn through concentrations determined by filters at 4 to 8 min, 9 to 15 min, 16 to 24 min, and 25 to 
35 min Two samples were taken simultaneously at 8-ft level at two points in room, at 25 1pm. Uniform concentration of cloud in the room was 
assumed. 

t Beginning with run C-67 leaks from the room were sealed. The percentage of the charge airborne at 28 min was noticeably increased. No CA runs 
were made after this time. 

$ Diffuser 8 in. long with 40 holes about inf in. in diameter. 


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DEVELOPMENT OF MUNITIONS 


541 


Table 2 ( Continued) 


Run 

No. 


1 

2 


Modification of bomb _ 

Weight Ratio exit 

Albumin of area to Release Cylinder 

sample • charge Diffuser area of pressure pressure Per cent airborne 

SP g tube bomb Deflector lb/sq in. lb/sq in. 5 min 11 min 28 min 

C 4~lb LC Canadian Bomb § 

1G7DC 770 .... .... .... .... .... 34 27 16 

170A 645 _ _ _ .... _ 30 24 15 


MW-3D “W” 298 

470- 
BM-199 


MW-3C “W” 508 

470- 
BM-199 


W3 “W” 

470- 
BM-199 


D Tests in Firing Pit at Dugway Proving Ground 10 
Cardox C0 2 unit 
1 No 600 

« 

Experimental air bomb 
1 No 800 


4-lb LC Canadian bomb 


10 


12 


18 


6.5 3.5 


7.5 3.5 


10 4 


§ Fired in room 30X100X15 ft with bomb suspended 6 ft off floor. 

Table 3. Powdered egg albumins used in tests on dispersal efficiency of bombs at Munitions Development Laboratory 
supplied by the duPont Company. 8 





Particle 

size distribution 






Per cent by weight 


Median dispersibility 

Designation 


below diameter 


Wt 

in gas- 

of albumin 

Preparation 

2m 

5m 

10m 

20m 

diameter ejection bombs 

SP-150 

Pebble milled 48 hr in ASK,* untreated, micro- 








pulverized 

3 

27 

56 

100 

8.7 

Good 

SP-152 

Steel ball milled 48 hr in ASK, untreated, micro- 








pulverized 

3 

34 

76 

100 

6.6 

Good 

SP-154 

As above but treated 1% diglycol laurate 

2 

30 

76 

100 

6.8 

Bad 

SP-156A 

Steel ball milled 72 hr, untreated, micronized, 








cyclone collected 

2 

39 

88 

100 

5.7 

Poor 

SP-158X 

Steel ball milled 96 hr, treated %% soya lecithin, 








micronized 3 times, products combined 

8 

70 

100 

. . • 

4.0 

Bad 

SP-167DC 

Steel ball milled 48 hr, untreated, micronized for 








4 times, cyclone collected 

1 

37 

98 

100 

6.0 

Excellent 

SP-170A ] 


12 

71 

98 

100 

3.8 

Very poor 

SP-170B \ 

Steel ball milled 96 hr in ASK and micronized 

50 

100 



2.0 

Excellent 

SP-170C J 


18 

76 

100 


3.4 

Good 

SP-172 

Yeast, micronized (one pass only) 

50 

100 

. . . 

• • • 

2.0 

Pooi- 

SP-174A 

Same as SP-167DC 

30 

100 

. . . 

• . . 

2.5 

Excellent 

SP-174B 

Same as SP-167DC 

30 

100 



2.5 

Excellent 

* Atlantic Safety Kleen — naphtha and chlorinated hydrocarbons. 







Table 4. Comparison of gas-ejection bombs and plastic bombs based on dispersion and stowage efficiency. 


No. of 



Per cent 

Weierht (fD Wt agent 

Wt agent 


Wt bombs Wt 


Wt 

airborne 

airborne 

Total wt 

500-lb 


empty per 500-lb filling 


agent 

at 

at 

bomb 

cluster 

Bomb 

g cluster g 


g 

50 min* 

50 min* 

g/g 

g 

Gas-ejection 2,400 38 350 


350 

4.12 

14.4 

0.128 

13,400 

Plastic 








55% albumin in acetone 450 110 350 


193 

4.70 

9.07 

0.241 

21,250 

Plastic 








35% albumin in CC1 4 450 110 483 


170 

3.2 

5.43 

0.183 

18,700 

* These two columns are comparisons based upon average tests using egg albumin in a static chamber. 


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542 


DISPERSAL OF SOLID PARTICLES 


pressure than the end disk so that the contents of 
the bomb were discharged immediately. Assessment 
of the resulting clouds from the two methods showed 
that they were essentially*the same, and the later 
design was adopted as being more suitable for con¬ 
taining the agent. 

The Cardox Bomb 

A device operating on somewhat the same principle 
as the gas-ejection bomb has been used for mining 
coal for several years. This is produced by the Cardox 
Corporation of Chicago, Illinois. It consists essentially 
of a chamber containing liquid carbon dioxide, which 
is vaporized by means of an electrically ignited heater 
cartridge. The energy of the gas released by means of 
the shear disk is utilized for breaking down coal for 
mining. The heater element contains a mixture of 
potassium perchlorate and carbon. 



10 


Figure 3. Gas-ejection bomb with liquid CCb cylinder. 

Through the cooperation of the Cardox Corpora¬ 
tion, development was made of a gas-ejection bomb 
using liquid carbon dioxide. The prototype model is 
shown in Figure 3. The liquid carbon dioxide and the 
heater element are contained in the carbon dioxide 
cylinder (9) and secured by the shear disk ( 8 ) and the 
fluted screw plug ( 6 ). This was screwed into the nose 
assembly (3) containing the firing pin (4), the piston 
spring (5), and a direct-acting fuze ( 2 ). This entire 
assembly fitted into the nose of the outer case ( 1 ) con¬ 
taining tail vanes and a shear disk held in place by 
the deflecting surfaces shown. Upon functioning, the 
heater was ignited by a primer initiated by the action 
of the firing pin. The expanding gas flowed through 
the six holes in the nose assembly (3) into the 
agent compartment and finally issued from the bomb 
tail, dispersing the agent into a cloud shaped by the 
deflectors. 

The optimum carbon dioxide charge to give proper 
functioning was found to be about 110 g. This re¬ 


quired a 10 -g heater cartridge and would disperse 
300 to 400 g of the powdered agent. 

The Air Bomb 

A study was made of the thermodynamics involved 
in the operation of the bomb using various liquefied 
gases, such as NH 3 , C0 2 , S0 2 , HCN, H 2 S, Cl 2 , CS 2 , 
and CH 3 CI . 22 It was assumed that the bomb might 
be used at temperatures from — 40 F to 150 F, and 
that it should provide a pressure of 600 psi at the 
release of the second shear disk. For such a tempera¬ 
ture range, it was evident that any of these propel¬ 
lants would give a wide variation in pressure in the 
gas compartment. Furthermore, at the higher ambi¬ 
ent temperatures, because of the excess heat available 
from the heater cartridge designed for functioning at 
low temperatures, the gas would enter the agent 
compartment with considerable superheat, and the 
particles might attain an instantaneous temperature 
of 500 F or more. 

Calculations were also made to determine the 
feasibility of using compressed air for the propulsion 
gas. It was concluded that satisfactory operation 
could be obtained with a pressure of not more than 
2,500 psi at — 40 F and 4,500 psi at 150 F. The func¬ 
tioning of this bomb is similar to that of the C0 2 
bomb, except that the firing pin merely punctures the 
retaining shear disk, permitting the escape of the 
compressed air. The outer case is the same for the 
two bombs and is similar in size to the M-69 and 
M-74 incendiary bombs so that the final munition 
can be clustered in the same cluster adapter as is 
used for these bombs. 

35.4.3 Dispersion Tests with the Gas- 
Ejection Bomb 

The results of several tests on the C0 2 bomb in a 
dispersion chamber are shown in Table 2 . Data on 
the dispersion of the same material in the Canadian 
4-lb light-case land mine are included for comparison. 
Table 3 shows the character of the egg albumin 
powder used in these tests. The airborne particles in 
every case consisted of large flaky aggregates and 
smaller three-dimensional aggregates formed by 
coagulation of primary particles at high concentra¬ 
tion. It was found that the method of preparation of 
the powdered agent was quite important. In general, 
the most finely divided powders were the most diffi¬ 
cult to disperse, but this was not always the case. The 
finely powdered albumin samples SP-170B gave 


SECRET 






FIELD TESTS ON MUNITIONS 


543 


good dispersibility in the C0 2 unit, but yeast of equal 
fineness was much more difficult to disperse. The 
albumin SP-167DC was the easiest powder to dis¬ 
perse and had an MMD of 6 microns. This was a 
relatively homogeneous sample with the over- and 
undersize materials removed in a classifier. 

Field trials at Dugway Proving Ground 23 showed 
that the coagulation of the particles at high concen¬ 
tration was most extensive in the center and more 
concentrated portion of the cloud, and that, when the 
cloud was produced from a group of bombs fired suc¬ 
cessively in a slow ripple manner, the coagulation was 
less than from a similar group of bombs fired simul¬ 
taneously. The simultaneous functioning of two 
groups of five of the air units, each containing 350 g of 
dry albumin, is shown 21 in Figure 4. Ground loss in 
the immediate vicinity of the bombs was negligible, 
but some albumin was observed to have been de¬ 
posited on the grass and on the vegetation as the 
cloud swept by. 

The Dugway results showed that neither the air 
bomb nor the C0 2 bomb denatures W. The Canadian 
4-lb LC bomb also gave little or no denaturation. 10 
This bomb produced aerosol clouds similar to those 
from the gas-ejection bomb but gave a greater ground 
loss of the agent, due to the force of the explosion. 

35.4.4 Development of the Plastic 
Bomb 24 

The possibility of using the lightweight plastic 
bomb, described in Chapter 34, for the dispersion of 
volatile suspensions of W was suggested when it was 
shown in field tests that dry W was not as easily de¬ 
natured as had been expected. Preliminary tests at 
Dugway Proving Ground 10 showed that suspensions 
of W in carbon tetrachloride could be dispersed with¬ 
out denaturation, if a nitroguanidine burster was 
used. A laboratory study of the factors involved in the 
dispersion of powder suspensions in liquids was made, 
using egg albumin as a simulant. It was found that 
the more concentrated the suspension was, the better 
the dispersion obtained, up to a concentration just 
sufficient to wet each particle. Of a number of organic 
liquids used for the suspension, acetone and carbon 
tetrachloride gave the best results, and hexane and 
chloroform were somewhat poorer. The texture, 
fluidity, and appearance of these suspensions varied 
with the liquids used. For example, 40% albumin in 
carbon tetrachloride is much less fluid than 55% in 
acetone. The desirable physical properties of a liquid 


to give good dispersion are high volatility, low viscos¬ 
ity, low density, and, possibly, low surface tension. 

The nitroguanidine bursters used in the plastic 
bomb varied from % in. to % in. diameter. Better 
dispersion efficiencies were obtained with the larger 
bursters. An attempt was made to increase the weight 
of the explosives in the burster by consolidating the 
nitroguanidine under pressure. This led to erratic 
initiation and low-order detonation of the bursters. 
When it was discovered thajt Pentolite bursters also 
did not seriously denature W, it was decided to use 
this explosive in the field tests on the bombs. 

Table 4 shows a comparison between the plastic 
bomb and the gas-ejection bomb on the basis of 
weight, dispersion efficiency, and stowage. The best 
overall efficiency is given by the plastic bomb filled 
with a concentrated acetone suspension. The air¬ 
borne particles dispersed from suspensions in the 
plastic bomb consisted of rather firmly bound ag¬ 
gregates, generally smaller than those from the gas- 
ejection bomb. Microscopic examination of the aero¬ 
sol particles showed that there were many more 
unitary particles from a suspension than from the dry 
powders. 

35.5 FIELD TESTS ON MUNITIONS 

A series of field tests was made in the Spring of 
1945 at the Canadian Field Experimental Station at 
Suffield, Alberta, to compare the dispersion of several 
dry agents and suspensions in the various munitions 
which have been described with those from British 
munitions developed for the same purpose. 17 - 25 

Duplicate layout tests were performed to compare: 

1. The dispersion of dry W from the gas-ejection 
bomb (air unit) with that from the Suffield 4-lb LC 
bomb, both fired statically. 

2 . The dispersion of 35% suspensions of W in 
CC1 4 from the plastic bomb with that from the SPD 
Mk 1 (Porton Type F) HE/chemical bomb, both 
fired statically. 

3. The dispersion of spray-dried, air-ground W 
from the gas-ejection bomb (air unit) with that from 
the Suffield 4-lb LC bombs, both bombs being 
launched from inverted mortars at their estimated 
terminal velocities. 

4. The dispersion of 35% suspensions of W in 
CCL from the plastic bomb with that from the (Type- 
F) HE/chemical bomb, both bombs being launched 
from inverted mortars at their estimated terminal 
velocities. 


SECRET 



544 


DISPERSAL OF SOLID PARTICLES 




2 SEC 


4 SEC 


6 SEC 


12 SEC 


30 SEC 


1 SEC 


SHOOT 
NO. 3 
7 MPH 
1.13 

SLIGHT 

LAPSE 


WIND 

R 

TEMP 

GRAD 

BURST 


Figure 4. Clouds from simultaneous firing of five gas-ejection bombs charged with powdered egg albumin. 


SECRET 





FIELD TESTS ON MUNITIONS 


545 


Total dosages were obtained by means of glass im- 
pingers as used at Port on. Particle size data were 
obtained from cascade impactors, sticky rods and 
coated slides. Bio-assays were made by exposing test 
animals to the clouds. All samplers were located on 
an arc 50 yd from the bombs. The bombs were com¬ 
pared on the basis of the standard dispersion figures 
and the volume-mass-median diameters [VMMD] 
of the particles in the clouds. These are shown in 
Table 5. 


Table 5. Comparison of munitions for dispersing W. 




VMMD of clouds 


SDF 

Static 

Launched 

Munition 

% 

bomb 

bomb 

Cardox C0 2 bomb — dry powder 
Suffield LC — 4-lb bomb — dry 

28 

19m 

38m 

powder 

SPD Mk I (Type F) bomb — 

37 

14m 

31m 

35% suspension in CCh 

Plastic bomb — 35% suspension 

57 

9m 

7m 

in CC1 4 

41 

7m 

8 M 


The dimensions of the initial clouds from all bombs 
were 10 to 15 ft high and 20 ft in diameter. At 50 yd, 
the clouds were 20 to 25 ft high and 60 to 65 ft wide. 
Ground contaminations were negligible for the 
suspensions and appreciable for the dry chargings. In 
all cases, the clouds contained unitary particles and 
aggregates. The munitions dispersing dry powders 
gave the coarsest aggregates, and those dispersing 
suspensions gave the largest numbers of unitary 


particles. About 19% of the dry agent and 30% of the 
suspended agent were dispersed as unitary particles. 
Little difference was noted in the structural charac¬ 
teristics of the aggregates from the two types of 
chargings except that the aggregates from suspensions 
were denser. 

A test to compare the plastic and Type F bombs 
for the dispersion of the bacteriological agent U in a 
water slurry of micronized peat showed no measura¬ 
ble difference in performance. Heavy ground con¬ 
tamination was observed in the vicinity of both 
bombs. Other tests in which acetone suspensions of 
peat alone were dispersed gave negligible ground 
contamination. 

The following conclusions regarding the dispersal 
of solid particulate agents were reached on the basis 
of these tests: 

1 . Solid particles may be dispersed more effi¬ 
ciently from suspensions in the proper liquid using 
high-explosive munitions than in the dry form from 
any available munition. 

2. The plastic bomb is as efficient as the metal 
SPD Mk I bomb of similar size and shape, with re¬ 
gard to particle size, and is slightly less efficient than 
the metal bomb with regard to SDF. This difference, 
however, is within the experimental accuracy of the 
tests. 

3. The 4-lb light-case bomb is somewhat better 
than the gas-ejection bomb with respect to both 
particle size and SDF. 

4. The performance of the munitions is strongly 
influenced by the nature of the chargings. 


SECRET 








Chapter 36 

DISPERSION OF HERBICIDES 

By H. F. Johnstone and H. C. Weingartner 


I t is well known that there are certain organic 
chemicals which, when present in the soil in ex¬ 
tremely low concentrations, can destroy or prevent 
the maturing of plant life. The best known of these 
are 2,4 dichlorophenoxy-acetic acid and its sodium 
salt. The possible use of these materials, as a chemical 
warfare agent to destroy essential crops on the 
Japanese mainland and on the by-passed occupied 
islands, was given close consideration during the last 
year of World War II, and the development of 
methods of dispersing the agents was proceeding 
under high priority. 

The nature of the agent permitted its application 
in the form of a solution or as a granulated solid. The 
methods of dispersion available were (1) spray of 
aqueous solution; (2) dusting of powdered solids; and 
(3) aimable airburst projectiles for either liquids or 
solids. Tactical restrictions required that the aircraft 
release the agent or munitions containing the agent 
below 500 ft or above 5,000 ft. Low-altitude attacks 
were considered for small targets to be treated with 
liquid agents released from existing available spray 
equipment. Dusting methods were not considered 
because of the lack of proper equipment in the com¬ 
bat areas, and because of the short time available for 
the development of equipment. For large target 
areas, i.e., rice paddies, emphasis was placed on the 
dispersal of the solid agent from aimable airburst 
projectiles. 

This project was the responsibility of the Special 
Projects Division, ASF; the organization to which 
NDRC assistance was directly given was Camp 
Detrick, Technical Department, in whose files de¬ 
tailed reports covering this work are to be found. 

36.1 PRINCIPLES 

The problem in dispersing a solid agent is to apply, 
as uniformly as possible, the desired dosage of agent 
over the largest possible area in the proper physical 
condition and form to be effective. 

The travel of solid particles released above the 
ground is similar to the travel of droplets of thickened 
liquid agents already studied. 1 It may be assumed 
that the granules quickly reach their terminal settling 


velocities relative to the air, and are accelerated to the 
horizontal wind velocity at every point in their paths 
to the ground. It follows then, that the distance D 
which a given particle falling in still air travels down¬ 
wind before reaching the ground is proportional to 
the height of release above the ground h, and to the 
resultant wind velocity v, and is inversely propor¬ 
tional to the settling velocity of the particle u , or 


where k = a constant. 

The length of a pattern (parallel to the resultant 
wind) is proportional to the vh product and depends 
upon the relative settling velocities of the largest and 
the smallest particles released. 



where u m \ n , u m& x = settling velocities of smallest and 
largest particles respectively. 

The distribution of agent along the pattern length 
is determined by the particle size distribution in the 
agent charge. The width (crosswind dimension) of a 
pattern from an airburst munition depends upon the 
vh product, but, to a lesser degree than the down¬ 
wind travel of a particle. It tends to approach a 
maximum as vh is increased, and within the limits of 
proposed tactics may be assumed to be between 
100 and 250 yd. 1 

36.2 DESIRED PARTICLE SIZE 
DISTRIBUTION 

The upper particle size limit was determined by a 
consideration of the relation between uniform gross 
contamination density and particle size in a given 
charging, for upon this relationship depends the rate 
of solution and concentration increase of agent in the 
water of the target rice paddies. On the basis of 
laboratory experiments, the upper size limit was 
established to be about that of a particle which just 
passes 6-mesh screen. The lower limit was chosen to 
include all particles falling in a predictable manner 
and not carried excessive distances by the wind. This 


546 


SECRET 


DESIRED PARTICLE SIZE DISTRIBUTION 


547 


Table 1 . Terminal velocities, particle densities, and desired size distribution of granules of agent — sample I. 


Screen size 
U.S. Std 

Size of 
opening 
mm 

Average wt 
per particle 
mg 

Settling 
velocity 
u ft/sec 

Reciprocal 
settling 
velocity 
l/u sec/ft 

Desired 
cumulative 
weight 
per cent 

21 

8.00 

235.0 

18.7 

0.0535 


3 

6.73 

157.0 

17.5 

0.0572 


31 

5.66 

100.0 

16.0 

0.0625 


4 

4.76 

65.0 

14.3 

0.0700 


5 

4.00 

41.0 

13.7 

0.0731 


6 

3.36 

26.0 

12.6 

0.0794 

' o’ 

7 

2.83 

16.6 

11.8 

0.0848 

9.0 

8 

2.38 

10.5 

10.9 

0.0917 

19.0 

10 

2.00 

6.7 

10.0 

0.1000 

31.0 

12 

1.68 

4.2 

9.3 

0.1075 

42.0 

14 

1.41 

2.6 

8.5 

0.1178 

57.5 

16 

1.19 

1.7 

7.9 

0.1266 

70.0 

18 

1.00 

1.1 

7.3 

0.1370 

85.5 

20 

0.84 

0.68 

6.8 

0.1470 

100.0 


limit was set arbitrarily at 20-mesh, since the diffi¬ 
culty of controlling particle size distribution in¬ 
creases as the size decreases. 

The crosswind concentration gradient follows the 
normal distribution law. As the value of vh is in¬ 
creased, this gradient decreases and the concentra¬ 
tion or dosages become more nearly uniform. 

Assuming a constant average crosswind contamina¬ 
tion, the particle size distribution, between set limits, 
to give a uniform downwind dosage may be deter¬ 
mined. This relationship requires that the cumulative 
weight per cent of the agent must vary linearly along 
the length of a given pattern. If a graph of this rela¬ 
tionship is plotted on rectangular coordinates, the 
line must pass through the points: cumulative weight 
per cent = 0, length = 0, and cumulative weight per 
cent = 100, L = L. For a given value of vh, the 
length is determined by the settling velocities of the 
extremes in particle size as shown in equation (2). 
The values of 1 / u max may be substituted for L = 0 
and 1/Wmin for L = L. The equation for the straight 
line relating the cumulative weight per cent to the 
settling velocity (and consequently the particle size) 
then is 

Cumulative weight per cent = 100——- 1 ** max - , 

1/^min 1/^max 

(3) 

where the cumulative weight per cent computed is 
that percentage of the agent, as charged, between 
sizes corresponding to settling velocities u max and u. 

The relationship between screen size and settling 
velocities must be determined experimentally for 
each type and form of agent to be used. Table 1 shows 


this relationship for a typical batch of granular agent 
together with the size distribution computed as 
described. The terminal velocity data are taken from 
a smooth curve correlating the experimentally meas¬ 
ured terminal velocities of carefully screened frac¬ 
tions of agent falling through relatively still air 
against the average particle size. 

36.2.1 Munitions 

Munitions were devised and tested for the purpose 
of dispersing granular agents. 

1 . The Type A container consisted of a modified 
shell of an M-16 cluster adapter (Ordnance) contain¬ 
ing four cylindrical cloth-bakelite molded agent con¬ 
tainers, each about 13 in. in diameter and 73^ in. 
deep. On release from the cluster at a predetermined 
time, the four containers were opened by means of 
static lines secured to the adapter shell. This muni¬ 
tion carried 125 lb of the granular agent shown in 
Table 1. The four containers were employed to pro¬ 
vide several points of release to minimize the con¬ 
centrating effect of a release from a point source. 

2. The Type B container consisted of a single sheet 
metal container shaped to fit the curved contours of 
the M10A1 cluster adapter in which it was held. 
Upon release, the container was split into three 
longitudinal sections by the explosion of strands of 
Primacord. This container carried 200 lb of the 
granular agent. 

It was observed that the dispersion from the Type 
B container occurred over a continuous finite dis¬ 
tance. Since this device was simpler, cheaper, more 
easily obtainable, and since its agent capacity was 


SECRET 









548 


DISPERSION OF HERBICIDES 


greater than that of the Type A containers, it was the 
only one used in subsequent field tests. 

Field tests were conducted by the Granite Peak 
Installation at Dugway Proving Ground. The muni¬ 
tions were dropped from a Mitchell B-25 bomber 
flying parallel to the resultant wind and from an alti¬ 
tude sufficiently high to allow them to lose most of 
their horizontal velocity components before func¬ 
tioning. The munitions were functioned over a wide 
range of wind velocities and heights of burst. Mete¬ 
orological data were taken at the control point and 
the necessary information was transmitted to the 
aircraft. The aiming point on the salt flat target area 
was identified by a black smoke signal. The heights 
of burst were determined by the use of theodolites. 
The resultant winds were measured as the munitions 
fell. 

A reference point was established in the approxi¬ 
mate center of the ground pattern. From this point 
by means of transit and stadia board, the pattern 
boundary, the vertical projection of the point of air- 
burst to the ground, and the sampling points, were 
located. 

Within the pattern, the concentrations were meas¬ 
ured by determining the mass of agent in a given 
area. Where possible, the particles were picked up, 
counted, and weighed. Where the particles were too 
small to be picked up they were counted and their 
sizes estimated visually. An experimentally deter¬ 
mined relationship between average particle sizes and 
weights permitted estimations of the mass of the 
small particles (see Table 1). Sampling points were 
selected to scan the entire pattern and to give 
representative estimations of the dosages. Depending 
upon the pattern size, from 30 to 60 samples were 
taken. 


Table 2. Comparison of actual and desired particle 
size distribution for granular agent-sample A. 


Screen No. 

U.S. Std 

Cumulative 

weight per cent 

Desired 

Actual 

4 

0.0 

0.0 

6 

12.0 

17.5 

8 

28.0 

48.0 

10 

39.0 

76.0 

12 

49.0 

77.0 

14 

62.0 

85.0 

16 

73.0 

89.0 

20 

100.0 

93.0 


The contamination densities and average particle 
sizes were plotted on a scaled diagram of the patterns, 
and constant dosage contours were drawn. The areas 


covered by various dosages, the overall pattern 
dimensions, and the distances from projected point 
of burst to the upwind edges of the patterns were 
measured. Material recoveries were determined, and 
the variations in granule sizes along the patterns 
were observed. 

US STD SCREEN SIZE CORRESPONDING TO PARTICLE TV 
ON LOWER SCALE 



1 RECIPROCAL OF TERMINAL VELOCITY OF PARTICLE 
u 

Figure 1 . Desired and actual particle size distribution 
of agent. Sample A based upon experimental determina¬ 
tion of terminal velocities of particles. 

The granule size distribution in the charging used 
in the field trials was different from that calculated to 
give a uniform downwind contamination. The weight 
fraction of the larger size particles was too high, and 
that of the smaller size particles was too low. Seven 
per cent of the agent was below 20 mesh. The fraction 
between 10 and 12 mesh was extremely small. The 
differences are shown in Table 2 and Figure 1. 

36.2.2 Results 

The data in Table 3 show the pattern dimensions, 
contamination, downwind travel, wind velocities, 
and heights of burst for the trials. 

Figures 2 and 3 show the approximate linear de¬ 
pendence of pattern length and downwind drift, 
respectively, on the vh product. This linear relation¬ 
ship cannot be expected to hold at low values of v or 
h because of the increased effect of the emission rate 
and track under those conditions. 

It was observed that the areas of highest concen¬ 
tration were in the upwind half of the pattern, and 
that a gradual classification of particles occurred 
along the pattern. The largest particles were found 
at the upwind edge and progressively smaller ones 
were found further downwind until the subsize par¬ 
ticles were so scattered that the definition of the 
downwind edge was uncertain. The upwind and side 
boundaries were well defined. 


SECRET 




























Table 3. Data for dispersion of granular agent (sample A) from aimable airburst projectile Type 


DESIRED PARTICLE SIZE DISTRIBUTION 


549 


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SECRET 




































































AREAS COVERED BY DOSAGES EQUAL TO OR GREATER THAN THOSE INDICATED IN ACRES 


550 


DISPERSION OF HERBICIDES 



vh * WIND VELOCITY (MPH) x HEIGHT OF BURST IN FT 

Figure 4. Area-Dosage; vh relationship for the 
charging used. 

In several patterns, areas of low concentration be¬ 
tween areas of higher concentration were observed in 
the portion of the pattern where the particle sizes 


were 10 to 12 mesh. These results are compatible with 
those which might be expected from a charge having 
the particle size distribution described. 

Figure 4 shows the relationship between areas 
covered by various contaminations and the vh prod¬ 
uct. The total area can be expected to increase indef¬ 
initely with vh, for a given charging. The areas cov¬ 
ered by higher contaminations can be expected to 
reach a maximum value. The highest contaminations 
will cover maximum areas at low vh values. Further 
increases will dissipate the material in an area of high 
contamination to increase the area of lower contami¬ 
nation . These relationships must be determined for each 
charging used. The maximum areas covered by a 
given contamination and the corresponding vh value 
for the charging used in these trials are given in Table 
4. The data are insufficient to determine the maxi¬ 
mum areas but show the approximate relationships. 

The results imply that a more nearly uniform 
coverage with larger areas covered by contamination 
up to 5 lb per acre could have been achieved had the 
particle size been adjusted to contain fewer large 
particles and more small particles. Since the correc¬ 
tion is in the direction indicated by the calculation 
described previously, the verification of that calcula¬ 
tion is indicated, thus permitting size distributions to 
be specified between any limits of particle size for any 
granular agent. 

Uniformly high concentrations probably could best 
be achieved by limiting the particle size to a narrow 
range, thus permitting the use of large vh products 
with decreased pattern lengths. Conversely, uniformly 
low dosages could be obtained with a charge contain¬ 
ing particles between broad size limits, again employ¬ 
ing high vh values for maximum uniformity. 


SECRET 




















Chapter 37 

PLASTICIZED WHITE PHOSPHORUS 

By H. F. Johnstone 


37.1 INTRODUCTION 

hite phosphorus was used extensively during 
World War II for producing smoke screens in 
ground combat and in landing operations, and as an 
antipersonnel agent against enemy troops. In burster- 
type munitions the efficiency of WP as a smoke agent 
is small. Most of the charging burns within a few 
seconds after the burst, producing a cloud in which 
the smoke concentration is many times that required 
for effective screening. Moreover, the temperature 
rise in the concentrated cloud creates such a density 
gradient that it pillars, or rises rapidly from the 
ground, and becomes totally ineffective for ground 
screening. For this reason the burning-tvpe smoke 
munitions, such as HC, were favored by the British 
Army almost to the exclusion of WP, and also found 
many tactical uses with the United States Forces. 
However, HC itself had certain limitations. For use 
in projectiles, it required a base ejection shell with 
low muzzle velocity and a low chemical efficiency. It 
was difficult to place by gunfire and was slow in 
developing a smoke screen. In high concentrations, 
and on prolonged exposure, its toxicity to troops was 
extremely hazardous. For these reasons, WP was 
much preferred by the American Army and Navy 
and was used extensively in the 4.2-in. chemical 
mortar supporting ground troops, in the 105 and 
155-mm howitzers and guns, and in the 5-inch/38 
caliber Navy guns for screening over water and on 
land. 

Early in 1943, the NDRC was asked to investigate 
means of reducing the pillaring characteristic of WP 
smoke, and otherwise improving the smoke effective¬ 
ness of phosphorus munitions. Consideration of the 
problem indicated that the low effectiveness of solid 
phosphorus in bursting-type munitions is primarily 
attributable to the extensive fragmentation and the 
consequent high rate of combustion of the phos¬ 
phorus. The temperature rise in the cloud immedi¬ 
ately surrounding the burst is sufficient to produce 
a strong thermal updraft which rapidly lifts the cloud 
from the ground. On the other hand, the temperature 
rise in a cloud of effective, but not excessive, screen¬ 
ing concentration would not be sufficient to develop 


thermal updrafts except under the most adverse 
atmospheric conditions. 

From these considerations two methods of improv¬ 
ing the smoke efficiency wer^ suggested, (1) reduce 
the heat of combustion, and (2) control the rate of 
combustion. The former can be effected only by 
substituting for the phosphorus some compound with 
a lower heat of combustion. To this end, considera¬ 
tion was given to the use of phosphorus trioxide and 
other phosphorus compounds. 1 The second method is 
the more attractive because it would control not only 
pillaring, but also would realize the ultimate smoke 
efficiency of the phosphorus, and thus increase the 
total screening time several fold. 

The following methods for controlling the rate of 
combustion by controlling the degree of fragmenta¬ 
tion were suggested. 

1. Mechanical reinforcement of the phosphorus 
with steel wool, asbestos, plastic tubes, wire screens 
or other devices, which would cause the ejection of 
the phosphorus in pieces of predetermined size. 

2. Alteration of the physical properties of phos¬ 
phorus, by addition of agents, to produce a plastic 
mass which would effectively resist shattering and be 
dispersed as pieces of moderate size. 

Experiments were made on each of these methods. 
The reinforcing agents showed some improvement in 
the smoke efficiency, especially with mortar shells 
filled with longitudinal screen cylinders %-in. di¬ 
ameter by 12 in. long. 2 It was also found that precast 
blocks of phosphorus could be used in some of the 
small bombs and these, on ejection as large masses, 
Avould burn for several minutes giving a nonpillaring 
smoke. Several types of plastic coatings were found 
suitable for keeping the blocks separated. 

The most promising method of controlling the 
fragmentation of phosphorus and the pillaring of the 
smoke was found in the development of a new smoke 
agent, known as plasticized white phosphorus 
[PWP], consisting of an intimate mixture of granu¬ 
lated WP in a viscous rubber solution. This material 
burns more slowly, and the flying particles do not 
disintegrate by melting. Consequently, the pillaring 
is almost completely prevented and the screening 
time is greatly prolonged. 



SECRET 


551 


552 


PLASTICIZED WHITE PHOSPHORUS 


37.2 TEMPERATURE RISE IN 

PHOSPHORUS SMOKE CLOUDS 

A rough estimate of the temperature rise in the 
smoke clouds from solid WP and PWP may be made 
from data obtained in field tests on fragmentation 
and particle dispersion. 3 

Data 

Heat of combustion of WP 10,600 Btu per lb 

Heat of combustion of PWP 12,000 Btu per lb 

C P of air 0.24 cal per g per degree C 

Density of air 1.2 X 10“ 3 g per cc 

Filling weights 

4.2-in. mortar shell 

WP 7.6 lb 

PWP 6.25 lb 

M47A2 bomb 

WP 86 lb 

PWP 72 lb 

Approximate dimensions of burst ( observed ) 



Radius 

Height 

Volume 


ft 

ft 

cu ft 

4.2-in. mortar shell 

WP 

90 

50 

1.27 X 10 6 

PWP 

150 

50 

3.54 X 10 6 

M47A2 bomb 

WP 

150 

90 

6.37 X 10 6 

PWP 

300 

90 

25.3 X 10 6 


Fraction of total filling weight burned in initial burst, 
and heat evolved 


Per cent burned Heat evolved 



(estimated) 

Btu 

4.2-in. mortar shell 

WP 

90 

72,500 

PWP 

60 

45,000 

M47A2 bomb 

WP 

80 

730,000 

PWP 

40 

346,000 


Calculated average temperature rise 


Munition 

Filling 

Temperature rise 
degrees C 

4.2-in. mortar shell 

WP 

1.75 


PWP 

0.37 

M47A2 bomb 

WP 

3.50 


PWP 

0.50 

The values shown 

are the 

average temperature 


rises in the initial clouds having the dimensions of the 


burst. Actually, the temperature rise at the center of 
the burst is much greater than shown and is zero 
at the assumed envelope. 

37.3 MANUFACTURE OF PWP 4 

In the production of PWP, the phosphorus is re¬ 
duced to an average particle diameter of about 
0.5 mm by a process of granulation, in which a 
violently agitated mixture of molten phosphorus and 


hot water is cooled below the freezing point of phos¬ 
phorus by the addition of cold water. The rubber 
solution is prepared as follows: GR-S rubber is re¬ 
duced to pieces in. to 34 m - i n diameter by shred¬ 
ding. The shredded rubber is mixed with the solvent 
and the mixture set aside for 6 to 24 hr until it be¬ 
comes homogeneous by diffusion. The rubber solu¬ 
tion is then mixed with the granulated phosphorus 
under water in a Cincinnatus-type mixer for 20 to 
40 min. A flow sheet of the process designed for the 
Navy Bureau of Ordnance is shown in Figure 1. 


TO WP BULK STORAGE 



unit). 

Two types of PWP were developed to meet the 
ballistic requirements of the various smoke muni¬ 
tions. These differ mainly in their apparent viscosity, 
or consistency. The mixture designated as “75-35” 
PWP contains 75% phosphorus and 25% rubber 
solution which is 35% rubber and 65% xylene. This 
formula was satisfactory for bombs and rockets, 
which do not have critical ballistics. Rotating pro¬ 
jectiles required PWP with a higher viscosity. Such 
a material is “75-40” PWP, which consists of 75% 
phosphorus and 25% rubber solution which is 40% 


SECRET 































MANUFACTURE OF PWP 


553 


rubber and 60% solvent. PWP 75-40 was superseded 
by a type with a still higher viscosity, which is 
designated as “75-40-30LO.” This formula contains 
75% phosphorus and 25% rubber solution which is 
40% GR-S, 30% xylene and 30% linseed oil. 

37.3.1 Granulation of Phosphorus 

The phosphorus used in the manufacture of PWP 
is the standard technical grade. It is transported in 
the molten condition in steel tank cars and is usually 
stored in 10,000-gal horizontal steel tanks with in¬ 
ternal steam coils to prevent solidification. In the 
PWP plant at Edgewood Arsenal, 5 the phosphorus 
was forced from these tanks by water displacement 
to a 500-gal vertical tank which served as a working 
storage. It was, in turn, transferred from this tank by 
water displacement to a 122-gal measuring tank from 
which it was sent to the granulators by displacement 
with a measured volume of water. All phosphorus 
fines were steam-jacketed and lagged. This method 
of handling phosphorus is safe and convenient, and 
it is easy to determine the amount of material trans¬ 
ferred from one tank to another by means of hot- 
water meters and liquid-level gauges. 

Batch Granulators 

The batch granulators used in the pilot plant and 
in the large plant consisted of steam-jacketed vessels 
with high-speed agitators. The most convenient size 
for large scale production, as determined by the time 
cycle on the loading machine, was 165-gal capacity. 
Two of these granulators served one mixer. The 
charge placed in the granulator consisted of 400 lb of 
molten WP and an equal volume of water, or about 
30 gal. The mixture was then agitated by means of 
two 3-bladed 7-in. impellers operated at 1,750 rpm by 
means of a 73^-hp motor. The agitation was con¬ 
tinued for 5 min, and then cold water was run into 
the granulator to lower the temperature from 120 to 
95 F. Within limits, the size of the particles could be 
altered either by varying the rate of agitation or the 
rate of cooling. Data taken in the pilot plants indi¬ 
cated that the desired rate of cooling should be about 
4 F per minute in order to give a particle size within 
the specification limits, namely, 75% between 0.2 
mm and 0.6 mm diameter, and not more than 5% in 
excess of 1.2 mm in diameter. 

After cooling, the phosphorus slurry was dis¬ 
charged through a flush-type plug valve to the mixer 
which was located on a lower level. In order to pre¬ 
vent inflaming of the small particles of phosphorus 


which floated on the surface of the water, it was found 
desirable to keep the mixer closed and to maintain 
an atmosphere of carbon dioxide above the surface 
of the slurry during the transfer operation. For con¬ 
venience, the fine between the granulator and the 
mixer was steam-jacketed in case it became plugged 
by the freezing of the phosphorus resulting from 
leakage of the flush valve. 

Continuous Granulator 
Some work was done at the experimental plant at 
the University of Illinois on a continuous method of 
granulating phosphorus. 4 This had a number of ad¬ 
vantages and probably would have been installed in 
the larger manufacturing plants if there had been 
time to work out the details. The process consisted of 
spraying molten phosphorus through a nozzle into 
a stream of hot water, as shown in Figure 2. The re¬ 
sulting mixture was cooled immediately by a merging 
stream of cold water, and the slurry was directed into 
the mixer. The particles of phosphorus from the jet 
granulator were smooth and round, in contrast with 
those from the batch granulator, which were rough 
and irregular in shape. The PWP made with the 
former had, on the average, a lower viscosity than 
that made using the batch granulator. 

The following operating conditions for the jet 
granulator were found to give PWP of good thermal 
stability: 

Pressure on phosphorus fine: 18 to 20 psi 
Orifice size: No. 44 drill 
Rate of phosphorus flow: 7 to 7.7 lb per min 
Hot water rate: 15 to 16 lb per min 
Hot water temperature: 167 F 
Cold water rate: 25 lb per min 
Cold water temperature: 45 to 50 F 
The particle size distribution for these conditions is: 
Above 0.8 mm diameter: 5% 

Between 0.2 and 0.8 mm diameter: 80% 

Smaller than 0.2 mm diameter: 15%. 

37.3.2 Preparation of Rubber Solution 

The GR-S rubber used in the manufacture of 
PWP was the 80-20 butadiene-styrene polymer made 
in the government rubber plants. The nature of the 
material from different plants and even from different 
lots from the same plant varied widely. These varia¬ 
tions affected the properties of the PWP to some ex¬ 
tent, especially those of the higher viscosity type. 
There was a continued improvement in the product, 


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554 


PLASTICIZED WHITE PHOSPHORUS 



however, as the rubber plants came under better 
control. 

Synthetic rubber is available either in bale or 
crumb form. The latter consists of irregular pieces 
34-to 34-in. diameter formed during the coagulation 
of the latex. This product is packaged after washing 
and drying. It is dusted sometimes with talc to pre¬ 
vent matting. In any case, unless the dusting is very 
thorough, compaction and cohesion of the particles 
occur in shipment and storage. The material must 
then be treated in the same way as the baled rubber 
which is made by pressing the crumb. The crumb 
form has the disadvantage that the dust is an un¬ 
known variable, and it is subject to more rapid 
deterioration because of the exposure of a large sur¬ 
face area to the oxj^gen of the atmosphere. 

Milling the Rubber 

The particle size of the rubber determines the time 
required to obtain a homogeneous solution. In the 
manufacturing process, it was desirable to keep this 
time at a minimum. The preparation and use of finely 
divided rubber offered certain difficulties. If too 
much shredding was carried on in a single stage, the 


heat developed was excessive and the particles had a 
tendency to adhere to each other. Additional labor 
and equipment were required to cool the material and 
keep it in a free-flowing state, and power require¬ 
ments were high. The best results were obtained with 
rubber reduced to an average of %6-in. to y£-in. size. 
This was obtained by a single-stage reduction of 1-in. 
to 134-i n - cubes from a cutting machine in a Jeffrey 
Rigid Hammer Mill. 

Preparation and Handling op the Rubber 
Solution 

In both the pilot plant and the large plant at Edge- 
wood Arsenal, it was found convenient to prepare the 
rubber solutions in 5-gal buckets which were trans¬ 
ported manually. For the Naval Ordnance Plant, 
special containers holding 60 lb of rubber and auto¬ 
matic handling equipment were designed and tested 
for serviceability. 6 

In practice, the milled rubber was poured into the 
required amount of solvent. This procedure was 
preferable to the reverse because it permitted better 
separation of the rubber particles and better wetting. 
The bucket was then closed tightly and tumbled by 


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LOADING PWP MUNITIONS 


555 


mechanical means until the liquid was viscous enough 
to prevent the partially swollen particles from sepa¬ 
rating out. The time required for this step depended 
upon the particle size of the rubber and the type of 
solvent used, and varied from 5 to 15 min, or even 
longer. Some difficulty was experienced in getting- 
good mixing when linseed oil was used in the for¬ 
mulas. The oil was mixed with the xylene before the 
rubber was added, but the two solvents diffused into 
the rubber at different rates and the composition of 
the remaining solution changed on standing. This 
difficulty could be largely avoided by prolonging the 
initial mixing time. 

After the preliminary mixing, the rubber solution 
was poured into a special aging bucket. In order to 
prevent the thick rubber mix from adhering to the 
metal, the inside of the bucket was coated with a 20% 
starch paste made with Arabol Adhesive NLG-15, 
which was obtained from the Arabol Manufacturing 
Company of New York. 

37.3.3 Mixing the Constituents 

In the development work, several types of mixers 
were used for mixing the granulated phosphorus par¬ 
ticles with the rubber gel solution. It was found that 
this operation was quite critical since, if the mixing 
operation was carried on for too long a time, it re¬ 
sulted in a break-down of the rubber, and if the mix¬ 
ing was poor, the phosphorus granules were not 
separated by films of rubber. Either of these condi¬ 
tions would result in a thermally unstable product 
which would allow the phosphorus to separate from 
the rubber matrix, when heated above the melting 
point of phosphorus. There was evidence that both a 
chemical and physical deterioration of the rubber 
takes place during the mixing operation, and there¬ 
fore, there is an optimum time of mixing for each 
type of PWP in a given mixer. Not only does exces¬ 
sive working in the mixing and loading operations re¬ 
sult in degradation of the rubber, but there is also 
evidence that the phosphorus itself causes an in¬ 
crease in the gel content of the rubber, especially if 
the temperature is allowed to rise due to the mechani¬ 
cal work on the viscous mixture. 

The most satisfactory type of mixer found was the 
jacketed double-bladed Cincinnatus-type mixer with 
blades operating at the same speed in opposite direc¬ 
tions. Mixers of 50-, 100-, and 300-gal capacity were 
used in the pilot plants and the large scale produc¬ 
tion. The 100-gal size was recommended because it 


had the proper capacity for coordination with the 
loading unit. 

The mixers were provided with a split cover, one- 
half of which was permanently fastened, whereas the 
front half is removable for charging the rubber solu¬ 
tion and discharging the product. Overhead sprays 
and an inlet pipe for C0 2 gas were also provided, as 
well as a drain hole near the top for removing the 
water. 

The general method of operation of the mixers was 
to discharge the entire contents of the granulator as a 
slurry into the mixer, and then add the proper 
amount of the rubber solution while the mixer was 
being flushed with carbon dioxide. The excess water 
was then drained off and the mixer started. After the 
rubber solution had picked up the granulated phos¬ 
phorus in 5 to 10 min, the water was run back into 
the mixer. The practice at this point was not always 
uniform but, in general, it was found better to have 
the water present during the mixing in order to aid in 
dissipating the heat. The mixing was continued for 
15 to 20 min. The entire batch was then dumped into 
a hopper from which it was transferred by screws 
into the loading system. 

37.4 LOADING PWP MUNITIONS 

Since the amount of mechanical work to which the 
PWP may be subjected without damage must be kept 
at a minimum, it was found that extrusion of the 
material through a small-diameter tube by means of a 
screw could not be used for loading munitions with 
small filling holes. This was satisfactory, however, for 
the 100-lb bombs which could be filled directly from 
the 6-in. screw conveyor through a short nozzle. The 
bomb was weighed in place to control the net filling- 
weight. 

For small munitions, such as rockets and shells, the 
loading was done by means of hydraulic pistons 
operated by oil pressure. These consisted of two ex¬ 
trusion cylinders attached to a four-way valve on the 
6-in. screw conveyor. While one cylinder was being 
filled, the contents of the other were being discharged 
into the munition by means of the piston. The cylin¬ 
ders were 4.5 in. ID and the pistons had a maximum 
stroke of 15 in. The stroke could be varied to control 
the delivery of the required amount of PWP for each 
munition. Both automatic and hand-operated con¬ 
trols were installed for operating the valve. It was 
found that a close weight tolerance could be main¬ 
tained with the automatic equipment, and, in the 


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556 


PLASTICIZED WHITE PHOSPHORUS 


case of the 4.5-in. Navy*rocket, the filling could be These figures agree approximately with those ob- 
carried on at the rate of two heads a minute. tained in the larger plant at Edgewood Arsenal. 


37.4.1 Control of Moisture Content 

The* moisture content of the product was deter¬ 
mined by the consistency of the mixture, the pH of 
the slurry, and the amount of compression exerted 
on the product during the loading process. For the 
less viscous mixture used in bombs and rockets, it was 
desirable to increase the amount of compression by in¬ 
stalling an orifice in the end of the 6-in. screw con¬ 
veyor in order to squeeze out some of the water. The 
addition of sodium carbonate or sodium phosphate to 
the phosphorus slurry resulted in an increased 
moisture content of the product. In the pilot plant, 
the moisture content usually ran from 8 to 10%, but 
in the larger plant, it was found somewhat higher. 
There was no evidence, however, of an adverse effect 
of the high moisture content on the smoke quality of 
PWP in bombs, rockets, or other munitions. 

37.4.2 Power and Services Required 

An estimate of the material and power require¬ 
ments in the manufacturing process was made on the 
basis of three months’ operation of the pilot plant at 
Victor Chemical Works as follows. 


37.4.3 Labor Required in the Manu¬ 
facturing Process 

The estimate made by the Victor Chemical Works 
for the labor requirements were as follows. 


Rubber, handling 
Granulating 
Mixing 
Loading 

Miscel. handling 
Supervision 


0.12 man hr per 100 lb 

0.33 

0.33 

0.33 

0.33 

0.15 


The Victor estimate does not include the labor re¬ 
quired for handling of the empty munitions and 
loaded munitions, and the painting and boxing of the 
finished munition. In any Ordnance plant these items 
are always very large. The estimate made on basis of 
the operation of the Edgewood plant was as follows. 


Labor required (for each shift) 

Phosphorus handling and granulation 3 

Mixing 4 

Loading 3 

Empty munition, inspection 2 

Empty munition, handling 2 

Loaded munition, handling 15 

Loaded munition, inspection 3 

Preparing rubber gel 6 

Laboratory inspection 2 

Supervision 4 


Basis: 100 lb PWP 


For 75-35 PWP 
Xylol 

Phosphorus 

GR-S 


14.5 lb 
67.75 
7.75 


Water 

10.00 

For 75-40 PWP 


Xylol 

13.375 lb 

Phosphorus 

67.75 

GR-S 

8.875 

Water 

10.00 

Gallons cooling water at 60 F 


Direct cooling 

10.0 gal 

Jacket cooling 

55.5 

Mixer cooling 

90.0 


155.5 

Estimated C0 2 usage 


Mixing 

30 cu ft 

Granulating 

15 


Power required = 4 h,p hr 


HP 

Volts 

Usage Service 

% 

440 

Continuous, hot water circulation 

3 

440 

Intermittent, granulated 



Phosphorus pump 

X 

440 

Intermittent, de-watering screw 

X 

440 

Continuous, loading screw 

5.0 

440 

Intermittent, rubber mill 

X 

110 

Intermittent, rubber gel mixer 

10.0 

440 

Intermittent, mixer 

X 

440 

Intermittent, granulator 


44 

About 60% of the labor performed in this plant was 
by women. The efficiency was not high, since it was 
the first large plant in operation and much of the 
production was of an educational nature. The plant 
had a manufacturing and loading capacity of 5,000 lb 
of PWP per 8-hr day. 

37.5 PWP MUNITIONS 

During the development of PWP a large number of 
munitions were filled and tested for comparison with 
other smoke munitions. These included the following: 
Shell, 4.2-in. CM, M2 
Shell, 4.2-in. RCM, E77 
Shell, smoke, 75 mm, M64 
Shell, smoke, 105 mm 
Shell, smoke, 155 mm 
Shell, smoke, 5-in./38 cal. Navy projectile 
Shell, smoke, 60 mm, M302 
Shell, smoke, 81 mm, M57 
Rocket, smoke, 2.36-in., M10 
Rocket, smoke, aircraft, 3.5-in., Mk 6 
Rocket, smoke, 4.5-in., Mk 10, Mod 0 
Rocket, smoke, 4.5-in., S.S., T-84 
Rocket, smoke, 5-in., S.S. 

Rocket, smoke, 7.2-in. 

Bomb, 100-lb, M47A1, 2, 3 
Grenade, smoke, M15 


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PWP MUNITIONS 


557 


All these munitions were designed for use with WP 
and not PWP. They were used for test firing as a 
matter of convenience only, and it was realized that 
further improvements might be obtained with each 
munition if a new design could be made available 
which would allow for the lower density of the filling 
compared with that of WP. 


37.5.1 Filling Weight 

Since PWP contains substances which vaporize at 
elevated temperature, it is necessary to leave a void 
in the filled munition. The maximum loading weight 
for each type of munition can be calculated from a 
knowledge of the minimum volume tolerance of the 
munition, the composition and density of the PWP, 
and the pressure allowable at the maximum tem¬ 
perature to which the munition is subjected during 
storage. Actually, PWP has a density lower than that 
calculated from the densities of its constituents, be¬ 
cause of numerous void spaces present in the mass of 
the material. 

Assuming that the temperature of the munition 
will not exceed 65 C and that the pressure due to the 
expansion of the filling and the heating of the air in 
the void space from 25 C should not exceed 50 psi, the 
following calculation was made to determine the 
minimum void space required. a 

Let u = volume of munition at 25 C; 
u x = volume of munition at 65 C; 
v = volume of total void space at 25 C; 

Vi = volume of total void space at 65 C; 
k = fraction of total volume occupied by 
filling at 25 C; 

1 — k = fraction of void space at 25 C; 

a = ratio of true density of filling at 25 C to 
that at 65 C; 

a = coefficient of linear expansion for steel: 
13.2 X 10~ 6 ; 

w = water content of PWP, lb per lb dry 
PWP; 

p = density, as indicated by the subscript. 

The density of PWP may be calculated from the 
densities of its constituents as follows: 

_ 1 + w _ 

P ' VP (.75/ p P ) + (.25 /p R ) + (w/p w ) 


The densities of the constituents are as follows: 


25 C 65 C 

Phosphorus, p P 1.824 g/cc 1.715 

Rubber and xylene, p R 0.8840 0.8145 

Water, Pw 0.997 0.9806 

The expansion of the munition shell is given by 


u 1 _ 1 

ui = 1 + 40 X 3a = 1.0016 * 
Assuming that the perfect gas law holds, 
Pv _ T 

■ P#i Ti ’ 

v = u( 1 — k), 


Then 


Vi = Ui — aku = w(1.0016 — ak). 


Pi 


PTi l 1 - k \ 
T \l.0016 - ak) ’ 


( 2 ) 

(3) 

(4) 

(5) 

( 6 ) 


The values of k were calculated for several values of 
w, for Pi = 64.7 psia, P = 14.7, T x = 338, and T — 
298. These are shown in Table 1 with the correspond¬ 
ing values of a. 


Table 1. Per cent void space required in any munition 
to give a maximum pressure of 50 psi at 65 C. 


Water content Ratio of densities 
of PWP at 25 C and 65 C 

lb/100 lb a 

Fraction 

filled 

k 

Per cent 
void 

100 (1 -k) 

0 

1.0725 

0.9130 

8.70 

2 

1.0710 

0.9147 

8.53 

4 

1.0694 

0.9165 

8.35 

6 

1.0679 

0.9182 

8.18 

8 

1.0663 

0.9200 

8.00 

10 

1.0648 

0.9217 

7.83 

12 

1.0633 

0.9234 

7.66 

14 

1.0619 

0.9250 

7.50 

16 

1.0604 

0.9267 

7.33 


The loading tolerances for 75-35 and 75-40 PWP 
containing 12% and 16% water are shown for several 
munitions in Table 2. These are based on volume 
tolerances reported by the Chemical Warfare Service. 

Figure 3 shows the relationship between the in¬ 
ternal void (occluded air) and the density of PWP 
containing 12% and 16% water and also the varia¬ 
tion of the external void space to be left in any muni¬ 
tion if the pressure is not to exceed 50 psi at 65 C. 


37.5.2 Ballistic Stability of PWP 
Munitions 


a The solubility of the air in the filling and the increase in 
vapor pressure of water and xylene are neglected. 


As a result of firing tests on several different types 
of munitions, it was observed that (1) nonrotating 


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558 


PLASTICIZED WHITE PHOSPHORUS 


Table 2. Loading tolerances for PWP in various munitions (12% and 16% H 2 0). 




Minimum 

Maximum 



Per 

loading volume 

weight 



cent 

of munition 

of loading 


Munition 

H 2 0 

cc 

g 

Load to 

4.2-in. CM shell 

12 

2,310 

2,914 

6 lb 5 oz ± 2 oz 


16 


2,878 

6 lb 5 oz ± 2 oz 

4.5-in. Mk 10 Navy rocket, 

12 

3,486 

4,402 

9 lb 9 oz ± 2 oz 


16 


4,343 

9 lb 7 oz ± 2 oz 

3.5-in. Mk 11 rocket 

12 

2,665 

3,365 

7 lb 5 oz ± 2 oz 


16 


3,320 

7 lb 3 oz ± 2 oz 

4.5-in. T84 rocket 

12 

1,694 

2,140 

4 lb 10 oz ±2 oz 


16 


2,112 

4 lb 9 oz ± 2 oz 

3.5-in. Mk 6 Navy rocket 

12 

2,192 

2,768 

6 lb 0 oz ± 2 oz 


16 


2,731 

5 lb 14 oz ±2 oz 

81 mm T9 shell 

12 

1,135 

1,433 

3 lb 1 oz ± 2 oz 


16 


1,414 

3 lb 0 oz ± 2 oz 

M47A2 bomb 

12 

26,219 

33,100 

72 lb 1 oz ± 1 lb 


16 


32,660 

71 lb 2 oz ± 1 lb 


75*40 AND 75-35 PWP 
•EXTERNAL VOID SPACE VERSUS 
DENSITY AT 25 C FOR WT OF \V° 







FILLING TO GIVE PRESSURE OF 

50 LSS PER SQ IN. GAUGE AT 65 ZyS 

yy 







7 

\° 














7' 75-40 AND 75-35 PWP 

INTERNAL VOID SPACE VERSUS — 
.DENSITY FOR 12% AND 16% H 2 0 


7 

< 

7 

7 * 

x^ 

/ V/UIN 1 LIN 1 O 

£ i 

mi cat 



7 







7 ^ 




_ 













_l_Z 

7 

v_ 



0 2 4 6 8 10 12 14 16 

PER CENT VOID SPACE 


Figure 3. External void required in PWP munitions. 


munitions (bombs and fin-stabilized projectiles) filled 
with any type of PWP are ballistically stable; (2) 
properly designed spin-stabilized rockets generally 
have stable flight with either 75-35, or 75-40, or 
stiffer mixes of PWP; (3) spin-stabilized shells with 
low-loading capacity (75 mm) are stable with both 
75-35 and 75-40 PWP; (4) spin-stabilized shells with 
higher loading capacity (4.2-in. mortar, 105 mm and 
155 mm) require a stiff thermally stable PWP if 
stable flight is to be obtained at maximum range or 
at elevated temperatures. 

Much work was done on developing a satisfactory 
PWP for use in the 4.2-in. mortar shell. It was deter¬ 
mined early in the program that mixes with low 
plasticity caused unstable flight when the shells were 
fired at long ranges (above 3,500 yd). Little is known 
about the behavior of gels and plastic solids in these 
shells. Set-back alone, caused by the forward ac¬ 


celeration of the shell from the gun, should not 
materially affect the balance. Instability, when it 
occurs, is perhaps caused by irregular flow of the 
filling as a result of the forward and spin accelera¬ 
tions. Suggested remedies are (1) to make the PWP 
stiffer and more resistant to flow, and (2) to make it 
less viscous and free to flow. To keep the advantages 
of the PWP as a smoke screening agent, all of the 
effort was directed toward making a stiff, thermally 
stable product. 

Data from the firing of several hundred shells filled 
with PWP made of rubber from four different manu¬ 
facturers and consisting of 75-35, 75-40, and 75-42 
compositions gave the following conclusions: 

1. Shells filled with 75-35 PWP with viscosity 
numbers (as measured on the standard plastometer) 
of 35 to 42 are not stable at maximum range. 

2. Shells filled with PWP mixes with viscosity 
numbers greater than 57 are generally stable in flight 
at all ranges. 

3. Heating the shell impairs the ballistic stability. 
This apparently is true only when thermal separation 
of the phosphorus takes place. 

In all these tests, the shells were fired at ambient 
temperatures ranging from 40 to 95 F. Further tests 
showed that the flight stability is affected by heating 
the shells to 100 F, although the effects were notice¬ 
able only at extreme ranges. Shells fired at 120 F were 
unstable at all ranges, although previous firings had 
shown these shells to have good ballistics at all ranges 
when stored and fired at ambient temperatures. It 
was concluded, therefore, that projectiles having 
critical ballistic properties, such as the 4.2-in. mortar 
shell, require PWP of high viscosity. 


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PWP MUNITIONS 


559 


Table 3. Summary of accelerated surveillance tests on 75-35 PWP made at pilot plant. 


Rubber 

manufacturer 

Ship¬ 

ment 

No. 

Batch 
or series 
numbers 

Number 

of 

batches Results 

Firestone Tire and Rubber Co 

6 

C and D series 

81 

“A” samples only, 66 batches showed no separation, 4 
batches showed slight separation, 6 batches were unsatis¬ 
factory, 5 were not tested. 

Firestone Tire and Rubber Co 

18 

E series 

67 

“A” samples only. All were satisfactory. 

B. F. Goodrich 

12 

30E-32E, 42E-45E, 
70E, 6F, 68F 

, 10 

All “A” samples were stable. Four “B” samples were un¬ 
stable. All “C” samples were stable. 

Goodyear Tire and Rubber Co 

13 

51E-53E, 60E, 4F, 
19F, 21F, 77F, 78F 

9 

All “A” samples were stable. Ifour “B” samples were un¬ 
stable. All “C” samples were\ essentially stable. 

National Synthetic Co 

14 

59E, 64E-66E, 

3F, 71F, 72F 

7 

Two “B” samples were unstable. All “A” and “C” samples 
were stable. 

Copolymer Corporation 

15 

63E, 67E-69E, 

IF, 18F 

6 

Four “B” samples were unstable. All “A” and “C” samples 
were stable. 

Copolymer Corporation 

19 

23F, 69F, 70F 

3 

All “A,” “B,” and “C” samples were stable. 

Copolymer Corporation 

31 

1H-4H 

4 

All “A,” “B,” and “C” samples were stable. 


37.5.3 Thermal Stability of PWP 

Phosphorus melts at 111 F and consequently PWP 
munitions in storage will often be subjected to tem¬ 
peratures above the melting point. While in this 
condition, complete separation of the phosphorus 
from the rubber matrix would result in pillaring of 
the smoke and would cause poor ballistics in critically 
balanced projectiles. Tests on the thermal stability of 
75-35 PWP made in the experimental plant indi¬ 
cated that little or no separation of the phosphorus 
takes place even when the material was held at 
150 F for as long as six months. In these tests, the 
samples were stored in glass bottles, and any separa¬ 
tion of the phosphorus or growth of the droplets by 
coalescence was readily discernible. The same results 
were found for samples from the pilot plant when 
tested in this way. It was observed, however, that the 
material loaded in mortar shells often showed some 
separation of the phosphorus after heating for a few 
days. This could be noticed by slushing of the liquid 
from one end of the shell to the other when the muni¬ 
tion was tipped, and was proved by opening the shell 
after cooling. At this time, a small-diameter loading 
screw was being used to extrude the PWP into the 
mortar shell. In order to have sufficient capacity, the 
screw was operated at a high speed and there was 
considerable slippage. Consequently, there was much 
mechanical working of the material as it was forced 
into the shell and flowed through the small openings 
in the longitudinal vane which partitions the shell 
into two parts. Because of the difference between the 
material in the glass bottles and in the shells, it ap¬ 
peared that the mechanical working was damaging 
the texture of the PWP so that it was no longer stable 


when heated. The screw extruder was then replaced 
with an extrusion cylinder of the type used at the 
experimental plant and the expected improvement 
was observed. It was also found at this time that 
many of the samples which were thermally unstable, 
because they had been overworked mechanically, 
would regain their thermal stability if allowed to stand 
for a few days before testing. Apparently, the net¬ 
work of rubber surrounding each phosphorus par¬ 
ticle was repaired by aging. In some cases, however, 
the material appeared to be so badly damaged that 
it never regained the original thermal stability after 
loading. These observations were confirmed by tests 
made by the Chemical Warfare Service in which the 
stability of 75-35 PWP in M47A2 bombs was found 
to be satisfactory, but the same material in 4.2-in. 
mortar shells often showed separation. 

Routine stability tests on the material produced in 
the pilot plant were made on three samples from each 
batch. One, designated “A,” was taken from the 
mixer or hopper as soon as the mixing was completed 
and was placed in the oven immediately. A “B” 
sample was taken from the loading head and was also 
tested immediately. A third sample, “C,” from the 
loading head was tested after aging for 24 hr. A 
summary of the results of these stability tests is 
shown in Table 3. 

A further study of the cause of the occasional in¬ 
stability of batches of 75-35 PWP was made by the 
Plants Division at Edgewood Arsenal. 5 This revealed 
that, as the particle size of the granulated WP de¬ 
creased so that more than 90% of the phosphorus was 
between 30 and 80 mesh, there was a greater number 
of unstable PWP batches. This result was consistent 
with the greater number of particles in the finer 


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560 


PLASTICIZED WHITE PHOSPHORUS 


Table 4. Summary of surveillance tests on 75-35 PWP in various munitions. 


Rubber 

manufacturer and 
shipment number 

Batch 

number 

Number in 
surveil¬ 
lance 

Thermal stability 
expressed as per 
cent phosphorus 
separating 

Days in 
surveil¬ 
lance 




A 

M/+7A2 ( 100-lb ) bomb 


Goodrich 

12 

68F 


1 

0 

60 

Goodyear 

13 

77F 


1 

0 

30 

National 

14 

72F 


1 

0 

60 

National 

20 

73F 


1 

0 

30 

Copolymer 

19 

70F 


1 

0 

60 




B 

4.5-in. naval rockets 


Firestone 

6 

36D 


4* 

23, 30, 30, 36 


Copolymer 

15 

18F 


2 

0, 2 


Goodyear 

13 

19F 


2 

0,2 


Goodyear 

13 

21F 


4 

0, 0, 0, 0 

90-180 

Goodrich 

12 

68F 


3 

0, 4, 21 • 

90-180 

National 

14 

71F 


3 

0, 0, 1 

90-180 

National 

14 

72F 


2 

0, 1 

90-180 

Copolymer 

19 

23F 


3 

0, 0, 10 

90-180 

Copolymer 

19 

69F 


2 

0, 0 

90-180 

Copolymer 

19 

70F 


2 

0, 6 

90-180 

National 

20 

73F 


3 

0, 0, 11 

90-180 




C 

3.5-in. naval rockets 


Firestone 

6 

30D 


5 

0, 0, 0, 1, 2 

15-30 

Copolymer 

22 

87L, 

95L, 100L 4 

0, 0, 8, 13.5 

15-30 

Copolymer 

23 

110L, 115L, 120L, 





125L, 130L 5 

0, 1, 3, 3, 4 

15-30 




D 

81-mm mortar shells 


Copolymer 

21 

1H, 2H, 3H 9 

A110 

60-90 


* Loaded by screw extruder. 


granulated material which presented more surface 
and decreased the film thickness of the rubber. 
Furthermore, it was found that many of the unstable 
batches had a higher density than the stable batches, 
indicating a higher phosphorus content. On the basis 
of several months’ operation of the plant, it was possi¬ 
ble to derive an instability factor represented by 

u = [100(apparent density — 1.26)] 2 + (% WP be¬ 
tween 30 mesh and 80 mesh standard screen — 70) # 

These results led to the conclusion that, under the 
conditions existing at the Edgewood Arsenal plant, 
and using the rubber then available, it was advisable 
to maintain the particle size of the granulated phos¬ 
phorus so that less than 60 to 70% passes a 30-mesh 
screen. Furthermore, careful control of the phos¬ 
phorus content of the PWP must be exercised so 
that it will not exceed 75%, corresponding to an 
apparent density of 1.26. 

A summary of the surveillance results on 75-35 
PWP in bombs and rockets loaded at the NDRC 
pilot plant at Victor Chemical Works is shown in 
Table 4. The explanation of the occasional unstable 


batches might well be found in the lack of control of 
the degree of granulation and the composition of the 
material as was the case at Edgewood Arsenal. 

When it became necessary to produce material of 
higher viscosity than 75-35 PWP in order to over¬ 
come the ballistic difficulties encountered with the 
critically balanced projectiles, the loading problem 
became more serious. PWP 75-40, which contains 
2.5% more rubber in the mixture, has a viscosity 
number nearly twice that of the 75-35 PWP. Conse¬ 
quently, the amount of work done on the material in 
forcing it through a small filling tube frequently 
caused the material to become thermally unstable 
regardless of the method used for loading. Somewhat 
better results were obtained on PWP with high 
viscosity made with vegetable oil plasticizers, but 
even here the results were erratic. 

Table 5 is a summary of the surveillance tests on 
75-40 PWP in 4.2-in. mortar shells filled at the pilot 
plant. Table 6 contains the results on representative 
batches from 6,500 shells filled at the same plant with 
PWP containing vegetable oils. 

Since the viscosity of PWP is an important prop- 


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PWP AS A SCREENING AGENT 


561 


Table 5. Summary of surveillance tests on 75-40 PWP in 4.2-in. mortar shells, M-2. 


Rubber 

manufacturer and 
shipment number 

Batch 

number 

Number of 
shells in 
surveillance 

Thermal stability as 
per cent of phosphorus 
separating 

Firestone 

6 

A Loaded with screw extruder 

34C, 25D 5 

11, 14, 31, 36, 39 

Firestone 

18 

19E, 25E 

6 

0, 0, 0, <1, <1, 3 

Goodrich 

12 

33E 

3 

>30, >30, >30 

Goodyear 

13 

49E 

3 

>30, >30, >30 

National 

14 

58E 

1 

10 

Copolymer 

Goodrich 

12 

61E 

B Loaded with hydraulic ram extruder 
7F 5 

| 

10, 13, 27, 33, >30 

Goodrich 

12 

22F 

7 

3, 4, 8, 17, 20, 20, 24 

Goodyear 

13 

5F 

6 

>30, 33, 38, 41, 44 

Goodyear 

13 

20F 

8 

4, 11, 18, 23, 43, 44, 46, 49 

Copolymer 

15 

2F 

5 

0.5, 0.5, 7, 7, 18 

Copolymer 

15 

8F 

3 

28, 50, 70 

Copolymer 

15 

9F 

2 

19, 31 

Copolymer 

15 

10F 

3 

11, 41, 70 

Copolymer 

15 

11F 

3 

6, 15, 36 

Copolymer 

15 

12F 

3 

9, 11, 27 

Copolymer 

15 

13F 

3 

7, 11, 36 

Copolymer 

15 

14F 

3 

<1, 3, 26 

Copolymer 

15 

15F 

3 

8, 13, 19 

Copolymer 

15 

16F 

1 

0 

Copolymer 

19 

24F 

5 

18, 25, 26, 28, 28 

Copolymer 

19 

25F 

2 

13, 34 

Copolymer 

19 

26F 

2 

10, 22 

Copolymer 

19 

27F 

2 

1.5, 5 

Copolymer 

19 

28F 

2 

2.5, 7 

Copolymer 

19 

29F-34F 

6 (1 each) 

0, 2, 6, 7, 18, 41 

Copolymer 

19 

35F-39F 

6 (1 each) 

2, 6, 11, 13, 20, 40 

Copolymer 

19 

40F-45F 

6 (1 each) 

10, 17, 18, 19, 19, 37 

Copolymer 

19 

46F-51F 

6 (1 each) 

1, 4, 6, 9, 11, 33 

Copolymer 

19 

52F-57F 

6 (1 each) 

4, 13, 16, 23, 25, 27 

Copolymer 

19 

58F-63F 

7 

0, 1.5, 3, 12, 20, 24, 43 

Copolymer 

19 

64F-66F 

4 (2 each) 

40, 40, 48, 48 

Copolymer 

19 

G1-G5 

2(1 each) 

0 , 0 


erty affecting the ballistics, it was desirable to know 
the effect of prolonged aging on this property. 
Measurements were made on a large number of 
samples over a period of several months. The results 
are summarized in Table 7 and show that, in general, 
the viscosity increases slightly for a few days after 
manufacture and then remains essentially constant. 

The cause of the thermal instability of high- 
viscosity PWP is not fully understood. Although it 
appears to be related to the physical structure of the 
mixture, there is also some evidence that the phos¬ 
phorus itself exerts a chemical effect on some rubbers, 
causing an increase in the gel content in the film 
surrounding the particles, thereby destroying the 
strength and elasticity of the membranes. This effect 
is greater in some rubbers than in others. Furthermore, 
it is influenced by the acidity and oxygen content of 
the mixture. It is concluded that the 75-35 PWP, 


which is the filling to be used for bombs, rockets, and 
projectiles without critical ballistics, can be made 
thermally stable and otherwise satisfactory from a 
surveillance standpoint, but the manufacturing de¬ 
tails of the more viscous filling for high-velocity, spin- 
stabilized shells have not yet been developed, and 
more information is necessary before a satisfactory 
product can be produced. 

37.6 PWP AS A SCREENING AGENT 

37.6.1 Tests on the 4.2-in. Chemical 
Mortar Shell and M47A2 Bomb at 
Dugway Proving Ground 

After the preliminary tests on screening efficiency 
of PWP, 4.2-in. CM shells and M47A2 bombs were 
tested at Dugway Proving Ground in the spring of 
1944. When compared with the same munitions filled 


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562 


PLASTICIZED WHITE PHOSPHORUS 



Figure 4. Comparison of 4.2-inch CM shells fired at 3,000 yards at about 1 minute intervals. (A) Standard WP. (B) Plas¬ 
ticized WP. 


Table 6 . Thermal stability of 75-40 PWP containing vegetable oil plasticizers in 4.2-in. mortar shells. 

Thermal stability 


Sample from filling 


Rubber 
manufacturer 
and shipment 

Batch 

number 

Composition 

head tested in 
glass after 24 hr 
% separation 

Age when 
placed 
in oven 

Days in 
surveil¬ 
lance 

% 

Separation 
of phosphorus 

Copolymer 

21 

K-l 

75-40-25LO 

0 

8 

14 

0 

Copolymer 

21 

K-2 

75-40-25LO 

0 

8 

14 

0 

Copolymer 

21 

K-5 

75-^0-25LO 

15 

7 

12 

30 

Copolymer 

22 

K-6 

75-40-25LO 

50 

6 

11 

30 

Copolymer 

22 

K-26 

75-40-25LO 

0 

10 

7 

0 

Copolymer 

22 

K-28 

75-40-25LO 

0 

9 

7 

2 

Copolymer 

22 

K-33 

75-40-25LO 

0 

9 

7 

10 

Copolymer 

21 

K-3 

75-40-30LO 

0 

7 

14 

0 

Copolymer 

22 

K-7 

75-40-30LO 

10 

13 

7 

10 

Copolymer 

22 

K-9 

75-40-30LO 

0 

6 

10 

15 

Copolymer 

22 

K-l 8 

75-40-30LO 

25 

13 

7 

0 

Copolymer 

22 

K-35 

75-40-20SO 

0 

9 

7 

3 

Copolymer 

22 

K-41 

75-40-20SO 

0 

9 

7 

0 

Copolymer 

21 

L-l 

75-40-30LO 

0 

7 

7 

0 

Copolymer 

21 

L-ll 

75-40-30LO 

3 

7 

7 

38 

Copolymer 

21 

L-23 

75-40-30LO 

5 

7 

7 

75 

Copolymer 

21 

L-41 

75-40-30LO 

0 

7 

7 

57 

Nat Syn 

20 

L-27 

75-40-30LO 

20 

7 

7 

75 

Nat Syn 

20 

L-51 

75-40-25LO 

15 

8 

7 

50 

Nat Syn 

20 

L-61 

75-40-25LO 

0 

7 

7 

3 

Nat Syn 

20 

L-62 

75-40-20SO 

0 

7 

7 

3 

Nat Syn 

20 

L-70 

75-40-25LO 

0 

9 

7 

8 

Nat Syn 

20 

L-80 

75-40-25LO 

0 

7 

7 

16 

Nat Syn 

20 

L-81 

75-40-25LO 

0 

7 

7 

16 


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PAYP AS A SCREENING AGENT 


563 


Table 7. Effect of aging on apparent viscosity of 
PWP. 


Rubber 
manufacturer 
and shipment 

Batch 

number* 

Viscosity 
Composition number 

Age 

days 

Copolymer 

15 

E-61 

75-40 

62 

18 





71 

154 

Goodrich 

12 

frl 

r 

00 

o 

75-35 

48 

40 





48 

58 

Goodrich 

12 

E-33 

75-40 

52 

11 





,58 

40 

Goodrich 

12 

E-34 

75-42 

57 

11 





58 

40 

Goodyear 

13 

E-51 

75-35 

52 

34 





57 

50 

Goodyear 

13 

E-60 

75-35 

52 

25 





41 

156 

National 

14 

E-64 

75-35 

49 

15 





51 

37 

National 

14 

E-65 

75-35 

46 

15 





55 

37 

National 

14 

E-71 

75-42 

75 

13 





71 

151 

Copolymer 

19 

N-90 

75-40-30LOf 

91 

37 





93 

72 

Copolymer 

19 

X-114 

75-40-30LO 

83 

2 





76 

5 





79 

43 

Copolymer 

19 

X-145 

75-40-30LO 

77 

2 





73 

28 

Copolymer 

19 

X-130 

75-40-10SOJ 

62 

1 





76 

36 

Copolymer 

19 

X-133 

75-40-20SO 

78 

1 





97 

35 

Copolymer 

19 

X-135 

75-40-30SO 

130 

1 





140 

37 

Copolymer 

19 

X-127 

75-40-10CO§ 

48 

1 





57 

36 

Copolymer 

19 

X-129 

75-40-20CO 

57 

1 





71 

36 

Copolymer 

19 

X-134 

75-40-30CO 

77 

1 





88 

35 

National 

20 

L-31 

75-40-25LO 

71 

1 





78 

37 

National 

20 

L-27 

75-40-30LO 

78 

1 





78 

3 





84 

38 

National 

20 

L-62 

75-40-20SO 

63 

1 





68 

16 

Copolymer 

19 

G-2 

75-40-20SO 

81 

2 





104 

29 

Copolymer 

19 

G-4 

75-40-30LO 

74 

2 





89 

30 

Copolymer 

21 

K-l 

75-40-30LO 

70 

1 





88 

5 


* X-batches made at MDL, all others at Victor Chemical Works, 
t Boiled linseed oil used as plasticizer. Percentage used in rubber mix 
indicated by number preceding LO. 
t Refined soybean oil used as plasticizer. 

§ Refined cottonseed oil used as plasticizer. 


with WP, the PWP rounds produced markedly 
superior smoke screens. Figure 4 shows the difference 
in the smoke screens produced by mortar shells with 
the two types of filling. In contrast to those from WP, 
the screen from the PWP is continuous and the 
pillaring is negligible. In the case of the M47A2 bomb, 
the plasticized phosphorus produced about one-half 
as much a pillar as the solid phosphorus. The ground 
screen from the former, in contrast with that from 
the standard munition, had/ no tendency to lift. The 
duration of the screen near the source was at least 
2.5 min compared with 1 min for the WP filling. 
Partial screening continued for several minutes 
longer. The area contaminated by the PWP was 
about 15,000 sq yd, whereas that contaminated by 
the solid WP was about 2,500 sq yd. 

In May and June 1944, extensive tests were con¬ 
ducted at Dugway Proving Ground to compare 
M47A2 bombs filled with WP, WPT, and PWP. As a 
result of these, the following conclusions were 
reached relative to the M47A2 bomb with PWP. 7 

1. The M-4 burster is too powerful for use with 
PWP in the M47A2 bomb on hard ground. 

2. The M-7 burster has insufficient brisance for 
the PWP-filled M47A2 bomb. 

3. The %6-in. TNT burster does not give sufficient 
distribution of the PWP when dropped in the M47A2 
bomb. The smoke screening is excellent, but possible 
antipersonnel effects are reduced. 

4. The J^-in. tetryl burster gives satisfactory re¬ 
sults on both hard and soft ground with M47A2 
bomb filled with PWP. 

5. The 75-40 PWP produced a slightly better 
smoke screen than either the 75-35 or the 75-42 mix, 
but has less effective antipersonnel distribution than 
the 75-35 mix. 

6. The PWP filling in the M47A2 bomb produced 
a better smoke screen and better antipersonnel distri- - 
bution than either the WP or WPT; the WPT ranks 
second in effectiveness. (WPT is a combination of 
WP and paper tubes, the latter adding mechanical 
strength and reducing the fragmentation of the 
phosphorus.) 

Comparison tests were later made by the Chemical 
Warfare Board on the relative screening effectiveness 
of 4.2-in. chemical mortar shells filled with WP, 
SWP, and PWP. (SWP is a mechanical mixture of 
steel wool pellets and phosphorus.) The reports of 
these tests indicate that the PWP rounds were dis¬ 
tinctly superior to the others, for either land or water 
impact. 


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564 


PLASTICIZED WHITE PHOSPHORUS 


37.6.2 PWP in the 4.2-in. Recoilless 

Mortar Shell 

For use at low-angle fire, PWP proved very suc¬ 
cessful when used in the 4.2-in. recoilless mortar 
shell. In a large scale simulated combat problem at 
Camp Hood, Texas, in July 1945, this round was 
used for firing against cave installations with excel¬ 
lent results. During one test, five rounds of PWP- 
filled shell were fired into a small cave entrance and 
the smoke completely prevented observation from 
the inside of the cave for more than 15 min. 8 

37.6.3 PWP in Other Army Munitions 

In addition to the munitions already mentioned, 
PWP was accepted for standardization in the follow¬ 
ing munitions used by the Army Ground Forces: 
60-mm mortar shell, 9 81-mm mortar shell, 9 4.5-in. spin- 
stabilized rocket, and 2.36-in. rockets. It was shown 
to be superior to WP for laying smoke screens in the 
75-mm, 105-mm, and 155-mm shells. Since these are 
seldom used to lay screens, however, but rather are 
used mainly as spotting rounds, WP has an advantage 
over PWP because of the pillaring effect of the smoke 
cloud. Therefore, it was not anticipated that these 
rounds will be filled with PWP. 

37.6.4 PWP in Navy Munitions 

PWP filling was first tested in Navy 4.5-in. bar¬ 
rage rockets in an extensive program on smoke 
tactics at the Amphibious Training Base, Fort 
Pierce, Florida, in June 1944. It was concluded that 
the new filling, because of its longer burning time, 
was superior to both FS and WP for land impact and 
about equal to FS and superior to WP for water 
impact. 10 

The superiority of the PWP over both FS and WP 
for screening landing operations was clearly demon¬ 
strated, in the tactical evaluation of the 4.5-in. rocket, 
the 7.2-in. chemical rocket and the 4.2-in. chemical 
mortar shells. 11 The munition requirements with 
PWP were appreciably less than those for the other 
fillings, and under some conditions, screens could be 
laid with PWP which were completely impractical 
with either FS or WP. These munitions were con¬ 
sidered most effective in laying flank screens with 
offshore winds, and in screening enemy positions at 
some distance from the landing beach. Effective burn¬ 


ing times up to 4 min were obtained. The 4.5-in. 
rockets functioned quite satisfactorily on both land 
and water impact. The chemical mortar shells filled 
with PWP functioned well on land, but on water the 
quantity of smoke was considerably reduced. Tum¬ 
bling of the shells was not observed at the ranges used 
(500 to 2,000 yd). The 7.2-in. rockets functioned 
satisfactorily on land impact, but produced no smoke 
at all on the water. Therefore, the %-in. tetrvl 
burster and the Mk 137 Mod 1 fuze were considered 
unsatisfactory for the PWP filling. As a result of 
these tests, it was recommended that PWP-filled 
4.2-in. mortar shells and 4.5-in. rockets be procured 
as quickly as PWP could be made available. 

In the course of the work at Fort Pierce, M47A2 
bombs filled with PWP were tested tactically in com¬ 
parison with the standard WP filled munitions. 12 The 
PWP-filled bombs were again found more satisfactory 
for screening landing operations than the WP-filled 
munitions. The modified M-4 burster, consisting of 
%6-in. diameter TNT pellets with a tetryl pellet at 
each end, gave better results than the standard M-4. 
The bombs were considered particularly useful for 
laying flank screens with offshore winds, six being 
required for a screen of 8 min duration. In general, 
the bombs were considered most satisfactory in 
screening areas removed from the landing beach so 
that the antipersonnel effect of burning PWP could 
be exploited without interfering with friendly troops 
after the landing. The procurement of M47A2 PWP- 
filled bombs for the Navy was recommended in view 
of their general utility for screening landings. 

A further demonstration of the effectiveness of 
PWP filling was carried out by the Amphibious 
Forces, U S Pacific Fleet, at Oahu in December 
1944. 13 Both 4.5-in. rockets and M47A2 bombs were 
used. Figures 5, 6, and 7 show pictures of the screens 
in comparison with screens from WP bombs. It was 
concluded that effective screens could be maintained 
for from 2 to 5 times as long as with an equal quantity 
of bombs and rockets filled with WP or FS. It was 
recommended that delivery of munitions with this 
filling to the theaters of operation be expedited. 
Large-scale procurement was therefore initiated, but 
unfortunately no munitions reached the forward 
areas in time to be used in any operation. 

As a result of the tests in Hawaii, a PWP filling for 
3.5-in. aircraft rockets was developed and adopted. 
These were tested in June 1945 at the Naval Proving 
Ground, Dahlgren, Virginia. The 75-35 mixture was 
considered satisfactory and a %-in. diameter tetryl 


SECRET 



PWP AS A SCREENING AGENT 


565 



Figure 5. Smoke screen from ninety 4.5-inch Navy rockets, MklO, PWP filled, fired from an LCI(G). Thirty-six rockets 
were fired in salvo after ranging in and then an additional 6 rockets were fired in salvo every 20 seconds. The screen was 
effective for about 9 minutes. (A) Aerial view of impact pattern of 36-round ripple. Streamers from individual rocket bursts 
show dispersion of large particles of PWP which have excellent antipersonnel effect. (B) Aerial view 1 minute after impact, 
showing PWP emitting smoke vigorously, and also the effect of eddy currents in spreading smoke over shoreward side and 
in crater of island. (C) Aerial view 4 minutes after initial impact showing very effective coverage of shoreward face of 
island and crater filled with smoke. (Official Navy Photo.) 

burster gave best results. However, rockets with the 
standard %-in. tetryl burster produced good smoke 
screens and were considered satisfactory until the 
smaller burster could be obtained. 

In addition to the above, the development of a 
canister and burster for PWP filling for the 5^-in. 
smoke shell was under way at the University of 
Illinois at the end of the war. Earlier experiments had 
shown that when the plastic filling was used in light 


munitions, a heavier burster was necessary than was 
used with WP filling. 14 A series of firing tests was 
carried out in June 1945, which showed that 30 g 
81-mm powder, or 40-50 g tetryl is required to give 
satisfactory smoke screens. 

37.6.5 Antipersonnel Effects of PWP 

White phosphorus munitions were often used dur¬ 
ing the war for antipersonnel effects. The results ob- 


SECRET 




566 


PLASTICIZED WHITE PHOSPHORUS 



Figure 6. Smoke screen produced from four 100-lb M47A2 bombs, WP filled, with ^-charge M7 black powder bursters. 
A large proportion of the smoke has risen in a pillar and is not effective for screening at the surface. Compare with Fig¬ 
ure 7. (A) Aerial view 1 minute, 30 seconds after initial bomb burst. (B) Surface view 1 minute, 30 seconds after initial 
burst. (Official Navy Photo.) 


tained depended upon the disposition, discipline, and 
morale of the enemy. Combat reports often cited 
instances where the use of WP was more effective 
than HE. In some situations, a combination of the 
two was used with good results. In other cases, the 
use of WP as an antipersonnel agent was disappoint¬ 
ing, especially when the enemy was well disciplined 
and made use of protective cover. 

The first tests designed to compare the relative 


antipersonnel effectiveness of PWP and WP were 
made at Dugway Proving Ground in May 1944. 15 
Chemical mortar shells filled with PWP and WP 
were fired at 2,200-yd range onto a target area con¬ 
taminating straw-filled dummies, dressed in one layer 
of HBT cloth, located in shallow slit trenches. In 
addition, closely clipped goats were exposed to the 
fragments of PWP and WP at a distance of 15 yd 
from statically fired shells. The evaluation of the 


SECRET 



PWP AS A SCREENING AGENT 


567 



Figure 7. Smoke screen produced from four 100-lb M47A2 bombs, PWP filled, with ^-charge M-7 black powder bursters 
The screen was effective for a distance of 1,000 yards downwind from the source of a period of 8 minutes. (A) Aerial view 
of flank screen 1 minute, 8 seconds after burst. (B) Surface view 2 minutes, 25 seconds after burst. Note the small amount 
of smoke in the pillar from PWP as compared with the smoke in the pillar from WP in Figure 6. (Official Navy Photo.) 


effectiveness of the phosphorus was based on the 
number, size, and location of hits on the dummies. 13 
Burns obtained on goats were assessed according to 
number, size, and severity. Insufficient hits were ob¬ 
tained to give an evaluation of the casualty producing 
effects, but comparison of the burns from the two 
types of phosphorus was made. Test results showed: 

1. There is no essential difference in the rate of 
healing of comparable burns from WP or PWP. 

2. Because of the wider distribution of larger par¬ 


ticles of PWP, a larger number of personnel will be 
hit with PWP than with WP. 

3. No antipersonnel merits are lost through the 
use of PWP instead of WP. 

Subsequent to these tests, the University of Illinois 
did considerable work on the fragmentation of PWP 
and WP in the burst of statically fired 4.2-in. chemi¬ 
cal mortar shells, the effect of burning PWP and WP 
on cloth, and on the temperature of burning pieces of 
PWP and WP. 3 The conclusions reached were as 


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568 


PLASTICIZED WHITE PHOSPHORUS 


follows: 

1. From a static burst of 4.2-in. chemical mortar 
shell charged PWP, as many as 4,900 burning par¬ 
ticles larger than 0.025 g reached the ground. The 
maximum concentration of the particles occurred 
about 30 ft from the burst where there were about 35 
particles per 100 sq ft. The amount of the filling 
reaching the ground was between 17 and 41%. For 
WP shells the amount of the filling available for anti¬ 
personnel purposes was less than 5%. The maximum 
concentration occurred within 15 ft of the burst, and 
the total number of particles greater than 0.0125 g 
varied from 100 to 2,650 for different bursts. 

2. The burns produced on cloth by WP and PWP 
were of approximately the same size as these particles 
produced on noninflammable material. The size of 
burn from a piece of PWP was considerably smaller 
than a burn produced by an equal weight of WP. 

3. Vaporized phosphorus from both WP and PWP 
was observed to diffuse through six layers of cloth. 

4. The flame temperature of PWP is higher than 
that of WP, but the burning of PWP does not cause 
it to become hot enough to cause the rubber to flow. 
The phosphorus and xylene are given off in both 
liquid and gaseous form. 

Additional work on the antipersonnel effects of 
WP, PWP, and SWP has been reported by the Medi¬ 
cal Research Laboratory at Dugway Proving Ground 
in weekly reports from February through August, 
1945. The comparative results may be summarized 
as follows: 

1. Tests on the penetration of two layers of cloth 
separated from 0 to 19 mm by an air space with 
100-mg pieces of WP and PWP showed the PWP 
to be inferior to the WP as measured by the time of 
penetration (3 sec vs 1 sec), size of burn on the cloth 
layers (18 mm diameter vs 28 mm diameter), and the 
thickness of air space they will penetrate (10 mm vs 
19 mm). 

2. The distribution of stain diameters on horizon¬ 
tal and vertical cards was determined for PWP, WP, 
and SWP from statically fired 4.2-in. chemical mortar 
shells. The ranges of stain diameters (in mm) used for 
classification were 60 to 100, 40 to 60, 25 to 40, 15 to 
25, and 5 to 15. Compared with results from WP, the 
number of stains in the range 5 to 15 mm diameter is 
less for PWP. For other ranges, the number of stains 
near the point of burst is about the same for each 
agent, but with PWP the density does not decrease 
as rapidly with increasing distance from the shell as 
with WP. Similar tests showed that with SWP, the 


stain size distribution was essentially the same as for 
WP. 

3. Tests were conducted to explore the effects of 
extremely heavy contaminations of WP in producing 
significant disability or death among closely clipped 
goats. In each test, four 4.2-in. chemical mortar shells 
were arranged symmetrically about the test animals 
placed on the ground surface and in slit trenches. The 
shell fillings were WP, PWP, and SWP. Goats were 
from 3.5 to 17.5 yd from the points of burst. Although 
in some cases, extensive second degree burns were ob¬ 
tained, none of the goats was more than mildly in¬ 
jured by the incendiary filling. It is concluded that, 
among closely clipped goats, neither death nor in¬ 
capacitating injury may be achieved by means of 
4.2-in. shells filled with WP, SWP, or PWP. There 
was little difference in the results obtained with the 
three types of fillings. 

On the basis of all these tests it may be concluded 
that PWP compares favorably with WP as an anti¬ 
personnel agent. The value of each depends on the 
tactical situation, the weather, and the discipline, 
disposition, attire, and morale of the enemy troops. 

37.7 SPECIFICATIONS AND CONTROLS 
USED IN THE MANUFACTURE OF PWP 

37.7.1 Plant Inspection Methods 

The following inspection procedures were used in 
the operation of the PWP plant at Edgewood 
Arsenal. 

Particle Size 

Specification. The white phosphorus shall be of 
such fineness that 75% shall be in the range of 0.2 mm 
to 0.6 mm in diameter, and not more than 5% shall 
be in excess of 1.2 mm in diameter. 

The particle size of the phosphorus was measured 
by sieve analysis on each batch. A check was made 
between the results obtained by this method and 
those by microscopic examination. The sieve analysis 
proved more complete and accurate. 

The analysis was run as follows: 

1. A sample of one-half pint of the granules is used. 

2. A series of three screens, 16-mesh, 30-mesh, and 
80-mesh, is used and the weight of granules retained 
on each of these screens is determined. 

The method of determining the weight of granules 
held on a given screen is as follows: 

1. A graduate is filled with water to a given mark 
and the weight of graduate plus water is determined. 


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CONTROLS IN THE MANUFACTURE OF PWP 


569 


2. The sample of granules is transferred to the 
graduate and the graduate refilled to the same mark 
with water and re weighed. 

3. The difference between the weights is deter¬ 
mined. 

4. The percentage in each range is calculated as 
follows: 

Let G = weight of graduate in grams; 

W = weight of water to fill graduate to 
mark; 

X = volume of WP granules; 

1.8X = weight of WP granules. 

Thus: Sp gr of water = 1.0; Sp gr of WP = 1.80. 

(1) Wt of graduate plus water to mark = G -f W 

(2) Wt of graduate plus water plus WP to mark 
= G + (W - X) + 1.8X = G + W + 0.8X 
Difference in wt, [(2) — (1)] = 0.8X, 

where 

X = difference in weight/0.8 = volume of WP 
1.8X = 2.25 X difference in weight = wt of WP 

_ . , „ ^ difference in weight 

% by wt = 100 X ——-:-— • 

2 (difference in weight) 

The accuracy of the method depends upon the error 
in reading the level in the graduate, and thus, the 
graduate should be as small in diameter as possible. 

Moisture 

Specification. Moisture content was tentatively set 
at a maximum of 12% by weight. 

In the early operation of the plant at Edge wood 
Arsenal the per cent moisture in the PWP was de¬ 
termined for each batch using samples from the mixer 
and from the extruder. The greatest source of error 
was in sampling. Because of the nature of the ma¬ 
terial and its tendency to exude water, it is doubtful 
that the results were accurate. Duplicate samples, 
however, gave fairly reproducible results. Later, the 
samples were taken from material extruded into a 
rocket body which was split and the halves clamped 
together. A 20- to 30-g sample was used. The water 
content was determined as prescribed in Federal 
Specification VV-L-791 (Method No. 300.14) using 
xylene as the solvent. 

Thermal Stability 

Specification. It was stipulated that not more than 
2% by weight of white phosphorus should separate 
from the material when tested as prescribed. 

A sample was taken from the mixer, and two 
samples were taken from the extruder for each batch. 
The mixer sample and one extruder sample were 


placed in the oven immediately. If the extruder 
sample showed less than 2% separation of the phos¬ 
phorus after heating to 150 F for 24 hr, the other 
sample, which had aged 24 hr, was put in the oven 
for surveillance. Initially, the sample was extruded 
directly into a bottle, but later it was taken from the 
split rocket body. 

The amount of separation was determined visually 
using the following code: 

O.K. no separation 0% 

Fair a few small droplets separation 0 to 2% 
Poor a pocket of separation covering 

less than half the bottom 2 to 5% 

N.G. anything from a layer covering 
the bottom to complete sepa¬ 
ration 5% or more 

Specific Gravity 

Specification. None. 

The specific gravity was determined on the sample 
used for moisture determination. 

The weighing vessel consisted of a wide-mouth 
container equipped with a sliding cover which closed 
the vessel without trapping air. Four weight deter¬ 
minations were necessary to determine the specific 
gravity: (1) the container filled with water, (2) the 
container partially filled with water, (3) the same 
plus the sample of PWP, and (4) the container with 
the PWP filled with water. 

The difference between (2) and (3) gives the weight 
of the sample. The difference between (4) and (1) 
subtracted from the weight of the sample gives the 
weight of water displaced by the sample and is there¬ 
fore equivalent to its volume. From the volume and 
weight of the sample the specific gravity was de¬ 
termined. 

37.7.2 Plant Control Methods 

Apparent Viscosity 

Specification. None. 

Apparatus. The extrusion plastometer used for 
measuring the viscosity of PWP is shown in Figure 8. 
It consisted of a cylinder having a cross-sectional 
area of 1.0 sq in., fitted with a piston, and with an 
orifice plug with an opening Y^-\n. diameter and 
in. long. The top of the orifice plug is tapered 
at a 45° angle to meet the diameter of the cylinder. 
Figure 9 shows the apparatus used to apply a known 
weight to the extrusion plastometer. The weights 
(25 and 50 lb each) are placed on a platform mounted 


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570 


PLASTICIZED WHITE PHOSPHORUS 




PISTON 

GUIDE 


plasticity 

CYLINDER 


PISTON 
(GROUND FIT ) 


l/4"ORIFICE 

PLUG 


I SCALE H 

Figure 8. Extrusion plastometer. 

on the shaft which was raised and lowered by the 
reversible motor mounted on top. In addition, a 
hydraulic press capable of exerting a force of 3,000 lb 
and a thermostatic bath were required. 

Method. The sample of PWP is brought to 25 C by 
storage in a water bath. The empty cylinder is fitted 
with a solid plug instead of the orifice and filled 
nearly to the top with the sample by tamping firmly 
with a rod. The sample is then compacted in the 
hydraulic press with a force of about 3,000 lb for a 
minute. This forces out the pockets of air and water 
and assures uniformity. The solid plug in the cylinder 
is then replaced by the orifice and the plastometer is 


200 TO 1 



Figure 9. Loading mechanism for extrusion plastom¬ 
eter. 


mounted in its holder in a can filled with water at 
25 C. The weighted shaft is lowered and the time re¬ 
quired for the piston to move through a distance of 
4 cm, after a preliminary 2 cm, is observed from 
calibration marks on the shaft. Generally two read¬ 
ings are obtained from the same sample by making 
a separate measurement of the time required to pass 
through a second 4 cm immediately following the 
first four. The time for the first 4 cm is referred to as 
h and the time for the second 4 cm as h. 

Calculation of Results. The shearing stress F and 
the indicated rate of shear S were calculated from the 
formulas: 17 




_ Pr JF 
~ 2 L = ttR- 2 L 
4 X 6.45 X F/60 


7t r 


7t(2.54/8) 3 


= 0.333IT 


= 4.28T = 


17.1 


where P = pressure on sample in psi, 
R = radius of cylinder in cm, 
r = radius of capillary in cm, 
L = length of capillary in cm, 
q = rate of efflux in cc per sec, 
F = stress in psi, 

S = rate of shear in sec -1 , 


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CONTROLS IN THE MANUFACTURE OF PWP 


571 



10 15 20 25 30 40 50 60 70 80 90 100 


F- SHEARING STRESS IN LB PER SQ IN. 

Figure 10. Rate of shear; shearing stress curves for 

PWP samples. 

V = rate of movement of piston in cm per min, 
W = weight in lb, 

t = time in minutes required for piston to 
travel 4 cm. 

In practice it was found that h is usually larger 
than U The average was used. 

If the values of F and S obtained by using several 
different weights are plotted on log-log paper as in 
Figure 10, straight lines are obtained. The consist¬ 
ency, or apparent viscosity, of the material at any 
shearing rate is simply the ratio F/S. As an arbitrary 
value, the stress required to produce a shearing rate 
of 100 sec -1 was chosen to characterize PWP. Since 
the values were not absolute this was called the 
viscosity number. 

Accuracy of the Method. Even though no absolute 
significance can be attached to the viscosity number 
determined with this instrument, the results were 
useful in comparing samples of PWP. The chief dif¬ 


ficulty in getting reproducible data resulted from the 
variation in particle size of the phosphorus which 
occurred from one batch to another. If a sample con¬ 
tained a large number of phosphorus particles that 
were near the size of the orifice, a high value was ob¬ 
tained. Even in a single sample there was likely to be 
a noticeable variation in consistency. This was par¬ 
ticularly true of samples that have been stored for 
some time, where the PWP on the surface was found 
to be stiffer than that underneath. 

If a sample contained no particles larger than 
1-mm diameter, and if care was taken in selecting a 
sample to fill the plastometer, the values obtained 
were generally reproducible to within 5%. 

Viscosity of Concentrated Rubber Solution by 
the Falling Ball Method 

Specification. None. 

Apparatus Used. 1. Test tubes, 150 x 16 mm, with 
marks etched or scratched 2 cm apart. 

2. Soft iron hexagonal plungers K6 x 1J4 i n - 

3. Machine for homogenizing the rubber solutions. 

4. Centrifuge. 

5. Constant temperature bath. 

6. Steel balls in., or 0.1588 cm). 

7. Cork fitted with small funnel, made by flanging 
the end of capillary tubing (2 mm), for introducing 
ball bearings into the center of the liquid surface. 

8. Stop watch. 

Method. The exact diameters of the ball bearings 
are measured with a micrometer and several are 
selected which are within 0.0005 cm of the same size. 
A known number of ball bearings is then weighed and 
their density calculated. Two marks, 2 cm apart, are 
scratched or etched on the walls of 150 x 16-mm test 
tubes. The internal diameters of the test tubes are 
measured with a micrometer. 

The clean rubber sample is weighed to the nearest 
milligram and a 16.5% solution is made up by dis¬ 
solving 1.700 ± 0.001 g of rubber in 10 ml of solvent. 
Ten milliliters of a solution of three parts of acetic 
acid to one thousand parts of CP xylene, by volume, 
is added from a pipet, and the test tube stoppered 
with a cork covered with tin foil. The rubber is al¬ 
lowed to swell and dissolve for at least 16 hr. Then a 
hexagonal plunger is placed in the test tube and the 
solution homogenized with the machine for 1 hr. See 
Figures 11 and 12. 

The test tube is taken from the machine, and the 
air bubbles in the solution are removed by centri¬ 
fuging. A cork fitted with a funnel prepared from 


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572 


PLASTICIZED WHITE PHOSPHORUS 



Figure 11. Apparatus for determining concentrated 
solution viscosity of rubber solutions. 


2-mm capillary tubing is placed in the test tube, 
which is then placed upright in a constant tempera¬ 
ture bath and equilibrated to 25 ± 0.1 C. The steel 
balls are dropped in, and the times of fall between 
the two marks on the test tube are measured with a 
stop watch. Measurements are made with three or 
four balls introduced one at a time. 

The viscosity in poises was calculated using the 
equation: 

gd 2 (o- - p) 

rj =- . 

18i> 

[1 - 2.104(d/D) + 2.09(d/D) 3 — 0.95(d/£>) 5 ] 
where rj = viscosity (poises), 

g = acceleration due to gravity (cm per sec 2 ), 
<7 = density of sphere (g per cubic cm), 



Figure 12. Magnetic stirrer. 


p = density of fluid medium (g per cubic cm), 
v = velocity of sphere relative to wall of tube 
(cm per sec), 

d = diameter of sphere (cm), 

D = internal diameter of test tube (cm). 
Sample Data. Typical data include: 

GR-S sample — Copolymer Rubber Corpora¬ 
tion, Shipment No. 19 (Received 28 November 
1944): 

d = 0.1577 cm 
I) = 1.341 cm 
a = 7.96 g per cc 
p = 0.90 g per cc 

v = 2/43.5 cm per sec (times of fall, 43.6, 
43.4 and 43.6 sec) 
g = 980.6 cm per sec 2 
t) = 157 poises 

Accuracy. The error of the measurements is from 

1 to 1.5%. The times of fall of several balls through 

2 cm of a particular rubber solution varied by about 
1 part in 70. The values for the viscosities of several 
samples of the same rubber also vary by about 1 part 
in 70. 

37.8 VARIATIONS IN THE MANUFAC¬ 
TURING PROCESS 

37.8.1 Types of Rubbers and Solvents Used 

All of the rubber used in the manufacture of PWP 
was the usual type of 80-20 butadiene-styrene 
polymer made by the emulsion process in the govern- 


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VARIATIONS IN MANUFACTURING PROCESS 


573 


ment synthetic rubber plants. The specifications for 
this type of rubber call for a Mooney viscosity be¬ 
tween 40 and 60. These rubbers contained approxi¬ 
mately 5% fatty acid, 2% antioxidant, 0.5% soap 
and less than 2% water. The gel content of several of 
the early shipments was very high. As a matter of 
fact, it was thought at first that this was essential for 
making good PWP, because much of the early pro¬ 
duction at the pilot plant was with a product which 
ran from 16 to 46% gel. Later, it was found that such 
a high gel content was unusual, and before the pro¬ 
duction was started at the Edgewood Plant, the 
specifications for this type of rubber were set to re¬ 
quire the gel content to be less than 3%. Nearly all 
of the later shipments had no gel whatever. 

The swelling coefficients, intrinsic viscosity, and 
concentrated solution viscosity of the rubber also 
varied considerably in the early shipments. It was 
found that there could be a considerable range of 
these values without much affecting the plasticity of 
the product. In order to prevent too great a variation, 
however, it was finally recommended that the con¬ 
centrated solution viscosity be held between 100 and 
200 poises at 16.5% in xylene. 

In order to determine if other rubbers might be 
available which would be more suitable than the 
GR-S, samples of several different compositions were 
obtained from rubber manufacturers. These included 
the 85-15, 65-35, and 50-50 butadiene-styrene poly¬ 
mers, acrylonitrile, polyisoprene, neoprene, and 75-25 
isoprene-styrene polymer. None of these appeared to 
have any advantage over the usual GR-S, and most 
of them were definitely inferior for use in PWP. 

In addition to varying the properties of the rubber, 
the possibility of modifying the composition by the 
addition of other agents was considered. Among 
those used were the tactifying resins, such as NXD- 
Galex (from the National Rosin Oil and Size Com¬ 
pany), Staybellite Resin 10 (from the Hercules 
Powder Company), dibutyl phthalate, vegetable oil, 
zinc oxide, and reclaimed rubber. The most promising 
of these were the vegetable oils, such as linseed, soya 
bean, and cottonseed oil, which acted as plasticizers 
and greatly increased the viscosity of the product. 
Products having viscosity numbers above 60 could be 
made easily by substituting these oils for 40 to 50% 
of the xylene. Materials with higher viscosities could 
be made also by substituting a part or all of the 
xylene with lubricating oil, fuel oil, or turpentine. 
Those made with turpentine were more unstable than 
those made with xylene. Several batches were also 


made with light naphtha as a solvent. None of these 
solvents appeared to give products superior to those 
made with xylene, although further investigation 
along these lines may be warranted. 

Higher viscosity products could be made by substi¬ 
tuting a part or all of the xylene with monomeric 
methylmethacrylate, or styrene, which could be 
polymerized to give a very tough product, provided 
the GR-S had no antioxidant in it. The batches made 
in the laboratory had the antioxidant removed by 
extraction with acetone. A special rubber from which 
the antioxidant was omitted was later furnished by 
the Government Rubber Laboratory at the University 
of Akron. This material had entirely different proper¬ 
ties and the PWP made with it was not thermally 
stable. It is possible that further work along these 
lines would produce a product which has low viscosity 
when made, thus improving the ease of shell filling, 
and then the viscosity could be increased in a curing 
process to give a stable material with the desired 
viscous properties. 

37.8.2 Recommendations for Future Work 

The variability in the thermal stability of the 
product that has been noted in the case of the high 
viscosity PWP, such as 75-40 and 75-40-30LO, indi¬ 
cates the necessity for further developmental work on 
this material. The fact that a thermally stable ma¬ 
terial has been made on many occasions, both in the 
experimental plant and in the pilot plant, shows that 
it is possible to make a satisfactory filling and that 
it is only necessary to get the manufacturing process 
under control and to specify the proper raw materials 
to produce a uniformly good material. This suggests 
that a fundamental investigation of the nature of 
PWP and the factors that control its thermal sta¬ 
bility is necessary. Some work was done along this 
line but there was not sufficient time to carry it to a 
definite conclusion. The results indicated that some 
of the synthetic rubbers are much more affected 
chemically by the phosphorus than others, so that 
the gel content increased rapidly during the mixing 
process. There was no increase in the gel content for 
other rubbers but there was a pronounced decrease in 
the concentrated solution viscosity of the rubber. 
Rubbers from the same manufacturers sometimes 
behaved differently. There was no correlation be¬ 
tween the effects of mixing and the original con¬ 
centrated solution viscosity. 

Other suggestions which have been made for 


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574 


PLASTICIZED WHITE PHOSPHORUS 


studies toward improving the quality of PWP are 
as follows. 

1. The molecular size and distribution in the rub¬ 
ber, the percentage of sol and gel rubber, and the 
structure of these materials are all important factors 
in determining the strength and stability of the 
swelled polymer. The spread from 40 to 60 permitted 
in the Mooney number by the present GR-S specifi¬ 
cations actually gives a very wide spread in the 
intrinsic rubber properties (especially in a process 
where the breakdown of the rubber is to be kept at a 
bare minimum) in distinction with ordinary rubber 
processing which introduces considerable breakdown 
followed by subsequent curing which tends to even 
out these variations. It is recommended that rubber 
be used with Mooney numbers between 50 and 55, 
and that the gel content be held between 2 and 5% 
rather than less than 3%. It is felt that these specifi¬ 
cations will give a more reproducible product. 


2. The tendency to form gel by chemical action 
of the phosphorus and phossy water is a typical char¬ 
acteristic of GR-S rubber. Other substances, such as 
copper, lead and manganese salts, peroxides, oxygen, 
and zinc oxide, produce the same results. The forma¬ 
tion of gel around the phosphorus particles could 
easily be the cause of the thermal instability. This type 
of hardening has been prevented in the case of air 
and light by use of large quantities of antioxidant. 

3. The effect of pigments and other occlusions, 
even small bubbles of air, should be studied. It is 
known that these have an important bearing on the 
physical properties of GR-S membranes. 

4. The possibility of other polymers to replace 
GR-S should be included in this study. This field 
could not be explored during the war because of the 
lack of time and the inadvisability of trying to de¬ 
velop a new product needed in such large quantities 
as the demand for PWP indicated. 


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PART V 


MISCELLANEOUS TOPICS 


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Chapter 38 

INSECT CONTROL —THE DEVELOPMENT OF EQUIPMENT 
FOR THE DISPERSAL OF DDT 

By Herbert Scoville, Jr. 


38.1 INTRODUCTION 

he advent of the war and the resultant rapid in¬ 
crease in personnel of the Armed Forces and their 
dispersal to many parts of the world, created a tre¬ 
mendous health problem whose importance was 
equalled by few other military considerations. One of 
the primary factors involved in this health problem 
was the control of insects, for, as an example, the 
number of casualties from malaria and other insect- 
borne diseases in the Pacific Theaters early in World 
War II, was equal to or greater than those from 
enemy action. From the point of view of morale of the 
fighting men, it was also important to reduce pest in¬ 
sects which often seriously hampered normal opera¬ 
tions and reduced the efficiency of our forces. It was, 
therefore, incumbent upon the medical officers of 
both the Army and Navy to develop methods of con¬ 
trolling insects, particularly mosquitoes and flies, in 
all areas occupied by allied forces. 

The necessity of placing men in localities that 
under ordinary circumstances would be considered 
uninhabitable increased the difficulty of obtaining 
adequate control measures. Almost inaccessible 
jungle areas were often the site of prolonged occupa¬ 
tion by our forces. Since, in some cases, it was desira¬ 
ble to carry out insect control measures in places 
still occupied by appreciable numbers of the enemy, 
new complications were added to insect control work. 
Although many new and difficult problems arose in 
the forward areas, there also existed the tremendous 
task of controlling insects in numerous camps spread 
throughout this country and in many vital civilian 
areas. 

Until the discovery of DDT, oil sprays containing 
pyrethrins were most generally used in controlling 
adult mosquitoes. However, the supply of this in¬ 
secticide was extremely limited, particularly since the 
occupation by the Japanese of many localities in the 
southwest Pacific had eliminated the main sources of 
supply. When the insecticidal value of DDT [1-tri- 
chloro-2,2-bis-(p-chlorophenyl) ethane] in tests with 
the Colorado potato beetle was first discovered by the 


Geigy Company, and when it subsequently was found 
effective against a wide variety of insects by workers 
in England and this country, itk possibilities in solving 
the insect control problems of the Services were con¬ 
sidered. As additional test data became available to 
show its extreme toxicity to mosquitoes, flies, lice, 
etc., the production of DDT was expedited and, by 
the end of the war, was more than sufficient to satisfy 
the demands of all our Armed Forces. 

Early tests with DDT, which proved to be both a 
contact and a stomach poison, showed that kills could 
be obtained in three ways: (1) contact kill, i.e., by 
collision of the airborne insecticide with the flying or 
resting adult, (2) residual kill, i.e., by pickup of the 
insecticide as a result of the insect moving over a 
contaminated surface, and (3) larval kill. Little was 
known, however, about the physical problems in¬ 
volved in obtaining efficient kills by any of these 
methods. It was particularly desirable to investigate 
the problem of optimum particle size for the dispersal 
of DDT insecticides under practical conditions. The 
concentrations of DDT, the best formulations and 
the dosages required, all needed study in order to 
obtain the maximum effectiveness from the DDT. 

With the discovery of DDT, much of the previously 
used dispersal equipment and the methods of treat¬ 
ment had become obsolete. The high toxicity of DDT 
formulations greatly reduced the volume of material 
required to obtain control. Since the Armed Forces 
wished to carry out control measures throughout 
large areas, new techniques had to be evolved in 
order to keep the expenditure of manpower, material, 
and time within reasonable limits. Aircraft dispersal 
of insecticides took on a larger importance in view of 
this requirement. Although dusting with aircraft had 
been used in the past with some success under limited 
conditions, early tests with DDT showed that this 
technique was not too satisfactory, and was not the 
answer to the problem. Ground equipment that had 
been used previously was, in general, quite bulky, dis¬ 
persed the insecticide solution at a rate too fast to be 
efficient with DDT, and produced only a coarse spray 
which was not completely satisfactory for many types 



SECRET 


577 


578 


INSECT CONTROL 


of insect control work. Development of new equip¬ 
ment designed primarily for the dispersal of DDT 
was, therefore, of primary importance. 


but no attempt was made to correlate this informa¬ 
tion with the insecticidal efficiency of the different 
bombs. 


38.2 CLARIFICATION OF THE PROB¬ 
LEM OF PARTICLE SIZE AS RELATED 
TO INSECT CONTROL 

38.2.1 Historical 

In order to design equipment for dispersing DDT 
efficiently, information was first needed on the opti¬ 
mum particle size in which the insecticide should be 
distributed. Without such information it would be 
impossible to take full advantage of the toxic proper¬ 
ties of DDT, material would be wasted, and control 
would frequently be impractical. The particle size 
required to obtain best results will depend not only 
on factors peculiar to the insecticide, such as suscepti¬ 
bility of the insect to the insecticide, its mode of ac¬ 
tion, and its chemical and physical properties, but 
also on such external conditions as meteorological 
factors, terrain, and method of treatment. 

The problem of optimum particle size of insecticides 
has been the subject of investigation of a number of 
workers even before the discovery of DDT. Smith 
and Goodhue of the U.S. Department of Agriculture 
have summarized 1 some of this earlier work on the 
relation of particle size to insecticide efficiency, and 
concluded that the toxicity of solid insecticides in¬ 
creased with decrease in particle size. With oil sprays, 
the quantity of oil appears to be more important 
than the size of the droplets. In 1938, Burdette 2 
described experiments in which honey bees were ex¬ 
posed to inhomogeneous oil aerosols of varying parti¬ 
cle size, and he concluded that droplets of 1 to 10 
microns in diameter had the greatest toxicity. From 
the point of view of practical application of insecti¬ 
cides, Searls and Snyder 3 concluded, as a result of 
work with cattle sprays, that very small droplets 
were unsatisfactory because of their failure to impact 
on the surface being treated. Druett 4 made some 
preliminary calculations of the pickup of spray drop¬ 
lets of different sizes by a mosquito. In order to ob¬ 
tain 100% collection by the antennae and legs, par¬ 
ticles larger than 10 microns are required. This same 
efficiency can be attained by the head only when the 
diameter is greater than 25 microns. In an investiga¬ 
tion of the drop size obtained from a number of 
different pyrethrum aerosol bombs A\ 7 hich had given 
good entomological results, 5 it was found that most 
of the drops were less than 10 microns in diameter, 


38.2.2 Theoretical Relationship between 
Particle Size and Dosage Required for 
Contact Kill 


As a part of the problem of determining optimum 
particle size for contact kill, it was considered desira¬ 
ble to make certain theoretical calculations 6 which 
could be used to check the laboratory and field tests, 
and which would provide a means for extrapolation 
to conditions not so susceptible to experimental con¬ 
firmation. The derivation of any relationship between 
the dosage required to obtain insect kills and the 
particle size of the dispersed insecticide requires con¬ 
sideration of the probability of an insect being hit by 
a number of drops equal to or greater than that neces¬ 
sary to cause mortality. 7 This probability will, in 
turn, be dependent on the dose M of DDT necessary 
to kill a single insect, and the efficiency of a drop in 
contacting -the insect. The lethal dose can only be 
obtained by experiment, but for the purpose of mak¬ 
ing calculations, a series of values in the proper range 
are assumed. The proper value can then be selected 
on the basis of laboratory tests. In the determination 
of the number of drops actually hitting an insect, two 
processes are recognized. 

1. Pickup by settling of the drops according to 
Stokes’ laAv: 



( 1 ) 


AA'here u = vertical velocity, 
d = drop diameter, 
p = drop density, 

7) = viscosity of the air, 
g = acceleration due to gravity. 

2. Impaction on the vertical surface of the insect: 
The fraction of drops which deposit on the frontal 
area of the mosquito is assumed to be given by the 
theory of Sell 8 and likewise increases Avith drop size. 

For the case of the resting mosquito, the entire 
pickup occurs according to the first process, i.e., by 
settling on the insect’s horizontal surface A. The air¬ 
borne dosage Ct, Avhich is required to have an 
average of ft drops hitting an area in time t, can be 
calculated by the folloAAdng equation: 


Ct = 

Ag 


( 2 ) 


SECRET 



PARTICLE SIZE AS RELATED TO INSECT CONTROL 


579 



I 2 3 4 56 78910 20 30 40 60 80 100 200 300 400 

DROP DIAMETER IN MICRONS 

Figure 1 . Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Resting mosquito. Computed 
for lethal dosage = 10“ 8 g. 



1 2 3 4 5 6 7 8910 20 30 40 60 80100 200 400 

DROP DIAMETER IN MICRONS. 

Figure 2. Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Resting mosquito. Computed 
for lethal dosage = 10 -9 g. 


where C = concentration of insecticide, 

/ = average number of drops hitting an area 
per unit time. 

If one assumes a value of M, the lethal dose, the 
number of drops n which are necessary to kill an 
insect for any concentration of DDT in inert solvents 
can be immediately determined. Calculation is then 
required of the average number of drops ft hitting an 
area so that there is a certain probability W n + that 
n or more drops hit any one area. Assuming that the 
drop distribution occurs at random, the following 
equation has been derived for the probability that n 
or more drops will strike the insect: 


W n 


—m 

K = 0 


• (3) 


This probability is the fraction of mosquitoes killed 
when n drops contain a weight M of DDT. If the 
average ft necessary is known, the Ct value is im¬ 
mediately obtained from equation (2). 

In order to determine the effect of different varia¬ 
bles on the dosage required to obtain certain per¬ 
centage kills of mosquitoes, the above equations have 
been solved for three cases: 50%, 90%, and 99%; i.e., 
W n + = 0.50, 0.90, and 0.99. Three values of M were 
assumed for the purpose of calculation: 10~ 8 (Figure 


1 ), 10 -9 (Figure 2), and 10~ 10 g (Figure 3), and the 
horizontal area of the mosquito was considered as 
4.7 X 10 -2 sq cm. The relationship between Ct of the 
aerosol and drop diameter derived, using these values, 
are shown graphically on a log-log scale in Figures 1, 
2, and 3. A definite minimum in Ct necessary for a 
given mortality or an optimum particle size is clearly 
predicted. The initial steep linear decrease in Ct re¬ 
quired for 50% kill has a slope of —2 and is due to 
the increase in settling velocity with the square of the 
drop size. It is interesting to note that there is a 
definite curvature with slopes less than —2 in the 
lower branch of the curve for higher percentage 
mortalities. The minimum is reached at approxi¬ 
mately the size where one drop contains a lethal dose 
of DDT, and, since the number of drops necessary 
to kill can no longer decrease, the curve increases 
linearly as the diameter is further increased. 

For the case of the flying mosquito, i.e., whenever 
the air is moving horizontally relative to the insect, 
the insecticide will be picked up both by settling and 
by impaction on the vertical surfaces. In horizontally 
moving air, a particle tends to move around any 
vertical surface unless there is a relative movement 
between the particle and the air. Inertial force, on the 
other hand, tends to keep the particle moving in a 


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580 


INSECT CONTROL 



Figure 3. Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Resting mosquito. Computed 
for lethal dosage = 10 -10 g. 


straight line toward such a vertical surface instead 
of swinging laterally around it, and this force is like¬ 
wise dependent on the square of the diameter of the 
particle. Sell’s work on deposition of the particles 8 
has been applied to the problem of insecticides. 9 ’ 10 
The deposition efficiency for different shaped objects 
is a function of the dimensionless parameter P. 

d 2 

P = 4.65 X 10- 6 pv- , (4) 

where D = characteristic length of the object in ft, 
v = velocity of insect relative to the air (mph). 
The viscosity of air (0.00018 poise) is in¬ 
cluded in the constant. 

These calculations have been applied to the flying 
mosquito which was assumed to have a vertical pro¬ 
jection similar to a flat plate with an area of 2.9 X 
10 -2 sq cm and a horizontal area of 9.9 X10 -2 sq cm. 
The equation for Ct taking into account both settling 
and impaction becomes as follows: 

(jl = _ ft _ 

(9.9 X 10- 2 g)/(3Tr V d) + (6 P X 2.9 X10 -%)/M 3 p) 

(5) 

The values of ft are calculated from probability con¬ 
siderations in the same way as for the resting mos¬ 
quito, and the relationships between Ct and d are 



Figure 4. Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Flying mosquito. Computed 
for lethal dosage = 10~ 8 g. 


plotted in Figures 4, 5, and 6. (M values are same as 
in Figures 1, 2, and 3 respectively.) 

By comparing these curves with Figures 1, 2, and 
3, it will be seen that the Ct necessary to obtain kills 
with flying mosquitoes is approximately one-half 
that required for the resting mosquito, and that this 
is principally due to the increased horizontal area of 
the flying insect. In addition, the minima have 
shifted to slightly higher drop sizes for the flying in¬ 
sect because P increases with the square of the drop 
size. 

38.2.3 Experimental Determination of 
Relationship between Particle Size 
and Contact Kill 

In addition to these theoretical studies, laboratory 
tests were undertaken to determine experimentally 
the optimum particle size for contact kill. This work 
was carried out with the cooperation of personnel 
from the Beltsville Laboratories of the US Depart¬ 
ment of Agriculture, working under contract with 
Division 5, Committee on Medical Research [CMR]. 
This group gave particular assistance in carrying out 
the entomological aspects of the work. The initial 


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PARTICLE SIZE AS RELATED TO INSECT CONTROL 


581 



1 2 3 4 5 6 7 8910 20 30 40 60 80 100 200 300400 


DROP DIAMETER IN MICRONS ' 

Figure 5. Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Flying mosquito. Computed 
for lethal dosage = 10 -9 g. 

experiments were done in a static chamber, 10 but, 
later, when the techniques had become further de¬ 
veloped, the tests were carried out in a wind tunnel 
constructed for this purpose. 11 

In order to conduct rigorous experiments it was 
necessary to obtain an aerosol of very uniform par¬ 
ticle size, since the inability to disperse the insecticide 
in this form had caused difficulty in interpretation of 
results of earlier investigators. In the course of the 
work on the development of screening smoke genera¬ 
tors, a laboratory model was designed, capable of 
producing a homogeneous aerosol by carefully con¬ 
trolling the formation of nuclei for the aerosol par¬ 
ticles. 12 ’ 13 This generator had to be modified for use 
with insecticides, 10 since certain oxides of nitrogen, 
which were obtained with the earlier models, also 
exhibited toxic effects on insects. Therefore, for 
entomological experiments, the nuclei for the aerosol 
particles were produced by heating NaCl deposited 
on an electrically heated nichrome wire. Control 
experiments showed that neither the gases exhausted 
with the aerosol nor an aerosol of pure oil had toxic 
effects. In the early experiments, it was found possi¬ 
ble to obtain homogeneous aerosol drops up to 15 
microns diameter (90% of the mass falling in the 
range ± 10% from the average size), but, later, 11 the 



1 2 3 4 5 6 7 8910 20 30 40 60 80 100 200 300400 


DROP DIAMETER M MICRONS 

Figure 6. Ct of aerosol for various mosquito mortali¬ 
ties vs aerosol drop size. Flying mosquito. Computed for 
lethal dosage = 10 -10 g. 

maximum particle size was increased to 20 microns. 
Automatic controls were used to maintain constancy 
of operation over a period of hours. 

For most of the work both male and female Aedes 
aegypti mosquitoes were used as the test insects, but 
it was discovered that the males were much less 
resistant to DDT. Therefore, all quantitative results 
were based on kills of females. The insects were ex¬ 
posed for varying periods to different concentrations 
of aerosols, and the mortalities for a constant particle 
size were plotted against the amount of aerosol to 
which the insects were exposed. Some typical curves 
are shown in Figure 7. In some of the later work 14 the 
statistical method outlined by Bliss 15 was used in 
order to define more clearly the significance of the 
results. From the dosage-mortality graphs, the me¬ 
dian lethal dosage for any given particle size could be 
read directly, and the values obtained for each drop 
size were plotted against the particle diameter on a 
log-log basis. Such an experimental curve is shown in 
Figure 8 in comparison with theoretical curves for 
toxicities of 10 -9 , 5 X 10 -10 , 2.3 X 10 -10 , and 10 -10 g 
of DDT per mosquito. The experimental curve has a 
slope very close to — 2 for the descending portion, and 
thus the data are in close agreement with those pre¬ 
dicted on the basis of Stokes’ law, which require a 


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582 


INSECT CONTROL 



Figure 7. The effect of DDT dosage upon mortality 
for Aedes aegypti (mosquitoes). 


proportionality to the square of the drop diameter for 
50% mortality. 

A minimum possible value for the lethal dose has 
been calculated, assuming that all the aerosol parti¬ 
cles reached the insect by settling 10 and that the 
horizontal area is 0.03 sq cm for the mosquito. This 
value, 2.4 X 10 -10 g of pure DDT, is slightly lower 
than the value estimated by comparison of the posi¬ 
tions of the curves in Figure 8. In view of the experi¬ 
mental difficulties and the number of assumptions 
made, however, the agreement would seem quite 
good. The optimum particle size, as calculated theo¬ 
retically, appears somewhat greater than that ob¬ 
tained by experiment, but it should be pointed out 
that the minimum in the experimental curve occurs 
at almost the largest particle size which could be used 
in the laboratory tests. Moreover, the differences are 
not great when considered from a practical point of 
view, since on an arithmetic scale the curves are quite 
flat. In practice, other factors will have greater in¬ 
fluence on the optimum drop size for dispersal. 

Further studies in the static chamber were made 
with fruit flies, Drosophila melanogaster , 16 The median 
lethal dosage of the aerosol for this insect was also 
found to be inversely proportional to the square of 
the drop diameter over the range studied (1 to 10 
microns diameter), but the toxic dose for these in¬ 
sects was found to be approximately 30 times as great 
as that for Aedes aegypti. 

Since it was recognized that, in practice, deposition 
on the insect will always occur, at least in part, as a 
result of the horizontal motion of the aerosol cloud, 
these laboratory studies were extended to a wind- 
tunnel investigation of the toxicity of DDT aerosols. 11 
The theoretical treatment r ’- 8 indicated the deposition 
upon the insect, and hence, the toxicity would be de¬ 
pendent upon the square of the drop diameter and 
the first power of the wind velocity relative to the 
insect. Adult Aedes aegypti were exposed in cages to 



O.l 1 10 too 


DROP DIAMETER IN MICRONS 

Figure 8. . Comparison of experimental and calculated 

dosages required for 50 per cent kill. Eight per cent 

DDT solution. 

homogeneous aerosols of particles up to 20 microns 
diameter in wind velocities of 2, 4, 8, and 16 mph. 
Although the mosquitoes flew about the cage in the 
absence of wind, there was little or no activity during 
the exposure period, and the insects remained quietly 
on the wire screen. At low velocities they tended to 
congregate on the front screen of the cage, but at 
16 mph they were almost all blown against the rear 
screen and held there by the air flow. The control 
experiments showed that the insects were not injured 
at 16 mph. Since the results obtained under the dif¬ 
ferent conditions showed no discontinuities, it was 
assumed that the different insect behavior did not 
affect the validity of the results. As a result of these 
experiments, the theoretical calculations were con¬ 
firmed. The dosage for 50% mortality was found to 
be inversely proportional to d 2 v (d = drop diameter 
in microns, and v = wind velocity in miles per hour) 
for low values of this product. However, for high 
values ( d 2 v > 1,000), when the deposition is essen¬ 
tially complete, the dosage becomes independent of 
wind velocity and particle size (see Figure 9). On the 
basis of the data obtained in the wind tunnel, the 
median lethal dose for the female Aedes aegypti was 
determined as 3 X 10 -8 g DDT. This figure is in close 
agreement with that reported by a number of in- 


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PARTICLE SIZE AS RELATED TO INSECT CONTROL 


583 



1 10 100 1000 10,000 


Figure 9. DDT in mg/sq ft required to kill 50 per cent 
females Aedes aegypti (as function of drop diameter, d , 
and wind velocity, v). 

vestigators using bio-assay as a method of analysis 
for DDT. 

It will be seen from the experimental results ob¬ 
tained both in the static chamber and in the wind 
tunnel, as well as from the theoretical calculations, 
that as the particle size is decreased below 10 microns 
in diameter, the dosage required to obtain kill of 
mosquitoes by direct contact with the aerosol in¬ 
creases rapidly. These observations are of extreme 
practical importance and proved very helpful in de¬ 
signing dispersal equipment. When DDT first came 
into use, many investigators had thought that dis¬ 
persal as a smoke, i.e., drops 0.4 to 0.7 micron in 
diameter, might give excellent results. However, it 
was now apparent that drops of this size would be 
relatively ineffective in obtaining kill, and it was 
realized that equipment would have to be designed 
so as to obtain larger particles. The maximum drop 
size which can be used efficiently could not, however, 
be determined as easily since somewhat different re¬ 
sults were obtained with different test conditions. 
According to the static chamber tests, the optimum 
drop diameter was in the neighborhood of 10 mi¬ 
crons, but results in the wind tunnel did not give any 
indication of the optimum size. They did, however, 
show that under most conditions, increasing particle 
diameter above 20 microns did not greatly increase 
the deposition on the insect. However, calculations 
of the median lethal dose, 3 X 10 -8 g DDT, showed 


that an 83-micron drop containing 10% DDT would 
be required for one drop to contain a lethal dose. 
Therefore the drop diameter above which the toxicity 
must start decreasing must lie somewhere between 20 
and 80 microns, the exact value being determined by 
probability considerations. This is in agreement with 
the theoretical calculations. 

An indirect confirmation of the relationship be¬ 
tween particle size and toxic (^ose was obtained from 
data taken in field tests of the exhaust generator on 
the TBM-1C plane. 17 The dosages obtained during 
the test were calculated from horizontal slides. The 
Ct d , i.e., the dosage for each drop size increment, was 
multiplied by the factor W d which is the computed 
relative efficiency of the drop size d for killing mos¬ 
quitoes as computed from the theoretical curve for 
the conditions of the test. The actual kills in the 
areas 2 hr after treatment were 86% and 88% while 
the corrected dosages predicted a kill of 99%. In view 
of the inevitable roughness of such field measure¬ 
ments, this agreement would appear quite good. 

38.2.4 Experimental Measurement of 
Factors Involved in Residual Kills 

Since it was recognized that the residual kill of 
insects, as well as contact kill, was an important 
factor in obtaining control, laboratory tests were 
carried out to assess this effect. 18 A knowledge of the 
contamination required for kill, the duration of 
the toxicity, the effect of external conditions on the 
toxicity of the deposit, the effect of varying the 
method of application, and the type of surface were 
all considered of utmost practical importance. To 
assist in the analysis of the deposits, a radioactive 
tracer of triphenyl phosphate was added to the DDT 
solutions, and the contamination was determined by 
exposing a measured area of the treated surface to a 
Geiger-Muller counter. A number of experiments 
were carried out, using cages which were dipped in 
the DDT solutions, but since the DDT was found to 
decompose rapidly on the iron wire, it was found 
necessary to coat the screens with a layer of glyptal 
resin. 

As a result of these tests, it was shown that the 
rate of knockdown was proportional to the contami¬ 
nation density, and for doses above 5 jug DDT per 
sq cm of screen (these doses should be multiplied by a 
factor 1.6 to obtain the contamination on the basis of 
wire area), complete knockdown occurred within 1 


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584 


INSECT CONTROL 


hr. Decrease in the concentration of DDT in the 
solvent oil increased the rate of knockdown for a 
given contamination density, and a maximum effec¬ 
tiveness was obtained with 1% solution DDT in 
Prorex D, a paraffinic oil. Certain methylated naph¬ 
thalene solvents, such as Velsicol NR-70 and Velsi- 
col-70 Special (a fraction obtained from the distil¬ 
lation of the NR-70) were found to be excellent 
solvents for DDT, and, in addition, to have some 
residual toxicity by themselves. The screen tests 
also showed that the rate of paralysis in mosquitoes, 
female Anopheles quadrimaculatus, was considerably 
more rapid than that in houseflies; 1 ng per sq cm 
screen gave nearly 100% kill of mosquitoes in 2 hr 
while 5 hr were required with flies. Tests were also 
made using leaves in place of wire surfaces. In this 
case, a deposition of 1 ng per sq cm of surface was re¬ 
quired to obtain 50% mortality with 2-hr exposure 
periods. No decrease in toxicity was observed over a 
period of 48 hr. When leaves were used, the 5% solu¬ 
tion of DDT was more toxic than a 2% solution, this 
result being in contrast to the data obtained on 
screen surfaces. This was attributed to failure to 
obtain a continuous film on the hairy leaf surfaces 
when such low dosages were used. 

These results were extended to a study of the ef¬ 
fects of surface on the residual kills of female 
Drosophil-a. 19 These results showed that DDT, 
whether sprayed in a volatile or nonvolatile solvent, 
was only about one-fifth as effective when deposited 
on leaf surfaces as when deposited on glass. The time 
required for 100% kill was used as a criterion, and 
approximately 1 ng per sq cm was used to obtain 
100% kills. There was some evidence that certain 
leaf surfaces were more satisfactory for obtaining 
residual kill than others. 

38.2.5 Relationship between Particle 
Size and Dosage Obtained in the Field 

Although the relationship between particle size and 
dosage required to obtain toxic effects is of funda¬ 
mental importance to the solution of the problem of 
proper particle size for dispersal, consideration must 
also be given to ability to obtain a toxic dose under 
field conditions with any given particle size. A number 
of factors must be considered in any attempt to set up 
a given dosage in the field. First, the meteorological 
conditions, which exist at the time treatment is 
carried out, will determine the dosage obtained. Since 
the dosage Ct is directly proportional to the time at 


which the insecticide remains at any one given posi¬ 
tion, the dosage obtained from a given source strength 
will be inversely proportional to the speed of the 
wind. With thermally stable air, aerosol clouds will 
settle and remain close to the surface, but when the 
air is unstable even relatively large particles may be 
carried to high altitudes, and the treatment be 
rendered completely ineffective. Second, the density 
of the foliage in both horizontal and vertical planes 
will also determine the dosage which can be obtained 
from particles of any given size. Large particles will 
deposit readily on all surfaces and settle rapidly to 
the ground, so that an insecticide dispersed in such 
form will penetrate a relatively short distance 
through thick foliage. However, small particles whose 
impaction efficiency is low may travel far and remain 
airborne for a long time even in dense undergrowth. 
In addition to its effect on deposition, the density of 
the foliage will determine the wind speed and, conse¬ 
quently, the travel of the insecticide cloud. 

Since it was recognized that these factors might 
completely outweigh toxicity considerations, at¬ 
tempts were made to study this problem both theo¬ 
retically and experimentally. A considerable amount 
of work on the travel of gas clouds had been carried 
out by both Americans and British. The British equa¬ 
tions for gas diffusion in the air were extended to in¬ 
clude aerosol clouds by taking into account finite 
settling velocity of the particles. 6 - 9 - 20 The funda¬ 
mental equation for a line source in this case is: 

Q - [ X CtFudx 


where Q is the product of the source strength and the 
time of emission, u is the settling velocity, v is the 
wind speed, x is the distance from the source, and 
B and m are meteorological constants, 

2 

m =-:- i 

1 + (log R)/ (log R + log 2) 

v at 2 meters 

R =- 

v at 1 meter 

By solving equation (6), it has been possible to de¬ 
termine F , the fraction of the agent remaining air¬ 
borne at any distance, as a function of the meteoro¬ 
logical conditions and the particle size. Results of 
these calculations are shown in Table 1. 

From these calculations it is evident that drops 
smaller than 10 microns in diameter will travel long 
distances downwind even at low wind velocities, as- 


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PARTICLE SIZE AS RELATED TO INSECT CONTROL 


585 


Table 1. The fraction F of agent remaining airborne of aerosol clouds under two different atmospheric conditions. 


Distance 

downwind 

(yards) 

0.8 

R = 1.05 (lapse), v = 5 mph 

R 

= 1.25 (inversion), v = 

2 mph 

Drop diameter (microns) 
8 12 

24 

0.8 

Drop diameter (microns) 

8 12 24 

100 

0.99 

0.98 

0.96 

0.85 

0.99 

0.89 

0.76 

0.32 

500 

0.99 

0.96 

0.94 

0.78 

0.99 

0.83 

0.64 

0.16 

1,000 

0.99 

0.96 

0.93 

0.74 

0.99 

0.78 

0.58 

0.11 

5,000 

0.99 

0.95 

0.90 

0.65 

0.99 

0.69 

0.42 

0.03 

10,000 

0.99 

0.95 

0.88 

0.59 

0.99 

0.63 

0.37 

0.02 



DISTANCE PENETRATED IN UNITS OF n 

Figure 10. Horizontal penetration of an aerosol through a forest. 


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586 


INSECT CONTROL 


suming that the only force driving the particles to the 
ground is gravity. With aircraft dispersal the down- 
draft from the plane will, however, frequently supply 
an added force. 

These calculations of aerosol cloud-travel in the 
open have been extended to wooded areas where depo¬ 
sition on the horizontal and vertical surfaces of the 
foliage is also a factor . 9 In order to characterize the den¬ 
sity of the foliage, two lengths 8 and y have been de¬ 
fined. The length 5 is the horizontal distance for which 
the sum of the vertical foliage surfaces in any cross 
section is equal to the cross section, and 7 is a similar 
distance in a vertical direction. For the purposes of 
calculation, it has been assumed that the foliage is 
twice as dense in a vertical direction as in a hori¬ 
zontal direction, i.e., 8/y = 2 . The fraction, A Q/Q, 
lost in traveling a horizontal distance, Ax, is given by 


A Q Ax Ay 


(7) 


where A 7 is the distance fallen in a vertical direction 
and A is the impaction efficiency of the particle on 
the vertical surface as given by Sell . 8 Impaction 



500 1000 

FEET FROM GENERATOR 


Figure 11. Local ground deposition vs distance from 
generator. 

efficiency A was assumed to lie between Sell’s values 
for a flat plate and a circular cylinder and is a func¬ 
tion of pvd 2 /D (D is a characteristic dimension of the 
foliage). From this relationship, F, the fraction pene¬ 
trating to a distance x downwind, has been calculated 
for various size drops and wind speeds of 1 and 5 
mph (see Figure 10). 

These calculations have been checked experimen¬ 
tally by measuring the variation in local ground de¬ 


position in various types of terrain, using the Hoch- 
berg-LaMer aerosol generator dispersing droplets 
under 15 microns in diameter . 21 These results are 
shown in Figure 11 . In addition, tests have been made 
using coarse sprays in a 7 mph wind . 22 The ground 
deposition in the open was also measured with 
the CWS E-12 (Hochberg-LaMer) generator with 
DNOC (dinitro-ortho-cresol) and DDT . 23 The pickup 
by various types of foliage was measured by exposing 
leaves in a wind tunnel at 4 mph to particles less than 
3 microns in diameter containing a radioactive 
tracer . 18 The efficiency for drops of this size was very 
low and in good agreement with the calculated values, 
although the pickup was apparently greater by some 
of the hairv leaves. 



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 

DISTANCE FROM TOP OF CANOPY IN UNITS OF n 

Figure 12. Vertical penetration of an aerosol through 
foliage. Crosswind velocity, 1 mph; no downdraft. 

Similar theoretical treatment has been made for 
the vertical penetration into foliage of an aerosol 
dispersed by aircraft . 6 The fraction penetrating to a 
depth y has been calculated for several particle sizes 
for a crosswind velocity of 1 mph and no downdraft 
from the aircraft (Figure 12 ). Under these condi¬ 
tions, it would appear that the larger drops will 
penetrate downward through the canopy more 
efficiently than smaller ones. The physical explana- 


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PARTICLE SIZE AS RELATED TO INSECT CONTROL 


587 



DISTANCE BELOW TOP OF CANOPY IN UNITS OF n 

Figure 13. Vertical penetration of an aerosol through foliage in presence of downdraft. wind velocity—1 mph; 
Vo, downdraft — 5 mph. 


tion for this effect is essentially that the larger drops 
fall faster and have less opportunity to impinge 
horizontally on the foliage than do the smaller ones. 
For no crosswind, u = 0, all sizes of drops penetrate 
the foliage to the same extent. 

If, on the other hand, the aerosol is dispersed by an 
airplane which is flying only a short distance above 


the forest canopy, the downwash of the plane will 
push the aerosol downward through the layers of the 
forest. The penetration efficiency of all size drops will 
be increased, but since the impingement on the foliage 
is a function of the square of the drop size, this down¬ 
ward component will increase the relative penetra¬ 
tion efficiency of the smaller drops. Since the down- 


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588 


INSECT CONTROL 


wash velocity will decrease with distance under the 
canopy, its effect will decrease as the height of the 
canopy becomes greater. Calculations of the penetra¬ 
tion efficiency of different drop sizes with initial 
downdraft of 5 mph have been made (Figure 13). 
It should be remembered that these calculations do 
not take into consideration inhomogeneities which 
are always present in a natural forest. Meteorological 
turbulence has also been neglected. 

Some confirmation for these calculations has been 
obtained from the results of aircraft dispersal tests 
carried out in Panama. Two types of equipment used 
were a simple vertical discharge sprayer, dispersing 
particles with a mass median diameter [MMD] of 
200 to 300 microns, and a TBM exhaust generator 
dispersing particles of 25 microns diameter. Although 
the entomological results from these two types of 
equipment were almost identical, it was observed that 
the penetration efficiency of the larger drops as ob¬ 
tained from the sprayer was greater than that of the 
smaller drops obtained from the exhaust generator. 

Because of the apparent importance of the down- 
wash on aircraft dispersal, an investigation was made 
of the factors which affected this velocity in order 
that the spray outlets could be positioned to take 
best advantage of this effect. 6 The optimum position 
would presumably be where the downdraft is utilized 
to best advantage and where none of the droplets 
are carried into the turbulent wake. This position 
would be ahead and below the forward edge of the 
wing at the point where the flow lines around the 
wing have maximum divergence. If the spray is too 
close to the trailing edge or lower surface of the air¬ 
foil, it may come out in the wake and be dissipated in 
turbulent motion. If the spray is too far below the 
airfoil, the downward component of the velocity may 
be quite small. 

38.3 GROUND DISPERSAL EQUIPMENT 

38.3.1 Historical 

Before DDT had come into general use, a large 
number of different types of equipment had been 
developed for dispersing insecticides. For the treat¬ 
ment of large areas, power sprayers requiring large 
quantities of compressed air to achieve liquid 
breakup had been widely used. Since the insecticide 
solution was dispersed in relatively large drops, the 
spread of the insecticide occurred almost entirely as 
a result of impetus provided by the compressed air. 


This seriously limited the area which could be treated 
in a single traverse, and increased the time and per¬ 
sonnel required to cover an area. Moreover, most of 
these sprayers were bulky and therefore impractical 
to use in the war theaters. Since the laboratory ex¬ 
periments and theoretical calculations, as described 
in Section 38.2, had shown that droplets in the range 
of 5 to 50 microns diameter were not only the most 
toxic but also would remain airborne for appreciable 
periods, the development of new equipment to dis¬ 
perse DDT in this form appeared desirable for treat¬ 
ment of large areas. 

Screening smoke generators had been developed by 
the NDRC and the Armed Services, but the particle 
size of the droplets produced ranged from 0.4 to 0.7 
micron in diameter, which was too small for in¬ 
secticide work. Attempts were made to modify the 
Hession generator, a combustion gas-type oil fog 
generator designed for screening smokes, in order to 
produce larger sizes by adding a large chimney in 
which condensation would proceed more slowly than 
in open air. Although theoretically sound, prelimi¬ 
nary experiments on this development were unsatis¬ 
factory, even Avhen a 6-ft chimney was attached to 
the outlet. 

Dr. Goodhueof the U.S. Department of Agriculture 
had developed a Freon bomb which has been success¬ 
fully used for the dispersal of pyrethrum and later 
DDT. 24 This bomb disperses the insecticide in drop¬ 
lets less than 10 microns in diameter, the atomization 
being obtained by expelling a mixture of the oil solu¬ 
tion and gaseous Freon 12 through a capillary at a 
pressure of about 75 psi. Although these bombs have 
great insecticidal effectiveness, their small size limits 
their use to enclosed spaces, and larger units would be 
impractical for treating extensive areas because of 
their weight and expense. 

38.3.2 The Hochberg-LaMer Type 
Generators 

This same principle of atomization, i.e., the mixing 
of the insecticide solution with a gas under pressure, 
has, however, been adapted to a generator which can 
be used for treating large areas. 25 Steam is used in 
place of Freon to break up the DDT-oil solution into 
small drops and eject them into the atmosphere. The 
mixture of steam and oil is obtained by pumping 
a 50-50 DDT-oil-water emulsion through a heater 
coil Avhere the water but not the oil is vaporized. The 
DDT-oil solution is broken up into small droplets by 


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GROUND DISPERSAL EQUIPMENT 


589 


the shearing action of the steam under pressure, and 
the drops are then discharged through nozzles into 
the air. The particle size of the insecticide solution 
which is dispersed depends on the composition of the 
emulsion, particularly the ratio of volatile to non¬ 
volatile material, the pressure and temperature at the 
input to the nozzle, and the characteristics of the 
nozzle. An increase in temperature results in a de¬ 
crease in particle size. Tests with one of the later 
models showed that a coil temperature of 450 F and a 
pressure of 80 psi gave an aerosol of particles with an 
MMD of 10 microns. Reduction of the temperature 
to 350 F produced particles with an MMD of 32 
microns. Even under optimum operating conditions, 
a small amount of smoke is produced by partial 
evaporation of the oil and subsequent condensation 
into very small drops. The production of these small 
smoke particles, however, does not decrease the 
effectiveness of the dispersal, since the nonvolatile 
DDT does not vaporize and is consequently not 
wasted in the very small drops which are insecticid- 
ally ineffective. Since DDT decomposes at elevated 
temperatures, care was required to avoid loss of 
DDT in this type of equipment. However, chemical 
and entomological tests have shown such decomposi¬ 
tion to be negligible as long as proper operating con¬ 
ditions are observed. 

The first, or inventor’s model, of the generators, 
known as the Hochberg-LaMer type, had a capacity 
of 20 gal of DDT emulsion per hr. 25 This was pumped 
through the coil by means of a gear pump with a 
suitable flow control system. When tested in the 
field, the inventor’s model generator gave excellent 
insecticidal results, but the capacity of only 20 gal 
emulsion per hr was considered insufficient for ob¬ 
taining practical control over large areas. Therefore, 
the manufacture of Hochberg-LaMer type generators 
of greater capacity was undertaken, 26 - 27 and a model 
dispersing as high as 90 gal per hr was eventually de¬ 
signed. After these generators were tested in the field, 
the development of more rugged and practical models 
was considered desirable. 

Since screening smoke generators which were suf¬ 
ficiently durable for use in the field had already been 
designed, the modification of this type of equipment, 
in order to disperse the DDT in drops of greater in¬ 
secticidal effectiveness than would be obtained with 
smoke, appeared very desirable. This was accom¬ 
plished on both the Besler 374 (Navy screening smoke 
generator) and the Army M2. 28 The primary changes 
required were the substitution of a new pump, 


capable of handling the required volume of emulsion, 
the alteration of a thermostatic control to permit 
operation at temperatures near 450 F instead of 
900 F, the insertion of a filter capable of removing the 
sediment present in DDT solution, and the inclusion 
of a more satisfactory flow control system. These 
models have found considerable practical use and 
gave good results in tests in the war theaters. 

In all the generators, considerable difficulty has 
been observed in obtaining satisfactory pumps. The 
gear pumps have an inherent weakness in that there 
is no way of taking up the wear. This is particularly 
serious when emulsions are being used instead of oil 
solutions. To avoid this difficulty, pumps with 
capacities in excess of those required were employed, 
and a certain amount of the liquid was continually 
by-passed back to the container. On the various 
models a number of different flow control systems 
have been used in order to maintain constant flow 
during operation. 28 By reduction of the quantity of 
liquid by-passed, the same flow was maintained 
through the generator even when the pump capacity 
had dropped off. However, this method of handling 
the wear is inherently unsatisfactory, and the design 
was changed to substitute a double plunger pump. 
With this method an emulsion was not required, since 
the oil-DDT mixture and water could be pumped 
separately and mixed directly in the heat coils. This 
greatly simplified the use of the generator because the 
problem of preparing suitable emulsions was elimi¬ 
nated. These pumps were employed successfully on 
both the Army M2 generator, which became known 
as the Disperser, Insecticide, Aerosol, Mechanical, 
E-12 29 (see Figure 14), and on the Besler 374. 

Various models of Hochberg-LaMer insecticide 
generators have been tested in many parts of the 
world in cooperation with the Navy, Army, U.S. De¬ 
partment of Agriculture, Tennessee Valley Authority, 
and British Commonwealth Scientific Office under a 
wide variety of conditions against a number of dif¬ 
ferent species of mosquitoes and flies. 22 - 3 °- 32 As a re¬ 
sult of these tests, it has been possible to suggest 
methods of use of these generators for the control of 
these insects in the field. 21 - 29 In order to obtain con¬ 
trol over large areas with an aerosol, the wind is used 
to distribute the insecticide, thus reducing the man¬ 
power and time required for treatment. As a conse¬ 
quence, aerosol dispersal is dependent on the wind to 
obtain results. The effect of the wind on the deposi¬ 
tion of DDT from a Hochberg-LaMer generator has 
been determined in the field, and the results are 


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590 


INSECT CONTROL 



ENGINE 


BURNER VALVE 


WATER 

STRAINER- 


GASOLINE 

STRAINER 


ENGINE CRANKCASE 
DRAIN PLUG 


DUAL PUMP 


FLUE PAN 


CHECK 

VALVE 


OUTLET 
1 -MANIFOLO 


WATER 


THERMOSTATIC 
-FUEL VALVE 


FURNACE 

ASSEMBLY 


HANDLE GRIP 


FRONT TANK 


GASOLINE TANK 


Figure 14. Hochberg-LaMer-type generator, CWS model, E-12. 


shown in Figure 11. These can be compared with 
values in Figure 10, which were calculated theoreti¬ 
cally. The deposition will also be dependent on the 
thermal gradient in the lower air, for with inversion 
conditions, all sizes of drops will remain close to the 
ground, whereas, with lapse conditions, even rela¬ 
tively large drops may be carried high in the air 
where they will be ineffective in obtaining insect kills. 
The airborne dosage of insecticide at any point, neg¬ 
lecting loss due to deposition, will be inversely propor¬ 
tional to wind speed, for a constant source strength. 
Consequently the source strength will have to be in¬ 
creased in high winds to obtain sufficiently high 
dosages. However, this will not necessarily mean in¬ 
creased output per unit area, since the distance be¬ 
tween swaths, which should be made crosswind, can 
be greater under these conditions. For example, in 
low winds frequent passes at short intervals down¬ 
wind will be required to cover an area, and this will 
often be a serious obstacle in jungle terrain where 
even relatively small drops may penetrate only a few 
hundred feet. 


Therefore, keeping these factors in mind, pro¬ 
cedures for the use of these generators have been 
evolved. 29 When possible, all treatment should be 
carried out under thermally stable atmospheric con¬ 
ditions and in moderate winds. When feasible, the 
distance between swaths should be kept small, 500 yd 
being a good swath width, for with wide swaths ex¬ 
cessive dosages will be required near the generator in 
order to obtain a sufficiently high dosage far down¬ 
wind. In low winds, the swath width should be even 
narrower. Within certain limits the particle size of 
the aerosol from these generators can be altered by 
changing the coil temperature so that when deposi¬ 
tion is desirable, operating conditions giving the 
larger drops should be used. Thus, when treatment in 
high winds or unstable thermal conditions is re¬ 
quired, the larger particles (40 microns) are desirable. 
Similarly, when larval control, which requires deposi¬ 
tion on the water, is the primary objective, opera¬ 
tional conditions producing the larger drops should 
also be used. However, in low winds the smaller diam¬ 
eters, 5 to 10 microns, are better since this will permit 


SECRET 






GROUND DISPERSAL EQUIPMENT 


591 


the insecticide to remain airborne for longer periods 
and cover a larger area. For contact kills of adults 
and larval control with the Hochberg-LaMer genera¬ 
tor, doses of 0.1-0.3 lb DDT per acre have, in general, 
been found satisfactory. Little or no residual effect is 
obtained with these amounts, but when dealing with 
insects of short flight range, retreatment will be re¬ 
quired only at 7- to 10-day intervals because of the 
time required for infiltration of new populations. 

In addition to these tests on mosquitoes and flies, 
the generators were tried out against several other 
forms of insects with varying results. These tests 
have shown that the aerosol generators have con¬ 
siderable promise for controlling cankerworms and 
black flies. 33, 34 When used with DNOC (dinitro- 
ortho-cresol), the Hochberg-LaMer generators gave 
promising results against grasshoppers at a dosage of 
approximately 4 lb per acre, but with DDT, negligible 
kills were obtained. 23 This test is particularly signifi¬ 
cant since it demonstrates the feasibility of using 
these generators with insecticides other than DDT, 
Tests with DDT against the spruce budworm showed 
that kills could be obtained, but the aerosol method 
appeared less efficient than aircraft sprays. 34 ’ 35 

38.3.3 Exhaust Generators for Motor 
Vehicles 

Although excellent results have been obtained w r ith 
the Hochberg-LaMer type generators, this type of 
equipment is essentially complicated, and a simpler 
type of disperser is very desirable for many situations 
in the field. Therefore, work was undertaken to de¬ 
velop a light, portable piece of equipment which 
could be rapidly installed near the area to be treated. 
For this purpose, an exhaust generator for motor 
vehicles has been designed. 36 This consists of a Ven¬ 
turi atomizer which employs the exhaust gases from 
the internal combustion engine to break up the in¬ 
secticidal solution, and uses gravity to inject the 
liquid into the Venturi. In this way the necessity for 
pumps, for supplementary heating systems, and for 
other mechanical items, which could get out of order, 
is completely eliminated. 

The atomization is obtained by the shearing forces 
on the liquid caused by the relative velocity be¬ 
tween the solution and the gas. The gas velocity, 
upon which the degree of atomization will depend, is 
limited in the exhaust of an engine by the back-pres¬ 
sure which can be practically used with the engine. 
Because of this, the Venturi principle has been 


adopted in order to achieve high gas velocity with 
low back-pressure. The throat diameter of the Ven¬ 
turi is chosen to give a velocity of 1,500 fps at the 
highest power setting which would be used for spray¬ 
ing, this setting being low enough so that almost 
continuous operation is possible without excessive 
overheating. Early tests showed that a certain 
amount of drooling was obtained out of the end of 
the Venturi, due to the impingement of the droplets 
against the wall of the divergent section. This diffi¬ 
culty was eliminated by cutting off the Venturi at a 
point where the exit diameter was less than twice the 
throat diameter, i.e., where the gas velocity was still 
greater than 300 fps. For the injection of the solution 
into the Venturi, several systems were tested, but a 
simple coaxial tube was found to give as good results 
as the more complicated arrangements. By using a 
tube of sufficiently large diameter, the liquid could be 
injected under the force of gravity with the aid of 
suction due to the Venturi. The use of the simple tube 
has the additional advantage that small particles of 
rust or sediment passed freely through it, and do not 
cause difficulty from clogging 

This principle has been successfully applied to the 
design of exhaust generators for the quarter-ton, 
4x4 truck, Jeep 35 (Figure 15), and the cargo carrier, 
M29C, Weasel. 37 Venturis of in- or % in. have 
been found best for the former, depending on whether 
the engine is in good condition or not, while a ^-in. 
Venturi has been selected for the Weasel. When 
these generators w r ere used on passenger or other 
civilian vehicles, the results have not been too suc¬ 
cessful because of over-heating due to the inadequate 
cooling system of the engines. However, in practice, 
it should be possible to design generators which will 
give satisfactory results with these vehicles, but some 
sacrifice in capacity may be required. 

Tests have shown that this type of equipment has 
a great many practical uses. Alteration of the solution 
flow rate by means of a simple gate valve makes it 
possible to disperse the insecticide in droplets ranging 
in diameter all the way from smoke (< 1 micron) to a 
coarse spray (> 150 microns). With the Jeep engine, 
which is rated at 40 to 60 hp, an aerosol with droplets 
from 10 to 50 microns in diameter can be dispersed at 
a rate of 5 to 10 gal per hr, and a coarse spray can be 
dispersed at 30 to 50 gal per hr. The operating condi¬ 
tions of the engine will also affect the particle size, 
and when possible, a speed of 6 mph in low gear is 
recommended. Because of the ability to change the 
drop size at will, the generator has great practical 


SECRET 



592 


INSECT CONTROL 




value for obtaining adult and larval control over 
small areas and for residual treatment of heavily 
infested localities. Several DDT formulations have 
been used successfully with these generators, but for 
general use a 5% solution in fuel oil is considered the 
most satisfactory. A 20% solution in Velsicol NR-70 
or other methylated naphthalene solvents, and the 
Army and Navy DDT emulsion concentrates can 
also be employed. Decomposition of DDT in these 
generators was found to be negligible due to the short 
contact time of the DDT with the hot gases. When 
volatile solvents, such as xylene, are used, evapora¬ 
tion is appreciable, and for this reason, these solvents 
are not considered so satisfactory as relatively non¬ 
volatile ones. 

These generators have been tested in numerous 
localities, and the results have been very promising. 36 
They are particularly useful for the treatment of camp 
areas, air fields, recreation centers, etc. For the treat¬ 
ment of larger areas, other equipment with greater 
output can frequently be used more efficiently. 


38.3.4 Thermal Candles 

During the war a requirement was voiced for the 
development of a smudge pot or a grenade for dis¬ 
persing an insecticidal aerosol. The British believed 
such a device would be useful for obtaining control by 
troops in forward areas. Since the thermal generator 
candle, F-7, had been developed for the dispersal of 
aerosols, 38 attempts were made to adapt this muni¬ 
tion directly for insecticidal purposes. 39 This device 
employs the hot gases from a fuel block to atomize 
the agent in a Venturi. These generators were filled 
with 2,300 g of a 20% DDT solution in Velsicol 
NR-70 and burned from 3 to 33^ min. In a single 
performance test, 30 of these were functioned so as 
to obtain a nominal dosage of about 2^ lb DDT per 
acre. Seventy-five per cent of the charge was dis¬ 
persed in droplets less than 5 microns in diameter, 
and as a consequence, this fraction was probably rela¬ 
tively ineffective in obtaining insect kills. However, 
the entomological results were excellent throughout 


SECRET 































AIRCRAFT DISPERSAL EQUIPMENT 


593 


the area treated. Despite the promise shown by this 
single test, no further work was done on this develop¬ 
ment, since it was considered that the method was too 
involved and relatively inefficient. The development 
of grenades was continued by the Chemical Warfare 
Service, who worked on the manufacture of a pyro¬ 
technic mixture containing DDT. 10 They were able 
to develop a munition which gave good entomological 
results, but the usefulness and economy of this 
method of dispersal has not been proven. The number 
of sources which would be required per unit length 
of front, in order that the separate aerosol clouds will 
merge within a reasonable distance downwind, neces¬ 
sitates the use of high dosages of insecticide. 

38.4 AIRCRAFT DISPERSAL EQUIPMENT 
38.4.1 Historical 

Prior to the discovery of DDT, no insecticide 
which could be produced economically in large 
quantities was sufficiently toxic to warrant the dis¬ 
persal on a large scale of aircraft sprays. Aircraft dis¬ 
persal with dusts had been used quite extensively, but 
its application was quite limited. However, with the 
production of DDT on a tremendous scale, the possi¬ 
bility of covering large areas by the dissemination of 
solutions or emulsions had opened a new field for 
dispersal of insecticides. The value of aircraft dis¬ 
persal was particularly great as a control measure in 
the war theaters, for it made possible the covering of 
inaccessible areas with a minimum of personnel and 
equipment. Moreover, a definite requirement existed 
for methods for obtaining control in areas where the 
danger from enemy action was still great, and the 
use of aircraft offered the only feasible method of ac¬ 
complishing this objective. 

First attempts at dispersing DDT from the air 
were made with standard Chemical Warfare Service 
spray tanks such as the M-10, M-33, or British SCI 
tanks. Even when these were modified by the addi¬ 
tion of restrictions to the outlet, the flow rates were 
irregular, and the liquid breakup poor. As a conse¬ 
quence, high doses of DDT were required, and the 
coverage was frequently spotty. The Orlando Labora¬ 
tory of the U.S. Department of Agriculture first de¬ 
signed a DDT sprayer for the Cub airplane (Hus- 
man-Longcoy apparatus). 41 Although the liquid 
breakup was not remarkably good, this equipment 
gave reasonably good entomological results. Since 
it required a wind-driven pump, a large Venturi, and 
nozzles, it was complicated for such a small plane 


and was not readily adaptable to larger and fast mili¬ 
tary aircraft which would frequently be required in 
many areas for control purposes. Therefore, the 
initiation of extensive research into the development 
of new equipment for the dispersal of DDT from 
both light and heavy planes was desirable. Such 
equipment should give good liquid breakup, distrib¬ 
ute the insecticide evenly over an area, and should, at 
the same time, be as simple and adaptable as possible. 
In attempts to accomplish the^e objectives, two lines 
of attack were followed: (1) the production of an ex¬ 
haust DDT generator, and (2) the development of 
efficient spray equipment which would employ the 
slipstream of the plane to atomize the liquid. 

38.4.2 Aircraft Exhaust Generators 17 

With an exhaust generator, the atomization of the 
insecticide solution is obtained by injection of the 
solution into the high-velocity exhaust gas stream. 
Since the gases are sufficiently hot to evaporate the 
solvent and eventually decompose the DDT, it is 
essential to reduce time of contact between the solu¬ 
tion and the hot gases to a minimum. This is ac¬ 
complished by injection of the solution near the exit 
of the exhaust stack, so that the droplets are emitted 
into the cold air immediately after the atomization 
is effected. Since it is essential to keep the back¬ 
pressure in the exhaust stack to a minimum in order 
not to affect the performance of the aircraft engine, 
use is made of the Venturi principle in order to in¬ 
crease the velocity of the gases with a minimum of 
back-pressure. 

In an investigation of the theory of atomization of 
liquids, a study was made of the empirical equations 
developed by Nukiyama and Tanasawa as a result of 
several hundred runs with small gas atomizing noz¬ 
zles. 42 The first equation is as follows. 

, 585V* , rm ( M V' 45 /1,000QlV'‘ ,o, 

do = wr +597 w ’ (8) 

where d 0 = diameter, in microns, of a single drop 
with the same ratio of surface to volume 
as a representative sample of the drops 
in the spray; 

v = difference in velocity between air and 
liquid at the vena CGntrada, in m per sec; 

Q L /Qa = volume flow rate of liquid/volume flow 
rate of air; 

p = liquid density, g per cc; 
p = liquid viscosity, poises; 
a = liquid surface tension, dynes per cm. 


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INSECT CONTROL 


The second empirical equation which expresses the 
data on distribution of drop sizes in liquid sprays is 
as follows: 

ad v e- bd ’, (9) 

da 

where d = drop diameter, in microns; 

n = total number of drops, in the sample 
chosen as a basis, which have diameters 
between zero and d microns. 
a, b, p, and q are constants. 

Nukiyama and Tanasawa found that, with their 
small atomizing nozzles, p = 2 and q = 1 over a wide 
range of conditions. At high values of d 0 , i.e., for 
poorly atomized sprays, q dropped to a value of l / 2 - 
The relationship between q, a, b, v, and d 0 when 
p = 2 has been calculated. The constant q is a meas¬ 
ure of the flatness of the drop distribution curve; a 
high value of q means that most of the drops are in a 
narrow range of sizes, whereas a low value corre¬ 
sponds to the spreading of drops over a considerable 
range of sizes. Experimental results indicate that q 
is constant for any given nozzle over a wide range of 
operating conditions, but that it is affected markedly 
by the type and size of the atomizing device used. 
Since it is frequently more useful to know the MMD 
of the spray than the value of d 0 , the relationship be¬ 
tween these two diameters has been calculated for dif¬ 
ferent values of q (for q equal to 1; MMD/d 0 = 1.14). 

Experimental work was undertaken to confirm 
these equations, and apply them to data obtained by 
other investigators in the field. While this work was 
preliminary and served primarily to point out the 
experimental difficulties involved in such an inves¬ 
tigation, it indicated that the relationships implicit 
in the equations were sound and could be used as an 
aid in designing equipment for the atomization of 
liquids. The following tentative conclusions were 
reached as a result of these studies. 

1. It is better to use relatively large diameter 
liquid jets than relatively small diameter jets with 
higher liquid velocities, since small jets have the 
disadvantage of high-pressure drop and do not give 
much better atomization. 

2 . As long as the liquid jet discharges into the 
neighborhood of the vena contrada of the orifice or 
nozzle, the angle from which it comes, the point in 
the region in the vena contrada at which it discharges, 
and the shape of the convergent part of the constric¬ 
tion that produces the high-velocity gas stream at the 
vena contrada , have little effect on the atomization. 


Consequently, the style of orifice or nozzle can be 
chosen on the basis of other factors, such as ease of 
manufacture, installation, and cleaning. 

3. In a Venturi atomizer, a decrease in gas density 
and an increase in gas viscosity reduce the degree of 
atomization. 

The throat diameter of a Venturi of an aircraft 
exhaust generator must be designed 42> 51 to obtain at 
normal engine operating conditions, a throat velocity 
sufficient to give the desired liquid breakup. On the 
other hand, the diameter must be sufficiently large 
to avoid excessive back-pressure on the engine. These 
factors can be determined by use of the gas laws and 
the equation for throat velocity in a Venturi accord¬ 
ing to the following equations. 


-fa 


K RTi 1 — (Pt/PiY 


iK-D/K 


2 ° c k-i m 


(D 2 /Di ) 4 


(P 2 /Pi) 27 *, 

( 10 ) 


w 

A 2 


M 
RT ! 



(ID 


Subscripts 1 and 2 refer to upstream and throat 
conditions respectively. 

V 2 = throat velocity (fps). This can be esti¬ 
mated for a desired mass median diame¬ 
ter from equation (8). In general, it will 
range from 500- 750 fps depending on the 
degree of liquid breakup desired. 

g c = dimensional constant, 32.2 (lb mass) (ft 
per sq sec) per lb force. 

K = C p /C v . 

R/M = specific gas constant in consistent units. 

T i = absolute upstream temperature (de¬ 
grees R). 

Pi, P 2 = static pressures (lb force per sq ft). 

A 2 = throat area (sq in.). 

Z>i, Dt = diameters (in.). 

W = exhaust gas flow (lb mass per sec). 

The first actual attempt to obtain an aerosol of 
DDT by injecting a solution into the exhaust of an 
airplane engine was made in 1944 by the Orlando 
Laboratory of the Bureau of Entomology and Plant 
Quarantine of the U.S. Department of Agriculture. A 
Cub plane was used, and with the injection rates 
used (120 gal per hr), both large droplets and smoke 
were obtained. Later in cooperation with the Ten¬ 
nessee Valley Authority, exhaust equipment was in¬ 
stalled on a 4-DX Stearman airplane which carries a 
450-hp engine. 39 In the earlier models, the solution 
was injected directly into a simple extension of the 


SECRET 





AIRCRAFT DISPERSAL EQUIPMENT 


595 


exhaust manifold. However, the back-pressure was 
too great when the diameter of the stack extension 
was sufficiently small to obtain satisfactory atomiza¬ 
tion. Therefore, instead of a straight stack, a Ven¬ 
turi which combined low back-pressure and high gas 
velocity was installed. A 2%-in. diameter throat 
proved most satisfactory with this plane, and the 
solution flow rate and engine power setting was 
selected so as to obtain an aerosol with an MMD of 
about 50 microns. The equipment was used to dis¬ 
perse a 20% DDT-Velsicol NR-70 solution for 
routine anopheline larviciding in the Tennessee Val¬ 
ley Authority during the past year, and a dosage of 
only 0.1 lb DDT per acre gave excellent results. As in 
the case of the Jeep generator, it was found that a 
more satisfactory drop spectrum and uniform distri¬ 
bution of insecticide is obtained by reducing the 
length of the divergent section of the Venturi to a 
point where the diameter is approximately 2.5 times 
the throat diameter. 43 When an aerosol of MMD of 
35 microns was used, the DDT was uniformly distrib¬ 
uted over a swath greater than 200 ft so that ex¬ 
cellent control was obtained with low doses without 
endangering other forms of wildlife. The good results 
obtained with the 450-hp Stearman prompted the 
design of a generator for the PT-17, a Stearman with 
a 220-hp engine. A 2-in. diameter Venturi is used on 
this plane, and results of normal control operations 
were excellent. Twelve of these generators were pro¬ 
duced by the Tennessee Valley Authority for use in 
Greece by the United Nations Relief and Rehabilita¬ 
tion Association. 

The promise shown by the exhaust generators on 
the Stearman planes warranted the development of 
similar equipment for use on large military aircraft. 
Exhaust screening smoke generators had been pre¬ 
viously designed for a Navy TBM-type aircraft. 44 
Since the general principles involved in the develop¬ 
ment of the smoke generator and the insecticide 
generator are very similar, it seemed desirable to try 
to design equipment for this type of aircraft which, 
with slight modification, could be used either for 
screening smokes or for insecticide work. 17 With the 
smoke generator, the fog oil is injected 8 to 10 ft from 
the exit of the exhaust stack in order to allow suffi¬ 
cient contact time for complete evaporation of the oil. 
Since a minimum contact time is required with in¬ 
secticides, the smoke generator had to be modified so 
as to inject the DDT-oil solution near the end of the 
stack. Thus, by mere alteration of the point of injec¬ 
tion of the solution, it proved possible to obtain either 


smoke or insecticide equipment. With this type of 
aircraft, which contained a Curtiss-Wright R2600-10 
engine rated at 1,510 hp at 2,400 rpm and 42 in. Hg 
absolute manifold pressure, a Venturi with a 3%-in. 
throat gave good results. The oil was pumped from 
a 270 gal bomb bay tank at 20 to 30 gal per min into 
the Venturi throat through Todd 28-10 Mayflower 
nozzles. Some difficulty was obtained with the clog¬ 
ging of these nozzles due to coking of the DDT solu¬ 
tion, and frequent cleaning of the nozzle plates was 
recommended. However, in exhaust generators de¬ 
veloped later it was found that the nozzles were not 
required to obtain atomization, so that the plates 
could be dispensed with entirely. This observation 
was in agreement with the predictions implicit in the 
empirical equations of Nukiyama and Tanasawa. 

By suitable alteration of the engine power setting 
and the solution flow rate, aerosol clouds can be ob¬ 
tained with a MMD varying all the way from 10 
microns to greater than 100 microns. Thus, with the 
engine operating at 2,400 rpm and 42 in. Hg mani¬ 
fold pressure and with a delivery rate of 25 gal of 20% 
DDT in Velsicol NR-70 per minute, a cloud with an 
MMD around 20 microns is obtained. At 30 in. Hg 
manifold pressure and 30 gal per min flow rate, an 
MMD diameter in the neighborhood of 100 microns 
is generated. 45 The evaporation of the Velsicol NR-70 
solvent increases as the power setting is raised and 
the flow rate lowered. At 2,400 rpm, 42 in. Hg, and 
a flow rate of 24 gal per min, the evaporation was 
about 30%. Analysis indicated that no decomposi¬ 
tion of the DDT was occurring. 

This equipment was given entomological evalua¬ 
tion in Florida and Panama, and the results were ex¬ 
cellent. 45 Doses of 0.3 to 0.4 lb DDT per acre, ob¬ 
tained by flying the aircraft in 100-yd swaths, gave 
virtually complete control of all adults and anopheline 
larvae. Observation indicated that the aerosol plume 
was pushed down by the slipstream of the plane at a 
rate of approximately 10 mph, the plume reaching 
the ground at all points when the plane flew at alti¬ 
tudes below 200 ft. Penetration of the aerosol into the 
foliage was excellent although the jungle canopy ex¬ 
tended 100 to 125 ft above the ground. In a test 
carried out under thermally unstable conditions and 
in a high wind, the ground deposition was negligible, 
but the reduction of mosquitoes was nevertheless be¬ 
tween 80% and 90%. 

The promise shown by this generator on the TBM 
prompted the design of similar equipment for use 
with other military aircraft such as the SB2C-4, 


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596 


INSECT CONTROL 



Figure 16. Installation of exhaust aerosol generator of SB2C-4 plane. 


PBJ-1H (B-25), and C-47 planes. 47 - 43 Since the com¬ 
bination of a smoke generator and an insect dis¬ 
perser no longer appeared tactically desirable, simpli¬ 
fication of the design was attempted. Instead of ex¬ 
tending the exhaust pipe down the fuselage of the 
plane, a short stack, comprising only a Venturi, was 
attached directly to the exhaust manifold of the en¬ 
gine. 47 (See Figure 16.) This model gave good results, 
and in most flight attitudes, contamination of the 
plane by the insecticide solution was negligible. The 
PBJ-1H airplane did not contain exhaust collector 
rings, but rings from a TBM aircraft could be in¬ 
stalled without serious modification to the plane. 
Since this plane contains two engines, it was possible 
to double the output per unit time in cases where 
particularly high dosages were desirable. Since pumps 
are required to inject the insecticide solution into the 
Venturi at the flow rates needed with fast military 
aircraft, the original installation of the exhaust equip¬ 
ment could not be accomplished too rapidly. With 
the SB2C-4 an estimate of 24 man-hours was made 
for the time required. 

The principle of the exhaust generator was also 
applied to small aircraft as a substitute for the 


Husman-Longcoy sprayers and breaker bar equip¬ 
ment designed for the L-5. These sprayers were com¬ 
plicated and had the disadvantage of requiring small 
orifices which gave frequent trouble from clogging. 
In order to make the exhaust equipment as simple as 
possible the use of pumps was dispensed with in a 
model installed on a Taylorcraft, and the insecti¬ 
cide solution fed by gravity into the Venturi. 50 This 
generator was very similar in design to the exhaust 
equipment for the Jeep 35 and Avas capable of dis¬ 
persing a 20% DDT solution in Velsicol NR-70 
at 45 to 100 gal per hr depending on the particle size 
desired. In order to insure getting the insecticide to 
the ground, it was considered desirable to use larger 
drops with this generator, since the downward push 
of the slipstream from these small planes is not as 
great as from the larger military aircraft. Preliminary 
design of an exhaust generator was also made from 
an L-5, but no installation has been made on this 
aircraft. 51 

38.4.3 DDT Spray Devices 

The initial spraying of DDT from aircraft was 
carried out with equipment designed for the dispersal 


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AIRCRAFT DISPERSAL EQUIPMENT 


597 


of chemical warfare agents, but since in most cases 
these were designed to produce large drops rather 
than small ones they did not prove entirely satis¬ 
factory. Moreover, the flow rates were very irregular, 
and this led to spotty coverage. Modification of this 
equipment by placing restrictions in the outlets im¬ 
proved the situation somewhat, but they were still 
not very satisfactory. 

Laboratory tests with pneumatic sprays indicated 
that when larger amounts of air were available, satis¬ 
factory fragmentation of liquids could be obtained. 52 
This observation suggested spraying the insecticide 
solution into the slipstream of an airplane in such a 
manner as to take best advantage of the air flow for 
achieving liquid breakup. Tests with air velocities of 
. 220 and 400 fps showed that volatile solutions of low 
viscosity were much more readily broken up than the 
nonvolatile ones. In order to make best use of the slip¬ 
stream, a spray apparatus which would employ a 
Venturi effect to increase the velocity of the air was 
suggested. Several models, which according to calcu¬ 
lations should give a velocity of up to about 800 fps 
at the point where the liquid is sprayed, were designed 
in cooperation with the Army Air Forces. Among 
these were a rectangular Venturi, a round Venturi, a 
streamlined pipe, a streamlined grid, and a simple 
vertical discharge pipe. 53 Measurements of particle 
size from the different devices in tests at Wright 
Field indicated that drops in the range of 150 to 300 
microns diameter were being obtained with all types 
when 5% DDT in fuel oil was being dispersed. Little 
improvement was obtained by using the more com¬ 
plicated Venturi systems. Although time did not 
permit extensive measurements, there was some indi¬ 
cation that the Venturis were not giving the calcu¬ 
lated air flow rates, probably because of the back 
pressure resulting when the solution was injected. 
Two of these devices, the vertical discharge pipe (see 
Figure 17) and the streamlined grid consisting of a 
series of Venturis arranged in a grid shape, were 
selected for extensive insecticide tests in Florida and 
Panama. 54 In order to keep the equipment as simple 
as possible, the solution is fed entirely by gravity 
from large bomb bay tanks, the rate being controlled 
with a 4-in. gate valve. Both B-25 and C-47 aircraft 
were used with these devices, and each contains two 
tanks with a total capacity of 550 and 800 gal for the 
B-25 and C-47, respectively. The flow rate is quite 
uniform for both types of sprayers until the tanks are 
nearly empty; the suction from the Venturis in the 
grid tends to improve this property. 


O 


'-C 


AIR STREAM 


VERTICAL PIPE 



Figure 17. Vertical discharge pipe and streamlined 
grid. 


In Panama, several tests were run over dense 
tropical jungle. With doses of 0.3 and 0.6 lb per acre, 
nearly 100% reduction of adults and anopheline 
larvae were obtained with both devices. Many drops, 
100 to 200 microns in diameter, penetrated through 
the 100-ft canopj r to the jungle floor. In view of the 
simplicity of the straight vertical discharge tube, this 
device was chosen as standard for dispersal of DDT 
by the Army Air Forces. This equipment would give 
satisfactory results on all large, fast military aircraft, 
but the air stream from small planes is inadequate to 
achieve satisfactory breakup. 

Later tests were carried out in Florida to compare 
the effectiveness of this straight discharge pipe with 
the C-47 exhaust generator. 49 Although more rapid 
kills were obtained with the exhaust equipment, the 
control by both types was about identical after 24 hr. 
Therefore, in view of its extreme simplicity and 
adaptability, the spray equipment is considered more 
feasible for routine control by the Army. The larger 
drops obtained with this device may be relatively 
less toxic to the insects, but they insure a greater 
dosage on and near the surface under all meteorologi¬ 
cal conditions. In these tests, 20% DDT in methyl¬ 
ated naphthalene solvents was used with the straight 
discharge tube as well as the exhaust generator. The 
results indicated that the more concentrated solu¬ 
tions were just as good when the same dosage of 
DDT was used per acre. Since the concentrates in- 


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598 


INSECT CONTROL 


crease the payload of a single flight of the airplane, 
their use is considered desirable whenever they can 
be made available in the field. 

38.4.4 Aircraft Bombs for Dispersing 
Insecticides 

The possibility of using insecticide bombs to be 
dropped from aircraft was considered. In order to 
obtain good control throughout an area such bombs 
should be small and capable of fitting in a standard 
cluster in order to get wide dispersion. As a solution 
to this problem, attempts were made to use a plastic 
bomb which was being developed for other purposes. 55 
One hundred and ten of these bombs which contain 
390 cc of agent fit into the M-17 cluster adapter. 
These bombs contain a tetryl burster to disperse the 
solution. Tests were made to determine the drop size 
of the dispersed insecticide in the area over which 
deposition occurred. When filled with 10% DDT, 
10% Velsicol NR-70, and 80% CCl 4 ,the MMD of the 
droplets was below 10 microns. As the per cent 
volatile material is decreased, the drop size increases. 
The area of burst from a single bomb covered about 
390 sq yd. With the cessation of hostilities, the re¬ 
quirement for this type of device has ceased to exist, 
although more extensive tests are pending. 

38.5 DDT FORMULATIONS 

When DDT first came into general use, two formu¬ 
lations were developed which could be generally used 
with the existent dispersal equipment. These were a 
5% solution in fuel oil or kerosene and an emulsion 
concentrate (the Army concentrate contained 25% 
DDT, 65% xylene, and 10% Triton X-100 and the 
Navy formulation contained 55% xylene and 20% 
Triton X-100). Although these formulations were 
satisfactory for many purposes, it seemed desirable 
to obtain another solvent to replace the kerosene or 
fuel oil in order that more concentrated nonvolatile 
solutions could be prepared. This would allow the 
shipment of concentrates to the field for subsequent 
dilution with readily available oils. Such a concen¬ 
trate should be stable at low temperatures in order to 
prevent separation of the DDT during storage or 
shipment. In order to be satisfactory for dispersal 
purposes, the solvent should be nontoxic and rela¬ 
tively nonvolatile, the viscosity should be low and 
the flash point high. 

In the search for such a solvent, an investigation 
was made of the polymethylated naphthalenes which 


are marketed by a number of companies under such 
trade names as Velsicol NR-70, AR-60, AR-50, and 
• AR-40, Koppers K-327, Aro-Sol 151B, APS-202, and 
Culicide oils. 56 - 57 These solvents are capable of dis¬ 
solving more than 33% DDT at room temperature, 
and 25% solutions may be diluted to any concentra¬ 
tion with kerosene or fuel oil without separation of 
DDT crystals even at 32 F. The physical properties 
vary somewhat from solvent to solvent, but they are 
generally satisfactory for most dispersal uses. How¬ 
ever, they attack rubber and, to a lesser extent, syn¬ 
thetics, so that metal gaskets and tubing are recom¬ 
mended in all equipment being used with these 
solvents. The Velsicol NR-70 has been used exten¬ 
sively in aircraft dispersal work and been shown to 
have some insecticidal potency of its own. 

For the Hochberg-LaMer-type generators, certain 
special problems had to be solved in developing satis¬ 
factory formulations. In addition to the ability to 
dissolve the requisite amount of DDT, it is necessary 
to obtain a solution with a volatility which would 
give the desired drop sizes with the normal operating 
conditions with the generator. If volatile solvents 
are employed, evaporation is excessive and the drops 
too small. Decomposition of the DDT might take 
place. For the earlier generators which used emul¬ 
sions, the following formula, which contained ap¬ 
proximately 5% DDT, has been developed. 25 - 58 

10 cc lube oil 

20 cc xylene 
9 g DDT 

2 g Atlas Tween 85 
100 cc water 

Other emulsifiers such as Triton X-100 and a mixture 
of Span 80 and Tween 80 were used successfully in 
place of Tween 85. Where more concentrated solu¬ 
tions are desired, 35% DDT in Aro-Sol 151B, a 
polymethylated naphthalene, is used in place of the 
lube oil-xylene mixture. 57 

Since the Army and Navy had xylene emulsion 
concentrates already available in the war theaters, 
formulations for the use of the concentrate in the 
Hochberg-LaMer generator were developed. 59 The 
addition of diesel and lube oil gives a formula, which 
under normal operating conditions for the Besler 374 
and E-12 generators, produces an aerosol of proper 
drop size. However, the coils on the E-12 generator 
are not made from stainless steel so that the emulsifier 
in the concentrate corrodes and reduces their life. 
Therefore, since this model does not require an 


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PHYSICAL METHODS FOR FIELD ASSESSMENT 


599 


emulsion because of its double plunger pump, the use 
of the concentrate with this generator is not recom¬ 
mended. 

In order to insure that all formulations had good 
insecticidal properties, tests were made in a wind 
tunnel to determine the relative effectiveness of 
DDT aerosols from different solvents in obtaining 
contact kill of adult mosquitoes. 14 As long as the sol¬ 
vent was sufficiently nonvolatile to prevent complete 
evaporation, no difference could be noted within the 
limits of experimental error. The relative value of the 
different formulations in obtaining residual kills has 
not been thoroughly investigated, but there is some 
evidence that emulsions or suspensions give a more 
effective deposit than some of the oil formulations. 60 

38.6 PHYSICAL METHODS FOR FIELD 
ASSESSMENT 

In the course of the development of new equipment 
for the dispersal of DDT, it became apparent that 
methods of assessing the value of the new devices 
must be found. Final evaluation of the usefulness of 
any equipment has of necessity to be made on the 
basis of its entomological effectiveness under different 
field conditions. However, since entomological tests 
require a great deal of effort, can be carried out only 
in certain places and under certain conditions, and 
frequently do not offer a clear-cut answer as to the 
relative value of different treatments, it is very 
desirable to evaluate new devices by physical meth¬ 
ods which can be correlated with entomological re¬ 
sults. Two physical properties which are considered 
important in this type of work are the particle size 
of the dispersed material and the insecticide dosage 
at any point. This latter measurement should include 
not only the airborne dosage, but also the deposit on 
the ground and other surfaces. 

In the work on screening smokes, a number of dif¬ 
ferent optical devices, such as the Owl 13 and Slope-o- 
Meter, 61 had been developed for the measurement of 
particle size, but none of these could be used satis¬ 
factorily for drops larger than 1 or 2 microns in 
diameter. Since such small drops have been shown to 
be relatively ineffective for insecticidal work, this 
type of apparatus is not of much use in this field. For 
measuring larger drops, it was found necessary to 
collect samples on slides and to measure and count 
the drops with a microscope. 

Two methods of collecting the drops have been 
used successfully under different conditions. One 


method of collection involved taking of a sample in a 
wide-mouth container and allowing the drops to settle 
on the slide which is placed on the bottom. This 
method picks up all sizes of drops equally efficiently, 
but requires some care in collecting the sample to 
insure that the larger sizes are not selectively de¬ 
posited on the walls of the container. 

By a second method, a slide is waved through the 
insecticide cloud, and the particles collected by im¬ 
pingement. A fairly representative sample is obtained 
as long as the drops are larger than about 25 microns 
in diameter. However, for smaller particles, the im¬ 
paction efficiency is appreciably less than 100%, and 
a correction must be made for the failure of the waved 
slides to pick up the smaller drops. The relative 
efficiency for the different sizes can be calculated 
according to data of Sell for a flat plate, 8 but for all 
practical purposes, an approximation (which is suf¬ 
ficiently accurate for most work), is obtained if it is 
assumed that the per cent of particles picked up is 
proportional to the square of the particle radius. 

A number of special devices have also been devel¬ 
oped which collect samples by impaction and give 
more accurate results than the manual waving of the 
slides. The cascade impactor, 62 in which the sample 
is drawn through a series of orifices so as to allow the 
particles to impact on slides, has been used quite 
extensively. The orifices are chosen so as to impact 
selectively different particle size ranges on the various 
slides, and, in this way, it is possible to separate the 
drops into four size groups. When a properly cali¬ 
brated instrument is used, counting the drops is un¬ 
necessary, and analysis of the quantity of material on 
the successive slides is sufficient to characterize the 
drop size distribution of the cloud. The largest drop 
size range which can be measured on this device is 
from 15 to 50 microns in diameter, and the smallest, 
1 to 5. However, since this instrument requires a 
source of suction to pull the sample through the im- 
pactor, it is somewhat cumbersome to use on a large 
scale in the field, and for most practical purposes, the 
simple waved slides give satisfactory results. 

Under various conditions, a number of different 
types of slides have been used successfully. Originally 
oleophobic slides coated with four monomolecular 
layers of copper barium stearate were used, but since 
these slides were difficult to prepare, another coating, 
NNO (mannitan monolaurate), was substituted by 
workers from the Department of Agriculture. Re¬ 
cently, it has been found quite satisfactory to use 
carefully cleaned plain glass slides, and calculate the 


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600 


INSECT CONTROL 


actual diameter of drops on a basis of an experi¬ 
mentally determined spread factor. For most solu¬ 
tions this spread factor is in the neighborhood of 0.4. 
These types of slides give good results for drops as 
small as 1 to 2 microns in diameter as long as the 
solvent is sufficiently nonvolatile. However, when 
volatile solvents are used, they are unsatisfactory 
since the drop will spread and evaporate before the 
counting can be completed. A photographic method 
of counting the drops has been developed by the 
Chemical Warfare Service, 63 and its use reduces the 
time required to obtain a record, but even with this 
apparatus, the plain glass and oleophobic slides are 
not too satisfactory. Another coating which has been 
found particularly useful when volatile solvents are 
used is magnesium oxide. 62 * 64 With this material a 
crater is left when the drop impacts on the slide, and 
a more or less permanent record of the drop size is 
obtained. Since the crater is a direct measurement of 
the diameter of the original drop, no spread factor is 
required with these slides. However, it is important 
that the thickness of the magnesium oxide layer be 
greater than the diameter of the drop in order to get 
accurate results. This method can be used for drops 
as small as 20 microns in diameter, but particles 
smaller than this do not leave a crater which can be 
accurately measured. A carbon coating has been sug¬ 
gested as a replacement for magnesium oxide, but the 
results with it have been found less reproducible. 64 

For the measurement of airborne dosage, the 
ordinary methods which had been useful for sampling 
toxic gas clouds are not completely satisfactory for 
correlation of physical data with entomological ef¬ 
fectiveness. Experimental data and theoretical calcu¬ 
lations have shown that the particle size of the cloud 
has a great effect on the dosage required for the kill 
of adult insects on the wing. Therefore, for adequate 
physical assessment it is necessary to know the air¬ 
borne dosage of each particle size or particle size in¬ 
crement. Since simple mass analysis does not provide 
any breakdown into particle size ranges, it is un¬ 
satisfactory for this type of work. 

A new method has therefore been suggested for 
determining airborne dosage by the use of horizontal 
slides, 6 since the deposition of particles of a given 
drop size is related to the dosage, Ct, of those particles 
in the air at that point. The relationship between Ct 
and the area deposit may be expressed as follows: 

^ N d M d 

Ltd = -> 

u d 


where Ctd = concentration-time product of drops 
having a diameter of d; 

Nd = average number of drops of diameter d 
deposited per unit area of horizontal 
surface; 

Md = weight of drop having a diameter d ; 

Ud = settling velocity of drops having diame¬ 
ter d. 

Since both M d and u d are proportional to the drop 
density, the above expression is independent of the 
drop density. If it is assumed that laminar flow oc¬ 
curs at a small distance above the plate, then Stokes’ 
law may be used for determining u d for drops smaller 
than 80 microns. For larger drops, this law no longer 
holds for the terminal velocity, and the Cl’s are 



Figure 18. Aerosol Ct as a function of horizontal area 
dosage. 


higher than those obtained using this law. In Figure 
18 a plot of Ct (mg min per cu m) per unit deposition 
density (drops per square centimeter) versus the drop 
diameter in microns is given. In using this method of 
determining dosage, the number of drops in each size 
increment is counted microscopically for a unit area. 
The dosage of each increment can be determined di¬ 
rectly from the product of this number and the proper 
factor from Figure 18. In order to obtain the total Ct at 
any point, a summation must be made overall the drop 


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SUMMARY AND CONCLUSIONS 


601 


sizes. With these horizontal slides, it has been found 
advisable to use a holder or plate so that the top of 
the slide is flush with the sides of the plate. This is 
necessary in order to avoid edge effects which would 
tend to give spurious results. With this method a 
considerable amount of microscopic counting is re¬ 
quired in order to obtain statistically significant re¬ 
sults. 

Another method for measuring airborne dosage has 
been suggested by workers at Chicago Toxicity 
Laboratory . 65 This method collects the sample on 
two or three vertical wires of different diameters and 
relies on the relative collection efficiency of the dif¬ 
ferent wires for different particle diameters in order 
to obtain the dosage. From the ratio of the pickup on 
different wires, the MMD of an aerosol cloud and the 
true area dose can be calculated from previously pre¬ 
pared graphs giving the correction factors. The Ct can 
be calculated from the area dose by dividing by the 
wind speed. With this method it is only necessary to 
determine analytically the amount of material col¬ 
lected on the different wires, so that no counting or 
measuring of the particles is required. 

A number of tests both in the wind tunnel and in 
the field have been carried out in an attempt to 
determine the practicability of using either of these 
two methods for measurement of airborne dosage of 
insecticides . 66 For comparison, Cascade impactors, 
filters, and electrostatic precipitators were used. The 
results of the horizontal slides were about as repro¬ 
ducible as those obtained by other methods, but the 
dosages were appreciably lower than those obtained 
with filters or electrostatic precipitators. The method 
involving the wires suffered from inability to obtain a 
good analytical method which was sufficiently sensi¬ 
tive to measure the small doses which are entomo- 
logically important in the field. The necessity of 
knowing the wind speed in order to calculate the 
dosage is also a disadvantage. No correlation between 
either of these methods and entomological results has 
yet been attempted, and until such data are available, 
it is difficult to draw any conclusions as to their 
merits. It must be emphasized again that the final 
evaluation of any dispersal device must depend on 
the entomological results obtained on treatment 
under a variety of field conditions. 

38.7 SUMMARY AND CONCLUSIONS 

As a result of the research carried out on the devel¬ 
opment of equipment for dispersing DDT, a number 


of conclusions have been reached which should prove 
of lasting value, with respect to the dispersal of 
DDT as well as insecticides in general. The optimum 
particle size for obtaining contact kills of adult in¬ 
sects on the wing has been experimentally determined 
within certain limits, and a theoretical basis for these 
observations has been worked out. It has been shown 
quite conclusively that as the particle diameter is 
decreased below 10 microns, the dosage required for 
contact kills increases rapidly. This significant ob¬ 
servation demonstrates conclusively the inadvisa¬ 
bility of using droplets of screening smoke size, 0.4 to 
0.7 micron, in insecticidal work. Since it has been 
shown that the ineffectiveness of the small drops is 
due to their failure to impinge on the insect rather 
than to any toxicity consideration peculiar to DDT, 
it is indicated that these small drops will be less ef¬ 
fective regardless of the insecticide used or the type 
of insect being treated. 

While no exact limit has been determined for the 
point where the drop size becomes too large to be 
insecticidally effective, it has been shown that the 
toxicity of drops between 10 and 60 microns does not 
vary widely. The theoretical calculations have shown 
that the point at which the effectiveness starts to de¬ 
crease as the particle size increases is dependent on 
the number of drops which must actually hit the in¬ 
sect to produce mortality. Since this will, in turn, de¬ 
pend on the concentration of insecticide in the solu¬ 
tion and its toxicity to the particular insect, any new 
insecticide or insect will have to be examined with 
these factors in mind. 

In addition to these laboratory studies on the 
toxicity of the different particle sizes, sufficient field 
work backed by theoretical calculations has been 
carried out so that recommendations can be made of 
the best manner of dispersing DDT under a variety 
of practical conditions. This information can be ap¬ 
plied to all types of insect control work. 

The experimental work on the residual effect of’ 
DDT has been much more limited. However, the 
studies that have been made were sufficient to point 
the way toward future research. The type of solution 
dispersed, the type of surface treated, the conditions 
of exposure, and the manner in which treatment was 
made, have all been shown to have a profound effect 
on the residual action. Fundamental studies correlat¬ 
ing the physical character of the deposit and the type 
of surface with the insecticidal effectiveness should be 
made. The relative importance of residual kill and 
contact kill should also be investigated. These studies 


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602 


INSECT CONTROL 


would be of great help in developing insecticide 
formulations and methods of treatment. 

Two new devices have been developed for the 
ground dispersal of insecticides. Thermal generators 
of the Hochberg-LaMer type have been produced to 
disperse a relatively homogeneous aerosol whose ef¬ 
fectiveness in killing adults and larvae has been 
clearly demonstrated in many regions of the world. 
The general principles involved in such devices have 
been clarified so that new equipment can now be 
designed without excessive experimentation. Further 
simplification is undoubtedly still possible and greater 
adaptability to different conditions should be at¬ 
tempted. Work is now under way on a generator 
which injects the DDT solution after the heating coil. 
If successful, this will eliminate a lot of the trouble 
due to coking and corroding and should simplify the 
use of new insecticide formulations. Although Hoch- 
berg-LaMer-type generators are large and complex, 
they can be operated easily after brief instruction. 
The controlled particle size should prove even more 
valuable for insecticide operations in civilian areas 
than in the war theaters because of the care which 
must be exercised under such conditions. Further 
work with this type of generator against agricultural 
pests should be carried on. 

The exhaust generator for motor vehicles has been 
enthusiastically received because of its extreme sim¬ 
plicity and should have wide use in the future. Al¬ 
though the dispersal is not as carefully controlled as 
with the more complicated Hochberg-LaMer gener¬ 
ators, this device should be extremely valuable for 
controlling a number of insect pests in small areas. 
The ability to vary at will the drop size from an 
aerosol to a coarse spray is an excellent feature. 
Further work is required to adapt this type of equip¬ 
ment to ordinary commercial vehicles such as trucks 
and tractors. 

In the field of aircraft dispersal, two methods have 
been developed, both having their respective ad¬ 
vantages. The simple sprays have proven very useful 
in the war theaters where simplicity and ease of 
installation and maintenance are prime requisites. 
The ability to use these sprays under a wide variety 
of meteorological conditions was an important factor 
in their use. Moreover, in these areas, the effects of 
the insecticide treatment on other forms of life do not 
have to be given serious consideration. The straight 
discharge pipe gives satisfactory results on fast mili¬ 
tary aircraft, but would not be satisfactory for slow 
light planes. Work on the development of the Ven¬ 


turi-type sprayers for military planes might be 
warranted. 

For civilian purposes, dispersal has to be carried 
out under more carefully controlled conditions in 
order to avoid damage to other forms of wild life 
and crops. Moreover, in civilian work, the complexity 
of the apparatus is not such an important factor since 
the equipment can be permanently installed. For 
these reasons, the aircraft exhaust generators should 
be of particular value in this type of work. The small 
aerosol droplets produced permit uniform deposition 
of the insecticide over the entire area, and the dosage 
used can be more carefully controlled. The ability to 
alter the drop size from a fine aerosol to a spray makes 
this type of equipment extremely useful under a wide 
variety of conditions. Design of Venturis for use on 
new types of aircraft should be continued. 

In addition to the design and development of actual 
devices for dispersal of DDT, research on the theory 
of atomization has been inaugurated. These studies 
are of prime importance in the design of any equip¬ 
ment for the dispersal of insecticides, and warrant 
continuation. The fundamentals involved in atomi¬ 
zation have never been clearly resolved, and results 
of research in this line should prove of value in many 
other fields as well as in the dispersal of insecticides. 

38.8 LIST OF MATHEMATICAL 
SYMBOLS USED 

M = dose DDT for kill. 

u = vertical velocity of drops. 

d = diameter of drop, 

p = density. 

g = acceleration due to gravity. 

t] = viscosity air. 

A = horizontal surface of insect. 

C = concentration. 

t = time. 

Ct = dosage. 

/ = average number of drops hitting area f5er unit time. 

n = number of drops. 

D = characteristic length of object (insect, foliage). 
v = horizontal velocity. 

P = dimensionless parameter (Sell). 

Cta = dosage for drop size increment. 

Wd = relative efficiency of drop size in killing an insect. 

W n + — probability n or more drops hit any one area. 

Q = source strength X time of emission. 

x = horizontal distance. 

m = meteorological constant. 

R = meteorological constant (^mMm). 

F = fraction of material remaining airborne. 

8 = horizontal distance for which the sum of the vertical 

foliage surfaces in any cross section is equal to the 
cross section. 


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LIST OF MATHEMATICAL SYMBOLS USED 


603 


7 

= vertical distance for which the sum of the horizontal 
foliage surfaces in any cross section is equal to the 

V 

= constant in empirical equation 
Tanasawa. 

of Nukiyama and 

A Q/Q 

cross section. 

= fraction lost travel horizontal. 

a 

= constant in empirical equation 
Tanasawa. 

of Nukiyama and 

y 

A 

= vertical distance. 

= impaction efficiency on vertical surface (Sell). 

b 

= constant in empirical equation 
Tanasawa. 

of Nukiyama and 

do 

= diameter of single drop with the same ratio of surface 

V 2 

= gas velocity in Venturi throat. 



to volume as a representative sample of the drop in 
the spray. 

gc 

= dimensional constant in equation 
in a Venturi. 

for throat velocity 

<r 

= liquid surface tension. 

= liquid viscosity. 

K 

= C p /Cv (specific heat at constant pressure/specific heat 
at constant volume). 

Qa 

= volume flow rate of gas. 

R/M 

= specific gas constant. 


Ql 

= volume flow rate of liquid. 

T 

= temperature. 


Ud 

= settling velocity of drops of diameter d. 

d% 

= diameter of Venturi throat. 


M d 

= weight of drop of diameter d. 

A 

= diameter of exhaust stack. 


N d 

= average number of drops of diameter d deposited per 
unit area. 

Pi 

P 2 

= exhaust stack pressure. 

= Venturi throat pressure. 


Q 

= constant in empirical equation of Nukiyama and 
Tanasawa. 

a 2 

w 

= Venturi throat area. 

= exhaust gas flow. 



SECRET 



Chapter 39 

INORGANIC TOXIC GASES 

By John C. Bailor , Jr. 


39.1 INTRODUCTION 

A mong the many toxic gases suggested or investi¬ 
gated during the war were several that are en¬ 
tirely, or in part, inorganic in nature. These include 
some well-known substances such as iron carbonyl, 
cyanogen, hydrogen cyanide, cyanogen chloride, and 
arsine. None of these, except cyanogen chloride, re¬ 
ceived a great amount ol study, as their use had been 
previously investigated and found impractical. Of the 
newly discovered gases, those containing fluorine 
proved to be of particular interest because some of 
them show great stability and high toxicity. It was 
hoped also that their high volatility would correlate 
with penetration of canisters. The most important 
members of this group which were studied by OSRD 
are disulfur decafluoride (S 2 Fi 0 , 1120 , F5, Z) and the 
fluophosphate esters. 

39.2 DISULFUR DECAFLUORIDE 

39.2.1 Preparation 

This substance was discovered by Denbigh and 
Whytlaw- Gray 1 as a by-product in the uncontrolled 
reaction of fluorine and sulfur. The yields in their 
experiments were less than 1%. The toxicity and 
stability of the substance, and its complete lack of 
odor or lacrimatory properties, suggested that it 
might be an ideal war gas. A great amount of effort 
was expended in studying its properties and in seek¬ 
ing a satisfactory method of preparation. The latter 
result was not achieved, and the effort was finally 
abandoned in the United States. It has been calcu¬ 
lated 2 that the cost of the fluorine used in making 
1120 would run between $21.00 and $140.00 per lb. 
The material used for tests on toxicity and other prop¬ 
erties amounted to about 3 kg, the preparation of 
which required the work of four men for about a year. 
However, further study of the nature of the material 
and of fluorination reactions may yet yield a suitable 
method. 

Methods Studied 

The Controlled Reaction of Fluorine and Sulfur. This 
has been the most successful method yet studied, giv¬ 


ing yields approaching 30% (based on sulfur) in some 
cases. For best results, the fluorine must be diluted 
with an inert gas, and the temperature must be care¬ 
fully controlled. Nitrogen has commonly been used 
as the inert gas. 3 The use of sulfur hexafluoride in 
place of nitrogen did not improve the result. 4 

In the most successful procedure, 3 purified fluorine 
is mixed with pure nitrogen in the ratio of 1/10 and 
passed over solid sulfur in a copper boat contained in 
a copper reaction tube, which is kept at room tem¬ 
perature by artificial cooling. The products of the 
reaction are caught in suitable traps. If the fluorine- 
nitrogen ratio is too low, the lower fluorides of sulfur 
(SF 2 and S 2 F 2 ) are formed in considerable amount; 
if the ratio is too high, SF 6 is almost the only product. 
Attempts to adapt this procedure to large-scale ap¬ 
paratus were not entirely successful, as the yield ob¬ 
tained was much decreased. The difference is prob¬ 
ably due to insufficient control of operating condi¬ 
tions, and could doubtless be overcome by further 
study. 5 

The fluorine used must be extremely dry. A fresh 
fluorine generator usually gives a poor yield because 
the issuing gas is slightly moist or contains OF 2 , 
which seems to exert a harmful effect. Best results 
are obtained only after the generator has run for 
several days; fair results can be obtained usually 
after the generator has operated for 24 hr. 

Many variants of this plan were studied. 4 - 6 The 
sulfur was finely divided and suspended in the nitro¬ 
gen; melted, vaporized in a stream of nitrogen, dis¬ 
solved in sulfur monochloride or carbon disulfide, or 
suspended in liquid hydrogen fluoride. 

It is probable that the reaction of sulfur with 
fluorine liberates enough heat to give a high tem¬ 
perature at the point of reaction. This seems to be 
essential to the formation of 1120; on the other hand, 
the 1120 must be removed from the hot zone immedi¬ 
ately or it is decomposed or further fluorinated. If 
this view is correct, the successful preparation of 1120 
from the elements depends upon the maintenance of 
proper conditions of temperature, rate of flow', and 
other physical conditions. Attempts to prepare 1120 
by allowing very hot sulfur vapor (700 C) to react 
with fluorine close to a cold condensing surface w'ere 


604 


SECRET 


DISULFUR DECAFLUORIDE 


605 


unsuccessful. The reaction gave only sulfur tetra- 
fluoride and sulfur hexafluoride. 

The Action 0 } Fluorine on Sulfur Compounds. Mer¬ 
curic sulfide, sulfur monochloride, sodium disulfide, 
potassium pentasulfide, antimony trisulfide, and 
sulfur tetrafluoride were studied, but with little suc¬ 
cess. These studies yielded excellent methods of 
preparation of other sulfur fluorides, however. It was 
observed that the action of fluorine on mercuric sul¬ 
fide gives pure sulfur hexafluoride, and it reacts with 
the vapor of sulfur monochloride to give sulfur tetra¬ 
fluoride of high purity in good yield. 

The Fluorination of Sulfur Chlorides hy Heavy Metal 
Fluorides. 1 This method seemed attractive in that it 
does not involve the use of elemental fluorine. At¬ 
tempts were made to fluorinate sulfur monochloride 
by means of the fluorides of several heavy metals. 
Evidently sulfur monofluoride (S 2 F 2 ) was formed, 
but it was quickly destroyed, either by reaction with 
the glass, or through its own instability. Whether 
S 2 F 2 could be further fluorinated to S 2 Fi 0 was, 
therefore, not determined. A valuable by-product 
of this research was the development of a method of 
making anhydrous fluorides of the heavy metals. 
According to this method, a mixture of dry hydrogen 
fluoride gas and an inert gas is passed countercurrent 
over the heated metal oxide in a rotary kiln. The 
water which is formed is swept away by the gas 
stream. For each of the metal oxides certain condi¬ 
tions of temperature, temperature gradient, and rate 
of flow of gases must be maintained. 

The Action of “Higher” Inorganic Fluorides upon 
Sulfur. This study amounted, for the most part, to a 
search for a nonelectrolytic method of preparing 
fluorine. Fluorides, such as 3KFHFPbF 4 , K 2 MnF 5 , 
K 2 MnF 6 , 3KF • 2CeF 4 • 2H 2 0, CeF 4 H 2 0, IF 5 , and 
ZrOF 2 , are said to be formed without the use of ele¬ 
mentary fluorine, and to yield fluorine upon heating. 
They might thus be used as regenerable sources of 
fluorine. Mixed with sulfur and heated, they might 
give the desired compound. It was found, 8 however, 
that the compounds were difficult to prepare and 
were poor sources of fluorine. 

The Action of Fluorinating Agents on Sulfur Com¬ 
pounds. 9 Sulfur chloride and the tetrafluoride were 
treated with such fluorinators as iodine pentafluoride, 
bromine trifluoride, and hydrogen fluoride. In the 
main, these methods give mixtures of the tetrafluoride 
and hexafluoride of sulfur. 

The Defluorination and Coupling of Sulfur Hexa¬ 
fluoride. It has been reported 10 that sulfur will 


react with sulfur hexafluoride at 400 C, but this could 
not be confirmed. Sulfur hexafluoride does react 
readily with many anhydrous salts, however. 4 Sodium 
and calcium iodides, sodium and barium bromides, 
and calcium sulfide were studied. In every case, free 
sulfur and the metallic fluoride were formed. 

The Electrolysis of Fuming Sulfuric Acid in Liquid 
Hydrogen Fluoride. This gave no sulfur-fluorine com¬ 
pounds. 6 - 11 

The Action of Hydrogen Fluoride upon Sodium and 
Barium Dithionates. This method was attempted be¬ 
cause the dithionate ion contains a sulfur-sulfur link. 
No sulfur fluorides were formed. 

Reaction of Fluorine Oxide with Sulfur and with 
Sulfur Dissolved in Sulfur Monochloride. The prod¬ 
ucts were sulfur tetrafluoride and the oxyfluorides 
of sulfur. 11 

39.2.2 Properties 

Disulfur decafluoride is a volatile, heavy liquid 
(density 2.08 at 0 C) 1 with a slight odor. When pure 
it melts at — 53 C, but the melting point is very 
sensitive to traces of impurities. Burg 12 has calcu¬ 
lated the boiling point to be 30.1 C from the vapor 
pressure equation 

logic p mm = - + l-751ogi„r ■- 0.008166 + 7.1348. 

Below the melting point, the solid follows the equa¬ 
tion 

, 0 _ 1607 

lOglO Pram 8.32 y, 

The substance is practically insoluble in water (less 
than 0.005% by weight). 

Disulfur decafluoride is inert to many chemical re¬ 
agents, such as caustic alkalies and strong acids, and 
does not attack steel. It is unreactive toward glass, 
paraffins, and Apiezon L stopcock grease, and can 
be dried over phosphorus pentoxide or potassium 
hydroxide. Although it does not react with the com¬ 
mon organic solvents, it dissolves in olive oil (with 
which it reacts slightly) to the extent of 4%. It is not 
attacked by fluorine, but reacts with chlorine with 
the formation of a slightly volatile liquid. Ethylene 
reacts slowly with 1120. 

The thermal stability of 1120 is truly remarkable, 
as decomposition proceeds very slowly below 200 C, 
and becomes marked only above 250 C. The reaction 
seems to give a mixture of sulfur tetrafluoride and 
sulfur hexafluoride. The same decomposition is 


SECRET 






606 


INORGANIC TOXIC GASES 


brought about by contact with animal tissues, vege¬ 
table oils, or charcoal. Since in each case the reaction 
proceeds to only a slight extent, it is supposed that 
it is catalytic and that the catalyst is readily poisoned. 
Early in the investigation it was hoped that the de¬ 
composition on charcoal in the gas mask canister 
might prove to be valuable in warfare, as the result¬ 
ing gases are extremely irritating and might cause the 
removal of the mask during a gas attack. However, 
the reaction products other than SF 6 (which is harm¬ 
less) are retained by absorbents. 

The thermodynamic properties of 1120 have been 
investigated thoroughly , 13 and numerous reactions 
of the sulfur fluorides have been predicted. 

39.2.3 Chemical Detection of S 2 Fi 0 

The fact that S 2 Fi 0 liberates iodine from a solution 
of potassium iodide or sodium iodide in acetone has 
been made the basis of a quantitative test for deter¬ 
mining S 2 Fio in air . 14 The liberated iodine can be de¬ 
termined colorimetrically or by titration with thio¬ 
sulfate, and the fluoride can be determined gravi- 
metrically by precipitation with triphenyl tin chlo¬ 
ride . 15 Obviously, any other oxidizing agents which 
may be present in the gas under analysis will also 
liberate iodine. It was shown, however, that the 
other substances, which might logically be present in 
S 2 Fio from shell explosions, either do not interfere 
in this analysis or can be removed readily before 
analysis. These substances include N0 2 , N 2 0, 
S0 2 F 2 , SF 6 , and SF 4 . The reaction of 1120 with iodide 
is evidently complex, and conditions must be con¬ 
trolled carefully if consistent results are to be ob¬ 
tained. For example, if the iodide-acetone solution 
contains water, the amount of iodine liberated is low. 
At the same time, however, a roughly equivalent 
quantity of acid is formed. Apparently, there are 
competing reactions, one of which liberates iodine, 
while another liberates hydrogen ion. 

S 2 Fio can be detected qualitatively through its 
reaction with p-phenylenediamine. A piece of paper, 
wet with a solution of the amine in acetone, is ex¬ 
posed to the atmosphere under investigation. A pink 
color indicates the presence of S 2 Fi 0 . As little as 
0.1 Mg of 1120 can be detected. 

39.3 DIALKYLMONOFLUOROPHOSPHATES 

Dialkylmonofluorophosphates were first prepared 

by Lange 16 who reported that inhalation of even 
minute quantities produces severe headache, followed 


by visual trouble. These effects last for several hours. 
These observations indicate that substances of this 
class might be of military value, and investigations 
were started independently in the United States, in 
England, and (as found out later) in Germany. New 
methods of preparation were developed, and several 
esters were prepared and studied. The work of the 
American investigators was finally set aside in favor 
of more pressing investigations. The fluorophosphates 
show such sufficient promise, however, that they 
should be investigated further. It is quite possible 
that esters not yet prepared will be found to be more 
toxic than any which have been studied. 

39.3.1 Preparation 

Lange’s method of preparation consisted of: 

1 . The preparation of ammonium fluorophosphate 
by fusion of phosphorus pentoxide with ammonium 
fluoride; 

P 2 0 5 + 3NH 4 F—>nh 4 hpo 3 f + nh 4 po 2 f 2 + nh 3 . 

2 . Conversion of the ammonium salt to the silver 
salt by metathesis Avith silver nitrate. 

3. Alkylation of the silver salt with an alkyl iodide. 
He reported an overall yield of about 12%. 

Several more direct methods at once suggest 
themselves: 

1. Reaction of alcohol with phosphorus oxychlo¬ 
ride 

2 ROH + POCl 3 —> (RO)oPOCl + 2HC1 

followed by fluorination of the product. 

2 . Partial fluorination of phosphorus oxychloride, 
followed by alkylation with the appropriate alcohol, 

POCl 3 + HF —> POCl 2 F + HC1, 

POCl 2 F + 2ROH —> (RO) 2 POF + 2HC1. 

3. Preparation of alkyl phosphites, followed by 
oxidation and fluorination, 

PC1 3 + 3ROH —► P(OR ) 3 + 3HC1 
P(OR ) 3 + Cl* —■> (RO) 2 POCl + RC1. 

4. Preparation of monofluorophosphoric acid, fol¬ 
lowed by esterification with olefines, alcohols, or 
ethers, 

P 2 O 5 + 3HF —► H 2 P0 3 F + HP0 2 F 2 . 

Method 1 proved to be a successful process for the 
preparation of the lower homologs . 17 For example, 
phosphorus oxychloride reacts practically quanti¬ 
tatively with two moles of methyl alcohol, yielding a 


SECRET 



DIALKYLMONOFLUOROPHOSPHATES 


607 


mixture of CH 3 OPOCl 2 , (CH 3 0) 2 P0C1 and (CH 3 0) 3 P. 
After removal of the hydrogen chloride, the mixture 
can be fluorinated, and (CH 3 0) 2 P0F can be isolated 
from the final mixture, the yield being about 30%. 

The reaction between phosphorus oxychloride and 
ethyl alcohol does not proceed to complete esterifica¬ 
tion so readily, so that better yields (about 45%) of 
the fluorinated product can be obtained. 

The preparation of the isopropyl ester by the same 
process, however, involves peculiar difficulties, for the 
reaction of isopropyl alcohol with phosphorus oxy¬ 
chloride yields several unidentified by-products, and 
the intermediate diisopropylmonochlorophosphate 
decomposes when heated in the presence of the hy¬ 
drogen chloride by-product. 18 Neutralization of the 
hydrogen chloride with dry ammonia gas made the 
method workable, however, and some diisopropyl- 
monofluorophosphate was obtained in this way. Mc- 
Combie’s method of preparing this ester 19 is much 
more satisfactory, however. This involves the esteri¬ 
fication of phosphorus trichloride, followed by oxida¬ 
tion with chlorine: 

3 fC 3 H 7 OH + PC1 3 —> 

(tC 3 H 7 0) 2 P0H + fC 3 H 7 Cl + 2HC1. 
(fC 3 H 7 0) 2 P0H + Cl 2 —>(zC 3 H 7 0) 2 P0C1 + HC1. 

The first of these reactions gives about a 70% yield, 
while the second is apparently quantitative. Most of 
the hydrogen chloride escapes, and the remainder 
may be destroyed by bubbling ammonia into the 
solution. Introduction of hydrogen fluoride gives an 
overall yield of 60% of the monofluorophosphate. (If 
the hydrogen chloride is not completely destroyed, 
none of the fluorophosphate is obtained.) It is not 
necessary to isolate any of the intermediate products. 

Some of the difficulties encountered in the prepara¬ 
tion of the isopropyl ester are evidently due to the 
branching of the chain, for the n-propyl and n-butyl 
esters can be prepared in the same manner as the 
methyl and ethyl compounds, though the yield in 
the case of the n-butyl ester is somewhat lower than 
in the other cases. 

In attempts to increase the toxicity of the fluoro- 
phosphates, chlorine substituted compounds were 
prepared. 20 Ethyl-/3-chloroethyl monofluorophosphate 
was prepared by the successive reactions of chlorohy- 
drin and ethyl alcohol with phosphorus oxychloride, 
followed by fluorination with sodium fluoride. All 
of these reactions proceed smoothly, and give good 
yields. Di-/3-chloroethyl monofluorophosphate was 
obtained in good yield in a similar manner. 


Toxicity tests indicated that ethyl fluorophosphate 
is more valuable from a military point of view than 
is the methyl ester. Since it is desirable to have the 
molecular weight of the ester as low as possible, at¬ 
tempts were made to prepare cyclic esters such as 


and 


CH 2 0 O 

\ / \ 

POF, C 6 H 4 POF, 

/ \ / 

ch 2 o o 


o 



POF. 21 


None of the experiments attempted were successful 
and the project had to be abandoned before its com¬ 
pletion. Further work would probably lead to suc¬ 
cessful syntheses. Ethylene glycol reacts with phos¬ 
phorus oxychloride, but under all conditions tried, 
the products obtained were polymers. Carre 22 has 
reported that glycerine a-monochlorohydrin reacts 
with phosphorus trichloride to give 
C1CH 2 - CH 2 - 0 

\ 

PCI, 

/ 

CH 2 - 0 

so it is probable that cyclic esters of pentavalent 
phosphorus may be obtained. Moreover, the com¬ 
pound 

O 

/ X 

C 6 H 4 POC1 



has been obtained. 23 Hydrogenation and fluorination 
of this compound would give the interesting cyclo¬ 
hexane monofluorophosphate. 

Reports from England indicated that cyclohexyl 
monofluorophosphate had very desirable properties, 
and the American military authorities began to re¬ 
quest samples of it before directions for its prepara¬ 
tion had been received from England. Accordingly, 
the preparative methods that had proved successful in 
the formation of the simpler esters were employed in 
attempts to prepare it. 24 Attempts were also made to 
reduce the phenyl ester catalyticallv. None of these 
methods gave the desired product; the only success¬ 
ful method devised is apparently that developed by 
McCombie and his co-workers in England. 25 This 
method involves the reaction of cyclohexyl alcohol 


SECRET 





608 


INORGANIC TOXIC GASES 


with phosphorus oxydichlorofluoride to give the de¬ 
sired product directly. However, the partial fluorina- 
tion of phosphorus oxychloride to POCl 2 F is difficult, 
for once the fluorination of the phosphorus oxychlo¬ 
ride starts, it is difficult to stop it short of complete 
replacement of chlorine by fluorine. Fortunately, the 
boiling point falls as fluorination becomes more com¬ 
plete, so that if the fluorination is carried out at the 
boiling point of phosphorus oxychloride, the phos¬ 
phorus oxydichlorofluoride can be drawn off as it is 
formed, and some of the desired product obtained. 
Booth and Dutton 26 have obtained 40% yields of 
POCl 2 F by the reaction of phosphorus oxychloride 
with calcium fluoride. Under the best conditions, the 
reaction of boiling phosphorus oxychloride and hy¬ 
drogen fluoride has been made to give yields of 60% 
of the dichlorofluoride. 27 

39 . 3.2 Properties 

The fluorophosphates are colorless liquids, the 
vapor pressures of which are only a few millimeters 
of mercury at room temperature. They are almost 
insoluble in water, and are attacked by it only very 
slowly, remaining unhydrolyzed when left in contact 
with water for many days. They do not attack glass 
or steel. 18 Their odor is faint and not unpleasant. In¬ 
haling them in minute quantities produces a con¬ 
striction of the pupils resulting in partial blindness 
which lasts for several hours. In larger quantities, 
they produce headache, convulsions, and death. 

39.4 ALKYLDIFLUOROPHOSPHATES 

These compounds were prepared by fluorination of 
the corresponding chlorophosphates. 28 Although the 
yields are not good, sufficient quantities of material 
were obtained for investigation. The ethyl ester is a 
colorless liquid having a density of about 1.25 and 
boiling at 85 C. It decomposes slowly above 50 C, but 
this may be due to reaction with the walls of the 
(glass) vessel rather than straight thermal decom¬ 
position. It is soluble in organic solvents and reacts 
vigorously with water. This is surprising in view of 
the great stability of the monofluoro esters. 

39.5 ALKYLMONOFLUOROTHIOPHOS- 

PHATES 

These esters cannot be prepared in an analogous 
manner to the oxy compounds as the reaction of 
thiophosphoryl chloride and alcohol does not proceed 
in the desired manner. With ethyl alcohol, ethyl 
chloride is produced quantitatively. However, in the 


presence of pyridine, a small yield of the mono- 
chlorothiophosphate is obtained. This is readily fluo- 
rinated. 18 The diethyl ester is a colorless liquid, 
heavier than water, and boiling at 55 C under 10 mm 
pressure. It is extremely stable toward hydrolysis. 

39.6 FLUOROSULFON ATES 

Because of the interest in fluorophosphates, some 
fluorosulfonates were prepared and their properties 
noted. 29 Fluorosulfonic acid was first prepared by 
Thorpe and Hermann 30 who obtained it from the 
action of liquid hydrogen fluoride upon liquid sulfur 
trioxide. Ruff and Braun 31 reported an almost theo¬ 
retical yield of the acid by the reaction of 60% oleum 
and fluorspar. The acid can also be made in theoreti¬ 
cal yields by the reaction of anhydrous hydrogen 
fluoride and chlorosulfonic acid. 

Meyer and Schramm 32 prepared esters of fluorosul¬ 
fonic acid by the reaction of the acid with absolute 
diethyl ether, ethylene, and diazomethane. The first 
two of these methods were repeated and found to give 
good results. Ethyl fluorosulfonate is a clear liquid 
having a density of 1.29 at 27 C, and boiling at 112 C 
at atmospheric pressure (42.5 at 55 mm). It decom¬ 
poses upon boiling but is remarkably stable toward 
hydrolytic decomposition, as it is not destroyed by 
refluxing with 20% sodium hydroxide for 2 hr. It 
does not fume in air and does not etch glass notice¬ 
ably even on standing for several weeks. It is de¬ 
stroyed, however, by nitric and sulfuric acids. It is 
soluble in the usual organic solvents. It has the typical 
ester odor, but is a lachrymator. 

The methyl ester (from the acid and absolute 
dimethyl ether) is similar, but is not so effective a 
lachrymator. Attempts to prepare the isopropyl ester 
were unsuccessful; this ester seems to be unstable, 
decomposing upon boiling, even in vacuo. 

39.7 OTHER GASES 

Many other inorganic gases were investigated, but 
none of great military interest was found. A few of 
the more interesting will be mentioned. 

Phosphorus trifluoride was prepared by the SbCl 5 
catalyzed reaction of phosphorus trichloride and 
antimony trifluoride. 33 It forms an unstable com¬ 
plex, (CH 3 ) 3 N • PF 3 , through which it can be purified, 
since SiF 4 and other impurities do not react with 
trimethylamine. The phosphorus trifluoride can be 
simply distilled with the complex, or the complex can 
be sublimed, and then decomposed to yield pure 


SECRET 



OTHER GASES 


609 


phosphorus trifluoride. The material is probably too 
volatile to become a useful war gas. (The vapor pres- 
sureis 376 mm at —111.9 C and 181 mm at -120.8 C.) 
By combination with trimethylamine, PF 3 can be 
given an effective boiling point of about 0 C. 34 

Dimethylamino phosphorus difluoride was prepared 
in accordance with the equation 

2(CH 3 ) 2 NH + PF 3 —> 

(CH 3 ) 2 NPF 2 + (CH 3 ) 2 NH 2 F. 33 
It is a liquid at ordinary temperatures, boiling at 50 C 
(logic P mm = 7.863 - 1610/T). 

The compound is not entirely stable, but at room 
temperature, it comes to equilibrium with its decom¬ 
position products when only 4 % decomposition has 
taken place. 

2(CH 3 ) 2 NPF 2 PF 3 + [(CH 3 ) 2 N] 2 PF. 

This latter compound, bisdimethylamino phosphorus 
fluoride, can be prepared also by the action of 
dimethylamine upon (CH 3 ) 2 NPF 2 . It was found to 
be relatively non toxic. 

Dimethylamino phosphorus difluoride hydrolyzes 
very slowly, so it was thought that it might penetrate 
into the lungs more deeply than phosphorus trifluo¬ 
ride itself. Whether this is true was not determined; 
the material is not strongly toxic. 

The closely related compound (CH 3 ) 2 NPOF 2 was 
prepared in an analogous manner and also by the 
reactions 

POCl 3 + 2(CH 3 ) 2 NH —> (CH 3 ) 2 NP0C1 2 + 

(CH 3 ) 2 NH 2 F 

followed by 

3(CH 3 ) 2 NP0C1 2 + 2SbF 3 —> 2SbCl 3 

+ 3(CH 3 ) 2 NPOF 2 (SbCl 5 catalyzed). 
This compound is not strikingly toxic. 

Action of dimethylamine on dimethylamine phos- 
phoryl difluoride yields bisdimethylamine phosphoryl 
fluoride [(CH 3 ) 2 N] 2 POF, which is an analogue of the 
very toxic aliphatic fluorophosphates, and which is 
also toxic (median lethal concentration of 0.095 mg 
per 1 on mice exposed for 10 min). This compound can 
also be prepared directly from phosphoryl fluoride 
and dimethylamine or from phosphoryl chloride and 
dimethylamine followed by fluorination with anti¬ 
mony fluoride. It is a liquid boiling at 50 C under a 
pressure of 2 mm. It is not readily hydrolyzed by pure 
water, but is quickly attacked by alkalis. It would 
seem that this compound, like the analogous fluoro¬ 
phosphates, deserves further study. 


Substitution of arsenic for phosphorus in the com¬ 
pound (CH 3 ) 2 NPF 2 did not produce a toxic com¬ 
pound. 33 This substance was prepared by the interac¬ 
tion of dimethylamine and arsenic trifluoride. 

A small yield of 2, 2', 2" trifluoro triethylamine, 
(FC 2 H 5 ) 3 N, was prepared by a very tedious fluorina¬ 
tion of the corresponding chloro compound with 
anhydrous silver fluoride. The substance was tested 
for vesicant action, but the results were negative. 35 

Nitrogen trifluoride, which was reported by Ruff 
to be highly toxic, was obtained from the electrolysis 
of molten ammonium bifluoride. After careful puri¬ 
fication, it was found to be relatively nontoxic. The 
substances NHF 2 and NH 2 F, which have been re¬ 
ported by Ruff to be even more toxic than NF 3 , 
could not be obtained at all. 

Acyl chlorides are known to be toxic, and some of 
them have found wide use as war gases. The cor¬ 
responding fluorides would be expected to be more 
volatile (and hence less readily adsorbed in a gas 
mask), less readily destroyed by hydrolysis, and 
more toxic. Unfortunately, they have been difficult 
to prepare. During the course of this work, however, 
a satisfactory method was developed. 36 This involves 
the conversion of acyl chlorides to the corresponding 
fluorides by the action of anhydrous hydrogen fluo¬ 
ride at suitable temperatures and pressures. Thus, 
phosgene can be converted to COFC1 or COF 2 and 
oxalyl chloride to oxalyl fluoride. In the former case, 
complete fluorination can be avoided by drawing off 
the partially fluorinated product as it is formed. 
Carbonyl chlorofluoride has an odor resembling that 
of phosgene, but the two can easily be distinguished. 
It is readily absorbed by bases. 

Arsine has often been suggested as a war gas, but it 
is too volatile to be persistent and too unstable to be 
kept for more than a few days. An attempt was made 
to find a solvent in which arsine would be stabilized 
and in which it would have a reasonably low vapor 
pressure. 37 The solvents used were thionyl chloride, 
p-ethylnitrobenzene, 1-nitropropane, triethyl borate, 
and tributyl borate. In thionyl chloride, arsine de¬ 
composes in a few minutes, and in the other solvents, 
within a few hours. In triethyl and tributyl borate, 
the vapor pressure is lowered by as much as 30%, so 
if a stabilizer can be found, these solutions may be of 
value. It should be borne in mind, however, that 
arsine is an endothermic compound; if it is to be 
stabilized, it will probably have to be mixed with 
some compound with which it forms a stable bond. 


SECRET 



Chapter 40 

THE PREPARATION OF FLUORINE 

By John C. Bailor , Jr. 


40.1 INTRODUCTION 

he element fluorine was first prepared by 
Moissan by the electrolysis of a solution of 
potassium fluoride in anhydrous hydrofluoric acid at 
about — 20 C in a platinum-iridium U tube. Corro¬ 
sion was severe, and the yield of fluorine was small. 
Nevertheless, modifications of this method have al¬ 
ways constituted the only practical method of mak¬ 
ing fluorine. It has frequently been suggested that 
fluorides of metals in their higher valence states might 
be thermally decomposed to liberate fluorine, but no 
practical method based upon this principle has been 
discovered. It is true that some metallic fluorides can 
be decomposed with the liberation of fluorine (AgF 2 , 
for example), but such fluorides can be prepared only 
by the use of elemental fluorine. The element is such 
a powerful oxidizing agent that metals in union with 
it are not readily reduced by heat alone. 

Electrolysis of anhydrous fluorides always employs 
mixtures of hydrogen fluoride and alkali metal or 
other metal fluorides. As the proportion of metal fluo¬ 
ride is increased, the melting point of the mixture 
rises, necessitating changes in the design and opera¬ 
tion of the cell. Low-temperature operation has 
obvious advantages, but the low-temperature baths 
are so rich in hydrogen fluoride that the vapor pres¬ 
sure of this constituent is high. Moreover, corrosion 
of the anodes and the electrolytic cell is often more 
troublesome in these baths than in those operating on 
molten salt mixtures. The best bath will contain a 
low-melting eutectic salt mixture with a small con¬ 
centration of hydrogen fluoride, the supply of which 
will be replenished at frequent intervals or continu¬ 
ously. Recent discoveries 1 at Massachusetts Insti¬ 
tute of Technology have shown that a bath of the 
composition RF • 1.5HF (where R is K containing a 
small percentage of Li) melts at about 70 C and 
serves as an excellent electrolyte for the preparation 
of fluorine. This is perhaps the best method dis¬ 
covered to date. In order to show why this is so, and 
to give a basis for further work, the use of several 
baths will be described. 


40.2 BATHS OPERATING AT ROOM 

TEMPERATURE 

A cell using a bath rich in hydrogen fluoride and 
liquid at room temperature was patented in 1936, 
and was restudied under OSRDA 3 - 4 It was found to 
be unsuited for large-scale production of fluorine. At 
the low temperature employed, hydrogen and fluorine 
dissolve in the electrolyte, so that each of the efflu¬ 
ent gases contains an admixture of the other in a mix¬ 
ture sometimes rich enough to be explosive. 3 More¬ 
over, corrosion of the nickel anodes and the walls of 
the vessel is serious. In one run, for example, 1 g of 
nickel was devoured for each 2.07 ± .02 g of fluorine 
produced. Attempts to decrease the corrosion by 
varying the current density and other operating 
factors were without effect. 5 Other metals were tried 
as anodes in place of nickel, but the results were even 
less promising. Graphite anodes are rapidly disinte¬ 
grated by the bath. Some iron from the walls of the 
vessel is also dissolved, and a heavy sludge of ferrous 
and nickel fluorides gradually forms in the electro¬ 
lyte, so that the run eventually has to be stopped to 
allow cleaning of the cell. 1 These low-temperature 
cells sometimes give a current efficiency of 80% when 
the run is first started, but this soon falls to about 
50% (based on fluorine delivered) and then remains 
constant. 7 The yield based on hydrogen, however, is 
always about 80%, 1 the difference indicating the loss 
of fluorine due to corrosion. The cells operate at 7 to 
9 v and 30 amp. Anhydrous hydrogen fluoride is 
added slowly while the cell is in operation. Since the 
vapor pressure of hydrogen fluoride over this bath is 
high, reflux condensers cooled by solid carbon dioxide 
or some other refrigerant must be provided. 

40.3 BATHS OPERATING AT MEDIUM 

TEMPERATURES 

Baths approximating the composition KF-2HF 
and KF-3HF have been used for many years. The 
former are operated at 100 to 110 C and the latter at 
70 to 100 C. The cells are heated by a steam jacket 



610 


SECRET 


POLARIZATION AND THE ANODE EFFECT 


611 


or electrically, though external heating is often un¬ 
necessary after electrolysis is begun. Here again, 
much hydrogen fluoride escapes as vapor and must 
be refluxed back into the cell or trapped out and re¬ 
plenished. Corrosion is severe, but not so severe as 
in the bath which operates at room temperature. 
From 7 to 8 lb of fluorine can be produced for each 
pound of nickel lost from the anode. Current effi¬ 
ciency based on fluorine often goes as high as 70 to 
75%. Certain types of carbon and graphite can be 
used as anode materials, though it is difficult to pre¬ 
dict how well a given sample of carbon will with¬ 
stand the attack of the bath. Ungraphitized carbon 
is ordinarily better than graphite. 6 Corrosion of the 
vessel is also much less marked than with the more 
acid baths. While low-silicon steel can be used, 
and usually is, copper or copper-plated steel is 
superior. This method of preparing fluorine has been 
fairly satisfactory in commercial use. With good 
carbon anodes, current efficiencies are much higher 
than with nickel anodes, sometimes being better 
than 90%. The major problem in the operation of 
this method is the swelling and disintegration of the 
carbon anodes at their point of union with the anode 
holders. A careful studj r of this has been made, 8 and 
it has been shown that corrosion is minimized if the 
carbon-metal bond is below the surface of the bath. 
Magnesium, brass, and copper are the best metals to 
use for electrode holders, whereas aluminum, nickel, 
and Monel are badly attacked. The destruction 
of the union between the carbon and the metal can 
be minimized by the use of colloidal graphite (Aqua- 
dag) as a joint compound between the metal and car¬ 
bon surfaces. 6 Another method of handling the prob¬ 
lem is to run the carbon anode through the cover of 
the cell, making the carbon-metal connection outside 
of the cell. 

The addition of a few per cent of lithium fluoride 
tends to lower the melting point of the bath, so that 
the hydrogen fluoride content can be cut without 
having to raise the operating temperature. Such a 
bath might have the composition 82.7% KHF 2 , 3% 
LiF, 14.3% HF, which approximates the formula 
RF • 1.5HF. This composition is maintained by direct 
addition of hydrogen fluoride while the cell is in 
operation. Because of its lower hydrogen fluoride 
content, this bath corrodes the vessel less than the 
low-temperature bath, so that steel vessels are quite 
acceptable. With copper-lined cells, the bath remains 
nearly free of corrosion products. This bath also has 
the advantages of being nonhygroscopic and of show¬ 


ing a much lower vapor pressure than the low-tem¬ 
perature bath. Nickel electrodes cannot be used, 
however, as the metal is destroyed rapidly and little 
fluorine is formed. 7 Carbon, on the other hand, is 
attacked hardly at all. At high-current densities, 
polarization sets in, seriously interfering with the 
production of fluorine. This phenomenon will be 
discussed later. When the cell is operating properly, 
current efficiencies of 95 to 98% can be obtained. 
Two such cells ran unattended (on a reduced am¬ 
perage) for 72 hr without any trouble. 9 

Cells operating at 130 to 150 C, but still using a 
bath of the general composition RF1.5HF, can be 
prepared by using 66.8% KHF 2 , 14.4% NaF, and 
18.7% HF. This seems to offer no advantage over the 
bath containing lithium fluoride, and the cell cor¬ 
rosion is much worse. 6 

40.4 BATHS OPERATING AT HIGH 

TEMPERATURES 

Baths of the composition MF-HF can be electro¬ 
lyzed at 250 C or higher, and have been widely used. 
This method of making fluorine is nearly as successful 
as that operating in the neighborhood of 100 C. 6 The 
cell must be heated to the required temperature by 
gas or electricity, but additional heating is not re¬ 
quired while electrolysis is under way. The cell must 
be of copper or Monel rather than of steel, and the 
anodes are of graphite or graphitized carbon. Sludge 
formation is slight, and current efficiencies are over 
90%. However, the composition of the bath must be 
carefully controlled. 

Baths containing no hydrogen fluoride have re¬ 
ceived some attention, but none have been found 
which can be electrolyzed to give fluorine at tem¬ 
peratures as low as 300 C, which seems to be the 
upper limit for operation with carbon in contact with 
fluorine. 6 Mixtures of potassium fluoride and lithium 
fluoride with the fluorides of antimony, zinc, lead, 
and cadmium have been studied. 5 ’ 7 This method 
holds promise, and further study of it should be 
made. 

40.5 POLARIZATION AND THE 

ANODE EFFECT 

When a cell with a carbon anode is operated at a 
high current density, polarization sometimes takes 
place. The voltage rises, often to 50 or 100 v, and the 
amount of current passing through the cell falls. 


SECRET 




612 


THE PREPARATION OF FLUORINE 


While the cell is operating at the higher voltage, no 
fluorine is formed, but the anode is attacked with the 
formation of carbon fluorides. This phenomenon of 
polarization is not clearly understood, and it cannot 
be produced at will. 10 Sometimes, but not always, it 
disappears spontaneously. If it does not, it can 
usually be overcome by resorting to certain practical 
and empirical remedies. These include breaking the 
current, short circuiting the cell, or reversing the 
current momentarily. Sometimes the polarization dis¬ 
appears if the anode is connected to the cell wall for 
an instant, or if alternating current is superimposed 
upon the direct current being used for electrolysis. 
The use of direct current from a rectifier is helpful. 
While the cell is polarized, the anode is enveloped in 
a multitude of tiny sparks. 10 It has often been sug¬ 
gested that polarization is due to impurities in the 
electrolyte, but it has been demonstrated that small 
quantities of sulfuric acid and of water do not pro¬ 
duce severe polarization. 8 Samples of anodes which 
have undergone polarization have not been demon¬ 
strated to contain any impurities that are not found 
in anodes which have functioned without polariza¬ 
tion. Yet the phenomenon seems to be inherent in the 
nature of the anode used. One example has been re¬ 


ported 11 of a carbon rod which became polarized re¬ 
peatedly. None of the usual methods of breaking the 
polarization was effective for more than a few min¬ 
utes. Even baking, scraping, and washing had no 
effect in decreasing the tendency of this sample to 
polarize. 

Carbon anodes do not seem to be wet by the fluo¬ 
ride electrolyte. As electrolysis proceeds, the surface 
of the anode often becomes glossy and increases in 
hardness. The nature of this glaze is not known, but 
it does not seem to be the cause of the anode effect, 
for highly glazed electrodes sometimes function per¬ 
fectly. The most logical explanation of the polariza¬ 
tion effect is that the electrode is surrounded by a 
thin but impervious gas film, which adheres tightly. 10 
There is some evidence that the presence of lithium 
fluoride in the electrolyte causes the liquid to wet the 
anode and also prevents polarization. 12 

Although the problems of corrosion and of polariza¬ 
tion of the cell remain as troublesome problems, it 
may now be said safely that the preparation of 
fluorine on a fairly large scale is feasible and practical. 
Several companies are producing fluorine commer¬ 
cially, and as its use increases, the price may fall to 
as little as $CK25 to $0.50 a pound. 12 


SECRET 



Chapter 41 

THE STABILIZATION OF CYANOGEN CHLORIDE 

By Anton B. Burg 


I 


41.1 INTRODUCTION 

C yanogen chloride is one of the promising non- 
persistent gases because it penetrates humidified 
canisters unless they are given special impregnation 
to protect against this agent. Other advantages of 
cyanogen chloride are its relatively high boiling point 
(13 C), which makes it easier to load into munitions 
than either cyanogen or phosgene, and its nonin¬ 
flammability, a great advantage over hydrogen 
cyanide. It also persists longer in the neighborhood 
of wet surfaces (e.g., vegetation) than does hydrogen 
cyanide or phosgene. 

The one great disadvantage of cyanogen chloride 
has been its instability. It may have a pronounced 
tendency to polymerize, often very suddenly and 
with little warning, yielding cyanuric chloride and a 
variety of other solid or liquid polymers as well as 
degradation products. Large bombs containing this 
agent have been known to detonate in normal stor¬ 
age, amply demonstrating the danger of storing the 
raw commercial product in contact with steel. Even 
if deterioration occurred without explosions, the loss 
of the cyanogen chloride could not be tolerated. It, 
therefore, was necessary to learn as much as possible 
of the conditions under which cyanogen chloride 
would become unstable, and to devise methods of 
preventing troubles arising from its instability, 
preferably without serious alteration of specifica¬ 
tions for the munitions destined to contain the 
material. 

Previous to World War II, very little was known 
of such matters. The only definitely recognized 
catalyst for the degradation process was hydrogen 
chloride, and by inference, other acids also were re¬ 
garded as harmful. No very effective stabilizer had 
been recognized. It was known to Wurtz 1 that 
chlorine causes polymerization of cyanogen chloride 
to the trimer, cyanuric chloride, provided that water 
and HCN are present as impurities. According to 
Jennings and Scott, 2 this effect could be understood 
as due to the formation of HC1, which Chattaway 
and Wadmore had recognized as a more direct cata¬ 
lyst for the polymerization process. 3 Various authors 
differ on the question of whether HC1 would cause 


explosions, but it can be argued that it will do so 
often if the sample is large enough so that the heats 
of hydrolysis and polymerization are not rapidly dis¬ 
sipated. Price and Green 4 found that the HCl-cata- 
lyzed hydrolysis of cyanogen chloride (to form 
NH 4 C1 and CO 2 ) proceeds far more rapidly than the 
HCl-catalyzed polymerization. There was general 
agreement that purification of cyanogen chloride 
improves its stability. 

NDRC work on this problem began in 1942 as a 
supplement to the investigation of absorbents. 5 The 
preliminary study checked much of the earlier knowl¬ 
edge and indicated that the bad effect of HC1 or of 
chlorine could be largely overcome by addition of 
magnesium oxide. Sodium cyanide was found to be 
harmful, yielding dark azulmic materials. Most of 
the tests with common materials were not carried on 
long enough to detect their bad effects, but the main 
inference, that munition storage of cyanogen chloride 
could be made feasible, was later shown to be sound. 

More detailed studies were attempted next by re¬ 
search personnel of the American Cyanamid Com¬ 
pany. 6 Although most of the experiments were some¬ 
what lacking in precision, it could be recognized that 
crude cyanogen chloride was far less stable in steel 
containers than in contact only with glass, that 
alkene oxides were not dependable stabilizers, that 
primary or secondary alcohols and other hydroxyl 
compounds were seriously harmful, and that crude 
cyanogen chloride from the pilot plant would meet 
the preliminary specification of freedom from de¬ 
terioration during 30 days, even in a steel container 
at 65 C. Other conclusions were overthrown by the 
more precise and extensive work which became 
possible after the main production began in the plant 
at Azusa, California. 7 

It was evident that the safe production, handling, 
and long-term storage of militarily useful quantities 
of cyanogen chloride would require far more detailed 
knowledge of its behavior under various conditions 
than the preliminary researches could give. A con¬ 
siderably expanded program of laboratory research 
therefore was undertaken under a new NDRC con¬ 
tract 7 in addition to the large-scale testing project 
at Dugway Proving Ground. The new program in- 


SECRET 


613 


614 


STABILIZATION OF CYANOGEN CHLORIDE 


eluded nearly 2,000 tests of the stability of cyanogen 
chloride, varying greatly in purity, with or without 
various artificial impurities, and in contact with 
numerous metals or other solids. Most of this work 
was directed toward recognition of harmful classes 
of substances, toward evaluation of various proposed 
stabilizers, toward understanding the process of 
deterioration, and toward the prediction of normal- 
storage stability from the results of thermally ac¬ 
celerated tests. 

For such purposes, it was necessary to develop and 
use a standardized surveillance test technique, such 
that all comparable samples would be tested in a 
similar manner, simulating munition storage as 
closely as feasible. Also, it was necessary to develop 
and use a number of new analytical methods for 
determining water, acidity, soluble and insoluble 
residues, and numerous deterioration products and 
intermediates. The techniques ranged in difficulty 
from simple titrations to the use of high-vacuum 
manifolds and low-temperature fractionating col¬ 
umns. Precise measurements of physical properties 
also were involved. The various results and con¬ 
clusions are summarized in this chapter. 

41.2 CONDITIONS AFFECTING STABILITY 
OF CYANOGEN CHLORIDE 

The stability of cyanogen chloride depends mark¬ 
edly upon the presence or absence of other substances, 
such as it may meet in munitions or retain as im¬ 
purities in manufacture, or which may be added for 
definite reasons. Some foreign substances strongly 
influence the effects of others, either increasing a bad 
effect, or protecting against it. 

41.2.1 Substances Specifically Harmful 
toward Cyanogen Chloride 7 

The following classes of substances proved so 
destructive toward cyanogen chloride that they must 
be definitely avoided or counteracted in munitions in 
which they might occur with it in long-term storage. 

1. All acids, especially in the presence of water or 
iron, or both, must be avoided. Addition of a 3% to 
5% proportion of concentrated hydrochloric acid 
usually causes explosion. 

2. All hydrogen compounds are dangerous, in¬ 
cluding hydrocarbons, greases, mineral or vegetable 
oils, alcohols, alkene oxides, water, and HCN, which 
sooner or later will react with cyanogen chloride to 
form HC1, leading to a rapidly accelerating process of 


destruction. Chlorine greatly increases the rate of 
this destruction, but is nearly harmless toward pure 
cyanogen chloride. Were it not too expensive, the 
removal of both HCN and water from crude cyano¬ 
gen chloride would be recommended. 

3. Iron, especially as rust or iron salts, accelerates 
the conversion by CNC1 of HCN or water to HC1. 
Oxidized, sulfidized, or nitridized coatings proved 
very bad, but with variable rate of effect. Ferric 
chloride proved to be about as harmful as metallic 
iron, and it is believed that some other iron com¬ 
pound is the real catalyst. Iron first removes free 
HC1, which returns after the iron is well coated. 

4. Certain other metals, such as copper, zinc, or 
their alloys, are especially destructive toward 
cyanogen chloride containing either HCN or water, 
but they have no bad effect upon pure cyanogen 
chloride. Aluminum is about as destructive as iron, 
and Dural is even more so, causing explosion of 
samples as small as 35 g. Tin is mildly harmful. 

5. Cyanides are harmful when water is present, 
and this means that any strong-base stabilizers 
(CaO, BaO) may be used only when the cyanogen 
chloride is low in HCN, or in water, or both. HCN in 
10% proportion has led to detonation in munition 
tests at 65 C. On the other hand, HCN has some 
protective effect against HC1, through formation of 
the solid H 2 C 2 N 2 -3HC1. 

6. Cyanuric chloride and such higher polymers as 
C 4 N 4 CI 4 are harmful toward crude cyanogen chloride 
through reaction with water to form HC1, or through 
oxidation of iron to form a catalyst activating the 
HCN. Another reaction product, C 2 HNC1 4 (always 
formed if there is a source of hydrogen), reacts 
directly with water or HCN to form HC1, or even 
yields HC1 by itself through Fe-catalyzed decom¬ 
position. 

7. Ammonium chloride, which results from the 
destruction of water by the quantitative reaction 
C1CN + 2H 2 0 = NH 4 CI + C0 2 , becomes dispro¬ 
portionately harmful at temperatures above 100 C. 
At any temperature, it is a source of the very harm¬ 
ful C 2 HNCL, but this effect is very slow at normal 
temperatures. 

41.2.2 Substances Inert toward 
Cyanogen Chloride 7 

Of the various substances produced by CK, related 
to it, or likely to meet it in munitions, the following 
are not harmful. 


SECRET 



MECHANISM OF DETERIORATION 


615 


1. Carbon monoxide, carbon dioxide, cyanogen, 
traces of air. 

2. Carbon tetrachloride (a fairly important by¬ 
product of degradation). 

3. Dry cyanuric chloride, cyanuric acid, or alkali 
cyanates (all in absence of iron or HCN). 

4. Neutral salts (NaCl, CaCl 2 ) become harmless 
as soon as the water is gone (by C1CN hydrolysis). In 
solution they promote corrosion of iron, introducing 
a catalyst for deterioration. 

5. Silver solder, Monel, and stainless steel become 
harmless when the cyanogen chloride is dry. Lead, 
magnesium, and manganese are quite harmless and 
cadmium actually has a stabilizing effect. Platinum 
and gold are inert. 

6. Pyrex glass, which was used as the container 
material in all tests, was recognized as inert toward 
cyanogen chloride in that variation of the wall-liquid 
ratio did not affect test results. 

7. Potassium dichromate (used to induce passivity 
of iron munition walls) is not seriously harmful to¬ 
ward cyanogen chloride. The same is true of small 
proportions of vapor-phase corrosion inhibitors fur¬ 
nished by the Shell Development Company (VPI-220 
and 260). 

41.2.3 Substances Acting as Stabilizers 
for Cyanogen Chloride 

Many different substances have been proposed as 
stabilizers for cyanogen chloride and most of these 
have been tested. 

The alkene oxides were favored at one time 8 be¬ 
cause they absorb HC1 and water without converting 
HCN to cyanide, but they proved useful only for 
especially unstable lots. 7 A normal lot of crude 
cyanogen chloride, which will survive surveillance for 
60 days with iron at 65 C, can only be harmed by 
alkene oxides, which ultimately yield far more HC1 
than they absorb. 

The dialkyl cyanamides also seemed very favorable 
at one time, for they doubled, tripled, or quadrupled 
the stability of ordinary crude cyanogen chloride and 
were effective at 0.1% concentration. 7 On the other 
hand, they ultimately permitted acid to develop, and 
better stabilizers were considered desirable. 

During the early stages of this work, it was as¬ 
sumed that no solid stabilizer would be acceptable, on 
account of the inconvenience of putting such material 
into munitions. In the absence of any really good 
liquid stabilizer, however, tests of solids were initi¬ 


ated at the University of Chicago. 9 Numerous metal 
salts or oxides were tried, and the most effective 
seemed to be those which would be expected to re¬ 
move soluble iron, thus preventing the very start of 
the series of reactions whereby HCN, NH 4 C1, or 
other sources of hydrogen, yield HC1. Thus, fluorides 
form FeF 6 , a very stable complex ion, and phos¬ 
phates also hold ferric iron very firmly. Of all such 
substances tried, sodium pyrophosphate (Na 4 P 2 0 7 , 
dry) seemed most spectacularly effective, and, in 
fact, a 5% addition of this substance to crude 
cyanogen chloride preserves it in contact with iron 
even at 100 C for almost indefinitely long periods of 
time. 

Experiments with solid stabilizers were carried on 
also at the University of Southern California 7 and 
at Dugway Proving Ground. 8 Calcium and barium 
oxides were rejected as too likely to cause dangerous 
heat effects on contact with wet cyanogen chloride. 
Sodium hexanotaphosphate and disodium hydrogen 
phosphate proved to be very good stabilizers but not 
so good as sodium pyrophosphate. Potassium pyro¬ 
phosphate was definitely inferior. A 2% proportion 
of Na 4 P 2 0 7 proved useful but inadequate. A badly 
(e.g., 20%) deteriorated sample can be saved by 
addition of 5% of Na 4 P 2 0 7 . This stabilizer has not yet 
failed to improve a sample of cyanogen chloride, 
although hundreds of varied tests have been done. 

Tests of sodium fluoride in proportions up to 2% 
indicated that this stabilizer might be nearly as ef¬ 
fective as similar proportions of Na 4 P 2 0 7 , but tests 
with 5% of either stabilizer at 100 C showed NaF 
to be far inferior; especially for saving bad samples. 7 

41.3 MECHANISM OF DETERIORATION 7 

It now seems probable that the actual catalyst, in 
all instances of normal deterioration of cyanogen 
chloride, is hydrogen chloride. This acid is always- 
found among the degradation products, and its con¬ 
centration reaches a maximum when the polymeriza¬ 
tion is happening most rapidly. Its action can be 
understood on the basis of an addition compound, 
C1CNHC1, in which the carbon atom is activated 
toward attraction of the nitrogen atom of a second 
C1CN molecule. The 1/1 addition compound actually 
has been made (at low partial pressure) and observed 
to decompose into C1CN, HC1, and polymer. The 
stability of such an addition compound may be ex¬ 
pected to decrease with rising temperature, counter¬ 
acting the usual increase of reaction rate with tem- 


SECRET 



616 


STABILIZATION OF CYANOGEN CHLORIDE 


perature. This balance of factors explains an ob¬ 
served slightly negative effect of temperature upon 
the rate of the HCl-catalyzed polymerization. 

The specific mechanisms, whereby HC1 is formed 
from other hydrogen-containing impurities, are com¬ 
plex and often obscure, but in general terms, one can 
recognize that cyanogen chloride behaves much like 
chlorine, having a similar oxidation potential, but 
less rapid reactions. Such a chlorinating effect must 
be responsible for the formation of C 2 HNCI 4 , a 
slightly volatile liquid which invariably is found 
whenever the deterioration process has occurred with 
the typical sudden acceleration. This substance evi¬ 
dently is not easily formed except by the effect of a 
catalyst, such as iron salts. Conversely, C 2 HNCI 4 
oxidizes iron more rapidly than C1CN does, and more 
of the iron catalyst thus becomes available. The 
C 2 HNCI 4 can break down in two ways: by HC1 
catalysis to form CC1 4 and HCN, or by iron-catalysis 
to form HC1 and a nonvolatile solid. It also reacts 
with either HCN or water to form HC1, and is 
formed, at least indirectly, from either HCN or 
water by reaction with cyanogen chloride. Thus, it is 
possible that C 2 HNCI 4 is formed and destroyed 
several times during the degradation of cyanogen 
chloride. 

Another strong oxidizing agent, resulting from the 
self-chlorinating effect of cyanogen chloride, is the 
nearly nonvolatile liquid C 4 N 4 CI 4 (in early reports 
regarded as an isomer of trimeric cyanuric chloride). 
This tetramer apparently has an open-chain structure 
with a = CC1 2 unit at one end and — CN at the other. 
It is very stable, but has enough chlorinating power 
to convert HCN to HC1 in the presence of an iron 
catalyst. Thus, it is another of the intermediates 
responsible for the rapid formation of HC1 toward the 
end of a long period of storage of cyanogen chloride. 
Others may be the less volatile liquids, gums, and 
solids which probably represent longer chains of 
similar structure. 

None of these intermediates seems effective 
against cyanogen chloride unless HCN, water, or 
some breakdown catalyst also is present. The most 
important is C 2 HNC1 4 , which alone could account for 
the usual rapid acceleration of the polymerization of 
crude cyanogen chloride. When pure C1CN is poly¬ 
merized by heating with only a little dry HC1, the 
reaction occurs very smoothly, without the usual 
acceleration. 

Since iron plays an important part in both the 
formation and the harmful effect of the reaction 


intermediates, the preventive effect of substances 
which hold ferric ion in harmless combination, such 
as fluorides or phosphates, is easily understood. 

41.4 EFFECT OF TEMPERATURE UPON 

RATE OF DESTRUCTION 7 

It appears that the various slow reactions in crude 
cyanogen chloride, leading ultimately to the forma¬ 
tion of catalytically important proportions of HC1 
(and consequent rapid destruction), are governed by 
the usual rule that the rate doubles with each tem¬ 
perature rise of 10 degrees C. This rule was veri¬ 
fied by the results of comparative stability tests at 
65 and 100 C, using 122 lots of cyanogen chloride 
from the plant at Azusa. Other comparative tests at 
35, 45, 55, and 65 C also verified the rule. Extensive 
analyses at different points in the degradation process 
showed that the reaction mechanisms are essentially 
the same at all temperatures below 100 C. On the 
other hand, tests at 125 C deviated completely from 
the usual temperature coefficient, for reasons which 
are not evident. It is also worthy of note that the 
HC1 catalysis is nearly independent of temperature; 
this reaction is fast, however, and involves no im¬ 
portant part of the total surveillance time. 

Thus it is possible to predict, within about 20%, 
the time when a given lot of crude cyanogen chloride 
will develop enough acidity for rapid (perhaps ex¬ 
plosive) deterioration, provided one has the results of 
a 65 or 100 C iron-contact surveillance test on the 
same lot. All but the first 40 lots produced at Azusa 
were fairly uniform, and most of this material should 
remain in good condition without stabilizers for about 
three years at normal temperatures (25 C). With 
sodium pyrophosphate it should be stable for more 
than a hundred years. 

41.5 ANALYTICAL METHODS FOR 

CYANOGEN CHLORIDE 

41.5.1 Acidity 

Determination of acid in cyanogen chloride b}^ 
titration in aqueous solution is not very satisfactory 
because HCl-catalyzed hydrolysis increases the 
acidity. Rapid withdrawal of the cyanogen chloride 
from the water by CC1 4 extraction, followed by 
titration of the aqueous layer, gives far more de¬ 
pendable results. If polymer is present, it is well to 
eliminate it by distillation, preferably in vacuo. 7 


SECRET 



SUMMARY 


617 


41.5.2 Water 

Three methods are suitable for determination of 
water in cyanogen chloride: observation of the tem¬ 
perature of cloud disappearance in a well-dried sol¬ 
vent (correcting for the effect of HC1), 7 distillation 
through a weighed P 2 0 5 tube and observing the 
gain in weight, 10 and measurement of the acetylene 
produced by reaction of the sample with calcium 
carbide. 7 The first two methods are suitable only for 
fairly fresh material containing no polymer, whereas 
the last method remains accurate until carbon tetra¬ 
chloride appears, when water would be absent in any 
case. These methods are dependable only if the 
operating personnel is especially trained in their use. 

41.5.3 Degradation Products 

Specific methods for determining the several prod¬ 
ucts of deterioration of cyanogen chloride are lacking. 
One can distinguish roughly between soluble and in¬ 
soluble residues, 10 and the former are well indicated 
by an increase in the density of liquid cyanogen 
chloride. 7 The absorption spectra of the soluble 


products are too similar for easy distinction in mix¬ 
tures. Volatile products, such as CCU, C 2 HNC1 4 , 
(CN) 2 , HC1, C0 2 , and CO, can be separated in the 
high-vacuum manifold and recognized by their 
physical properties. 7 

41.6 SUMMARY 

The chief objection to the use of cyanogen chloride 
as a CW agent has been its tendency toward ex¬ 
plosive polymerization. This reaction is now well 
understood as due chiefly to acid catalysis, and the 
substances which cause this are known. Since it is 
not economical to eliminate the three most common 
sources of trouble, namely, hydrogen cyanide, water, 
and iron, it is well to stabilize the crude product by 
addition of a substance which works against both 
iron and acidity. Organic liquid stabilizers have not 
proved adequate, but cyanogen chloride stabilized by 
sodium pyrophosphate seems to be permanently de¬ 
pendable. The stability of the cyanogen chloride 
produced at Azusa is predicted to be maintained for 
about three or four years, without stabilizers. 


SECRET 




Chapter 42 


STABILIZATION AND FLAME INHIBITION OF HYDROGEN CYANIDE 

By Anton B. Burg 


42.1 INTRODUCTION 

ydrogen cyanide has long been known as a 
very fast-acting and efficient toxic gas, suffi¬ 
ciently cheap, easy enough to handle in munitions, 
and having adequate volatility, for satisfactory use 
as a nonpersistent chemical warfare agent. It offers 
the further advantage of fairly easy penetration of 
many gas mask canisters, without any very strong 
warning odor. In spite of such favorable properties, 
this agent has two major disadvantages in that it is 
occasionally unstable and it is frequently destroyed 
by flame during dispersal from bursting bombs. The 
problem of stability seems to have been fairly well 
solved, but inflammability remains a major difficulty, 
not wholly avoidable by present methods except 
under certain special conditions. 

42.2 STABILIZATION 

The question of the stability of high-purity hydro¬ 
gen cyanide was quite serious at one time, for storage 
of this substance as a liquid in steel containers 
usually resulted in a brown discoloration followed by 
powerful explosions, destructive of personnel and 
materiel. This trouble has nearly disappeared as a 
result of investigations of stabilizers during the 
period between world wars. Both the du Pont Com¬ 
pany and American Cyanamid Company were active 
in such research, and more than three thousand com¬ 
pounds were tested as stabilizers. As a result, du Pont 
chose phosphoric acid, which works against a destruc¬ 
tive accumulation of basic catalysts for decomposi¬ 
tion, while Cyanamid preferred sulfur dioxide for its 
action as both antibase and antioxidant. The Chemi¬ 
cal Warfare Service now specifies addition of 0.07% 
H 3 PO 4 and 0.25% S0 2 for combined action. Ac¬ 
celerated tests at 65 C, in munitions at Dugway 
Proving Ground, and on the laboratory scale in 
Pyrex tubes with steel inserts (by NDRC), have 
shown that it is quite safe to store the doubly stabi¬ 
lized HCN during long periods of time at ordinary 
temperatures. Tests in Pyrex tubes further indicate 
that it will be safe to use containers made of or lined 


with aluminum or copper (but not magnesium) for 
HCN containing the stabilizers. 

The glass tube experiments have shown that the 
combination of two stabilizers forHCN really is better 
than either stabilizer alone. One reason may well 
be that due to the protective action of S0 2 , the steel 
walls of the container tend less to deplete the supply 
of phosphoric acid. With phosphoric acid alone, this 
depletion may be serious, although occasional re¬ 
newal of the phosphoric acid by direct addition will 
save even very discolored hydrogen cyanide. 

As a result of such studies, personnel at Dugway 
Proving Ground developed a technique for forcing 
phosphoric acid into large (M78 and M79) bombs, as 
an effective means of saving off-color HCN in such 
bombs. 

In relation to the use of hydrocarbons in HCN (in 
order to inhibit ignition of the expanding cloud from 
a bomb) the effects of 70-octane gasoline, pentanes, 
and hexanes, upon the stability of HCN, were 
studied. 1-3 In glass tubes with steel inserts, HCN 
stabilized by S0 2 and H 3 P0 4 survived over a year at 
65 C, with or without the hydrocarbons. 

Further NDRC studies on the stability of HCN 
included investigation of the effects of various ma¬ 
terials likely to be met in munitions. Lead carbonate 
luting pastes have long been recognized as damaging 
to stability, but a special Ti0 2 -base luting paste 
proved quite harmless. Solvents such as CC1 4 or 
C 2 C1 4 also have no ill effects. Tests in Pyrex tubes in¬ 
dicated that powdered copper (found in captured 
Japanese frangible glass HCN grenades) is a very 
effective stabilizer. Cyanogen chloride (5%) is an 
even more effective stabilizer for HCN in contact 
with iron in Pyrex tubes, but becomes quite destruc¬ 
tive in proportions above 20%. It is to be reiterated 
that these tests were done in Pyrex containers, which 
may not perfectly duplicate actual steel munitions. 
Thus, it is possible that stabilizers having only an 
antibase action will work well against the alkaline 
effect of glass, but have far less effect against oxidiz¬ 
ing agents, or that a stabilizer which works well in a 
steel container will be far less effective in the presence 
of glass. On the whole, however, it is believed that a 



618 


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FIELD STUDY OF ANTIFLASH AGENTS 


619 


stabilizer may safely be trusted if it works well in a 
glass tube test, whereas the rejection of a stabilizer 
on the basis of such tests may not always be final. 

42.3 INFLAMMABILITY OF HYDROGEN 

CYANIDE 

Inflammability was recognized as a major problem 
when field experiments on hydrogen cyanide were 
attempted at Dugway Proving Ground, at Bushnell, 
Florida, and in Panama. The exact conditions which 
will lead to flashing, or ignition, during the bursting 
of the HCN-filled munition, are not known with any 
high degree of certainty; it is known only that some 
HCN munitions are less likely to flash than others, 
but that some which are presumed safe from flashing, 
ultimately may perform badly under new circum¬ 
stances. 

The actual manner of ignition during a bomb- 
burst is fairly clear: during the first phase of the 
burst, no ignition can occur because there is too little 
air to support combustion; then as the HCN be¬ 
comes diluted with air the small flame of the burster 
spreads through the expanding cloud. Thus, three 
general approaches to the problem are recognizable: 
(1) the use of cold burster charges, which will not 
ignite any inflammable gas cloud; (2) increasing the 
power of the burster to such an extent that the agent 
flies outward at a rate faster than the flame can 
follow; or (3) adding some substance to the HCN 
which will either wholly suppress its inflammability 
or so slow the rate of flame propagation that the 
burster flame cannot follow the expanding cloud. The 
first two approaches wou Id have required new specifica¬ 
tions on bursters, and a great deal of field work which 
could hardly be accomplished during the relatively 
short period of our war effort. The third approach 
was the subject of much laboratory and field work, 
leading to some improvement over the original situa¬ 
tion. 

42.4 LABORATORY STUDY OF FLAME 

INHIBITORS 

The laboratory work was started on the assump¬ 
tion that the burning of HCN in air might involve a 
free-radical chain mechanism, which might be sup¬ 
pressed by addition of some other substance capable 
of capturing the radicals and breaking the chain re¬ 
action. A number of additives actually do lower the 
upper concentration limit of inflammability, and 
some quite specifically decrease the rate at which the 


flame travels through the HCN-air mixture. Such 
effects, however, seem not to be correlated with any 
tendency of the additives to capture free radicals. 
Thus CC1 4 , C 2 CI 4 , C 2 HCI 3 , C1CN, AsC 1 3 , S0 2 , SOCl 2 , 
water, CH 3 Br, propylene oxide, cyclohexane, tetra- 
methyl lead, methyl formate, acetaldehyde, and 
methanol, used in proportions of 0.1 to 12 mole per 
cent, either have no noticeable effect, or actually in¬ 
crease the violence of HCN explosions. Some hydro¬ 
carbons compete with HCN for reaction with oxygen, 
thereby lowering the upper limit of inflammability. 
Many of these also decrease the rate of flame travel 
even at medium concentrations of HCN in air. 

The failure of several typical chain-breaking sub¬ 
stances to inhibit the HCN-air explosion leads to 
doubt of the free-radical hypothesis. This doubt 
seems entirely justified in view of other experiments 
designed to test the free-radical mechanism. Un¬ 
like most chain reactions, the HCN-air flash shows 
but little dependence upon pressure or upon surface 
area. Photochemical activation, at temperatures 
just below the flash point, also seems to be ineffective; 
apparently such free radicals as may be formed are 
not able to initiate any chain reaction. 

In default of the free-radical hypothesis, or any 
other evident source of understanding of the flame 
reaction, further laboratory work becomes empirical. 
Mild inhibiting effects were observed after addition 
of acetone, ethyl ether, methyl cyclopentane, ethyl¬ 
ene, 1,2-dibromoethane, methyl chloride, methyl 
iodide, carbon disulfide, benzene, cyclopentane, or 
propane. Much more effective were hydrogen selenide 
and mixtures or single isomers of amylene, pentane, 
hexane, or heptane. These usually lowered the upper 
limit of inflammability far more than in proportion 
to the amount added. Instead of the usual sharp ex¬ 
plosion of HCN in air, the reaction was slowed down 
to an observable flame front, moving as slowly as 
2 fps in some cases. 

42.5 FIELD STUDY OF ANTIFLASH 
AGENTS 

As a result of the visual evidence that hydrocar¬ 
bons in the light-gasoline range serve both to lower 
the upper limit of inflammability of HCN in air and 
to decrease the rate of travel of the flame through 
the HCN-air mixture, field tests of the effects of such 
hydrocarbons in actual bombs were undertaken at 
Dugway Proving Ground. M47A2 bombs were chosen 
for these tests because of the earlier experience that 


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STABILIZATION AND FLAME INHIBITION OF HCN 


about 35% of all such bombs would flash the HCN 
during dispersal. The tests were quite successful, in 
that 39 M47A2 bombs, which were filled with ordi¬ 
nary stabilized HCN and 3 or 5% of isopentane, 
neohexane, 2-methylbutene-2, mixed amvlenes, or 
70-octane gasoline, were exploded without flash, 
while three of the eight control-test bombs (without 
hydrocarbon) ignited the HCN in a great blaze. One 
hydrocarbon-treated bomb did flash, but this was a 
case of low-order bursting, in which only the upper 
half of the bomb was opened. A pool of liquid HCN 
remained in the lower half and was ignited. This case 
serves to emphasize that hydrocarbons are useful 
flash inhibitors only for normally bursting bombs. 
They will not prevent ignition of a stationary pool or 
slowly expanding cloud of HCN. 


The extent to which hydrocarbons will inhibit 
flashing of HCN in larger bombs remains uncertain 
after tests by the Dugway Mobile Unit at Bushnell, 
Florida. Some M79 bombs flashed in spite of added 
gasoline, but adequate control comparisons were 
lacking. Another difficulty was that the miscibility 
of the gasoline in HCN was limited to 3%, and this 
small proportion might not be very effective. Hexane 
is far more miscible (4 to 7%, depending upon tem¬ 
perature), but pentane is preferred because it is still 
more so (6 to 11%). Proper field testing of the effect 
of 5 to 10% pentane in large HCN bombs is a matter 
for further recommendation. This could not be done 
at Dugway Proving Ground, because the large bombs 
seldom flash at that altitude, but such tests, with 
proper controls, should be feasible at sea level. 


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Chapter 43 

WIND-TUNNEL STUDIES OF FOG DISPERSAL, GAS DIFFUSION, 
AND FLOW OVER MOUNTAINOUS TERRAIN 

By Hunter Rouse 


43.1 INTRODUCTION 

P roblems of fluid motion which are too complex 
for analytical solution and too extensive for full- 
scale investigation are, in such fields as aeronautics 
and hydraulics, generally handled by means of tests 
on scale models. Once the conditions essential to 
dynamic similarity between model and prototype 
have been established, such model tests are certain to 
result in a tremendous saving in time and expense, 
for the variables may be controlled with laboratory 
precision over as great a range as desired, and ex¬ 
ploratory measurements convertible to full-scale 
conditions may rapidly be made for any arbitrary 
combination of variables. 

Three types of problem in fluid motion posed by 
the Armed Services of World War II were of a nature 
which recommended use of the model technique yet 
differed sufficiently from standard practice to require 
the development of new facilities and new methods of 
testing. Preparation of a low-velocity wind tunnel 
for this purpose is described herein, and details are 
given of the experimental apparatus and the general 
methods of measurement and evaluation of results. 
Use of the test facilities in determining heat require¬ 
ments for the burner method of fog dispersal, as re¬ 
quested by the Navy Bureau of Aeronautics, is dis¬ 
cussed, and a generalized analysis of heat-diffusion 
measurements is presented and applied to a specific in¬ 
stallation in the Aleutians. The development of high- 
capacity burners for either gasoline or fuel oil is ex¬ 
plained. Attention is given to the use of both heated 
wind curtains and wind-curtain-and-bumer combina¬ 
tions as means of reducing the waste of fuel charac¬ 
teristic of the burner method. A detailed analysis is 
also made of the relative costs of burner and wind- 
curtain systems. 

Application of the model technique to problems of 
gas and smoke diffusion for the Chemical Warfare 
Service is next described. Through use of schematic 
structural forms, it is shown that the eddy patterns 
and the corresponding rates of diffusion in urban 
districts are controlled by the boundary geometry, 


regardless of scale or wind speed, and that the model 
results may therefore be generalized. The results of 
tests for steady gas release in models of schematic 
urban districts and typical Japanese cities are then 
presented in generalized form. Thereafter, a means 
of evaluating the concentrations that would be 
caused by full-scale bursts is indicated from model 
measurements of continuous gas release. Correlation 
of model tests with field measurements completes the 
discussion of gas diffusion. 

A brief description follows of the model study of 
terrain effects upon wind structure, as undertaken 
for the Army Air Forces. The results of exploratory 
measurements of velocity and turbulence distribu¬ 
tion over a model of the Tokyo region are described. 
Preliminary tests upon the influence of vertical dis¬ 
tortion of the boundary, preparatory to studies of 
wind patterns over models of Puerto Rico under 
direct contract with the AAF, are finally interpreted. 

43.2 MODEL TECHNIQUE IN THE 
LOW-VELOCITY WIND TUNNEL 

Despite the great advancements which were made 
in the science of fluid motion between World Wars I 
and II, only a few flow problems of technical im¬ 
portance became subject to complete analytical solu¬ 
tion. On the other hand, application of similitude 
principles known long before World War I progressed 
to such an extent that every new airplane, projectile, 
and battleship was finally designed on the basis of 
scale-model investigations in the wind tunnel, water 
tunnel, or towing tank. 

The similitude principles in question stem from 
three fundamental relationships of fluid mechanics. 
For a given geometrical form of the flow boundary, 
the pattern of motion (and hence the distribution of 
pressure, velocity, and turbulence) is known to be a 
unique function of three dimensionless parameters 
called the Froude number, the Reynolds number, and 
the Mach number. The Froude number is a measure 
of gravitational influence upon the flow; it has the 
form V/V.Lky/p, in which V is a velocity, L a length, 


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WIND-TUNNEL STUDIES 


A7 a difference in specific weight, and p a density. 
The Reynolds number is a measure of viscous influ¬ 
ence upon the flow; it has the form TLp/p, in which 
p is a viscosity and V, L, and p have the same sig¬ 
nificance as before. The Mach number is a measure 
of elastic effects; it has the form V/\/E/p, E being 
the bulk modulus of elasticity. 

As a first approximation, any flow problem may be 
regarded as predominantly gravitational, viscous, or 
elastic. The flow characteristic under study should 
then be obtainable analytically or experimentally 
as a function of the corresponding dimensionless 
parameter. Since a dimensionless plot of this function 
is not restricted to any one scale or fluid, it should be 
equally applicable to model conditions in the labora¬ 
tory and prototype conditions in the field. In a word, 
determination of the function by model tests at once 
makes available the required characteristics of full- 
scale design. 

Under many circumstances it is not necessary to 
establish the entire trend of such a functional rela¬ 
tionship, particularly if only one specific set of 
prototype requirements is to be determined. Since 
this set of requirements automatically establishes a 
particular value of the Froude, Reynolds, or Mach 
number, it is merely necessary to conduct a model 
test at the same value of this number to yield the 
desired information. 

Inasmuch as gravitational, viscous, and elastic ef¬ 
fects in actuality seldom occur singly, such approxi¬ 
mations sometimes require further refinement if con¬ 
siderable accuracy is to be obtained. This is particu¬ 
larly true if gravitational and viscous influences are 
of the same order of magnitude. Unfortunately, as 
inspection of the Froude and Reynolds numbers will 
show, it is impossible to secure both viscous and 
gravitational similitude between model and prototype 
if the same fluid is used, since one requires an increase 
in velocity, and the other a decrease, as the linear 
scale is reduced. 

In spite of these limitations, the model method of 
analysis provides manifold advantages in the approx¬ 
imate solution of such complex phenomena of flow as 
the majority of technical problems involve. Since the 
time and expense of a test program vary nearly as the 
cube of the linear scale, the economy of small-scale 
tests in comparison with full-scale investigations is 
obviously tremendous. In the laboratory, moreover, 
the essential variables may be controlled at will, with 
the twofold result that exploratory studies may be 
made over a range that would be prohibitive in the 


field, and yet any set of conditions may be dupli¬ 
cated at any time. To offset the very pertinent dis¬ 
advantage that it is impossible to reproduce in a 
model every single factor that may influence the 
prototype phenomenon, one need only note that the 
possible combinations of such factors are usually so 
vast in number that their S3 r stematic field investiga¬ 
tion would likewise be out of the question. 

With the greatly increased complexity of present- 
day warfare, it is not surprising that new problems of 
fluid motion, never before studied at model scale, 
should arise. Three of these in turn were proposed to 
the Iowa Institute of Hydraulic Research of the State 
University of Iowa: (1) the characteristics of gas 
diffusion in urban districts; (2) the characteristics of 
heat diffusion in fog-dispersal installations; and (3) 
the characteristics of eddy diffusion in winds over 
mountainous terrain. For the first of these experi¬ 
mental projects a special low-velocity wind tunnel 
was constructed, together with the necessary meas¬ 
uring apparatus. The basic similarity of the second 




Figure 1 . Wind-tunnel details. 

and third projects, however, permitted much of the 
same equipment and experimental technique to be 
used. In fact, the first and third, though differing 
considerably in ultimate goals, were almost identical 
in fundamental nature; the second differed only to 
the extent that gravitational effects played the funda¬ 
mental role. 


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MODEL TECHNIQUE IN LOW-VELOCITY WIND TUNNEL 


623 


The wind tunnel constructed for these studies 1 
consisted of a 20-ft duct of uniform rectangular cross 
section 6 ft wide and 4 ft high. At the inlet end (see 
Figure 1) was a large stilling chamber provided with 
baffles to eliminate disturbances in the air drawn 
from outside the laboratory structure, a bell entrance 
and honeycomb yielding an even velocity distribu¬ 
tion and low degree of turbulence in the tunnel test 
section. The outlet of the duct was connected to the 
suction side of a 35,000-cfm fan, which exhausted 
outside the building. Adjustable louvers between the 
tunnel and blower permitted a fine control of the wind 
speed from 1 to 25 fps. Along the ceiling of the tunnel 
was a four-rail track providing longitudinal travel of 
a gauge carriage, which in turn provided lateral and 
vertical motion of any instruments mounted thereon. 
Scales and verniers yielded coordinate locations of the 
instruments to 0.001 ft. These instruments, as well 
as the wind speed, were controlled from closed obser¬ 
vation chambers on either side of the test section. 

Instruments used in flow measurements were the 
following: (1) a direct-reading generator anemometer, 
for approximate observation of the mean wind speed; 
(2) a sensitive anemometer (Figure 2) with revolution 



Figure 2. Anemometer; runner diameter lM inches. 

indicator for local wind speeds from 0.75 to 10 fps; 
(3) a Prandtl-Pitot tube and Wahlen gauge, for wind 
speeds above 5 fps; (4) a 6-tube direction-indicating 
instrument (Figure 3) which, in combination with the 
Wahlen gauge, provided readings of the magnitude 
of the velocity vector and its horizontal and vertical 
deviations from the longitudinal direction; (5) a 
Dickinson meter for determining gas concentrations, 
the intake and cell of which were mounted on the 
gauge carriage for point sampling; and (6) a series of 
copper-constantan thermocouples, and a portable 
precision potentiometer for temperature traverses. 


Jet manifolds for propane gas were located in the 
stilling chamber, or could be inserted in the tunnel 
floor at desired locations, to produce thermal strati¬ 
fication of the wind stream. Dry ice was also used for 
this purpose. S0 2 could be introduced through the 
same manifolds, or from suitably located point 
sources. For visual or photographic study of flow 
patterns by means of smoke filaments, air which 
passed over titanium tetrachloride could be injected 
through similar point sources. The large-scale genera¬ 
tion of smoke for observational purposes was accom¬ 
plished by vaporizing oil in the exhaust duct of a 
small gasoline engine. 



Figure 3. Directional velocity indicator. 


In general, the technique of experimentation was 
as follows. On the basis of existing theory and ex¬ 
perience, the essential variables of the problem in 
question were combined through the II theorem of 


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WIND-TUNNEL STUDIES 





Figure 4. Variation in vertical temperature traverse with x , H, and V. 


dimensional analysis into a series of dimensionless 
parameters, one of which was expressed as a function 
of the others. Since these parameters formed the 
basis of the required similarity of model and proto¬ 
type conditions, whenever possible the validity of the 
parametric grouping was checked experimentally at 
different magnitudes of the individual variables (such 
as scale or velocity). Once such a check was at hand, 
the detailed model tests were conducted, the dimen¬ 
sionless form of the results making them immediately 
applicable to prototype scale. In most cases, known 
field conditions were simply duplicated at specific 
values of the dimensionless parameters. Sometimes, 
however, it was desirable to determine, or at least ap¬ 
proximate, the form of the functional relationship. 
This was accomplished by judicious selection of the 
flow variables, so that the desired range of variation 
could be covered systematically without wasting 
time in haphazard measurements. The function was 
then evaluated graphically in terms of the pertinent 
parameters as coordinates. 


43.3 EXPERIMENTS ON FOG DISPERSAL 

Soon after the beginning of the mass bombing of 
Axis countries by planes based in England, it became 
apparent that more planes were being lost through 
crash landings in English fog than through flak and 
fighter attack over the continent. For this reason the 
problem of freeing landing fields from fog was given 
very high priority, and all possible methods of im¬ 
proving visibility were tested by British and Ameri¬ 
can scientists and engineers. 

Such methods may, in brief, be grouped into three 
classes: (1) the induced coalescence of fog droplets to 
form drops of sufficient size to fall as rain, (2) the re¬ 
moval of excess moisture from the air by chemical 
drying, and (3) the evaporation of the fog by raising 
the air temperature. Of the first class, the possibility 
of spraying water into the air to combine with the 
fog droplets was suggested but never tried, while the 
use of low-frequency sirens to produce coalescence by 
vibratory means received but one inconclusive field 


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EXPERIMENTS ON FOG DISPERSAL 



^| 0.6 y 0.2 


Figure 5. Composite plot of vertical temperature traverses for all values of x , H, and V . 


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WIND-TUNNEL STUDIES 


UJ 

LlJ 


u_ 


t- 

X 

o 


X 




0 100 200 300 400 500 600 0 100 200 300 400 500 600 700 800 900 

DISTANCE IN FEET FROM HEAT SOURCE 



DISTANCE IN FEET FROM HEAT SOURCE 


Figure 6. 


Typical 5 F isotherms for various crosswind velocities and distances of heat source from centerline of runway. 


test. Of the second class, the injection of calcium 
chloride into the air with portable blowers was tested 
extensively 2 but not brought into practical applica¬ 
tion. The third class of dispersal method, however, re¬ 
ceived steadily increasing attention from the British, 
after it was determined that a temperature rise of 5 
to 7 degrees Fahrenheit would effectively dispel the 
radiation type of fog prevalent in England. Early 
tests were made of burning coke in long trenches 
bordering the landing strips, but too much time was 
required to ignite and control the fires. Fuel oil, in 
turn, proved to yield too smoky a blanket of heated 
air to improve visibility. Ultimately, gasoline was 
found to give the desired results, and very extensive 
systems of preheaters and burners surrounding the 
field were devised, which would clear a satisfactory 
zone over the runway in the radiation type of fog 
without undue loss of time. These were described in 
a long series of British reports. 

Such English fogs are characterized by relatively 
small thickness and near-stagnant air conditions. In 
fact, the heated clearance zone frequently extended 
entirely through the fog blanket, while the air flow 
induced by the thermal currents often resulted in 
local winds of greater magnitude than those accom¬ 


panying the fog formation. On the other hand, if 
natural winds of appreciable speed prevailed during 
the clearance operation, the zone of clearance tended 
to be shifted off the runway in the downwind direc¬ 
tion. Since fog formation in the United States and its 
possessions is generally not of the radiation type and 
may be accompanied by winds of considerable speed, 
the British experience with clearance methods was 
not considered a sufficient basis for the design of 
American fog-dispersal installations. 

43.3.1 Burner Studies 

At the request of the Navy Bureau of Aeronautics, 
the Iowa Institute undertook in the fall of 1943 the 
determination of heat requirements and proper 
burner location for securing clearance conditions over 
runways at various wind speeds. Instead of assuming 
a particular model scale for wind-tunnel measure¬ 
ments, an effort was made to analyze experimentally 
the general problem of heat diffusion from a line 
source at right angles to the direction of flow. 3 

The floor of the tunnel test section was suitably 
fireproofed, and a manifold containing a series of 
closely spaced jets for burning propane gas was built 


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EXPERIMENTS ON FOG DISPERSAL 


627 



CROSS-WIND VELOCITY V IN FEET PER SECOND 

Figure 7. Curves of H vs V for various distances of heat source from runway centerline (AT = 5 F). 


in across the tunnel. Means were at hand of varying 
the wind speed, the rate of combustion, and the 
elevation and longitudinal position of a thermocouple 
carriage. Preliminary vertical temperature traverses 
at various distances from the heat source (Figure 4) 
showed that the heated zone expanded essentially 
linearly with distance downwind, the rate of expan¬ 
sion increasing with increasing rate of heat output 
and decreasing with increasing wind speed. A series 
of vertical temperature traverses was then made, 
systematically covering the available range of wind 
speed, heat output, and distance downwind. 


Analysis of the experimental results indicated that' 
all temperature traverses, could, as a close approxi¬ 
mation, be superposed to yield a single generalized 
distribution curve (Figure 5) if the ordinate and 
abscissa scales, respectively, had the form zV u2 /xH 0A 
and xA T/H 0A V 0 - 2 , in which 

x = distance downwind, in feet; 
z = elevation, in feet; 

V = wind speed, in feet per second; 

H = rate of heat output in Btu per foot per 
second; 

AT = temperature rise, in degrees Fahrenheit. 


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WIND-TUNNEL STUDIES 



WIND SPEED V IN MILES PER HOUR 

Figure 8. Recommended burner characteristics for Shemya installation. Plotted points and temperatures are typical 
data from recommended 10-ft burner with 36 jets. 


Although these coordinate parameters are not 
dimensionless, it is to be noted that their product, 
when multiplied by y and c p (the unit weight and 
specific heat of the air), is truly a dimensionless 
quantity. The area of the surface bounded by the 
experimental curve, when multiplied by yc p , there¬ 


fore represents a numerical value embodying the ap¬ 
proximate solution of the problem in question. 
That is, 

y -^- J A Tdz = 0.94. 

Since the process of thermal convection is es- 


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EXPERIMENTS ON FOG DISPERSAL 


629 


sentially independent of viscous effects at the rela¬ 
tively high temperature differences studied in the 
wind tunnel, there appears no reason to doubt the 
validity of the function at prototype as well as model 
scales. In fact, the Froude criterion for similarity 
( V 2 ^ LAT) is perforce embodied in the general 
functional relationship. That is, since for geometrical 
similarity z/x must be constant, the ordinate parame¬ 
ter indicates that H ~ F 3 , substitution of which in 
the abscissa parameter yields F 2 ~ xAT. 

Interpretation of the generalized function is as 
follows: Let it be assumed that in a wind of speed F, 
a given rise in temperature A T is to be produced to a 
height z over a runway Ax wide by a burner located 
a distance x upwind from the runway centerline. If, 
for simplicity, the actual function of Figure 5 is 
approximated by the straight line 

zV 1 - 2 rAT 

solution thereof will yield the required heat output H ; 
moreover, the curve z — f(x) for the corresponding 
values of F, AT, and H will enclose the zone through¬ 
out which A T is at least as great as that required (see 
Figure 6). If it is further assumed that the burner 
location is the most economical for the given wind 
speed (i.e., that H is as low as possible), the high 
point of the curve z = f(x) will correspond to the top 
of the clearance zone. It follows that a change in 
either wind speed for the given burner location or in 
location for the given wund will result in asymmetnr 
of the curve if AT is to remain constant. As a matter 
of fact, a burner properly located for a given wind 
will be inefficiently placed for a wind of any other 
speed, owing to the required increase in heat output 
to produce the necessary coverage in lower or higher 
winds. 

If the temperature rise for clearance is specified, it 
is possible from the generalized diagram or simplified 
equation to plot a family of curves of heat require¬ 
ments versus wind speed for a series of distances from 
burner to runway, as shown in Figure 7. Such a 
diagram will then permit rapid determination of most 
efficient burner location for most frequent operating 
conditions, and the heat requirements for all other 
wind speeds will be immediately at hand. However, 
even cursory inspection of the individual curves for 
a given burner-runway spacing will indicate the tre¬ 
mendous waste of fuel which must occur at all wind 
speeds which differ appreciably from that for which 
the design is made. 


At the request of the Army Air Forces, the Bureau 
of Aeronautics of the Navy in 1943-44 installed on 
the island of Amchitka in the Aleutians a burner 
system based essentially upon the British methods. 
This installation was found to provide satisfactory 
clearance at low-wind speeds, but at moderate to 
high speeds the clearance zone was shifted off the 
runway in the downwind direction. When a similar 
request was made for an installation on the island of 
Shemya in 1944, the Iowa Institute was asked to 
make recommendations for burner locations and 
capacities based upon its previous findings, and upon 
further studies on relief models of the island. 

After careful statistical evaluation of available 
weather data, 4 - 5 it was decided to adopt the value 
V = 20 mph as the maximum for design purposes. 
Since investigation of existing terrain effects upon 
the rate of heat diffusion failed to reveal any ap¬ 
preciable change in the basic function, this function 
was then used to prepare the accompanying diagram 
(Figure 8) of heat requirements vs wind speed. In 
order to eliminate the considerable waste of fuel 
caused by use of a single burner line at other than the 
designed wind speed, it was recommended that the 
following three lines of burners be installed on the 
prevailing windward side: first, a line having an 
output of 30 therms per yd per hr at a distance of 
250 ft from the runway centerline; second, a 60-therm 
line 600 ft from the centerline; third, a 90-therm line 
1,000 ft from the centerline. For stagnant or near- 
stagnant conditions, similar 30-therm burners on 
opposite sides of the runway would provide the 
necessary circulation of heated air over the landing 
zone, as in the British installations. At wind speeds 
up to 9 mph the windward 60-therm line would be 
sufficient, and from 9 to 14 mph the 90-therm line 
would be used. For speeds as high as 20 mph, the 60- 
and 90-therm lines could be used in parallel. 

As may be seen from the diagram, fixed-output 
burners w’ould still result in an appreciable waste of 
fuel. This could be greatly reduced, however, through 
proper control of the heat output in approximate ac¬ 
cordance with the magnitude of the actual wind 
speed. In other words, the series of abrupt steps on 
the diagram would then be replaced by the lower 
series of curves, which more nearly approach the 
minimum line. 

Since the capacity of the larger burners required for 
this installation was well above that of the normal 
British burner systems, and since the Bureau of 
Aeronautics was desirous of having a burner which 


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WIND-TUNNEL STUDIES 



O 20 40 60 80 100 120 

HEAT OUTPUT IN THERMS PER YARD PER HOUR 



0 20 40 60 80 100 120 

HEAT OUTPUT IN THERMS PER YARD PER HOUR 

Figure 9. Design curves of pressure vs heat output 
for various jet and preheater-pipe arrangements. 


would operate on fuel oil as well as gasoline, the Iowa 
Institute undertook the development of two types of 
large-capacity burner for this purpose. One of these, 
produced by the Department of Mechanical En¬ 
gineering of the University of Iowa, 6 consisted of a 
rectangular preheater coil and central jet manifold 
in 6-ft units placed in shallow trenches. Twelve pre¬ 
heating jets in the bottom of the manifold continu¬ 
ously vaporized th incoming fuel, which burned with 
a luminous flame from eight main jets along the top. 
The capacity of this fuel-oil burner varied from 20 
therms per yd per hr at 20 psi line pressure to 100 
therms at 40 psi. 


The burner developed by the Institute 7 consisted 
of a series of horizontal preheater pipes feeding a 
single jet manifold in the path of the horizontal flames 
from the jets. This burner had a capacity of 25 to 90 
therms when using fuel oil, and 25 to 120 therms with 
gasoline, utilizing adjustable line pressures varying 
from 30 to 80 psi. In connection with its develop¬ 
ment, empirical diagrams (Figure 9) relating line 
pressure, thermal output, jet spacing, and number of 
preheater pipes were prepared. 

Although the Shemya installation was never under¬ 
taken, owing to the unexpectedly rapid progress of 
the war with Japan, the several forms of burner were 
tested under field conditions at the Landing Aids 
Experiment Station [LAES] of the Bureau of Aero¬ 
nautics at Areata, California. Financed by the Iowa 
contract, but not supervised by the Institute, was the 
development 8 of a spring-loaded, high-pressure jet 
which would vary in outlet area as well as in velocity 
with change in line pressure. LAES reports on the 
performance of these burners were not available at 
the time of writing this report. 


43.3.2 Wind-Curtain Studies 

In view of the necessarily low efficiency of the 
burner method of fog dispersal, both British and 
American agencies experimented for several years 
with the general scheme of directing preheated air 
over the landing strip by means of blowers. Early 
attempts to mount heaters and blowers upon trucks 
proved impractical, because the great weight of the 
units deprived them of necessary maneuverability 
except on dry ground. Thereafter, the University of 
Illinois investigated, by means of model experiments, 9 
the feasibility of forcing heated air through ducts 
terminating in long slots on each side of the landing 
strip. The vertical curtains of hot air formed by these 
slots induced a downward return flow over the land¬ 
ing strip at low to moderate crosswinds, the mixing 
of the heated air in the zone of circulation effectively 
raising the temperature in the clearance zone by the 
desired amount. 

In order to determine the possibility of using a 
single wind curtain over a considerable range of wind 
speed, the Iowa Institute followed its burner studies 
with a series of wind-tunnel tests of wind-curtain 
characteristics. 10 Exploratory observations indicated 
that a vertical curtain of air in a cross wind would be 
deflected downwind in such manner (Figure 10) as to 
form a large ground eddy with axis parallel to the 


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EXPERIMENTS ON FOG DISPERSAL 


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DISTANCE * FROM SLOT IN FEET 

Figure 10. Velocity and temperature characteristics of a heated wind curtain. 


slot and having a height approximately one-fourth 
as great as its width. The height h of this eddy evi¬ 
dently depended upon the wind speed V, the slot 
width b, and the efflux velocity v 0 . The general re¬ 
lationship of these variables was then determined 
through systematic variation of all three, the data 
falling upon the empirical curve 



over the maximum available range of variation. Since 
the phenomenon of air entrainment by jets is one of 
turbulent rather than viscous flow, the relationship 
determined in the wind tunnel is probably sufficiently 
free from scale effects as to be applicable to field as 
well as laboratory conditions. 

If heated air is forced through such slots, on the 
other hand, one must assume that a Froude number 
V/y/LAT should have the same magnitude in both 


model and prototype if the conditions are to be truly 
similar. However, subsequent wind-tunnel tests with 
heated air failed completely to disclose any effect of 
buoyancy upon the eddy form; thermal phenomena, 
in other words, appeared to be entirely secondary to 
the inertial reaction between the jet and the on¬ 
coming air. Moreover, the process of diffusion be¬ 
tween the deflected curtain and the underlying eddy 
invariably resulted in a relatively uniform distribu¬ 
tion of heat from the curtain throughout the under¬ 
lying eddy, with the result that the heated wind 
curtain gave promise of being a far more efficient 
method of fog dispersal than the burner. 

Evaluation of the heat requirements for a specific 
temperature rise, AT = 5 F, over a 100-ft zone above 
a runway as a function of wind speed resulted in the 
linear relationship for power vs speed shown in 
Figure 11. The wind-curtain slot is assumed to be 
located 100 X 4/2 = 200 ft upwind from the runway 


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WIND-TUNNEL STUDIES 



centerline, and the power requirements include the 
cost of fuel for both the heaters and the engines for 
the blowers. Although the heat required remains the 
same, the power requirement is seen to vary with the 
width of curtain slots. In any event, the cost of opera¬ 
tion of the wind curtain is found to be only 35% of 
the very minimum for the burner under identical 
wind conditions. 

Owing to the fact that an appreciable portion of 


the heated air discharged from the curtain slot passes 
downwind without being entrained in the ground 
eddy, the possibility of increasing efficiency and re¬ 
ducing installation costs through combination of a 
nonheated wind curtain with a surface burner was 
investigated. A burner line was placed on the down¬ 
wind side of the runway, but within the zone of re¬ 
verse flow of the ground eddy (see Figure 10). The 
heat from the burner was diffused throughout the 


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EXPERIMENTS ON GAS DIFFUSION 


633 


eddy to a desirably uniform degree, and evaluation 
of temperature traverses yielded the line of heat re¬ 
quirements shown as a broken line in Figure 11. 
Evidently, a further saving of some 10% of burner 
costs can be expected from such an arrangement. 

Since the foregoing tests were restricted to winds 
at right angles to runway and wind curtain, supple¬ 
mentary studies were made for other wind orienta¬ 
tions. It was found that while use of the wind speed 
itself yielded computed values of the eddy width 
(measured normal to the runway) which were smaller 
than those measured, use of the normal component 
of the velocity vector gave results which were as 
much too large. Therefore, evaluation of the curtain 
velocities for required eddy widths could safely be 
based upon the actual magnitude of the wind speed 
for angles as low as 30° between wind direction and 
runway centerline. For winds down the runway, an 
end curtain extending perhaps 4 times the runway 
width and having twice the capacity of the longitudi¬ 
nal curtains should, in combination with both longi¬ 
tudinal curtains, provide ample distribution of heat for 
clearance. Since a curtain would be required along 
each side of the runway to counter winds from any 
direction, a double curtain would thus be available 
for w T ind speeds approaching zero. 

The primary disadvantage of the wind-curtain in 
comparison with the burner method is the relatively 
great initial cost of the engines, blowers, and ducts 
which it requires. In the belief that its greater economy 
of operation might nevertheless offset this disad¬ 
vantage, the Iowa Institute undertook the compila¬ 
tion of estimated costs of constructing and operating 
the two tjrpes of fog dispersal under identical con¬ 
ditions. 11 

From information obtained at Wright Field, the 
cost of installing burners along the two sides of a 
runway would be approximately $40,000 per 1,000 ft 
of runway. Based upon current cost of labor and ma¬ 
terials, construction of a similar double length of the 
wind-curtain system would require some $1,500,000. 
Minimum operating costs of the burner in a 15-mph 
wind would amount to about $4,000 per hr, and for 
the wind curtain about $1,000 per hr, i.e., an hourly 
saving of $3,000. If it is assumed that fog and landing 
frequencies require perhaps 200 hr of clearance per 
year, little more than two years would evidently be 
needed to retire the increased initial cost of the wind- 
curtain system through its relative economy of fuel 
consumption. 

Under the Iowa contract, but independently of 


Institute supervision, an analytical investigation 12 
was made of the probable increase in efficiency of the 
wind-curtain system through adaptation of the so- 
called thrust augmentor used effectively in jet pro¬ 
pulsion. Although tests were not made to verify 
the assumed conversion factors, it was estimated by 
the investigator that the gain in jet efficiency (and 
hence the reduction in cost of installation and opera¬ 
tion) would be some 33%. This wmild obviously 
represent a considerable lowering of the time required 
to offset the initial cost through relative economy of 
operation. 

At the time of writing this report, tentative plans 
have been laid for testing a section of a wind-curtain 
installation at Areata under fog conditions. It is not 
known whether such plans will actually be carried to 
completion. 

43.4 EXPERIMENTS ON GAS DIFFUSION 

Tests made in England and in this country on 
the rate of gas diffusion and dissipation in specific 
open streets, courts, and buildings, led the Uni¬ 
versity of Illinois in 1942 to propose a more general 
series of exploratory measurements upon schematic 
structures from wlrch conclusions could be drawn 
which would not be restricted to the particular 
boundary forms already investigated. Although it 
was originally intended to perform these tests in the 
field at full scale, in the spring of 1943 a subcontract 
was written with the Iowa Institute to prepare a 
special wind tunnel for laboratory tests on model 
structures, which was expected to result in a great 
saving of time and expense. The tunnel constructed 
for this purpose 1 was almost immediately requisi¬ 
tioned for the fog-dispersal tests already described, 
but the measurements on gas diffusion discussed in 
the following pages were conducted intermittently 
whenever the higher priority investigation would 
permit. 

In order to formulate and check the scale relation¬ 
ships which would be used to convert model results to 
prototype values, a series of hollow cubes was first 
constructed having dimensions of 24, 12, 6, 3, and 
l}/2 in. These were placed, in turn, at the midpoint 
of the test section with open side up, and carefully 
filled with a known quantity of S0 2 . The rate of dis¬ 
sipation of the S0 2 in winds of constant speed was 
then measured against time with a standard Dickin¬ 
son meter. It was soon noted that the diffusion of the 
gas from even the largest cube in the lowest wind was 


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634 


WIND-TUNNEL STUDIES 



Figure 12. Model buildings in Japanese urban district. 


so rapid that the Dickinson-meter indication repre¬ 
sented its own rate of clearing rather than the rate at 
which the gas was removed from the cube. Search for 
a concentration meter with a response of the required 
rapidity proved fruitless. Since small-scale experi¬ 
ments are characterized by a reduction in time inter¬ 
vals roughly comparable to the reduction in the 
length dimension, it was concluded therefore that 
further efforts to investigate gas diffusion in the wind 
tunnel as a function of time should not be made. 

The preliminary studies with the cubes of various 
sizes were then revised to include only the spatial 
variation of concentration under conditions of steady 
gas release. Each cube in turn was placed in the 
tunnel with its open side downwind, gas was re¬ 
leased at a controlled rate within the cube, and con¬ 
centration traverses were made in the downwind 
direction at various wind speeds and various rates of 
gas release. Owing to the angularity of the cubic form 
of body under study, the scale and intensity of the 
downwind eddies which produced the diffusion of the 


gas proved to be independent of the Reynolds number 
except at very low wind speeds or very small dimen¬ 
sions of the cube. It was, therefore, possible to reduce 
the variation in gas concentration in the downwind 
direction to a single dimensionless function 13 b} r 
measuring longitudinal distances in terms of the 
dimension h of the cubes and by referring the point 
concentration c to the quantity Q/v 0 h 2 , in which Q is 
the volume rate of gas release and v 0 the wind speed. 
The resulting function should, therefore, be inde¬ 
pendent of scale and wind speed, provided only that 
the diffusion was the result of eddies produced by a 
structure of the specified geometry under neutral 
conditions. 

In a subsequent study to determine the effect of 
multiple cubic structures regularly spaced, some 72 
6-in. cubes were placed at regular 12-in. intervals over 
the entire floor of the tunnel, and concentration 
traverses were made at three levels with various loca¬ 
tions of the point of injection, various rates of gas re¬ 
lease, various wind speeds, and several different 


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635 



Figure 13. Concentration contours for gas diffusion in a Japanese urban district. 


orientations of wind direction. It was found possible 
to reduce all such measurements to a series of rela¬ 
tive concentration contours superposed upon the plan 
view of the block arrangement, the contours having 
geometrically progressive values of the dimensionless 
parameter cv 0 Ji 2 /Q. The fact that these contours were 
independent of wind speed and rate of gas release in¬ 
dicated that they should also be independent of scale 
as in the case of the earlier experiments with single 
structures. Although the schematic nature and ar¬ 
rangement of the structures limited the direct use¬ 
fulness of the test results in foretelling field conditions 
for specific urban districts, nevertheless they revealed 
a very pronounced rate of vertical diffusion with 
distance downwind which should rapidly reduce the 
gas concentration at street level in any urban area. 

In order to apply the foregoing method to the in¬ 
vestigation of diffusion under urban conditions of 
specific interest, photographs of a series of Japanese 
cities were carefully studied, and a series of typical 
building proportions were formulated therefrom. 14 
These building types were then reproduced at a scale 
of 1/72 in multiple units of such number (some 1,000 
in all) as to pave the entire tunnel floor with the series 
of repeating city blocks shown in Figure 12. Instead 
of releasing the gas from a point source as in the fore¬ 
going tests, lateral manifolds were prepared which 


would simulate the initial pancake widths of bursts 
from 500- and 1,000-lb bombs at street level, either 
centered on one of the intersections or midway be¬ 
tween two intersections. Concentration traverses, 
made in the same manner as in the case of the cubes, 
resulted in dimensionless contour plots such as that 
reproduced in Figure 13, the length L of the model 
and prototype foot being used instead of a building 
height h as the characteristic linear dimension in 
the quantity N = Q/vqL 2 . 

As shown by this plot, the vertical diffusion is 
relatively great, while the lateral spread is quite 
limited. In other words, bursts would have to be 
closely spaced both laterally and longitudinally to 
result in a reasonably high concentration. To check 
the principle of contour superposition for the deter¬ 
mination of the required spacing, the results obtained 
from runs with the two release manifolds placed ap¬ 
proximately end to end, and then individually in the 
same positions, were compared. As may be seen from 
Figure 14 for a typical lateral section, the sum of the 
concentrations for the individual runs is very nearly 
identical with the distribution for the combined run, 
indicating that simple addition of superposed contour 
values will permit determination of the required 
bomb spacing for any desired minimum concentra¬ 
tion. 


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WIND-TUNNEL STUDIES 


10 

tc. 8 

ID 

K 

3 

Q: 

ID 

Q. 

O 6 
5 
2 

I* 

q: 

K 

2 

ID 

O 

2 9 
O 2 

o 


0 

2.5 2.0 1.5 1.0 0.5 0 0.5 1.0 

LATERAL DISTANCE IN FEET FROM CENTERLINE OF TUNNEL 

Figure 14. Test of superposition principle. 

Since such small-scale experiments are perforce re¬ 
stricted to steady-state conditions until better means 
of measuring rapidly changing concentrations are 
available, means were next sought of foretelling from 
steady-state measurements the diffusion which would 
occur following bursts of the same pancake propor¬ 
tions. An analytical investigation of the diffusion 


CHECK ON ADDITIVE EFFECT 
OF OVERLAPPING SOURCES 
DESCRIPTION OF SOURCES 
DISCHARGE RATE IN MG PER SEC 
FROM 

SMALL LARGE OPERATION 




Figure 15. Contours of 


Cm 

M 


X 10 7 for 500-pound bomb. 


process 14 indicated that the unsteady rate of diffusion 
would follow a different spatial variation, so that the 
steady-state contours would not yield directly even 
the relation between the peak concentrations C m to be 
expected downwind from bursts. Nevertheless, the 
mathematical forms of the two diffusion functions ap¬ 
peared to provide a means of converting results from 
one to the other in a quantitative manner, once the 
numerical constants had been determined from wind- 
tunnel and field measurements of steady and burst 
conditions, respectively, for the same boundary con¬ 
ditions. 

At the Dugway Proving Ground of the Chemical 
Warfare Service, a so-called Japanese Village, already 
in use for incendiary studies, appeared suitable for 
field tests of the type required. With the cooperation 
of the CWS, 500- and 1,000-lb bombs of N0 2 were 
exploded upwind from this village, and the concen¬ 
trations at 27 points within the village were measured 
against time by means of Dickinson meters. Evalua¬ 
tion of the C m ax and Ct values from these measure¬ 
ments 15 yielded contour patterns of the type shown 



Figure 16. Contours of — x 10 4 for 1,000-pound bomb. 


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EXPERIMENTS ON GAS DIFFUSION 


637 


Table I. Field measurement and wind-tunnel predictions. 


Point 

C m 

Computed 

JM 

Measured 

Ct/P 

Computed Measured 



500-lb bomb 


A 

7.4 X 10~ 7 

6.5 X 10~ 7 

1.6 X 10~ 4 

4.5 X 10~ 4 

B 

1.5 X 10- 7 

2.0 X 10- 7 

0.3 X 10~ 4 

<1.0 X 10~ 4 

C 

0.7 X 10- 7 

2.5 X 10~ 7 

0.2 X 10 -4 

2.5 X 10~ 4 

D 

5.8 X 10~ 7 

2.5 X 10- 7 

1.3 X 10- 4 

1.5 X 10- 4 



1,000-lb bomb 


A 

4.1 X 10- 7 

3.0 X 10~ 7 

1.3 X 10~ 4 

2.5 X 10~ 4 

B 

7.3 X 10~ 7 

0.7 X 10 -7 

1.3 X 10~ 4 

0.5 X 10~ 4 

C 

2.4 X 10~ 7 

0.7 X 10- 7 

0.8 X 10~ 4 

<0.5 X 10~ 4 

D 

3.5 X 10~ 7 

1.0 x 10- 7 

1.1 x 10- 4 

1.0 X 10“ 4 


in Figures 15 and 16, the contour parameters C m /M = 
C m L*/q and Ct/P = CtL 2 V/q involving the volume of 
gas released q in place of the. steady release rate Q. 
Immediately following these field tests, wind-tunnel 
measurements were made with steady release of S0 2 
at similar upwind points for a 1/72 scale reduction of 
the village structures (see Figure 17). As may be seen 
from the resulting contours shown in Figure 18, the 
laboratory measurements were necessarily far more 
detailed and reproducible; the field tests, in fact, 
showed the usual difficulty of variable wind speed 
and direction and proper meter placing. Neverthe¬ 
less, evaluation of the numerical constants involved 
in the conversion from the steady to the burst dif¬ 
fusion function resulted in the comparison between 
field measurement and wind-tunnel predictions 
shown in Table 1. 

Although considerable scatter is apparent, the ac¬ 
curacy of the predictions will be found to be as great 
as the reproducibility of the field measurements. 

To the extent that the diffusion pattern of gas is 
controlled by the eddies shed by structural irregulari¬ 
ties, small-scale studies of urban districts should yield 
quite as dependable results as field tests, with a vast 
saving in time and expense. If, however, bombing is 
to occur under the most advantageous conditions 




Figure 17. Model of Japanese village. 


(i.e., very low wind speed and stable temperature 
gradient), then the present impossibility of reproduc¬ 
ing viscous and thermal effects at small scale makes 
the wind-tunnel prediction of such phenomena out of 
the question. It is nevertheless believed that many 
situations in which wind plays the predominant role 
may be studied profitably in the manner outlined 
herein. 

As an outgrowth of certain photographic studies of 
eddy patterns conducted in the wind tunnel of the 
Iowa Institute, a portion of the contract involved the 



Figure 18. Contours of ~ir T X 10 4 from model simulat- 
N 

ing field test with 500-pound bomb. 


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WIND-TUNNEL STUDIES 


preparation of a 400-ft reel of 16-mm motion pictures 16 
intended for training purposes by the CWS. This film 
illustrated the following phenomena by means of 
smoke and specially prepared models: the relative 
rates of smoke or gas diffusion under neutral, lapse, 
and inversion conditions; the effect upon diffusion of 
boundary roughness such as rocks or shrubbery; the 
effect of orchard and forest growth upon smoke or gas 
released upwind from and within the wooded section; 
eddy forms produced by screens, walls, and individual 
buildings; and, finally, the influence of building 
clusters. The film was originally submitted with 
descriptive titles, with the understanding that a 
sound film with running comments was to be prepared 
therefrom by the CWS. 

43.5 EXPERIMENTS ON WIND FLOW 
OVER TERRAIN MODELS 

At the request of the Weather Division of the Army 
Air Forces, the Iowa Institute undertook in the spring 
of 1945 a series of preliminary measurements of the 
distribution of velocity and turbulence over a relief 
model of the Tokyo Bay region. At that time Ameri¬ 
can bombers were experiencing unexpected gustiness 
of the atmosphere during westerly winds which made 
precision bombing of Tokyo difficult, and all possible 
clues to the cause of the difficulty were desired. Al¬ 
though it was fully realized that model tests in the 
Iowa wind tunnel could clarify at best only a portion 
of the problem (that resulting from eddies shed by 
the mountainous region to the west) it was hoped 
that such information might be correlated with such 
other effects as those due to thermal instability. 

The rubber relief model supplied by the Navy had 
a horizontal scale of 1/50,000 and a vertical distor¬ 
tion of 1.6/1. Though certain sections of the model 
were missing, those at hand were placed upon the 
floor of the wind-tunnel test section, and vertical 
velocity traverses were made at typical points be¬ 
tween the mountains and the city. Thereafter, cor¬ 
responding turbulence traverses were made at the 
same points, using the method of gas diffusion for the 
evaluation of the relative velocity of fluctuation and 
the coefficient of eddy diffusion. Such measurements 
clearly demonstrated the change in wind structure 
caused by the mountainous terrain, and permitted a 
qualitative evaluation of the height to which the 
disturbance extended. 17 

Specific use of such information was prevented by 


two unrelated circumstances. On the one hand, the 
fact that it was impossible to perform the model tests 
at the same Reynolds number as that of the proto¬ 
type precluded accurate quantitative conversion of 
the test results to full-scale conditions; in other words, 
boundary-layer growth in the model was not neces¬ 
sarily the same as that to be expected in the actual 
atmosphere over Tokyo, although the pronounced 
roughness of the model tended toward minimum 
rather than maximum viscous effects. On the other 
hand, it was found impossible during war conditions 
to obtain sufficient weather information for the 
Tokyo region to permit correlation of the model 
indications with actual occurrences. 

In view of the fact that such model studies would 
permit considerable simplification of wind-structure 
analysis, once small-scale results had been proved 
dependable, it was believed advisable to conduct 
experiments of a similar nature over models of regions 
for which extensive weather data were at hand. A 
model of the island of Guam was provided for this 
purpose, but the model scale was too small and the 
available weather reports too incomplete to warrant 
further tests. Since the island of Puerto Rico ap¬ 
peared more suitable for the investigation, it was 
decided to have relief models of this island made at 
several different vertical distortion ratios. 

During the preparation of these models by the 
Army Air Forces, the Iowa Institute conducted tests 
of the effect of distortion 18 upon three series of 
boundary forms: semi-ellipsoids, cones, and paral¬ 
lelepipeds of similar base dimensions but having 
heights varying in geometric progression. Theoretical 
analysis of the flow pattern around ellipsoids of vari¬ 
ous axis ratios showed at once that in no simple way 
could measurements of the flow pattern around any 
ellipsoid be converted to yield usable results for any 
other ellipsoid, indicating that the distortion of a 
boundary and the resulting distortion of the flow 
pattern are not geometrically comparable. The 
measurements over the several series of schematic 
boundary irregularities (made with the specially con¬ 
structed three-dimensional velocity meter shown in 
Figure 3) checked both the theoretical distribution 
for the semi-ellipsoids and the conclusions derived 
therefrom. In some instances it was found possible to 
approximate the velocity distribution for one of the 
boundaries from that obtained from its “distorted” 
counterpart, but in practically every instance the 
error was essentially the same order as the effect 
which it was desired to measure. 


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EXPERIMENTS ON WIND FLOW OVER TERRAIN MODELS 


639 


The OSRD contract under which these studies 
were conducted terminated before the foregoing tests 
had been completed, and they were continued under 
direct contract with the Army Air Forces, together 
with measurements over the Puerto Rico models. It 
must be concluded from these tests that measure¬ 
ments over small-scale terrain models are unlikely to 
yield useful quantitative information, unless the 


boundary configuration is so extreme as to require no 
vertical distortion for the required precision of indi¬ 
cation. As an example of desirable terrain charac¬ 
teristics for wind-tunnel study, reference may be 
made to successful observations made over a model 
of Gibraltar, which has sufficient relative height to 
yield a pronounced eddy pattern that is essentially 
independent of Reynolds number effects. 




> 


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Chapter 44 

RADIOACTIVE TRACERS 

By W. D. Walters 


44.1 INTRODUCTION 

n a number of studies undertaken by investigators 
in Division 10, radioactive materials were employed 
as tracers. The various types of investigations that 
were performed in connection with the charcoal and 
smoke filter problems will be described briefly in the 
pages which follow. In the present summary the re¬ 
sults of the radioactive tracer experiments will not be 
discussed in detail, since the significance of the re¬ 
sults with respect to the general problems of the be¬ 
havior of absorbents and filters has been considered 
in earlier chapters. 

44.2 PREPARATION OF WAR GASES 
CONTAINING RADIOACTIVE ELEMENTS 

For the utilization of the radioactive tracer tech¬ 
nique, it was necessary to have a source of the desired 
radioactive elements and rapid methods of prepara¬ 
tion of small quantities of radioactive toxic agents. 
Although some investigators obtained radioactive 
elements in small quantities without charge or by 
direct purchase order, a large fraction of the radio¬ 
active starting materials needed in the Division 10 
program was supplied through contracts with the 
University of California and with Harvard Uni¬ 
versity. 

The methods (shown in Table 1) for preparing the 
radioactive compounds, such as phosgene and arsine, 
from available radioactive starting materials were 
usually developed by the groups which subsequently 
used the radioactive compounds for studies of ad¬ 
sorbents or filters. However, at the Pennsylvania 
State College a study was made to determine the 
most feasible methods for synthesizing various radio¬ 
active war gases. In this study the methods were 
actually investigated by the use of nonradioactive 
substances, but consideration was given to the state 
of combination in which the radio-element would be 
obtained. In Table 1, in order to indicate that the 
method was developed for the incorporation of a 
given radioactive element, but not used for a radio¬ 
active sample of the element, the element is marked 
with an asterisk. 


It is evident that in most cases the methods of 
preparation given in Table 1 were not new reactions 
but were adaptations of known methods to the 
preparation of radioactive toxic agents. The refer¬ 
ences to the earlier studies reported in the open 
literature are given in the reports cited, but they 
have not been included here on account of the 
shortage of space. 

44.3 APPARATUS 

As in the case of the preparation of materials, 
general methods for the detection of radioactive 
substances had been developed prior to the NDRC 
investigations and various types of apparatus were 
available. Therefore, the apparatus employed in any 
Division 10 investigation usually represented a modi¬ 
fication of existing apparatus to fit the needs of the 
particular problem being studied plus new items of 
apparatus designed on the project. 

One of the pieces of apparatus used quite exten¬ 
sively was a Geiger counter tube which had mica 
windows of thickness 2 to 3 mg per sq cm, and which 
was used for the determination of the activity of 
compounds of radio-sulfur or any other beta emitter 
with energy of radiation 100,000 volts or greater. 3 
When the tube was shielded by 2 in. of lead, the 
background amounted to only 20 counts per minute. 
The tube was developed at the California Institute 
of Technology, and on the same project a counting 
rate meter circuit of the Evans-Alder-Kip type was 
constructed. This circuit was found to be very useful 
in combination with a recording milliammeter. In 
addition, a scale of 32 circuit was built and used for 
the determination of radioactivities. 

In the early NDRC work it appeared that, under 
favorable conditions, radioactive H 3 might be em¬ 
ployed for the measurement of small concentrations 
of hydrogen-containing compounds. 4 Therefore, a 
Geiger-Muller counter suitable for the measurement 
of the activity of H 3 in very low' concentrations was 
developed at the Radiation Laboratory of the Uni¬ 
versity of California. To measure the activity of H 3 , 
the hydrogen must be converted into elementary 
hjMrogen before it is introduced into the counter, and 


640 


SECRET 


STUDIES OF CHARCOALS AND WHETLERITES 


641 


Table 1. War gases or simulated war gases containing radioactive elements. 


Compound 


COCl, 

COCl, 

C0C1 2 

COCl, 

AsH 3 

AsH 3 

H 2 S 

SFg 

CNC1 


Radio-element 
(half-life ) a 


Method of 
producing 
radio-element 


Process for 
preparation 
of compound 


C 11 (20.5 min) 
Cl 38 (37 min) 

Cl* 

Cl*, O*, or C* 
As 74 (16 days) 

As 74 (17 days) 
S 35 (88 days) 
S 35 (88 days) 
N* 


B, d-n 
Cl, d-p 


Ge, d-n 

Ge, d-n 


CO-^>COCl 2 

hv 

LiCl-Cl, exchange 

PO 

ciA^-coci, 
AgcT^eoa, 
co + C 1 *-^ 0001 ’ 

Na3As04 

br ( Ge ° 2 )^^ AsV 

HC1 in 

li^ As z^ AsH ’ 


c T(Ge0 2 ) — 

BaS04~^ 

A 

KIs 

h 2 s— >s 


Zn 

►As v ——> AsH 3 

H 


BaS 
f 2 


H + 


• H,S 


sf 6 

h 2 0 


nh 3 


Ca 

(i) N 2 —>■ Ca 3 N 2 — 

A A 

(ii) NH 3 + C0 2 ——>-KCN 

A 

(iii) KCN-^>CNC1 


Reference 


8 

8 


2,9 


6, 10, 9 
3 
3 

12, 9 


CNCl 

c* 

As in (ii) and (iii) above 

NaCN 

12, 9 

CNC1 

Cl* 

Cl,->CNC1 

12, 9 

HCN 

N* or C* 

KCN prepared as in (i) and (ii) 
aso^ 

FeSO< 

15, 9 

SeF 6 

Se* 

F 

Se—>SeF 6 

17, 9 

CCl 3 NO, 

Cl* 

(CH 3 ) 2 CO + HN0 3 + HC1—>- 

CCl 3 NO, 9 

(C 6 H 5 0) 3 P0 

P 32 ? 

Rad P0 4 -^>P —^PC1 5 

1 


CeHsOH 

PClo- > (C 6 H 5 0) 3 P0 


a Reported value not always in agreement with the value accepted at the present time. 
b T^GeCh) denotes target material, GeO*, was subjected to the treatment indicated. 
c For details of separation and preparation see reference (6). 


for this reason, as well as others, the method found 
little use in the Division 10 program. 

44.4 STUDIES OF CHARCOALS AND 
WHETLERITES 

44.4.1 Concentration of Agent in the 
Effluent Gas Stream 

By the use of toxic gas-air streams containing 
molecules of radioactive agent as well as molecules of 
non radioactive agent, it was found that the total 
concentration of the agent in the gas stream before 
and after passage over a charcoal bed could be de¬ 
termined readily and accurately by the measurement 
of radioactivity. In this work, calibration experi¬ 


ments were, of course, necessary. Concentrations of 
arsine, 5 phosgene, 8 hydrogen sulfide, 3 and sulfur 
hexafluoride 3 were determined by passing the gas 
stream through glass vessels covered with a thin film 
of aluminum which was placed next to the mica- 
covered Geiger counter tube. Although a number of 
factors may influence the sensitivity of the method, 
it was observed that with the apparatus and activity 
of radio-samples available at the time of these in¬ 
vestigations, the radioactive tracer technique could 
be used to obtain concentrations as low as the follow¬ 
ing: 

Substance Concentration Accuracy 

H 2 S 0.32 mg per cu m 30 to 40% 

SF 6 0.3 mg of S per cu m 10% 

AsH 3 10 mg per cu m 25% 


SECRET 




















642 


RADIOACTIVE TRACERS 


As would be expected, the accuracy was better for the 
determination of higher concentrations. 

Another method of obtaining a sample of a gas mix¬ 
ture from a static system or from a flowing stream 
was also devised. 3 A glass hypodermic needle was 
used to remove a few cubic centimeters of the gas 
mixture, and this sample was then injected into a 
closed vessel through a small hole covered with a 
rubber band. By locating the aluminum or cellophane 
window of the vessel near a Geiger counter, the 
activity of the sample could be measured. Concen¬ 
trations as low as 0.1 mg S per cu m in a 5- to 10-cc 
sample of an air-H 2 S mixture or an air-SF 6 mixture 
could be measured by this method. 

The flow method mentioned above was of con¬ 
siderable value in the measurement of effluent con¬ 
centration as a function of time during adsorption 
and desorption experiments. In general, the results of 
the radioactive tracer technique proved useful in 
(1) measuring the performance of charcoals and 
whetlerites, 5 - 8> 13 (2) determining the sensitivity and 
the efficiency of certain chemical breakpoint indi¬ 
cators, such as the silver nitrate indicator for ar¬ 
sine, 5 ’ 14 and (3) testing various theoretical adsorp¬ 
tion equations. 5 - 8 

44.4.2 Reaction Products in the Effluent 
Gas Stream 

In a consideration of the application of the radio¬ 
active tracer method to the study of the removal 
of toxic agents by charcoal, it is apparent that the 
radioactivity of the effluent stream represents the 
radioactivity not only from the unremoved toxic gas, 
but also from any radioactive reaction products ap¬ 
pearing in the effluent gas stream. In the case of 
arsine containing radioactive arsenic, the reaction 
products containing arsenic are essentially nonvola¬ 
tile compounds readily retained by the charcoal. 
However, with phosgene containing radioactive car¬ 
bon, and under certain conditions with phosgene 
containing radioactive chlorine, an appreciable frac¬ 
tion of the radioactivity in the effluent stream may 
be due to radioactive reaction products. By carrying 
out experiments first with phosgene containing C 11 
and then with phosgene containing Cl 38 , the group 
on project OEMsr-28 at the California Institute of 
Technology obtained results which were useful in the 
identification of the reaction products and the deter¬ 
mination of the concentration under different experi¬ 
mental conditions. 816 


44.4.3 Distribution of Toxic Agent or 
Reaction Product in the Charcoal Bed 

By means of radioactive war gases it was possible 
to observe the accumulation of the adsorbed toxic 
agent or of radioactive reaction products in the char¬ 
coal bed. Experiments with radio-arsine were per¬ 
formed to measure the accumulation of arsenic at a 
single position in the charcoal bed as a function of 
time and also to determine the distribution of arsenic 
along the charcoal bed. At the California Institute 
of Technology the change in the radioactivity of the 
top layer of the charcoal bed with time was obtained 
by the use of the previously described counting ap¬ 
paratus when a lead slit 3 mm wide and 100 mm 
thick was placed adjacent to the top of the charcoal 
bed. 5 For the investigation of the distribution of the 
radioactive arsenic along the charcoal bed, a 3-mm 
lead slit was used to scan the bed after radio-arsine 
had been passed through the bed for a definite time. 
Another method employed in the distribution experi¬ 
ments was the use of fine brass screens to divide the 
charcoal bed into sections which could be removed 
after passage of the gas and their separate activities 
determined. 

At the University of Rochester, on Project 
NDCrc-76, the distribution of As 74 (from radio¬ 
arsine) in the charcoal bed was also studied. 6 Experi¬ 
ments were performed in order to determine how the 
distribution depended upon the time of passage of the 
gas, initial concentration of arsine, moisture content of 
the charcoal, and humidity of the gas stream. The dis¬ 
tribution of arsenic along the bed was obtained by sepa¬ 
rating the charcoal bed into sections and measuring 
the activity of a definite weight of charcoal from each 
section. The separation into sections was accom¬ 
plished by means of a screw arrangement for lifting 
the entire bed so that successive layers of charcoal 
of the desired size could be removed (without the use 
of screens). 

One of the significant results revealed by the ex¬ 
periments at Pasadena and at Rochester was that 
the top layer of the charcoal bed is not completely 
saturated when the silver nitrate breakpoint is 
reached. 

In the case of phosgene containing radioactive 
chlorine, the accumulation of labeled chlorine in the 
charcoal layer on the influent side of the bed was 
measured at the California Institute of Technology. 
It was found that the amount of chlorine increased 
rapidly with time until the breakpoint was reached 


SECRET 



FIELD USE OF RADIOACTIVE TRACERS 


643 


(activity of effluent 1% of influent), but after the 
breakpoint the accumulation in the top layer 
practically ceased. 8 

44.4.4 Location of the Reaction Product 

in the Individual Particles of Whetlerite 

Another application of the radioactive technique 
to the study of the removal of war gases was an in¬ 
vestigation at the University of Illinois (Project 
NDCrc-152) to ascertain the location of the reaction 
product (probably As 2 0 3 ) from arsine in a single 
particle of charcoal or whetlerite. 7 Various charcoals 
were treated with arsine containing radioactive ar¬ 
senic. A thin section could be prepared by grinding 
down a single particle, and when the section was 
placed in contact with a photographic plate, the 
radioactivity produced an image showing the loca¬ 
tion of arsenic in the particle. Radioactive ash skele¬ 
tons were also prepared by carefully ashing a few 
particles of the exposed whetlerite. Radiographic 
images of these ash skeletons could be obtained upon 
a photographic plate. In this work the treatment of 
the particles with radio-arsine was carried out at 
Rochester and at Pasadena. The results of these 
radiographic studies were of considerable interest and 
showed among other things that the reaction product 
from arsine lies near the surface of the whetlerite 
particle. This layer of reaction product was quite 
thin in the case of extruded charcoals, particularly 
along the smooth, cylindrical sides of the particle. 

44.4.5 Distribution of the Catalyst in 
the Individual Particles of Whetlerite 

In addition to the study of the location of the re¬ 
action product, the radioactive tracer method was 
employed at the University of Illinois to determine 
the location of the catalyst in the whetlerite par¬ 
ticles. 7 ’ 18 Impregnating solutions containing radio¬ 
active elements, such as cobalt, phosphorus, and 
thorium, were used to treat blocks of charcoal, and 
the sides of the dried blocks scraped off so that the 
activity of the layers could be measured. In the later 
work, thin sections of impregnated charcoal particles 
containing Cu 64 , NaS 35 CN, or Ag 106 were prepared, 
and radiographs obtained as mentioned above. The 
charcoals impregnated with NaS 35 CN had been 


prepared at the University of California, and those 
with Ag 106 at the Northwestern Technological Insti¬ 
tute. Radiographs of the ash skeletons were also pre¬ 
pared. In this study it was observed that, in general, 
the soaking method of silver impregnation distributed 
the catalyst throughout the particle, but the spraying 
procedure tended to produce a thin outer layer of 
catalyst. 

44.5 STUDY OF SMOKE FILTERS 

One of the earliest uses of radioactive tracers in the 
program of Division 10 (or its predecessors, Sections 
B-5 and B-6) was in connection with the testing of 
filter materials. 1 The problem of determining the 
performance of smoke filters, especially against 
liquid smokes, was quite important, and on Project 
NDCrc-49 at the University of Illinois a method was 
developed for testing filter materials by the use of 
aerosols produced from radioactive triphenyl phos¬ 
phate. An aerosol of triphenyl phosphate containing 
radioactive phosphorus was passed through a series 
of circular pads prepared from the filter material 
being tested. These pads were in contact under a 
definite pressure. After passage of the smoke for the 
desired period of time, the pads were separated and 
each pad counted on a Geiger counter. The results 
obtained by this method contributed to the develop¬ 
ment of a theory of filtration. Moreover, the results 
showed that the existing method of testing gas¬ 
mask filters was objectionable from several stand¬ 
points and that immediate steps should be taken to 
produce better smoke filters. 

44.6 FIELD USE OF RADIOACTIVE 

TRACERS 

As an extension of the use of the radioactive tracer 
procedures employed in laboratory work, it might be 
expected that, under certain conditions, radioactive 
tracers might be used to determine ground con¬ 
tamination, aerosol concentration, or vapor concen¬ 
tration of toxic agents during field tests. In this con¬ 
nection it is interesting to note that the radioactive 
method for measuring the ground contamination 
from mustard-filled munitions was investigated by 
the Chemical Warfare Service at the Dugway 
Proving Ground. 


SECRET 


















































































































GLOSSARY 


A. Angstrom. 

AC. Symbol for hydrogen cyanide. 

AD. Apparent density; the weight of 1 ml, not the true 
density because of the free space between particles. 

AL. Woodpulp. 

AR-50. Designation for relative humidity of charcoal and air 
in test; charcoal as received, air at 50 per cent RH. 

ASC. Designation for impregnated charcoal which contains 
copper, silver and chromium. 

ASM. Impregnant for whetlerite made with molybdenum in 
place of chromium. 

ASV. Impregnant for whetlerite made with vanadium (same 
as above). 

BC charcoal. Barnebey-Cheney, prepared from nut shells or 
peach pits. 

BW. Biological warfare. 

C. Critical bed depth. 

CFI charcoals. Colorado Fuel and Iron Company. Experi¬ 
mental gas mask charcoal made from coal. 

CG. Symbol for phosgene. 

CK. Symbol for cyanogen chloride. 

Cl. Concentration-time; product for gas exposure. Units are 
either mg min per liter or mg min per cubic meter. The 
former is often used for non-persistent gases and the latter 
for persistent. 

CtA. Product of gas dosage by area covered. See Chapter 16. 

CWSC. Designation for charcoal prepared by the Carlisle 
Company, using the Prest-o-log process. See Chapter 3. Also 
referred to as Seattle or Crown-Zellerbach charcoal. 

CWSE1-TE1. Designation for a sample of Type A whetlerite 
prepared from coconut charcoal at Edgewood Arsenal. 

CWSN. Designation for charcoal manufactured by National 
Carbon Company, by zinc chloride process. A number 
indicates the particular batch, e.g., CWSN5, CWSN44, etc. 

Cyan DA. CWS symbol for Diphenylchloroarsine. 

DBT. Dibutylphthalate. 

DC. Symbol for diphenylcyanoarsine. 

Diol. Trade name of oil used for screening smoke. 

DM. Symbol for Adamsite. 

DOP. Dioctylphthalate. 

E6. Designation for thiocyanates impregnated whetlerite. 
This was never put into production. 

EN. Symbol for ethylenimine. 

fpm. Foot per minute. 

fps. Foot per second. 

FS. Fuming sulfuric acid. Used to produce smoke. 

gph. Gallons per hour. 

gpl. Grams per liter. 

H. Symbol for mustard gas. Also designated as HS prior to 
1942. 

HBT. Herringbone twill cloth used in clothing. 

HC. Symbol for hexachlorethane, used for producing smoke. 
HC pot is a smoke pot employing this chemical. 

HCE. British for hexachlorethane. 

HD. Distilled mustard. 

HE. High explosive. 

HN-3. Nitrogen mustard N(C1CH 2 CH 2 )3. 


HTU. Height of a transfer unit. 

IAS. Indicated air speed. 

IR. Voltage drop. 

IT. Index of turbulence. 

lpm. Liters per minute. 

LST. Local standard time. 

MB. Methylene blue. 

MCE. German war gas Tabun. 

MDL. Abbreviation for Munitions Development Laboratory 
at University of Illinois. 

MMD. Mass median diameter. 

mmg. Microgram or 10 -3 mg. 

MSV. Moisture saturation valve. 

HG. Microgram. 

National. National Carbon Company. Charcoal prepared 
by the N. C. Co. is frequently referred to a “National” 
Charcoal. It is made by the zinc chloride process. Designated 
as CWSN. 

N. Gas capacity of absorbent at saturation. See Chapter 2. 

NRL. Naval Research Laboratory. 

PCC. Pittsburgh Coke & Chemical Company. 

PCI. Pittsburgh Coke and Iron Company now known as 
PCC Company. 

ppm. Parts per million. 

PS. Symbol for chloropicrin. 

psi. Pounds per sq inch. 

PWP. Plasticized white phosphorus. 

R. Symbol for ratio of wind velocities at two different levels. 
See Chapter 14. 

RH. Relative humidity. 

Retentivity. A term used to describe the ability of charcoal 
to retain an adsorbed gas. 

SA. Symbol for arsine. 

Seattle charcoal. Charcoal prepared by carbonization and 
activation of Prest-o-logs from wood sawdust. Designated as 
CWSC. Sometimes called “Carlisle” since made by the 
Carlisle Company. 

SDF. Standard dispersion figure. See Chapter 35. 

SIP Indicator. Indicator used for CK tests. See Chapter 2. 

SN. Sulfur-citrate mixture used for smoke production. See 
Chapter 32. 

STP. Standard temperature and pressure. 

Space velocity (hr). “In quantitative work on heterogeneous 
catalysis, it is customary to express rates in terms of the 
volume of feed gases introduced to the catalyst in unit time. 
Specifically, the term ‘space velocity’ (hr) is equal to the 
volume of feed gases in liters per hour (measured at standard 
temperature and pressure) divided by the apparent volume 
of the catalyst measured in liters.” (Definition by Dr. 
Pease.) 

SWP. Mechanical mixture of steel wool and white phosphorus. 
See Chapter 37. 

Tabun. German war gas. 

TCP. Tricresyl phosphate. 

TPP. Triphenyl phosphate. 

Type A whetlerite. Charcoal impregnated by copper oxide. 


SECRET 


645 


646 


GLOSSARY 


See Chapter 4. Type ASC whetlerite contains copper, 
silver, and chromium. 

Type D mixture. Gas mask absorbent containing 20 per 
cent soda lime and 80 per cent Type A whetlerite by 
volume. 

VMMD. Volume mass median diameter. See Chapter 35. 

Whetlerite. All impregnated gas mask charcoals which 
contain copper are known as whetlerites. The usage dates 


back to 1918 when copper impregnated charcoal was pre¬ 
pared by Whetzel and Fuller. 

WP. White phosphorus used as smoke munition. 

WPT. White phosphorus loaded into bombs in paper tubes. 
See Chapter 37. 

Xerogel. A granular ion-exchange resin prepared as gas 
absorbent. See Chapter 4. 

Z. Symbol by British for S2F10. 


SECRET 



BIBLIOGRAPHY 


Abbreviations for Official Titles of Reports 


DPGSR 

DPGMlt 

EATR 

FM 

FMTR-MIT 

MIT-MR 

MSR 

NDRC 


OSRD 

SJPR 

TCIF 

TDMR 

TM 


Dugway Proving Ground Special Report 

Dugway Proving Ground Memorandum Report 

Edgewood Arsenal Technical Report 

Field Manual. War Department publication 

Foreign Material Technical Report from MIT laboratory 

Massachusetts Institute of Technology Memorandum Report 

Monthly Summary Report Sections 10.1 and 10.5, NDRC 

Informal Reports from Division 10 or Section B-6. The latter have 

Roman serial numbers 

Formal reports from OSRD 

San Jose Project Report 

Technical Command Informal Report 

Technical Division Memorandum Report 

Technical Manual. War Department publication 


Numbers such as Div. 10-200-M5 indicate that the docu- to the index volume and to the microfilm, consult the Army 
ment listed has been microfilmed and that its title appears in or Navy agency listed on the reverse of the half-title page, 

the microfilm index printed in a separate volume. For access 


Chapter 1 

1. Chemicals in War, A. M. Prentiss, McGraw-Hill Book 
Co., 1937. 

2. War Department Basic Field Manual , FM-21-40, Septem¬ 
ber, 1942. 

3. War Department Technical Manual, TM-3-205, October, 

1941. 

4. Summary of Results in Section B-6, December 1941 to 


August 1942 (Final Report), W. A. Noyes, Jr., OSRD 
1182, OEMsr-660, Service Projects CWS-7, NL-B26, and 
others, University of Rochester, Feb. 6, 1943. 

Div. 10-200-M5 

5. Bimonthly Reports of Division 10, NDRC. 

6. Standard U. S. Army Gas Masks and Components, S. H. 
Katz, TDMR 878, Aug. 2, 1944. 


Chapter 2 


1. Some Aspects of the Physical Chemistry of the Respirator, 
C. J. Danby, J. G. Davoud, et al, Oxford University 
extra-mural report, not dated. 

2. Standard Methods of Test (Chemical and Physical ) Em¬ 
ployed in CW Investigations, S. A. Mumford, Porton 
Memorandum No. 17, Mar. 7, 1942. 

3. Correlation Between the British Volume Activity and the 
United States Chloropicrin Tube Life, J. C. Arnell, Chem¬ 
ical Warfare Laboratories, Ottawa, Proofing Section Re¬ 
port No. 10, Oct. 25, 1943. 

4. An Intermittent Flow Canister Test Machine, J. W. Zabor, 
W. C. Pierce, R. K. Brinton, et al, OSRD 1193, OEMsr- 
282, Service Project CWS-7, Jan. 28, 1943. 

Div. 10-201.1-M12 

5. The Effect of Tube Diameter and Type of Air Flow on Char¬ 
coal Breakdown Times, J. R. Arthur, E. J. Brockless, et al, 
Oxford University Research Report No. 43.20. 

6. A Critical Examination of the Correlation of Tube and Con¬ 
tainer Gas Test Results, K. D. Wadsworth, Porton 2001 
(U. 138). 

7. Chemical Warfare Service Pamphlet No. 2. Part I. Canister 
Test Methods. Part II. Absorbent Test Methods. Part III. 
Collective Protector Test Methods. 

8. A Comparison of Tube and Container Gas Tests for Various 
Charcoals, Oxford University Research Report No. 44.16, 
July 10, 1944. 


9. A Study of Charcoal Adsorption and Methods of Testing 
Charcoals for Use in Gas Mask Canisters, R. Macy, 
EATR 52, May 10, 1942. 

10. Correlation of Tube and Canister Tests for Service Life of 
ASC Impregnated Charcoal, G. B. Wilson, TDMR 764, 
Nov. 3, 1943. 

11. Canister Test Methods and Apparatus. Tube Test Efficien¬ 
cies at Break Points, G. B. Wilson, TDMR 321, Nov. 10, 
1941. 

12. Canister Test Methods and Apparatus. Tube Tests — A 
Concentration Time Study, G. B. Wilson, TDMR 324, 
Nov. 15, 1941. 

13. Comparison of Gas Penetration Concentrations on U. S. 
German and Japanese Gas Mask Canisters, L. A. Jonas, 
TDMR 770, Nov. 29, 1943. 

Preliminary Report on the CC Penetration Through and 
Desorption From Japanese Army Service Canisters, L. A. 
Jonas, TCIR 146, June 23,T944. 

14. Performance of the M-10 Canister Against HS Under 

Humid Tropical Conditions, W. C. Pierce and J. W. Zabor, 
OSRD 1194, OEMsr-282, Service Project CWS-7, Feb. 3, 
1943. Div. 10-201.1-M13 

15. Fundamental Factors in the Design of Protective Respiratory 

Equipment. Inspiratory Air Flow Measurements of Human 
Subjects With and Without Resistance, L. Silverman et al, 
OSRD 1222, Mar. 4, 1943. Div. 11-204.2-MI 


SECRET 


647 


648 


BIBLIOGRAPHY 


Chapter 3 


1. Kimberley-Clark Process for Production of Activated Carbon 
From Lignin-Wood Flour Mixtures, Final Report, CWS 
Contract W-266-CWS-238, undated. 

2. Manufacture of Activated Charcoal in New Zealand from 
Coconut Shell Charcoal , Coal Survey Division, Dominion 
Laboratory, Wellington, New Zealand, A. C. L. 31, 
Jan. 6, 1943. 

3. Activation of Charcoal by Chlorine , M. E. Barker, Memo¬ 
randum, CWS-334.8/149, Nov. 26, 1941. 

4. The Effect of Treating Activated Charcoal with Air or Air- 
Steam Mixtures at Elevated Temperatures, C. R. Bierman, 
G. L. Pratt, and B. A. White, OSRD 5240, OEMsr-282, 
Service Projects CWS-7 and NS-338, June 21, 1945. 

Div. 10-202.13-M25 

5. Changes in Properties of PCI Charcoal and Whetlerite Dur¬ 
ing Activation, F. E. Blacet and T. Skei, OSRD 1349, 
OEMsr-282, Service Project CWS-7, Apr. 20, 1943. 

Div. 10-202.13-M12 

6. G. L. Cabot Carbon Black Charcoals, F. E. Blacet and T. 
Skei, OEMsr-282, Service Project CWS-7, NDRC Report 
10.1-15, Northwestern University, June 3, 1943. 

Div. 10-202.1-M12 

7. The Non-Uniform Activation of Charcoal, F. E. Blacet and 
T. Skei, OEMsr-282, Service Project CWS-7, NDRC 
Report 10.1-18, Northwestern University, June 15, 1943. 

Div. 10-202.13-M 14 

8. Effect of Activation Time on Properties of PCI Charcoal and 

Corresponding Whetlerites ( Second Report), F. E. Blacet, 
W. Conway Pierce, and T. Skei, OSRD 1746, OEMsr-282, 
Service Project CWS-7, Northwestern University, 
Aug. 10, 1943. Div. 10-202.11-M6 

9. Ultra Fine Structure of Coals and Cokes, H. K. Lewis and 
Company Ltd., p. 224. 

10. A Study of the Carbonization of Coal Materials, B. A. 

White, L. Byman, et al, OEMsr-282, Service Project 
CWS-7, NDRC Informal Report 10.5-49, Northwestern 
University, Nov. 24, 1944. Div. 10-202.12-M15 

11. Whetlerization of Apricot Pit Charcoals, E. Conroy, Cen¬ 
tral Laboratory Job Report W-7, Dec. 11, 1943. 

12. A Study of the Effect of Uniformity of Activation of Sieve 
Fractions on CC Canister Performance for Mixtures of 
PCI Charcoal, J. C. Cooper and R. J. Kunz, NDRC 

10.5- 21, Mar. 14, 1944. Div. 10-201.1-M23 

13. Nitrogen Surface Area Measurements on a Series of PCI 
Samples Subjected to Steam Activation for Various Periods 
of Time, P. H. Emmett and J. T. Kummer, NDRC 

10.5- 20, Mar. 1, 1944. Div. 10-202.13-M19 

14. The Production by Messrs. Sutcliffe, Speakman & Co., 
Ltd., of Briquetted Coal Charcoal on the Semi-bulk Scale, 
Porton Report No. 2453, Nov. 26, 1942. 

15. Zinc Chloride Activated Wood Charcoal, G. W. Heiseetal, 

OSRD 4324, Sept. 30, 1944. Div. 10-202.13-M24 

16. The Man ufacture of Activated Carbon, S. Hormats, TDMR 
1083, July 4, 1945. 

17. Studies of Impregnated Charcoals, H. F. Johnstone and 
G. L. Clark, OSRD 172, Nov. 8, 1941. 

Div. 10-202.14-M4 


18. A Study of Impregnated Charcoal, H. F. Johnstone and 
G. L. Clark, OSRD 1143, Dec. 9, 1942. 

Div. 10-202.143-M4 

19. Atlas Charcoal Plant, H. F. Johnstone, Memorandum to 
W. A. Noyes, Jr., Jan. 29, 1943. 

20. A Study of Pore Development and ASC Whetlerite Per¬ 
formance of Charcoals Prepared from Briquetted Coal, 
A. Juhola and T. Skei, NDRC 10.1-46, June 28, 1944. 

Div. 10-202.111-M3 

21. Determination of Pore Diameters in Charcoal, A. Juhola, 
NDRC 10.1-58, Jan. 24, 1945. Div. 10-202.111-M4 

22. Memorandum of Conference of Representatives of G. L. 
Cabot Company and Division 10, R. J. Kunz, Aug. 3, 1942. 

23. The ASC Whetlerization of Barnebey-Cheney Coquito Nuts, 
Peach Pits and English Walnut Shell Activated Charcoals, 
R. J. Kunz, Central Laboratory Job Report ECL-3, 
Nov. 19, 1943. 

24. Whetlerization of Atlas Apricot Pit Charcoals, R. J. Kunz, 
Central Laboratory Job Report W-7, Dec. 11, 1943. 

25. R. J. Kunz, MSR, June 15, 1944. Div. 10-200-M7 

26. R. J. Kunz, MSR, July 15, 1944. 

27. Activation of Charcoal, W. L. McCabe, NDRC LVIII, 
Carnegie Institute of Technology, Dec. 29, 1941. 

Div. 10-202.13-M2 

28. Activation of Charcoal. Effect of Varying Gas Mixture and 

Gas Temperatures, W. L. McCabe, NDRC LXXIII, 
Feb. 15, 1942. Div. 10-202.13-M4 

29. Preparation of Wood Charcoal, W. L. McCabe, OSRD 

1002, Oct, 21, 1942. Div. 10-202.12-M6 

30. Memorandum on Visit to Carlisle Lumber Company, W. L. 
McCabe, Mar. 8, 1943. 

31. Preparation of Wood Charcoal Suitable for Activation, W. L. 
McCabe et al, OSRD 1856, Sept. 29, 1943. 

Div. 10-202.12-M11 

32. Activation of Charcoal and of Anthracite, W. L. McCabe 

and R. York, Jr., NDRC LXXXVI, Carnegie Institute 
of Technology, Mar. 15, 1942. Div. 10-202.13-M5 

33. Activation of Charcoals by the Jiggler Process, R. J. Kunz 
and R. B. Rogge, OSRD 4283, Oct. 23, 1944. 

Div. 10-202.131-M13 

34. Properties of Gas Coke Samples, T. Skei, Central Labora¬ 
tory Job Report 58, Oct. 16, 1942. 

35. Properties of NRL-MP-60 Wood Char, T. Skei, Central 
Laboratory Job Report 61, Oct, 28, 1942. 

36. Properties of Kimberley Clark Carbons, T. Skei, Central 
Laboratory Job Report 74, Dec. 7, 1942. 

37. Whetlerizability of Saran Samples, T. Skei, Central Labo¬ 
ratory Job Report 89, Jan. 26, 1943. 

38. Cliffs-Dow Char, T. Skei, Central Laboratory Job Re¬ 
port 87, Jan. 26, 1943; ibid, No. 116, Apr. 24, 1943. 

39. Whetlerization and Surveillance Studies on PCI Charcoal 

at Various Stages of Activation, T. Skei, OSRD 4112, 
Sept. 9, 1944. Div. 10-202.13-M23 

40. Carbonization of Peach Pits and Their Preparation into 

ASC Whetlerite, B. A. White and R. J. Kunz, NDRC 

10.5-39, July 15, 1944. Div. 10-202.134-M4 

41. The Effect of A ir Carbonization in the PCC Charcoal Process 


SECRET 



BIBLIOGRAPHY 


649 


Upon the Whetlerite Qualities of the Adsorbent, B. A. White 
et al, OSRD 5115, May 24, 1945. Div. 10-202.14-M31 

42. Studies of the Preparation of Activated Charcoal Suitable 

for Whetlerization from Coconut Shells , B. A. White et al, 
OSRD 5116, May 24, 1945. Div. 10-202.134-M5 

43. The Effect of Primary Particle Size in the Processing of 

PCC Type Charcoal , B. A. White et al, OSRD 5234, 
June 21, 1945. Div. 10-202.18-M4 

44. The Reactivation in Oxygen of CWS Charcoals , T. F. 
Young, OSRD 4104, Sept. 7, 1944. Div. 10-202.132-M2 

45. A Laboratory Study of Activation, R. York, Jr., NDRC 

CXXXVI, June 15, 1942. Div. 10-202.13-M6 

46. Activation of Charcoal, R. York, Jr., NDRC CLXIV, 

July 15, 1942. Div. 10-202.13-M8 

47. Activation of Gas Charcoal by a New Jiggler Process, 
R. York, Jr., OSRD 956, July 31, 1942. 

Div. 10-202.131-M3 

48. Activation of Charcoal, R. York, Jr., Informal Progress 
Report Contract NDCrc-124, Aug. 15, 1942. 

49. Activation of Charcoal, R. York, Jr., Informal Progress 
Report Contract NDCrc-124, Oct. 15, 1942. 


50. Activation of Charcoal, R. York, Jr., Informal Progress 
Report Contract NDCrc-124, Nov. 15, 1942. 

51. Further Development of a Laboratory Type Jiggler for 
Activating Gas Charcoal, R. York, Jr., OSRD 1521, 
Carnegie Institute of Technology, June 17, 1943. 

Div. 10-202.131-M4 

52. Composition of Gases Evolved During Activation, R. York, 
Jr. et al, NDRC 10.4-30, Aug. 1, 1943. 

Div. 10-202.13-M16 

53. Activation of Carbonized Peach Pits and Black Walnut 

Shells in PCI Reports, R. York, Jr., NDRC 10.5-9, 
Dec. 15, 1943. Div. 10-202.134-M3 

54. Activation of Charcoal in a Boiling Bed Furnace, R. York, 
Jr., OSRD 4011, Aug. 12, 1944. Div. 10-202.13-M21 

55. Gas and Chemical Activation of Charcoal, R. York, Jr. 
et al, OSRD 5278, June 29, 1945. Div. 10-202.13-M26 

56. Effect of Pore Size and Pore Size Distribution on Perform¬ 
ance of ASC Whetlerite at High Humidities, J. W. Zabor 
and A. Juhola, NDRC 10.1-40, Feb. 11, 1944. 

Div. 10-202.111-M2 


Chapter 4 


1. Cyanogen Chloride II, W. M. Latimer, OSRD 363, Re¬ 
port 168, University of California, Jan. 21, 1942. 

Div. 10-202.152-M3 

2. Progress Report on L-ll Project 54, J. C. Elgin, Apr. 15, 

1941. 

3. A Search for New Reactants, F. E. Blacet and W. G. 
Young, OSRD 472, Mar. 12, 1942. Div. 10-202.141-M7 

4. A Study of the Physical Variables in the Production of 
Whetlerite and Silvered Whetlerite, F. E. Blacet, D. H. 
Volman, and R. P. Connor, OSRD 621, June 9, 1942. 

Div. 10-202.12-M3 

5. Miscellaneous Experiments with National Charcoals. The 

Minimum Requirements of CWSNC-1 Charcoal, F. E. 
Blacet, D. H. Volman, and G. J. Doyle, NDRC CCXXIV, 
Nov. 10, 1942. Div. 10-202.14-M17 

6. Adsorption of Constituents from a Standard Whetlerizing 
Solution, F. E. Blacet, D. H. Volman, and G. J. Doyle, 
NDRC CCXXIII, Nov. 5, 1942. Div. 10-202.14-M16 

7. The Adsorption of Silver on Charcoal from Whetlerizing 

Solution, F. E. Blacet, D. H. Volman, and G. J. Doyle, 
NDRC CXX, May 18, 1942. Div. 10-202.14-M9 

8. The Minimum Silver Requirements for Different Activated 

Charcoals, F. E. Blacet and D. H. Volman, NDRC 
CLXVIII, July 28, 1942. Div. 10-202.14-M13 

9. Experiments with Type AS Whetlerites at Fostoria, Colum¬ 

bus, and Zanesville, Ohio, F. E. Blacet, OSRD 1126, 
Dec. 9, 1942. Div. 10-202.1-M7 

10. An Investigation of the Possible Explosion Hazard Pre¬ 
sented by Silver Whetlerizing Solutions and Residues, F. E. 
Blacet and D. H. Volman, OSRD 1527, June 21, 1943. 

Div. 10-202.14-M26 

11. A Study of Impregnated Charcoal by X-Ray Diffraction 

Methods, H. F. Johnstone and G. L. Clark, OSRD 1143, 
Dec. 9, 1942. Div. 10-202.143-M4 

12. Composition of Gases Evolved from Drying Whetlerites, 

F. E. Blacet and D. H. Volman, OSRD 1201, NDRC 
10.1-4, Jan. 4, 1943. Div. 10-202.14-M20 


13. A Study of the Partial Vapor Pressures of the Volatile Con¬ 
stituents in Whetlenzing Solutions, F. E. Blacet and D. H. 
Volman, OSRD 1351, Apr. 20, 1943. 

Div. 10-202.19-M3 

14. An Additional Study of the Partial Vapor Pressures of the 
Volatile Constituents in Whetlerizing Solutions, F. E. 
Blacet and D. H. Volman, OSRD 1626, July 3, 1943. 

Div. 10-202.14-M27 

15. C. G. Aging of Type AS and ASC Whetlerites, F. E. Blacet, 

W. C. Pierce, T. Skei, R. K. Brinton, OSRD 1691, Aug. 
6, 1943. Div. 10-202.16-M12 

16. The Absorption of HCN by Whetlerites and Other Ab¬ 
sorbents, E. O. Wiig, L. V. M’Carty, H. Scoville, N. L. 
Morse, F. Zimer, NDRC CLXXXIV, Sept. 15, 1942. 

Div. 10-202.154-M26 

17. The Removal of HCN and C 2 N 2 by Absorbents, E. O. Wiig, 
L. V. M’Carty, H. Scoville, N. L. Morse, F. Zimor, 
NDRC CCXVIII, Nov. 23, 1942. Div. 10-202.154-M29 

18. Absorption of AC, C 2 H 2 and SA by Whetlerites and Other 
Absorbents, E. O. Wiig, L. V. M’Carty, H. Scoville, N. L. 
Morse, F. Zimor, NDRC CCIII, Oct. 15, 1942. 

Div. 10-202.154-M28 

19. The Effect of Impregnation on the Removal of Ethylene 
Irnine. Break Times for Di-, Tri-, and Penta Methylene 
Imines, P. A. Leighton, NDRC LXX. 

Div. 10-202.14-M33 

20. Behavior of Sulfur Dioxide and Several Other Gases on 

Whetlerite, P. A. Leighton, NDRC CXXXVII, June 15, 
1942. Div. 10-202.156-M14 

21. A Summary of Tests on Soda Lime, W. C. Pierce, OSRD 

970, Oct. 21, 1942. Div. 10-202.2-M4 

22. Preliminary Study of Hexamine Impregnation, F. E. 
Blacet and J. G. Roof, NDRC CXXII, May 22, 1942. 

Div. 10-202.141-M9 

23. The Preparation and Suneillance of Hexamethylene Texa¬ 

mine Impregnated Charcoals, F. E. Blacet and J. G. Roof, 
OSRD 1352, Apr. 20, 1943. Div. 10-202.14-M23 


SECRET 



650 


BIBLIOGRAPHY 


24. The Deterioration of Thiocyanate Whetlerites, W. M. 
Latimer, OSRD 132, Sept. 8, 1941. Div. 10-202.16-M2 

25. I. Solubility of AgSCN in Whetlerizing Solutions; II. The 

Adsorption of Ag + and SCN~ by Charcoals from Solu¬ 
tions, F. E. Blacet and D. H. Volman, NDRC CLXXVII, 
Aug. 3, 1942. Div. 10-202.14-M14 

26. A Study of Thiocyanate Treated Whetlerites, F. E. Blacet 
and T. Skei, NDRC CCX, Sept. 17, 1942. 

Div. 10-202.14-M 15 

27. Summary of Test Data on E-6 Whetlerite, W. C. Pierce 
and J. W. Zabor, NDRC CIX, May 9, 1942. 

Div. 10-202.16-M5 

28. Catalysis, Berkmann, Morrell, Egloff, Reinhold Pub. Co. 

1940. 

29. Cyanogen Chloride, W. M. Latimer, OSRD 102, June 16, 

1941. Div. 10-202.152-MI 

30. Behavior of Hopcalite, Whetlerites, etc. toward CK, W. M. 

Latimer, H. W. Anderson, and H. Kerlinger, NDRC 
LXVI, Jan. 15, 1942. Div. 10-202.152-M2 

31. Stability of CK. Constants for Various Charcoals, W. M. 

Latimer, H. W. Anderson, and H. Kerlinger, NDRC CII, 
Apr. 14, 1942. Div. 10-202.152-M4 

32. The Use of Mercury Compounds in the Impregnation of 
Activated Charcoal, F. E. Blacet, R. J. Grabenstetter, and 
C. H. Simonson, OSRD 629, May 25, 1942. 

Div. 10-202.141-M10 

33. Iodine, Halogen Acids, and Their Salts as Charcoal Im¬ 
pregnants, F. E. Blacet, R. J. Grabenstetter, and C. H. 
Simonson, NDRC CLXIII, July 27, 1942. 

Div. 10-202.141-M 11 

34. Analytical Chemistry of Industrial Poisons, M. B. Jacobs, 
Reinhold Publishing Co. 

35. A Study of the Poisoning of Various Absorbents toward 
Arsine by HCN, E. O. Wiig, OSRD 628, June 6, 1942. 

Div. 10-202.154-M22 

36. The Effect of Impregnation on the Absorption of Ethylene 

Imine and Other Basic Materials, P. A. Leighton, NDRC 
LXX. Div. 10-202.14-M33 

37. Summary of Protection Data on Ethylene Imine, P. A. 
Leighton, NDRC LXXII, Jan. 23, 1942. 

Div. 10-202.156-M7 

38. Studies of Absorbents, P. A. Leighton, NDRC LXXXVIII, 

Mar. 15, 1942. Div. 10-202.151-M3 

39. Ethylene Imine; Polymerization; Thermal Effects, etc., P. A. 
Leighton, NDRC CVI, Apr. 15, 1942. 

Div. 10-202.156-M10 

40. One-Step Impregnation with Whetlerizing Solutions Con¬ 

taining Copper, Silver, and Either Molybdenum, Vanadium 
or Tungsten, F. E. Blacet and R. J. Grabenstetter, NDRC 
CLXXVI, Aug. 5, 1942. Div. 10-202.141-M12 

41. One-Step Impregnation with Copper, Silver, and Either 

Molybdenum, Vanadium, or Zinc, F. E. Blacet, R. J. 
Grabenstetter, and C. H. Simonson, NDRC CCXXV, 
Nov. 10, 1942. Div. 10-202.141-M 15 

42. Progress Report on ASM Whetlerite, E. O. Wiig, OSRD 

1455, May 25, 1943. Div. 10-202.12-M9 

43. Type ASMT Whetlerite Prepared in Rotary Driers, 

Laboratory Scale, E. O. Wiig, F. E. Blacet, et ai, OSRD 
1693, Aug. 6, 1943. Div. 10-202.12-M10 


44. An Investigation of the Applicability of ASC Type Whetler¬ 
izing Equipment to the Preparation of ASM Whetlerite, 
R. J. Kunz, NDRC 10.5-28, Mar. 15, 1944. 

Div. 10-202.12-M13 

45. Progress Report on ASCM Whetlerite, E. O. Wiig, H. 
Scoville, et al, OSRD 1454, May 25, 1943. 

Div. 10-202.1-M11 

46. Preparation and Properties of A5F Whetlerites, E. O. 
Wiig, H. Scoville, et al, OSRD 1912, Oct. 13, 1943. 

Div. 10-202.12-M12 

47. Picoline as Impregnant for Gas Mask Absorbents, E. O. 
Wiig, OSRD 3130, Jan. 15, 1944. Div. 10-202.141-M 17 

48. One-Step Impregnation with Whetlerizing Solutions Con¬ 

taining Copper, Silver and Chromium, F. E. Blacet, R. J. 
Grabenstetter, and C. H. Simonson, NDRC CXCVI, 
Oct. 15, 1942. Div. 10-202.141-M 14 

49. Determination of Pore Diameters in Charcoals, F. E. Blacet 
and A. Juhola, NDRC 10.1-58, Jan. 24, 1945. 

Div. 10-202.111-M4 

50. Second Report on the Use of Copper, Silver and Chromium 
Solutions as Charcoal Impregnants, F. E. Blacet et al, 
NDRC CCXXII, Dec. 21, 1942. Div. 10-202.141-M 16 

51. Study of Zinc Chloride Carbon I, G. W. Heise and J. A. 

Slyh, NDRC 10.5-11, Dec. 10, 1943. See also NDRC 
10.5-15, -17, -22, -29, -32, -38, -39, -43, -46 for more data 
on zinc chloride carbons. Div. 10-202.133-Ml 

Div. 10-202.13-M18 

Div. 10-202.134-M4 

52. Preliminary Report on the Aging of ASC Whetlerite under 
Various Atmospheres in Sealed Systems, F. E. Blacet, 
J. G. Roof, J. N. Pitts, NDRC 10.1-29, Sept. 22, 1943. 

Div. 10-202.16-M14 

53. The State of Impregnants on ASC Charcoal. Magnetic 
Susceptibility Studies, I. M. Klotz and R. J. Grabenstetter, 
NDRC 10.1-39, Jan. 28, 1944. Div. 10-202.141-M 18 

54. Optimum Operating Conditions for a Laboratory Size 
Rotary Batch ASC Whetlerite Drier, L. C. Weiss and 
G. L. Pratt, Central Laboratory Job Report ECL-7, 
Dec. 28, 1943. 

55. Additional Study of the Partial Vapor Pressure of the Vola¬ 
tile Constituents in Whetlerizing Solutions, F. E. Blacet 
and D. H. Volman, NDRC 10.1-16, July 3, 1943. 

Div. 10-202.14-M27 

56. Reactions Involving Chromium which Occur when ASC 

Whetlerizing Solution is in Contact with Charcoal, F. E. 
Blacet, D. H. Volman, G. J. Doyle, NDRC 10.1-17, 
June 11, 1943. Div. 10-202.14-M25 

57. Effect of Moisture on 5-4, AC, and CK Tube Lives for Two 

Type ASC Whetlerites, F. E. Blacet and T. Skei, NDRC 
CCXXI, Dec. 10, 1942. Div. 10-202.17-M6 

58. Second Report on the Aging of ASC and ASCP Whetlerite 

Containing Various Amounts of Water in Sealed Systems, 
F. E. Blacet, J. G. Roof, J. N. Pitts, NDRC 10.1-36, 
Nov. 12, 1943. Div. 10-202.17-M8 

59. Surveillance of Base Charcoals, F. E. Blacet, R. J. Graben¬ 
stetter, C. H. Simonson, NDRC 10.1-25, Aug. 10, 1943. 

Div. 10-202.16-M13 

60. The Reactivation in Oxygen of CWS Charcoals, T. F. 

Young, S. W. Weller, S. L. Simon, M. G. Buck, OSRD 
4104, Aug. 4, 1944. Div. 10-202.132-M2 


SECRET 



BIBLIOGRAPHY 


651 


61. Surveillance Studies on Whetlerites at Northwestern Uni¬ 

versity. A Summary of Work from 1942 to 1944, T. Skei, 
OSRD 4346, Nov. 15, 1944. Div. 10-202.16-M20 

62. Adsorption of Cyanogen by Charcoal. Amine Impregnated 
Charcoals, W. M. Latimer, H. W. Anderson, H. Iverlinger, 
NDRC CXLIX, June 15, 1942. Div. 10-202.152-M5 

63. Impregnated Charcoal. Specific Impregnants for Increasing 
CC Protection, F. E. Dolian and S. Hormats, TDMR 767, 
Nov. 12, 1943. 

64. The Use of Pyridine and Picoline in Gas Mask Charcoals, 

L. C. Weiss, G. L. Pratt, et al, NDRC 10.1-56, Nov. 16, 
1944. Div. 10-201.1-M32 

65. S ummary of Pilot Plant St udies of the Preparation of A SC 

Whetlerite, R. J. Kunz, E. H. Conroy, et al, OSRD 4129, 
Sept. 14, 1944. Div. 10-202.12-M14 

66. Design and Construction of the Whetlerization Pilot Plant 

at the NDRC Division 10 Central Laboratory, R. J. Kunz, 
OSRD 1778, Sept. 6, 1943. Div. 10-202.14-M29 

67. The Effect of Backfceding on the Quality of ASC Whetlerite, 

R. J. Kunz and E. H. Conroy, NDRC 10.5-30, May 6, 
1944. Div. 10-202.19-M5 

68. Reclamation of Type A Whetlerite, R. J. Kunz and E. H. 
Conroy, NDRC 10.5-23, Mar. 9, 1944. 

Div. 10-202.19-M4 

69. Leaching and Rewhetlerization: Their Effect on Whetlerite 
Quality, L. C. Weiss, H. Waggoner, and M. Bierman, 
NDRC 10.1-54, Sept. 18, 1944. Div. 10-202.16-M18 

70. Use of Aminated Phenol-Formaldehyde Xerogels as Gas 
Adsorbents, G. F. Mills, OSRD 1771, Sept. 4, 1943. 

Div. 10-202.21-M6 

71. Further Studies on the Characteristics and Impregnation of 
Aminated Phenol-Formaldehyde Xerogels, P. A. Leighton 
and S. W. Grinnell, NDRC CCXI, Nov. 15, 1942. 

Div. 10-202.21-M2 

72. Use of Amine Resins as Gas Adsorbents, G. F. Mills, 

NDRC 10.4-46, Jan. 20, 1944. Div. 10-202.21-M7 

73. Catalysts for the Oxidation of Carbon Monoxide in Air, 
R. N. Pease, OSRD 3071, Jan. 4, 1944. 

Div. 10-202.2-M6 

74. Journal of Industrial and Engineering Chemistry, Bray 
and Fraser, 1920. 

75. X-Ray Studies in Whetlerites, H. F. Johnstone and G. L. 
Clark, NDRC CLXXVIII, Aug. 15, 1942. 

Div. 10-202.143-M3 

76. Charcalite, a Calcium Chloride Impregnated Charcoal Dry¬ 

ing Agent, R. N. Pease and J. H. McLean, OSRD 3776, 
June 15, 1944. Div. 10-202.142-M2 

77. An Exploratory Study of Carbon Monoxide Protection on 
Charcoal and Other Carriers, D. H. Volman and G. J. 
Doyle, NDRC 10.1-41, Feb. 7, 1944. Div. 10-202.153-MI 

78. Factors in Canister Design, I. M. Klotz and H. Cutforth, 

OSRD 5239, June 7, 1945. Div. 10-202.156-M20 

79. Conversion of Types A and AS Impregnated Charcoals to 
Type ASC Impregnated Charcoal, S. Hormats and B. M. 
Zeffert, TDMR 824, Apr. 18, 1944. 

80. Conversion of Types A and AS Impregnated Charcoals to 
Type ASC Impregnated Charcoals in Laboratory Pilot 
Plant, R. A. Fisher and E. Croft, Jr., TDMR 833, Apr. 22, 
1944. 

81. Relative Ignition Temperatures of Impregnated Charcoals, 
F. E. Dolian, TDMR 897, Sept. 22, 1944. 


82. Reworking Impregnated Charcoals, R. A. Fisher, J. Y. G. 
Walker, Jr., and E. Croft, Jr., TDMR 976, Jan. 30, 1945. 

83. The Protection Afforded by Respirators Against Cyanogen 
Chloride, and the Improvement Effected by Pyridine Im¬ 
pregnation of the Charcoal Filling, Ptn. 4221 (T. 10533A), 
Aug. 10, 1943. 

84. Impregnated Charcoal. Pyridine as an Impregnant, F. E. 
Dolian, B. Zeffert, and S. Hormats, TDMR 727, Aug. 23, 
1943. 

85. Use of Pyridine in the Preparation of a Whetlerite with In¬ 
creased CC Protection, S. N. Naldrett, Chemical Warfare 
Laboratories, Ottawa, Research Section Report No. 30, 
Sept. 15, 1943. 

86. Impregnation of Charcoal with A mines to Improve Cyanogen 
Chloride Protection. S. N. Naldrett, Chemical Labora¬ 
tories, Ottawa, Research Section Report No. 29, Oct. 15, 
1943. 

87. Type ASCP Impregnated Charcoal, S. Hormats and B. M. 
Zeffert, TDMR 803, Feb. 19, 1944. 

88. Whetlerite Process Development. Experimental Production 
of Type Ell Impregnated Charcoal at Zanesville CWS 
Plant, F. E. Dolian and B. M. Zeffert, TDMR 818, 
Mar. 27, 1944. 

89. Reactants for CC, R. P. Graham and R. G. Davis, McMas- 
ter University, C. E. 160, June 15, 1944. 

90. The Properties of Coppered Coal Charcoals Containing 
(a) Molybdenum (b) Pyridine, Oxford University, Re¬ 
search Report No. 44.19 (Z. 12697), Sept. 22, 1944. 

91. Protection Against Cyanogen Chloride. Charcoal Impreg¬ 
nated with Pyridine, Pin. 4221 (T. 4868), (Y. 3228), 
Apr. 12, 1943. 

92. Improved Impregnated Charcoal. Preparation and Test of 
Whetlerites Containing Sodium Hydroxide and Amines, 
J. C. Goshorn and P. O. Rockwell, EATR 153, May 29, 

1934. 

93. Service Canister (10). Development of a Manufacturing 
Process for Impregnated Charcoal E6, P. A. Hartman, 
EATR 326, Aug. 2, 1940. 

94. Impregnated Charcoal Type A and E-6. Effect of Impu¬ 
rities in Base Charcoal, S. Hormats, TDMR 295, Sept. 5, 
1941. 

95. Adsorption Characteristics of Charcoal Impregnated with 
Thiocyanate, R. S. Brown, C. E. 87, Dec. 15, 1941. 

96. Chemical Warfare Monograph, Vol. 47, June 1919. 

97. H. V. Wright, EACD 438, November 1927. 

98. Anti-Gas Dept. Weekly Reports for Project D 1.1-14, 
1927-28. 

99. R. S. Brown and J. G. Hartnett, EATR 200, December 

1935. 

100. R. S. Brown and J. B. Hartnett, EATR 220, April 1936. 

101. Compilation of No and \ c Values for Miscellaneous Whet¬ 
lerites before and After Aging, D. B. Ehrlinger, L. C. 
Weiss, G. L. Pratt, J. B. Fehrenbacher, J. W. Zabor, and 
T. Skei, NDRC 10.1-48, Aug. 12, 1944. 

Div. 10-202.16-M 17 

102. Manufacture of Whetlerite in the Experimental Plants, 
H. V. Wright and F. Bellinger, EACD 510, Apr. 8, 1929. 

103. Impregnated Charcoal Type A, Improved. Copper Am¬ 
monium Carbonate Impregnating Solution, S. Hormats, 
F. C. Whitney, and S. C. Malkiewicz, TDMR 275, 
Apr. 15, 1941. 


SECRET 



652 


BIBLIOGRAPHY 


104. Studies on Arsine Protection, W. C. Pierce, B. M. Abra¬ 
ham, and H. G. Monteith, NDRC XL, Oct. 25,1941. 

105. Performance of Canisters after Wearing Tests at Camp 
Sibert, Alabama , W. C. Pierce, J. W. Zabor, and H. S. 
Joseph, OSRD 3058, Dec. 31, 1943. 

Div. 10-201.1-M22 


106. Nickel Impregnated Charcoal , L. Williams, C. E. 21, 
Dec. 15, 1941. 

107. Study of Impregnation , J. C. Elgin, OSRD 586, Apr. 9, 

1942. Div. 10-202.14-M7 

108. Impregnation of Activated Charcoals to Obtain High SA 
Lives , A. P. Colburn, OSRD 853, Sept. 1, 1942. 

Div. 10-202.141-M13 


Chapter 5 


1 . Surveillance Studies on Whetlerites at Northwestern Uni¬ 

versity — A Summary of Work from 1942-1944, T. Skei, 
OSRD 4346, Nov. 15, 1944. Div. 10-202.16-M20 

2 . Preliminary Report on the Aging of ASC Whetlerite under 
Various Atmospheres in Sealed Systems, J. G. Roof, F. E. 
Blacet, et al, NDRC 10.1-29, Sept. 22, 1943. 

Div. 10-202.16-M14 

3. Second Report on the Aging of ASC and ASCP Whetlerite 

Containing Various Amounts of Water in Sealed Systems, 
J. G. Roof, F. E. Blacet, et al, NDRC 10.1-36, Nov. 12, 

1943. Div. 10-202.17-M8 

4. Performance of Canisters After Wearing Tests at Camp 

Sibert, W. C. Pierce, J. W. Zabor, and H. S. Joseph, 
OSRD 3058, Dec. 31,'1943. Div. 10-201.1-M22 

5. Additional Surveillance Tests on Canisters Used in the First 
Sibert Surveillance Study, T. Skei, OSRD 4015, July 1944. 

Div. 10-201.1-M29 

6 . Performance of M10 and M9A2 Canisters After Regular 
Use at Camp Sibert, Alabama, T. Skei, J. W. Fehren- 
bacher, and H. S. Joseph, OSRD 4014, July 1944. 

Div. 10-201.1-M28 

7. Canister Surveillance Studies, I, T. Skei, R. K. Brinton, 
and W. C. Pierce, NDRC 10.1-32, October 1943. 

Div. 10-201.1-M17 

8 . Whetlerization and Surveillance Studies on PCI Charcoal 

at Varying Stages of Activation, T. Skei, OSRD 4112, 
Sept. 9, 1944. Div. 10-202.13-M23 

9. Surveillance of Types ASC and ASCM Whetlerites, E. O. 
Wiig, et al, OSRD 1873, Oct. 1, 1943. Div. 10-202.16-M15 

10. Picoline as Impregnant for Gas Mask Absorbents, E. O. 
Wiig, et al, OSRD 3130, Jan. 15, 1944. 

Div. 10-202.141-M17 

11. Impregnated Charcoal. Pyridine as an Impregnant , F. E. 
Dolian, B. Zeffert, and S. Hormats, TDMR 727, Aug. 23, 
1943. 


12. Impregnated Charcoal. Stability of Type ASC Impregnated 
Charcoal, F. E. Dolian, B. Zeffert, and S. Hormats, 
TDMR 714, Aug. 7, 1943. 

13. Comparative Evaluation of Types ASC, ASM, and ASV 
Impregnated Charcoals, B. M. Zeffert and S. Hormats, 
TDMR 765, Nov. 10, 1943. 

14. Impregnated Charcoal. Specific Impregnants for Increasing 
CC Protection, F. E. Dolian and S. Hormats, TDMR 767, 
Nov. 12, 1943. 

15. Surveillance of ASC Impregnated Charcoal, Series 1, 
P. C. I. Base Charcoal Impregnated at Edgewood Arsenal 
in April 1943, H. J. Allison, Jr., TDMR 799, Jan. 28, 

1944. 

16. Type ASCP Impregnated Charcoal, S. Hormats and B. M. 
Zeffert, TDMR 803, Feb. 19, 1944. 

17. Whetlerite Process Development. Experimental Production 
of Type Ell Impregnated Charcoal at Zanesville C. W. S. 
Plant, F. E. Dolian and B. M. Zeffert, TDMR 818, 
Mar. 27, 1944. 

18. Compilation of No and \ c Values for Miscellaneous Whetler¬ 

ites Before and After Aging, T. Skei, et al, OSRD 4013, 
Aug. 12, 1944. Div. 10-202.16-M17 

19. Surveillance Tests on ASC, Ell, and E13 Whetlerites , T. 
Skei, OSRD 4232, Oct. 12, 1944. Div. 10-202.16-M19 

20. Performance of M10, M10A1 , and MlAl Canisters After 
Use in the Southwest Pacific Area, J. B. Fehrenbacher, 
F. E. Blacet, et al, OSRD 4928, Apr. 12, 1945. 

Div. 10-201.1-M35 

21. The Preparation and Surveillance of Hexamethylenetetra¬ 

mine-Impregnated Charcoals, J. G. Roof and F. E. Blacet, 
OSRD 1352, Apr. 20, 1943. Div. 10-202.14-M23 

22. The Use of Pyridine and Picoline in Gas Mask Charcoal, 
L. C. Weiss, et al, NDRC 10.1-56, Nov. 16, 1944. 

Div. 10-201.1-M32 


Chapter 6 


1. Brunauer and P. H. Emmett, J. Am. Chem. Soc., 57, 
1935, p. 1754. 

2. P. H. Emmett and Brunauer, ibid., 59, 1937, p. 1553. 

3. Brunauer, P. H. Emmett, and Teller, ibid., 60, 1938, 
p. 309. 

4. Harkins and Jura, ibid., 66, 1944, pp. 919, 1362. 

5. Harkins and Jura, ibid., 66, 1944, p. 1366. 

6. P. H. Emmett, ibid., 68, 1946, p. 1784. 

7. P. H. Emmett and DeWitt, Ind. Eng. Chem., Anal. Ed., 
13, 1941, p. 28. 

8. P. H. Emmett in Kraemer’s Advances in Colloid Science, 
Interscience Publishers, New York, 1942, pp. 1-36. 


9. “Symposium in New Methods for Particle Size Deter¬ 
mination,” P. H. Emmett, Am. Soc. for Testing Materials, 
1941, p. 95. 

10. Cassie, Trans. Faraday Soc., 41, 1945, p. 450. 

11. Hill, J. Chem. Physics (to be published). 

12. P. H. Emmett, Ind. Eng. Chem., 37, 1945, p. 639. 

13. Deitz and Gleysteen, J. Research Natl. Bur. Standards, 
29, 1942, p. 191. 

14. Joyner, Weinberger, and Montgomery, J. Am. Chem. 
Soc., 67, 1945, p. 2182. 

15. Pickett, J. Am. Chem. Soc., 67, 1943, p. 1938. 

16. Hill, ibid., 68, 1946, p. 535. 


SECRET 



BIBLIOGRAPHY 


653 


17. Survey of Pore Structure in Charcoal, A. Juhola, OSRD 

5500, June 1945. Div. 10-202.111-M5 

a. E. O. Wiig, Madison, and A. Juhola, Monthly Progress 
Report to CWS Feb. 1, 1946. 

18. Beebe, Beckwith, and Honig, J. Am. Chem. Soc. f 67, 1943, 
p. 1554. 

19. Schmidt, Z. physik. Chem., 133, 1928, p. 280. 

20. P. H. Emmett and DeWitt, J. Am. Chem. Soc., 65, 1943, 
p. 1253. 

21. Barrer, J. Soc. Chem. Ind., 64, 1945, p. 130. 

22. Barrer and Ibbitson, Trans. Faraday Soc., 40, 1944, 
pp. 195, 206. 

23. Absorption and Surface Area Measurements on Whetlerites 
and Charcoal Samples, P. H. Emmett, H. A. Pohl, J. 
Holmes, and J. T. Rummer, OSRD 1777, Sept. 6, 1943. 

Div. 10-202.15-M18 
a. Physical Adsorption, Brunauer, Princeton Press, 1941, 
p. 444. 

24. Physical Chemistry of Activation of Charcoal, T. F. Young, 

OSRD 5354, July 21, 1945. Div. 10-202.13-M27 

25. Lemieux and Morrison, Canadian Report C. E. 151, 
Sept. 20, 1943. 

a. P. H. Emmett, J. Holmes, and J. T. Rummer, NDRC 

10.1-1, Dec. 15, 1942. Div. 10-202.15-M11 

b. P. H. Emmett, J. Holmes, H. A. Pohl, and J. T. Rum¬ 
mer, NDRC 10.4-26, May 27,1943. Div. 10-202.15-M16 

26. Absorption of Nitrogen on CWSN Base Charcoals, P. H. 

Emmett, J. Holmes, J. T. Rummer, and Mace, NDRC 
10.5-3, Sept. 11, 1943. Div. 10-202.11-M8 

27. P. H. Emmett, J. Holmes, H. W. Anderson, J. T. Rum¬ 
mer, Mace, and Jenkins, OSRD 5065, May 30, 1945. 

Div. 10-202.15-M 19 

28. Determination of Pore Diameters in Charcoal, A. Juhola 
and F. E. Blacet, NDRC 10.1-58, Jan. 24, 1945. 

Div. 10-202.111-M4 

29. A. Juhola and T. Skei, NDRC 10.1-46, June 28, 1944. 

Div. 10-202.111-M3 

30. P. H. Emmett, J. Holmes, and J. T. Rummer, NDRC 

CLXXIX, Aug. 15, 1942. Div. 10-202.15-M11 

32. P. H. Emmett, J. Holmes, J. T. Rummer, Mace, and 
H. W. Anderson, OSRD 4959, Apr. 20, 1945. 

Div. 10-202.17-M9 

33. Lawson, Trans. Faraday Soc., 32, 1936, p. 473. 

34. Polanyi and Goldman, Z. physik. Chem., 132, 1928, p. 321. 

35. Rate of Sorption of Water Vapor from Humid Air Streams 
by Activated Carbons, A. P. Colburn, OSRD 849, Sept. 1, 
1942. 

36. A. P. Colburn, NDRC Cl, Apr. 15, 1942. 

Div. 10-202.17-M3 

37. A. P. Colburn, NDRC CXXXIII, June 17, 1942. 

Div. 10-202.17-M5 

38. Lowry, J. Am. Chem. Soc., 46, 1929, p. 824. 

39. Coolidge, ibid., 48, 1926, p. 1795. 

40. McBain, Porter, and Sessions, ibid., 55, 1933, p. 2294. 

41. Sorption of Gases and Vapors by Solids, McBain, G. 
Routledge & Sons, London, 1932. 

42. P. H. Emmett and H. W. Anderson, J. Am. Chem. Soc., 
67, 1945, p. 1492. 

43. Fineman, Guest, and McIntosh, Canadian Report C. E. 
147, Nov. 20, 1943. See also Can. J. Research, 24B, 1946, 
p. 109. 


44. A Treatise on Physical Chemistry, edited by H. S. Taylor, 
D. Van Nostrand Co., Rraemer, Chapter XX, p. 1661. 

45. Cohan, J. Am. Chem. Soc., 60, 1938, p. 433. 

46. Morrison and McIntosh, Canadian Report C. E. 147, 
Aug. 8, 1944. See also Can. J. Research, 24B, 1946, p. 137. 

47. H. F. Johnstone and G. L. Clark, NDRC LXXXIX, 

Apr. 9, 1942. Div. 10-202.17-M2 

50. Washburn, Proc. Nat. Acad. Sci., 7, 1921, p. 115. 

51. Lamb and Woodhouse, J. Am. Chem. Soc., 58, 1930, 
p. 2637. 

52. P. H. Emmett, H. A. Pohl, and J. T. Rummer, NDRC 

CXXIII, May 15, 1942. Div. 10-202.15-M11 

53. Brunauer, Deming, Deming, and Teller, J. Am. Chem. 
Soc., 62, 1940, p. 1723. 

54. Beeck, Reviews of Modern Physics, 17, 1945, p. 61. 

55. Anderson, Z. phys. Chem., 88, 1914, p. 191. 

56. Foster, Trans. Faraday Soc., 28, 1932, p. 645. 

57. National Carbon Co., NDRC 10.5-34, June 10, 1942. 

Div. 10-202.13-M18 

58. National Carbon Co., NDRC 10.5-43, Aug. 10, 1944. 

Div. 10-202.13-M 18 

59. National Carbon Co., MSR, Sept. 15, 1944. 

61. Ritter and Drake, Ind. Eng. Chem., Anal. Ed., 17, 1945, 
p. 782. 

62. Drake and Ritter, ibid., p. 787. 

63. P. H. Emmett, MSR, Mar. 15, 1944. Div. 10-202.1-M8 

64. J. W. Zabor and A. Juhola, NDRC 10.1-40, Feb. 11, 1944. 

Div. 10-202.111-M2 

65. P. H. Emmett, NDRC LII, Dec. 22, 1941. 

Div. 10-202.13-M3 

66. P. H. Emmett, NDRC CLXXIX, Aug. 15, 1942. 

Div. 10-202.15-M 11 

68. F. E. Blacet and T. Skei, NDRC 10.1-8, Mar. 12, 1943. 

Div. 10-202.13-M 10 

69. P. H. Emmett and J. Holmes, NDRC 10.5-12, Nov. 12, 

1943. Div. 10-202.111-MI 

70. Dewey and Lefforge, Ind. Eng. Chem., 24, 1932, p. 1045. 

71. Lowry and Hulett, J. Am. Chem. Soc., 42, 1920, p. 1393. 

72. Lowry and Hulett, ibid., p. 1408. 

73. T. F. Young, OSRD 4104, Sept. 7, 1944. 

Div. 10-202.132-M2 

74. Lambert, Trans. Faraday Soc., 32, 1926, p. 452. 

75. Rhead and Wheeler, J. Chem. Soc., 103, 1913, p. 461. 

76. Lepin, Physik. Z. Sowjetumon, 4, 1933, p. 282. 

77. Schilow, Schatanowskaja, and Tschmutow, Z. physik. 
Chem., 150, 1930, p. 31. 

78. Schilow, Schatanowskaja, and Tschmutow, Z. physik.. 
Chem., A 149, 1930, p. 211. 

79. Ring, J. Chem. Soc., 1937, p. 1489. 

a. Shah, /. Chem. Soc., 1929, pp. 2661, 2676. 

80. Barrer, J. Chem. Soc., 1936, p. 1261. 

a. Stock, Z. Anorg. Chem., 195, 1931, p. 158. 

81. P. H. Emmett, NDRC 10.1-1, Jan. 13, 1943. 

Div. 10-202.15-M 11 

82. Reyes and Marshall, J. Am. Chem. Soc., 44, 1927, p. 152. 

83. Blench and Garner, J. Chem. Soc., 1924, p. 1288. 

84. Marshall and Maclnnes, Can. J. of Res., 15B, 1937, p. 75. 

85. Aharoni and Simon, Z. physik. Chem., B4, 1929, p. 175. 

86. Juza and Langheiss, Z. Elektrochemie, 45, 1939, p. 689. 

87. Analysis of Base Charcoals, E. O. Wiig and J. F. Flagg, 

NDRC 10.1-26, June 1943. Div. 10-202.11-M7 


SECRET 




654 


BIBLIOGRAPHY 


88. Brunner, Z. Elektrochemie, 38, 1932, p. 58. 

89. Surveillance of Base Charcoals , F. E. Blacet et al, NDRC 

10.1-25, Aug. 10, 1943. Div. 10-202.16-M13 

90. Allmand, J. Phys. Chem., 33, 1929, p. 1682 a. 

91. Allmand, Proc. Roy. Soc. (London), 1294, 1930, p. 235. 

92. Allmand, Proc. Roy. Soc. (London), 130A, 1930, p. 193. 

93. Allmand, Proc. Roy. Soc. (London), 134A, 1932, p. 554. 

94. Allmand, Proc. Roy. Soc. (London), 1694, 1938, p. 25. 

95. Allmand, Trans. Faraday Soc., 28, 1932, p. 225. 

96. Muller and Cobb, J. Chem. Soc., 1940, p. 177. 

97. Stenhouse, Ann. der chem. Pharm., 101, 1897, p. 243. 

98. Vander Ley and Wibaut, Rev. trav. chim., 51, 1932, 
p. 1143. 

99. Bente and Walton, J. Phys. Chem., 47, 1943, p. 329. 

100. Ruff, Kolloid Z., 37, 1935, p. 270. 

104. Stratton and Winkler, Ind. Eng. Chem., 34, 1942, p. 603. 

105. J. T. Rummer, Thesis, The Johns Hopkins University, 
Dept. Chem. Eng. (1946). 

109. London, Z. physik. Chem., Bll, 1930, p. 222. 

110. Denbigh, Trans. Faraday Soc., 36, 1940, p. 936. 

111. Studies on Activated Charcoals and Whetlerite, P. H. 
Emmett, NDRC LII, Dec. 22, 1941. Div. 10-202.13-M3 

112. Ferguson, Sheffer, and Waldock, Canadian Report, 
C E. 107-20, Apr. 10, 1942. 

113. Ferguson and Barnartt, Canadian Report C. E. 107, 
Report No. 3, III-1-763, Apr. 12, 1943. 

114. Ferguson and Barnartt, Canadian Report, C. E. 107, 
III-1-1519, Mar. 6, 1944. 

a. Stevens, Canadian Report, C. E. 161, Report No. 2, 
III-1-1625, May 16, 1944. 

115. Study of Zinc ; Chloride Carbon, G. W. Heise and J. A. 
Slyh, NDRC 10.5-11, Dec. 10, 1943. 

Div. 10-202.133-MI 


116. Trost and Morrison, Canadian Report, C. E. 151, III-l- 
1815, Aug. 25, 1944. 

117. Absorbents for Gas Masks, E. O. Wiig, MSR, Dec. 15, 

1944. Div. 10-202.1-M8 

118. Retentivity of Charcoals, D. H. Volman, G. J. Doyle, and 
F. E. Blacet, OSRD 5236, Apr. 23, 1945. 

Div. 10-202.15-M20 

119. Stevens, Canadian Report C. E. 161, III-1-1806, Sept. 9, 
1944. 

120. Mackenzie and Stevens, Canadian Report, C. E. 161, 
III-1-1852, Oct, 20, 1944. 

121. Chemisorption of Gases on Charcoals and Type A Whet- 
lerites, P. H. Emmett, H. A. Pohl, and J. T. Rummer, 
NDRC 10.4-29, July 8, 1943. Div. 10-202.15-M17 

122. X-Ray Studies, H. F. Johnstone and G. L. Clark, NDRC 

CLXXVIII, Aug. 31, 1942. Div. 10-202.143-M3 

123. Study of Impregnated Charcoal by X-Ray Diffraction, 

H. F. Johnstone and G. L. Clark, OSRD 1143, Dec. 9, 
1942. Div. 10-202.143-M4 

124. Lamb, Ind. Eng. Chem., 11, 1919, p. 429. 

a. Garner and Ringman, Trans. Faraday Soc., 25, 1929, 
p. 24. 

125. Application of the Electron Microscope to the Study of 

Charcoal, H. F. Johnstone and G. L. Clark, OSRD 1686, 
Aug. 3, 1943. Div. 10-202.143-M5 

126. T. F. Young, NDRC V, June 18, 1941. 

Div. 10-202.11-MI 

127. Robe, J. Ch. Ed., 8, 1931, p. 236. 

128. Bangham, Proc. Roy. Soc., 147A, 1934, p. 175; Trans. 
Faraday Soc., 33, 1937, pp. 1459, 1463. 

129. Hendricks, Melson, and Alexander, J. Am. Chem. Soc., 
62, 1940, p. 1457. 

130. Cornet, J. Chem. Phys., 11, 1943, pp. 5, 217. 


Chapter 7 


1. The Nature of the Product Desorbed from Charcoal Brought 
Halfway to the Break Point with PS, G. P. Baxter and 
H. W. Anderson, Informal Report C. 

2. The Increase in Weight of Charcoal at the Break Point, 
M. Dole, NDRC XXVI, Aug. 29, 1941. 

Div. 10-202.11-M2 

3. A Study of the Penetration of Charcoal by Chloropicrin by 

Means of an Ultraviolet Photometer, M. Dole and I. M. 
Rlotz, NDRC LXIV. Div. 10-202.155-MI 

'4. Effect of Activation Time on Properties of PCI Charcoal 
and Corresponding ASC Whetlerite (Second Report), T. 
Skei, F. E. Blacet, and W. C. Pierce, NDRC 10.1-23, 
OSRD No. 1746, Aug. 10, 1943. Div. 10-202.11-M6 

5. Performance of the M10 Canister Against HS under Humid 

Tropical Conditions, W. C. Pierce, OSRD 1194, Feb. 3, 
1943. Div. 10-201.1-M13 

6. Unpublished Work on the Performance of the MW Canister 
Against HNS Under Humid Tropical Conditions, J. W. 
Zabor and W. C. Pierce. 

7. “The Behavior of Gas Mask Charcoal Towards Phosgene 
and Chlorine,” J. B. Nielsen, Zeitschrift Fur das gesamte 
Schiess- und Springstoffwesen mit der Sonderabteilung 
Gasschutz, 27, 1932, pp. 136-139, 170-173, 208-211, 244- 
248, 280-284. 


8. Adsorption Studies on Chloropicrin and Phosgene, M. 
Dole, I. M. Rlotz, and S. W. Weller, NDRC CLXXII, 
July 15, 1942. 

9. An Investigation of the Mechanism of Removal of Phosgene, 
etc., D. M. Yost, R. W. Dodson, D. S. Martin, and W. P. 
Nies, OSRD 903, Sept. 25, 1942. Div. 10-202.155-M5 

10. Unpublished Work on the Mechanism of Removal of CG, 

J. W. Zabor and W. C. Pierce. 

11. An Intermittent Flow Canister Test Machine, W. C. 
Pierce, NDRC 10.1-3, OSRD No. 1193, Jan. 28, 1943. 

Div. 10-201.1-M 12 

12. Variation of the CG Life of Various Humidified Adsorbents 
with Decreasing Temperature, J. W. Zabor and W. C. 
Pierce, NDRC CC, Nov. 4, 1942. 

13. Preliminary Tests with COCIF, J. W. Otvos and R. G. 
Dickinson, NDRC CCVI, Oct. 21, 1942. 

Div. 10-202.156-M16 

14. Tube Tests with HF, J. W. Otvos, H. F. Johnstone, and 
R. G. Dickinson, NDRC CXLVIII, June 29, 1943. 

Div. 10-402.2-M3 

15. Retentivity Tests with HF, H. F. Johnstone and R. G. 
Dickinson, NDRC CCVII, Oct. 10, 1942. 

Div. 10-202.15-M 14 

16. Chemisorption of Gases on Charcoals and Type A Whetler- 


SECRET 




BIBLIOGRAPHY 


655 


17. 


18. 

19. 


20 . 


21 . 

22 . 


23. 

24. 


25. 


26. 

27. 

28. 


1 . 

2 . 


3. 

4. 

5. 

6 . 


ties, R. A. Pohl, J. T. Kummer, and P. H. Emmett, 
NDRC 10.4-29, July 8, 1943. Div. 10-202.15-M17 

Retention of HCl by the MIXAl Canister , R. K. Brinton 
and W. C. Pierce, NDRC CLXVII, July 29, 1942. 

Div. 10-201.1-M7 

Removal of H 2 S, D. M. Yost, NDRC XXIV. 

Div. 10-202.15-M3 

Action of Nitrogen Dioxide on Activated Charcoals, Whet- 
lerites and Other Substances , W. B. Lewis, R. K. Brinton, 
W. J. Blaedel, and F. E. Blacet, NDRC 10.1-20, June 25, 
1943. Div. 10-202.156-M18 

Toxicity of Nitrogen Oxides and Container Penetration 
Tests, S. F. Penny and J. F. Leib, Chemical Warfare 
Laboratories, Ottawa, Physiological Section Report 
No. 29, Dec. 28, 1943. 

Behavior of S0 2 and of Several Other Gases on Whetlerite, 
P. A. Leighton, NDRC CXXXVII, June 15, 1942. 

Div. 10-202.156-M 14 
Phosphorus Trifluoride Removal by Whetlerite and by Soda 
Lime-Whetlerite Mixtures, A. J. Stosick, J. W. Otvos, and 
R. G. Dickinson, NDRC XCI, Apr. 6, 1942. 

Div. 10-202.156-M8 
Selenium Hexafluoride. Break Times at Various Temper¬ 
atures and Water Contents, R. G. Dickinson, NDRC 
XXXII. Div. 10-202.15-M23 

Comparative Retentivities of Whetlerites and Type D Mix¬ 
tures for SeF 6 and for 1120, A. J. Stosick, J. W. Otvos, 
C. W. Gould, Jr., and R. G. Dickinson, OSRD 616, 
May 9, 1942. Div. 10-202.156-M12 

Preliminary Tube Tests with COCIF, J. W. Otvos, H. F. 
Johnstone, A. J. Stosick, and R. G. Dickinson, NDRC 
CCVI, Oct. 21, 1942. Div. 10-202.156-M 16 

Toxicity, Pathological and Charcoal Penetration Studies of 
Sulfur Pentafluoride, E. M. K. Geiling, OSRD 3030. 
Preliminary Examination of 1120 Removal, A. J. Stosick, 
J. W. Otvos, C. W. Gould, Jr., and R. G. Dickinson, 
OSRD 300, Dec. 18, 1941. Div. 10-202.156-M4 

Summary of a Review on Hydrogen Cyanide, Cyanogen, and 
Cyanogen Chloride Removal by Gas Mask Absorbents, H. 
Scoville, C. Wagner, and E. O. Wiig, OSRD 1268, Mar. 17, 
1943. Div. 10-202.154-M31 


29. The Hydrogen Cyanide-Cyanogen Reaction on Type A 
Whetlerite and the Absorption of Cyanogen by Charcoals, 
L. \* M’Carty — Ph.D. thesis, University of Rochester, 
1945. 

30. HCN and C 2 N 2 Absorption, CWS Report. 

31. Animal and Chemical Tests on Cyanogen in the Effluent 
Air Stream After Adsorption of HCN, J. W. Zabor and 
W. C. Pierce, NDRC CCIX, OSRD 1090, Dec. 7, 1942. 

Div. 10-202.152-M8 

32. Mechanism Studies on the Removal of Cyanogen Chloride 
from an Air Stream by Charcoal, F. Zimer— Part I, Ph.D. 
thesis, University of Rochester, 1945. 

33. I. M. Klotz, MSR, Dec. 15, 1943. 

34. The Use of Pyridine Bases as Specific Impregnants for In¬ 
creasing the Protection of Charcoal Adsorbents Against 
Cyanogen Chloride, F. J. Ball, — Ph.D. thesis, University 
of Rochester, 1945. 

35. Compilation of N 0 and \ c Values for Miscellaneous Whetler¬ 

ites Before and After Aging, T. Skei and J. W. Zabor, 
OSRD 4013, Aug. 12, 1944. Div. 10-202.16-M17 

36. Unpublished Work on the Sorption of Ammonia by Gas 
Mask Adsorbents, J. W. Zabor and W. C. Pierce. 

37. Ammonia Protection Afforded by the Service Canister, J. H. 
Dinius, S. M. Jessop, and J. W. Thomas, TDMR 377, 
May 25, 1942. 

38. A Study of the Distribution of Arsine in Impregnated Char¬ 
coal by Means of Radioactive Tracers, J. W. Hickey, Ph.D. 
thesis, University of Rochester, 1942. 

39. The Effect of Water on the Adsorption of Arsine and Hydro¬ 
gen Cyanide by Impregnated Charcoals, H. Scoville, Jr., 
Ph.D. thesis, University of Rochester, 1942. 

40. Temperatures in Canisters and Tubes During SA Removal, 

I. M. Klotz, R. K. Brinton, and M. Dole, NDRC CLXII, 
July 25, 1942. Div. 10-201.1-M6 

41. The Location and Identification of Reaction Products in 

Whetlerite Treated with Arsine, H. F. Johnstone, OSRD 
704. Div. 10-202.14-M10 

42. Calorimetric Studies on the Removal of Arsine, J. B. 

Hatcher, G. B. Guthrie, and H. M. Huffman, NDRC 
CXCVIII, Oct. 15, 1942. Div. 10-202.156-M 15 


Chapter 8 


“Rates of Water Vapor Adsorption from Air by Silica 
Gel,” J. E. Ahlberg, Ind. Eng. Chem., 31, 1939, p. 988. 
The Effect of Tube Diameter and Type of Air Flow on Char¬ 
coal Breakdown Times, J. R. Arthur, E. J. Brockless, and 
J. W. Linnett, Oxford University, Research Report 
No. 43.20, (Y. 9896). 

“Concentration of Dilute Solutions of Electrolytes by 
Base-Exchange Materials,” R. H. Beaton and C. C. 
Furnas, Ind. Eng. Chem., 33, 1941, p. 1500. 

“Some Aspects of the Behavior of Charcoal with Respect 
to Chlorine,” G. S. Bohart and E. Q. Adams, J. Am. Chem. 
Soc., 42, 1920, p. 523. 

Rate of Sorption of Water Vapor from Humid Air Streams 
by Activated Carbons, A. P. Colburn, E. O. Kraemer, and 
L. W. Schmidt, OSRD 849, Aug. 1, 1942. 

G. Damkohler, Z. Elektrochem., 42, 1936, p. 846; 43,1937, 

p. 1* 


7. Some Aspects of the Physical Chemistry of the Respirator, 
C. J. Danby, J. G. Davoud, D. H. Everett, C. N. Hinshel- 
wood, and R. M. Lodge, Oxford University. 

8. “The Theory of Chromatography,” D. De Vault, J. Am. 
Chem. Soc., 65, 1943, p. 532. 

9. Adsorption Studies on Chloropicrin and Phosgene, M. Dole, 

I. M. Klotz, and S. Weller, OSRD 972, July 15, 1942. 

Div. 10-202.155-M4 

10. The Adsorption Wave, T. B. Drew, F. M. Spooner, and 

J. Douglas, NDRC 10.5-48, Nov. 17, 1944. 

Div. 10-202.157-M8 

11. Design of Collective Protectors, T. B. Drew, OSRD 993, 

Oct. 15, 1942. Div. 9-212.11-M3 

12. “Cation-Exchange Water Softening Rates,” J. du Do- 
maine, R. L. Swain, and O. A. Hougen, Ind. Eng. Chem., 
35, 1943, p. 546. 

13. “Adsorption Studies of Vapors in Carbon Packed Tow- 


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656 


BIBLIOGRAPHY 


ers,” H. C. Engel and J. Coull, Trans. Am. Inst. Chem. 
Eng., 38, 1942, p. 947. 

14. “Heat Transfer from a Gas Stream to a Bed of Broken 
Solids,” C. C. Furnas, Trans. Am. Inst. Chem. Eng., 24, 
1930, p. 1942. 

15. “Heat, Mass and Momentum Transfer in the Flow of 
Gases Through Granular Solids,” B. W. Gamson, G. 
Thodos, and ,0. A. Hougen, Trans. Am. Inst. Chem. 
Engrs., 39, 1943, p. 1. 

16. “Fluid Flow Through Porous Carbon,” M. R. Hatfield, 
Ind. Eng. Chem., 31, 1939, p. 1419. 

17. Drying of Gases, O. A. Hougen andF. W. Dodge, OSRD123. 

18. “Solid Catalysts and Reaction Rates,” O. A. Hougen and 
K. M. Watson, Ind. Eng. Chem., 35, 1943, p. 529. 

19. “Principles of Reactor Design. Gas-Solid Interface Re¬ 
actions,” D. H. Hurt, Ind. Eng. Chem., 35, 1943, p. 522. 

20. The Nature of Air Flow Through Granular Charcoal Beds, 
B. N. P. Hutchesson and K. D. Wadsworth, Porton Re¬ 
port No. 2607, Mar. 17, 1944. 

21. Problem of Gas Removal, L. S. Kassel, NDRC XV, (n.d.). 

Div. 10-202.15-M22 

22. Factors in Canister Design and Tube Testing: Critical Bed 
Depth and the Nature of Gas Flow Through Charcoal, I. M. 
Klotz, OSRD 3774, June 23, 1944. Div. 10-201.1-M26 

23. Critical Bed Depths in Removal of CC by the E3 Canister, 

I. M. Klotz, J. B. Fehrenbacher, and V. Johnson; Critical 
Bed Depths and Mechanism of Removal of Six Gases, W. L. 
McCabe, I. M. Klotz, W. E. Roake, H. G. Cutforth, and 

J. W. Thomas, OSRD 5239, June 7, 1945. 

Div. 10-202.156-M20 

24. A Systematic Study of Pressure Drop in Beds of Charcoal, 

R. J. Kunz, and D. G. Anderson, NDRC 10.5-26, Apr. 24, 
1944. Div. 10-202.11-M10 

25. Calculation of the Effect of Reversible Absorption on the 
Charcoal on Respirator Characteristics, M. W. Lister, Re¬ 
port on Canadian Project C. E. 4, May 29, 1941. (See 
also summary by J. F. Kincaid, NDRC XII.) 

Div. 10-202.15-M21 

26. A Study of Charcoal Adsorption and Methods of Testing 
Charcoals for Use in Gas Mask Canisters , R. Macy, 
EATR 52, Report completed July 1,1930; issued May 10, 
1942. 

27. Gas Mask Canister Design and Charcoal Testing, D. 
MacRae, TDMR 942, Dec. 15, 1944. 


28. “Layer Filtration, a Contribution to the Theory of Gas 
Masks,” W. Mecklenburg, Z. Elektrochemie, 31, 1925, p. 
488; Kolloid 52, 1930, p. 88. 

29. Considerations of the Adsorption Wave in Canister Design, 
F. G. Pearce, MIT-MR 132, Apr. 2, 1945. 

30. Variation of the CG Life of Various Humidified Adsorbents 

with Decreasing Temperature , W. C. Pierce, OSRD 
1055, Nov. 26, 1942. Div. 10-202.16-M10 

31. Studies of Canister Performance at High Humidities and 
Flow Rates, W. C. Pierce, OSRD 1081, Dec. 7, 1942. 

Div. 10-201.1-M11 

32. Mesh Size Studies, W. C. Pierce, J. W. Zabor, D. R. 

Ehrlinger, J. Fehrenbacher, A. L. Hart, and A. Juhola, 
NDRC 10.1-11, Apr. 12, 1943. Div. 10-201.21-Ml 

33. Design Methods for Adsorbent Section of Canisters, O. A. 
Short and F. G. Pearce, MIT-MR 114, Nov. 25, 1944. 

34. A Study of Humidification and Dehumidification of Char¬ 
coal in Collective Protector Canisters, O. A. Short, F. G. 
Pearce, and K. R. Nickolls, MIT-MR 97, Aug. 25, 1944. 

35. “Heterogeneous Ion Exchange in a Flowing System,” 
H. C. Thomas, J. Am. Chem. Soc., 66, 1944, p. 1664. 

36. A Critical Examination of the Correlation of Tube and Con¬ 
tainer Gas Test Results, K. D. Wadsworth, Ptn. 2001 
(U. 138), 1943, (Y. 23256). 

37. “Studies on Adsorption and Desorption in Beds of Gran¬ 
ular Adsorbents,” E. Wibke, Kolloid Zeitschrift, 93, 1940, 
p. 129. Translated by M. Dole NDRC XLVI, 1941; also 
translated by C. A. MacConkey, National Research 
Council of Canada, Ottawa, 1942. 

38. Adsorption Studies of PS on CWSN-19 and CWSC-11, 
R. H. Wilhelm, J. C. Whitwell, and S. F. Williams, Final 
Report, Contract No. NDC-rc 108, Dec. 15, 1943. 

39. A Brief Investigation of Removal of Arsine in Air-Arsine 
Mixtures by Charcoal Using the Radioactive Tracer Method , 
D. M. Yost, OSRD 361, Jan. 7, 1942. 

Div. 10-202.154-M12 

40. An Investigation of the Mechanism of Removal of Phosgene 
from Phosgene-Air Mixtures by Charcoal, Using the Radio¬ 
active Tracer Method, D. M. Yost, OSRD 903, Sept. 25, 

1942. Div. 10-202.155-M5 

41. Some Mathematical Theories for Charcoal Tube Testing, 
D. M. Yost and D. S. Martin, NDRC 10.1-12, Apr. 30, 

1943. Div. 10-202.1-M9 


Chapter 10 


1. Report on Aerosols, W. H. Rodebush, OSRD 77, Mar. 12, 

1941. Div. 10-500-MI 

2. Report on Aerosol Filter Materials, W. H. Rodebush, 

OSRD 58, July 24, 1941. Div. 10-201.22-MI 

3. Report on Filter Materials, W. H. Rodebush, OSRD 101, 

June 12, 1941. Div. 10-201.2-Ml 

4. Report on Aerosol Filter Materials, W. H. Rodebush, 

OSRD 168, Nov. 7, 1941. Div. 10-201.22-M3 

5. Report on Filtration of Aerosols and the Development of 
Filter Materials, W. H. Rodebush, I. Langmuir, and V. K. 
LaMer, OSRD 865, Sept. 4, 1942. Div. 10-201.22-M5 


6. Smokes and Filters, I. Langmuir and K. Blodgett, OSRD 

3460, Apr. 12, 1944. Div. 10-201.22-M14 

7. Preparation of Superfine Organic Fibers from Cellulose 

Esters, Tennessee Eastman Corporation, OSRD 1048, 
Nov. 26, 1942. Div. 10-201.22-M7 

8. Reports on Asbestos Bearing Filter Paper, A. D. Little, 
Inc., OSRD 336, OSRD 431, OSRD 962, OSRD 4378. 

Div. 10-201.22-M2 
Div. 10-201.22-M4 
Div. 10-201.22-M6 
Div. 10-201.22-M15 


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BIBLIOGRAPHY 


657 


Chapter 11 


1. Status Summary on the Protection Against Non-Persistent 
Agents hy Allied and Enemy Canisters Under Tropical 
Conditions, Project Coordination Staff, Edgewood Arse¬ 
nal, Report No. 2, July 19, 1944. 

2. Gas Protection Afforded hy Japanese Canisters, J. B. 

Fehrenbacher and F. E. Blacet, OSRD 5238, May 30, 
1945. Div. 10-201.31-M4 

3. Gas Protection Afforded hy German Canisters , J. B. 

Fehrenbacher and F. E. Blacet, OSRD 4929, Apr. 12, 
1945. Div. 10-201.31-M3 

4. NDRC MSR for period ending Nov. 15, 1944. 


5. German VM 40 Civilian Gas Masks , R. Munro and J. E. 
Kaufman, FMTR-MIT 45, Mar. 17, 1945. 

6. German Civilian Air Defense Gas Masks, P. Gilmont and 
J. E. Kaufman, FMTR-MIT 44, Mar. 17, 1945. 

7. Evaluation of British Mk II/L Respirator Containers, J. E. 
Kaufman, FMTR-MIT 48, Apr. 26, 1945. 

8. The Protection of United States and Enemy Canisters 
Against Nitrogen Dioxide, W. B. Lewis, J. W. Thomas, 
and F. E. Blacet, OSRD 5343, July 18, 1945. 

Div. 10-201.32-M3 


Chapter 12 


1. Charcalite: A Calcium Chloride Impregnated Charcoal Dry¬ 
ing Agent, R. N. Pease, OSRD 3776, June 15, 1944. 

Div. 10-202.142-M2 

2. Catalysts for the Oxidation of Carbon Monoxide in Air, 
R. N. Pease et al, OSRD 3071, Jan. 4, 1944. 

Div. 10-202.2-M6 

3. Volume Requirements for a Carbon Monoxide Canister for 


Use with Diluler-Demand Regulator Equipment, R. N. 
Pease, NDRC 10.1-47, June 15, 1944. 

Div. 10-201.1-M27 

4. Carbon Monoxide Asphyxia, C. K. Drinker, Oxford 
University Press, 1938, p. 89. 

5. Lamb, Bray, and Frazier, Ind. Eng. Chem., 12, 1920, 
p. 213. 


Chapter 14 


1. “Recording Nocturnal Radiation ,” A. Angstrom, Medell. 
Stat. Meteor. Hydrogr. Anst. Stockholm, 6, No. 8, 1936. 

2. “Transfer of Heat and Momentum in the Lowest Layers 
of the Atmosphere,” A. C. Best, Geophysical Memoirs, 7, 
No. 65, 1935. 

3. “Notes on Radiation in the Atmosphere,” D. Brunt, 
Quart. J. Roy. Met. Soc., 58, 1932, p. 389. 

4. Physical and Dynamical Meteorology, D. Brunt, MacMil¬ 
lan Co., London, 1939. 

5. “Professional Note No. 6,” E. H. Chapman, M. O. 232, 
1919. 

6. Special Report to General Kabrichfor Revision of TM 3-240, 
R. G. Dickinson, T. S. Gilman, and H. S. Johnston, 
October 1944. 

7. “The Climate of the Layer of Air Near the Ground,” R. 
Geiger, Die Wissenschaft, 78, Braunschweig, 1927. 

8. Physics of the Air, W. J. Humphreys, McGraw-Hill Book 
Co., 1940. 

9. Jelinek, Beit. z. Phys. der f. Atm., 24, 1937, p. 3. 

10. Micrometeorology of Woods and Open Areas Within the 
Withlacoochee Land Use Project, Florida, H. Johnston 
assisted by A. Pardee, A. Englander, and W. Ironside, 
DPGSR 35, Sept. 11, 1944. 

11. Correlation of Gas Concentrations with Meteorological 
Data, W. M. Latimer, S. Ruben, K. S. Pitzer, and 


W. D. Gwinn, OSRD 2086, Dec. 29, 1943. 

Div. 10-302.1-Ml 8 

12. Weather Analysis and Forecasting, S. Petterssen, McGraw- 
Hill Book Co., 1940, p. 99. 

13. “Strahlungsstudien,” M. Robitzsch, Arb. Obs. Linden- 
berg, 15, 1926, p. 194. 

14. Phys. Ocean, and Met., C. G. Rossby, MIT, 1935. 

15. “Das Massenaustausch bei der ungeordneten Stromung 
in freier Luft und seine Folgen,” Wilh. Schmidt, Wiener 
Ber., 126, 1917, p. 757. 

16. “Temperatures of the Soil and Air in a Desert,” J. G. 
Sinclair, M. W. Rev., 1922, S. 142. 

17. O. G. Sutton, Proc. Roy. Soc., 146, 1934, p. 701. 

18. “Theory of Diffusion,” G. I. Taylor, Proc. Math. Soc., 20, 
1929, p. 196. 

19. M. D. Thomas, NDRC 10.3A-17, Apr. 17, 1943. 

Div. 10-302-M1 

20. Evaluation of Meteorological Data of the Lowest Atmosphere, 
Salt Lake City, Utah, Mrs. R. Wexler. 

21. Meteorology of Ground Layer, R. Wexler, Special Report, 
Dugway Proving Grounds, November 1943. 

22. Resume of Recent Knowledge on the Technical Aspects of 
Chemical Warfare in the Field, Project Coordination Staff, 
Edgewood Arsenal, Report No. 9, May 17, 1945. 

23. SJPR 22, October 1944. 


Chapter 15 


1. “Transfer of Heat and Momentum in the Lowest Layer 
of the Atmosphere,” A. C. Best, Geophysical Memoirs, 
No. 65, 1935. 

2. A Comparison of Three Types of Cup Anemometers at Low 

Velocities, R. G. Dickinson and H. S. Johnston, NDRC 
10.3A-38, Oct. 26, 1943. Div. 10-301.1-MI 


3. A Remote Indicating Cup Anemometer with Magnetic 

Coupling, R. G. Dickinson and D. L. Kraus, NDRC 
10.3A-44, May 30, 1944. Div. 10-301.1-M2 

4. An Apparatus for Temperature Profile Measurement, R. G. 

Dickinson, R. L. Mills, and H. S. Johnston, NDRC 
10.3A-45, Apr. 11, 1944. Div. 10-301.2-M3 


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BIBLIOGRAPHY 


658 


o. 

6 . 


7. 

8 . 


9. 


1 . 

2 . 

3. 

4. 

5. 


6 . 


7. 


8 . 


9. 


10 . 

11 . 


12 . 


13. 


1 . 


Dugway Recording Instruments, S. W. Grinnell, Special 
Dugway Report. 

Micrometeorology of Woods and Open Areas Within the 
Withlacoochee Land Use Project, Florida, H. Johnston 
assisted by A. Pardee, A. Englander, and W. Ironside, 
DPGSR 35, Sept. 11, 1944. 

Meteorological Instruments, W. M. Latimer, S. Ruben, 
K. S. Pitzer, and W. D. Gwinn, NDRC 10.3A-6, Feb. 15, 
1943. Div. 10-301-MI 

Investigation of the Micrometeorology of a Medium Dense, 
High Canopy Jungle on a Small Tropical Island, W. W. 
Stone, R. G. Dickinson, D. L. Kraus, T. S. Gilman, and 
R. D. Mills, SJPR 22, Oct. 9, 1944. 

7. Meteorological Instruments: II. Observations in the Field, 
W. M. Latimer, S. Ruben, K. S. Pitzer, and W. D. Gwinn, 
NDRC 10.3A-14, Apr. 15, 1943. Div. 10-301-M2 


10. Meteorological Instruments; Wind Velocity Measurements , 

D. M. Yost, and R. Dodson, NDRC 10.3A-1, Dec. 15, 
1942. Div. 10-301.11-M 1 

11. Graphically Recording Bi-Directional Vanes, D. M. Yost 
and R. W. Dodson, NDRC 10.3A-40, Nov. 1, 1943. 

Div. 10-301.11-M3 

12. Experiments on the Measurement of Air Temperatures with 

Thermocouples, D. M. Yost, J. B. Hatcher, and R. Scott, 
NDRC 3A-26, July 20, 1943. Div. 10-301.2-MI 

13. Thermocouple Experiments, D. M. Yost, J. B. Hatcher, 
R. Scott, NDRC 10.3A-32, Aug. 27, 1943. 

Div. 10-301.2-M2 

14. Meteorological Instruments (second edition), W. E. K. 
Middleton, University of Toronto Press, 1943. 


Chapter 16 


The Meteorology of Chemical Warfare, Porton Memoran¬ 
dum No. 6, 1939. 

Radius of Pan-Cake Cloud, Dugway Proving Ground 
Report No. 18. 

Comparison of Experimental Data and British Theory, 
Dugway NDRC Weekly Report No. 37. 

The Behavior of Non-Persistent Gas Clouds Released from 
Bombs in the Tar ghee National Forest, M. Dole and F. X. 
Webster, DPGMR 12, Dec. 4, 1943. 

Large-Scale Field Tests with 4-2-Inch Mortar Using Non- 
Persistent Agent. Part A. Factual, W. S. Guthmann and 
J. T. Nolen, Apr. 25, 1944, Part B. Evaluation, W. S. 
Guthmann and J. W. Zabor, DPGMR 13, June 13, 1944. 
Florida Forest Field Trials of Non-Persistent and Per¬ 
sistent Agents, I. Non-Persistent Agents, M. Dole and 
J. T. Nolen, DPGMR 15, May 19, 1944. 

500-lb, 1000-lb, 2000-lb, and 4000-lb Bombs Filled With 
Non-Persistent Agents, DPGMR 18, June 2, 1944. 
Meteorology for Chemical Warfare and Smoke, 2nd edition, 
Meteorological Office, Air Ministry, Great Britain, S. D. 
No. 216, 1942. 

Wind-Tunnel Studies of the Diffusion of Gas in Schematic 
Urban Districts, NDRC 10.3A-46, OSRD 3859, July 5, 
1944. Div. 10-401.121-M2 

Correlation of Gas Concentrations with Meteorological Data, 
OSRD 2086, Dec. 29, 1943. Div. 10-302.1-M18 

Gas Concentration from Line Sources in a Forested Area, 
OSRD 3049, Dec. 29, 1943. Div. 10-302.2-M3 

Gas Concentration from Line Sources and C. W. Bombs on a 
Beach Area, OSRD 3059, Dec. 31, 1943. 

Div. 10-302.2-M4 

Resume of Recent Knowledge on the Technical Aspects of 
Chemical Warfare in the Field, Project Coordination Staff, 
Edgewood Arsenal, Report No. 9, May 17, 1945. 


14. Determination of the Burst Radii and Pancake Radii of 
CC- and CG-Filled 1000-lb Bombs Functioned Statically in 
Jungle, W. D. Gwinn, J. G. Roof, and R. J. Graben- 
stetter, SJPR 2, June 15, 1944. 

15. Behavior of CC and CG Clouds Released by Simultaneous 
Functioning of Eight 1000-lb Bombs in Tropical Forest, 
W. D. Gwinn, J. G. Roof, and J. W. Otvos, SJPR 6, 
July 15, 1944. 

16. Factors Influencing the Behavior of Nonpersistent Agents in 
Tropical Forests, W. D. Gwinn, J. G. Roof, and J. W. 
Otvos, SJPR 7; July 15, 1944. 

17. Relative Effects of Ground Slope and Wind Direction and 
Velocity on Movement of Gas Clouds, J. G. Roof and W. D. 
Gwinn, SJPR 12, Sept. 10, 1944. 

18. Dropping Trials of 1000-lb M79 Bombs in Jungle, E. 
Nelson and J. G. Roof, SJPR 14, Sept. 29, 1944. 

19. Static and Drop Trial of 500-lb M78, CC Filled Bombs in 
Jungle, E. Nelson, SJPR 15. 

20. Behavior of Gas Clouds of CC and CG Formed by Dropping 
of 96 1000-lb Bombs on Rough Jungle Terrain, J. G. Roof 
and T. J. Hogan, SJPR 16. 

21. Large Scale Field Tests with the 4-2-Inch Chemical Mortar 
Firing CC-Filled Shells in the Jungle, F. J. Zalesak and 
T. J. Hogan, SJPR 17, Oct, 11, 1944. 

22. The Assessment in Open Country of 4000 -lb A/C Bombs 
Charged Non-Persistent Gas, B. A. Griffith, Suffield Re¬ 
port No. 110-A, Apr. 25, 1944. 

23. The Diffusive Properties of the Lower Atmosphere. An Ac¬ 
count of Investigations at the Chemical Defence Experi¬ 
mental Station, Porton, Wilts, 1921-1942, O. G. Sutton, 
Issued by Meteorological Research Committee, Air 
Ministry, Great Britain, M. R. P. 59, Dec. 29, 1942. 

24. Evans and Levy, OSRD 1176. Div. 10-401.123-MI 


Chapter 17 


An Ultraviolet Photometer for the Detection and Quantitative 
Estimation of Very Small Concentrations of Noxious Gases 
in Air, M. Dole, OSRD 170, Nov. 7, 1941. 

Div. 10-402.21-M 1 


2. Sampling Methods for Field Experiments, W. M. Latimer, 
NDRC CLXXXVI, Sept. 15, 1942. Div. 10-402.2-M4 

3. Determination of Ammonia Concentrations in Field Tests, 
F. E. Blacet, NDRC 10.1-5, Jan. 16, 1943. 

Div. 10-402.2-M7 


SECRET 



BIBLIOGRAPHY 


659 


4. A Portable Continuous Gas Concentration Meter, R. G. 
Dickinson, NDRC 10.3A-9, Feb. 24, 1943. 

Div. 10-401.111-MI 

5. Measurement of CC with the Portable Continuous Gas Con¬ 

centration Meter, R. G. Dickinson, NDRC 10.3A-12, 
Mar. 15, 1943. Div. 10-401.111-M2 

6. Measurements of AC, CC and Mixtures of the Two with the 
Portable Continuous Gas Concentration Meter, R. G. Dick¬ 
inson, NDRC 10.3A-13, Apr. 15, 1943. 

Div. 10-401.111-M3 


7. The Hot Wire Analyzer for Gas Concentrations, W. M. 
Latimer, OSRD 3048, Dec. 3, 1943. Div. 10-401.11-Ml 

8. Operation Manual for Dickinson Field Conductivity Meter, 

R. K. Brinton and J. W. Otvos, OSRD 5344, July 18, 
1945. Div. 10-402.3-MI 

9. Dugway Proving Ground Field Sampling Methods for Non- 
Persistent Gases, M. Dole and C. W. Huffman, DPGSR 
19, Sept. 14, 1944. 


Chapter 18 

1. Colloid Chemistry, A. W. Thomas, McGraw-Hill Book Co., 2. Report on Aerosols, W. H. Rodebush, OSRD 77, Mar. 12, 
1934, p. 15. 1941. Div. 10-500-MI 


Chapter 19 


1. Filter Penetration by Aerosols of Very Small Particle Size, 
W. H. Rodebush et al, OSRD 2050, Nov. 24, 1943. 

Div. 10-201.22-M13 

2. Smoke, Whvtlaw-Grav and Patterson, Edward Arnold & 
Co., London, 1932, p. 184. 

3. The Preparation of Solid Materials for Dispersion as 
Aerosols, F. C. McGrew, OSRD 3902, July 17, 1944. 

Div. 10-504.3-M2 

4. “The Removal of Mist by Centrifugal Methods,” C. F. 
Goodeve, Trans. Faraday Society, 1936, p. 1218. 

5. Clouds and Smokes, Wm. E. Gibbs, J. and A. Churchill, 
1924, p. 43. See also Ref. 1, p. 96. 

6. Hydrodynamics, H. Lamb, Fifth Edition, p. 567. 

7. Reference 1, p. 72. 

8. Micromeritics, J. M. Dalla Valle, Pitman, New York, 
1943. 

9. Hatch and Choate, J. Franklin Institute, 207, 1929, p. 371. 

10. T. Hatch, J. Franklin Institute, 215, 1933, p. 27. 

11. The Kinetic Theory of Gases, L. B. Loeb, McGraw-Hill, 
1934, p. 402. See also Reference 5, p. 48. 

12. Ibid., p. 394. 

13. See Reference 2, p. 57. 

14. Unpublished Report, D. E. Goldman. 

15. See Reference 2, p. 67. 

16. Applied Math. Panel, Memo 100.1 M, NDRC, 1944. 

17. “The Motion of a Sphere in a Viscous Fluid,” H. S. Allen, 
Phil-Mag. (5), 50, 1900, p. 323. 

18. E. A. Progress Report to Col. Fleming, H. A. Abramson, 
July 7, 1942. 

19. Unipolar Smoke and Filter Penetration, V. K. LaMer et al, 

NDRC 10.2-2, August 1943. Div. 10-201.22-M12 

20. Paranjpe, Proc. Ind. Acad. Sci., 4a, 1936, p. 423. 

21. Thermal Forces as a Means of Determining Size and Size 

Distribution in Aerosols, V. K. LaMer et al, NDRC 
10.2-5, Sept. 23, 1943. Div. 10-501.11-M8 


22. Analysis of Inhomogeneous Smoke, V. K. LaMer and D. 

Sinclair, OSRD 155, Nov. 5, 1941. Div. 10-501.11-MI 

23. “The Coagulation of Smoke by Supersonic Vibrations,” 

E. N. deC. Andrade, Trans. Faraday Soc., 42, 1936, 

p. 1111. 

24. “Experiments on Coagulation by Supersonic Vibrations,” 

R. C. Parker, Trans. Faraday Soc., 42, 1936, p. 1115. 

25. “The Aggregation of Suspended Particles in Gases by 
Sonic and Supersonic Waves,” O. Brandt and E. Hiede- 
mann, Trans. Faraday Soc., 42, 1936, p. 1101. 

26. Sonic Floccidator as a Fume Settler: Theory and Practice, 

H. W. St, Clair, U. S. Bureau of Mines, R. I. 3400, 1936, 
p. 51. 

27. “Hydrodynamisch-Akustische Untersuchung,” Walter 
Koenig, Ann. Physik, 42, 1891, pp. 353 and 549. 

28. Fog Types, etc., Meteorological Office, Air Ministry, 

S. D. T. M. 45. 

29. Electricity and Magnetism, J. H. Jeans. 

30. Georg Thomas, Ann. d. Physik, 42, 1913, p. 1079. 

31. “On the Circulations Caused by the Vibration of Air in a 
Tube,” E. N. deC. Andrade, Proc. Roy. Soc., 134, 1931, 
p. 445; also “On the Groupings and General Behavior of 
Solid Particles Under Influences of Air Vibrations in 
Tubes,” Phil. Trans. Roy. Soc., 4230, 1932, p. 413. 

32. J. Robinson, Proc. Lond. Phys. Soc., 25, 1913, p. 256. 

33. “The Action of Sound Waves Upon Droplets of Fog,” 

S. V. Gorbatchev, Russian Journal Physical Chemistry, 

7, 1936, p. 536. 

34. a. Dissipation of Water Fog by Intense Sound of Audible . 

Frequency, V. K. LaMer and D. Sinclair, OSRD 1667, 
Aug. 17, 1943. Div. 10-503.2-MI 

b. Report of Tests of Sonic Dissipation of Fog in California, 
V. K. LaMer, NDRC 10.2-13, Apr. 13, 1944. 

Div. 10-503.2-M3 

35. E. F. Burton et al, Toronto Report, C. E. 42, November 
1942, also Reference 6, Chap. 21. 


Chapter 20 


1. Production of Smokes of Homogeneous Particle Size for 
Screening Tests and Development of Dyes from Thermally 
Dispersed Smokes, V. K. LaMer et al, OSRD 364, Jan. 29, 
1942. Div. 10-501.11-M3 


a. Portable Optical Instrument for the Measurement of the 
Particle Size in Smokes, the “ Owl ”, an Improved Homo¬ 
geneous Aerosol Generator, V. K. LaMer and D. Sinclair, 
OSRD 1668, Aug. 3, 1943. Div. 10-501.11-M6 


SECRET 




660 


BIBLIOGRAPHY 


2 . 

3. 


1 . 

2 . 


3. 

4. 

5. 

6 . 


7. 


1 . 

2 . 

3. 

4. 

5. 

6 . 

7. 

8 . 
9. 

10 . 


11 . 

12 . 

13. 


1 . 

2 . 


Dispersal and Persistence Properties of Solid Aerosols, 
V. K. LaMer et al, NDRC 10.2-9, Nov. 12, 1943. 

Div. 10-504.3-MI 

The Optical Characterization of Any Aerosol in the Labora¬ 


tory or Field. The Production of Aerosols from Powdered 
Solid Materials , V. K. LaMer, J. Q. Umberger, D. Sin¬ 
clair, F. E. Buchwalter, OSRD 4904, Oct. 31, 1944. 

Div. 10-601.2-MI 


Chapter 21 


G. Mie, Ann. der Phys., 25, 1908, p. 377. 

Hans Blumer, Zeits. f. Phys., 32, 1925, p. 119; 38, 1926, 
pp. 304, 920; 39, 1926, p. 195. 

Engelhard and Friess, Koll. Zeits, 81, 1937, p. 129. 

R. Ruedy, Canadian Journal of Research, 19A, 1941, 
p. 117. 

Electromagnetic Theory, J. A. Stratton, McGraw-Hill 
Book Co., Stratton and Houghton, Physical Review, 38, 
1931, p. 159. 

Verification of the Mie Theory, V. K. LaMer, D. Sinclair, 
jet al, OSRD 1857, Sept. 29, 1943. Div. 10-501.1-M2 
Scientific Papers, Lord Rayleigh, Cambridge University 
Press, 1899, Vol. I, pp. 92-93. 

Lord Rayleigh, Loc. Cit., 4, 1903, p. 400, eq. 13. 

a. Production, Analysis, and Use of Aerosols of Uniform 

Particle Size, V. K. LaMer and D. Sinclair, OSRD 119, 
Aug. 8, 1941. Div. 10-501-MI 

b. Measurement of Particle Size in Smokes, the Owl, V. K. 
LaMer and D. Sinclair, OSRD 1668, Aug. 24, 1943. 

Div. 10-501.11-M6 

Screening Smokes, W. H. Rodebush, et al, OSRD 940, 
Part II, Sec. 2, Oct. 5, 1942. Div. 10-502-M5 


8. W. S. Stiles, Phil. Mag., 7, 1929, p. 204. 

9. G. Wolfson, Handbuch der Physik, XX, 314. 

10. Reference 7, Part II, Sec. 1. 

11. L. Brillouin, NDRC Applied Math. Panel Report, Nos. 
87.1 and 87.2. 

12. Determination of Particle Size Distribution in Smokes by 
Analysis of Scattered Light, V. K. LaMer and D. E. Gold¬ 
man, NDRC 10.2-4, July 28, 1943. Div. 10-501.11-M5 

13. “Owl” Settings for DOP Smokes, F. T. Gucker, Jr.,et al, 

NDRC 10.1-27, Sept. 7, 1943. Div. 10-501.11-M7 

14. Tests of the Owl, V. K. LaMer et al, NDRC 10.2-3, July 23, 

1943. Div. 10-501.11-M4 

15. W. Lotmar, Helv. Chim. Acta., 21, 1938, p. 792. 

16. R. S. Krishnan, Proc. lnd. Acad. Sci., 7A, 1938, p. 21. 

17. Private communication from E. I. DuPont de Nemours 
Experimental Station, E. D. Bailey. 

18. Testing of Daytime Distress Signals, V. K. LaMer et al, 

OSRD 4539, Jan. 5, 1945. Div. 10-501.23-M3 

19. T otal Scattering Function for Complex Indices of Refraction, 
A. N. Lowan et al, Math. Tables Project, National 
Bureau of Standards. 


Chapter 22 


K. R. May, Porton Report No. 2463; see also Monthly 
Progress Reports NDRC Munitions Development Labo¬ 
ratory, 1944-45. 

V. J. Schaefer, private communication. 

Dissipation of Water Fog by Intense Sound of Audible Fre¬ 
quency, V. K. LaMer et al, OSRD 1667, Aug. 17, 1943. 

Div. 10-503.2-MI 

Smoke, Whytlaw-Gray and Patterson, Edward Arnold 
and Co., London, 1932. 

K. E. Stumpf, Roll. Zeits, 86, 1939, p. 339. 

Studies of Particle Size in Smokes, H. Eyring, OSRD 292, 
Dec. 8, 1941. Div. 10-501.11-M2 

Preparation of Solid Materials for Dispersion as Aerosols, 
F. C. McGrew, OSRD 3902, July 17, 1944. 

Div. 10-504.3-M2 

Chemical Engineers Handbook, J. H. Perry, McGraw-Hill 
Book Co., 1934, p. 709. 

E. L. Anderson, Journal Industrial Hygiene, 21, 1939, 
p. 39. 

H. H. Watson, Trans. Faraday Soc., 32, 1936, p. 1073. 
Porton Report No. 2521. 

W. H. Rodebush et al, OSRD 865, Sept. 4, 1942. 

Div. 10-201.22-M5 

Production, Analysis, and Use of Aerosols of Uniform 


Particle Size, V. K. LaMer and D. Sinclair, OSRD 119, 
Aug. 8, 1941. Div. 10-501-MI 

14. Analysis of Inhomogeneous Smoke, V. K. LaMer and D. 
Sinclair, OSRD 155, Nov. 5, 1941. Div. 10-501.11-MI 

15. Dispersal and Persistence Properties of Solid Aerosols, 
V. Iv. LaMer et al, NDRC 10.2-9, Nov. 12, 1943. 

Div. 10.504.3-MI 

16. Optical Characterization of Any Aerosol, V. K. LaMer et al, 

OSRD 4904, Oct. 31, 1945. Div. 10-601.2-MI 

17. a. Measurement of Particle Size in Smoke, the Owl, V. K. 
LaMer and D. Sinclair, OSRD 1668, Aug. 24, 1943. 

Div. 10-501.11-M6 

b. Characteristics of Different Models of the Owl, V. K. 
LaMer and D. Sinclair, NDRC 10.2-3, July 23, 1943. 

Div. 10-501.11-M4 

c. Concentration of Sound for Use in Fog Dissipation, 

V. K. LaMer and D. Sinclair, NDRC 10.2-6, Oct. 15, 
1943. Div. 10-503.2-M2 

18. Physics of the Air, W. J. Humphreys, McGraw-Hill Book 
Co., 1940, p. 551. 

19. Hilding Kohler, Trans. Faraday Soc., 32, 1936, p. 1153. 

20. Wilson, Cambridge Philos. Soc., 32, 1936, p. 493. 

21. The Slope-O-Meter, V. K. LaMer and S. Hochberg, 

NDRC 10.2-15, June 19, 1944. Div. 10-501.11-M9 


Chapter 23 

Report on Aerosols, W. H. Rodebush, OSRD 77, Mar. 12, terials, W. H. Rodebush, I. Langmuir, and V. K. LaMer, 

1941 - Div. 10-500-MI OSRD 865, Sept. 4, 1942. 

Filtration of Aerosols and the Development of Filter Ma- Div. 10-201.22-M5 


SECRET 



BIBLIOGRAPHY 


661 


3. Smokes and Filters. Supplement to Section /., I. Langmuir 
and K. Blodgett, OSRD 3460, Apr. 12, 1944. 

Div. 10-201.22-M14 

4. Filter Penetration of Aerosols of Very Small Particle Size, 

W. H. Rodebush, C. E. Holley, Jr., and B. A. Lloyd, 
OSRD 2050, Nov. 24, 1943. Div. 10-201.22-M13 

5. Final Report on Filtration Efficiency and Particle Size. 
III-I-2000, C. E. 42, University of Toronto, November 
1944. 

6. Filter Material, W. H. Rodebush, OSRD 101, June 12, 

1941. Div. 10-201.2-MI 

7. Preparation of Asbestos Fibers of Small Diameter and Dis¬ 


persion of Solids, OSRD 431, A. D. Little, Inc. Mar. 2, 
1942. Div. 10-201.22-M4 

8. Asbestos Bearing Filter Paper, T. L. Wheeler and E. 
Stafford, OSRD 4378, Nov. 23, 1944. 

Div. 10-201.22-M15 

9. Aerosol Filter Materials, W. H. Rodebush, OSRD 168, 

Nov. 7, 1941. Div. 10-201.22-M3 

10. Aerosol Filter Materials, W. H. Rodebush, OSRD 120, 

July 24, 1941. Div. 10-201.22-MI 

11. Preparation of Superfine Organic Fibers from Cellulose 

Esters, OSRD 1048, Tennessee Eastman Corporation, 

Nov. 26, 1942. Div. 10-201.22-M7 


Chapter 24 


1. Test Methods Conference, CWS Development Laboratory, 
MIT. Group VI-Filter Tests, Sept. 2, 1942, pp. 1-2 and 
45-63 deal with general recommendations on smoke 
testing. 

2. Reference 1, pp. 8 and 50-51. 

3. Production, Analysis, and Use of Aerosols of Uniform 

Particle Size, V. K. LaMer and D. Sinclair, OSRD 119, 
Aug. 8, 1941. Div. 10-501-MI 

Also Measurement of Particle Size in Smoke, V. K. LaMer 
and D. Sinclair, OSRD 1668, Aug. 24, 1943. 

Div. 10-501.11-M6 

4. Development of the DOP Smoke Penetration Test for Filter 
Materials, J. H. Dinius and A. W. Plummer, MIT-MR-52, 
Jan. 8, 1944. 

5. Development of Smoke Penetration Meters, H. W. Knudson 
and L. White, Naval Research Laboratory Report No. 
P-2642, Sept, 14, 1945. 

6. Reference 1, pp. 12-16 and 41-43. 

7. Canister and Charcoal Test Methods, CWS Pamphlet No. 2, 
Part 1, Section C, DM, Apr. 3, 1943. 

8. Gas Mask Filters and Filter Materials, DM Tests January 
1934 to September 1941, P. A. Hartman and E. K. Long, 
EATR 362, Feb. 24, 1942. 

9. Reference 6, Section D, DA. 

10. Reference 12, pp. 17-18 and 43-45. 

11. Canister Test Methods Section H — Methylene Blue, CWS 
Pamphlet No. 2, Part 1, Jan. 4, 1943. 

12. Methylene Blue Penetration Tester MIT-E2, A. W. Plum¬ 
mer, MIT-MR-5, May 6, 1942. 

13. Evaluation of the Methylene Blue Penetration Tester MIT- 
E2, H. J. Allison, Jr., and E. K. Long, TDMR 440, 
Sept. 23, 1942. 

14. Report on Aerosols, W. H. Rodebush, OSRD 14, Sept, 12, 
1941. 

15. Design of Apparatus, MIT-E1R1, for Filter Testing Using 
Radioactive Triphenyl Phosphate Smoke, B. Vonnegut, 
MIT-MR-6, July 18, 1942. 

16. Reference 1, pp. 40-41. 

17. Reference 1, pp. 26-39. 

18. Optical Smoke Penetration Meter, B. Vonnegut, MIT- 
MR-2, Mar. 16, 1942. 

19. Optical Smoke Penetration Meter, E1R1, D. W. Beaumont, 
MIT-MR-27, Mar. 6, 1943. 

20. Ionization Penetrometer, A. R. Hogg and A. J. Roenn- 
feldt, C. D. Note No. 14 from Munitions Supply Labora¬ 
tories, Maribyrong, Australia, Nov. 18, 1943. 


21. “A Photoelectric Smoke Penetrometer,” A. S. G. Hill, 
J. Sci. Inst., 14, 1937, p. 296. 

22. Reference 1, pp. 8-11. 

23. Carbon Smoke Penetration, L. Yaffe, R. L. McIntosh and 
W. Boyd Campbell, McGill University and the Pulp and 
Paper Research Institute of Canada, Progress Reports 
Nos. 1-4, Montreal, 1942. 

24. Canister Development Studies, W. K. Lewis, OSRD 850. 

25. Filtration of Aerosols and the Development of Filter Ma¬ 
terials, W. H. Rodebush, I. Langmuir, and V. K. LaMer, 
OSRD 865, Sept. 4, 1942. This report contains The Bal¬ 
anced Photoelectric Smoke Penetrometer by S. Hochberg. 

Div. 10-201.22-M 5 

26. A Sensitive Photoelectric Smoke Penetrometer, F. T. Gucker, 

Jr., H. B. Pickard, and C. T. O’Konski, OSRD 5499, 
Aug. 28, 1945. Div. 10-201.22-M 16 

27. Photoelectric Smoke Penetration Meter MIT-E2, W. B. 
Nottingham, D. W. Beaumont, and J. H. Dinius, MIT- 
MR-203, Oct, 11, 1945. 

28. A Particle-Counting Smoke Penetrometer, F. T. Gucker, 
Jr., H. B. Pickard, C. T. O’Konski, and J. N. Pitts, Jr., 
OSRD 5501, Aug. 31, 1945. 

29. Development of Stable Thallous Sulfide Photoconductive 
Cells for Detection of Near Infrared Radiation, R. J. Cash- 
man, OSRD 5997, Oct. 31, 1945. 

30. Smoke Penetration Meter E3, Engineering Tests, H. Scherr, 
EATR 237, Feb. 7, 1938. 

31. Smoke Penetration Meter E3, Final Report on Project D 1.3- 
lal, L. Finkelstein and H. Scherr, EATR 331, Aug. 28, 
1940. 

32. Operation of Smoke Penetration Meter E3 for Production 
Testing of MIXAl Canister Filters, CWS Directive 
No. 40A, June 6, 1942. 

33. Canister Test Methods, Section K — Smoke Penetration, 
CWS Pamphlet No. 2, Part I. 

34. Smoke Penetration Tests of Canadian and U. S. Army 
Canisters, P. A. Hartmann and E. K. Long, TDMR 332, 
Nov. 10, 1941. 

35. Effect of Oil Smokes from Esso Jr. and Oil-O-Matic Screen¬ 
ing Smoke Generators on Filters as Determined by Field 
Tests, MIT-MR-14, Sept. 28, 1942. 

36. The Effect of Oil Smokes and Amyl Stearate Smokes on 
Filters, P. A. Hartmann and J. E. Kaufman, TDMR 364, 
Apr. 28, 1942. 

37. Tests of British Light-Type Respirator Canisters, J. H. 
Dinius, TDMR 556, Jan. 31, 1943. 


SECRET 




BIBLIOGRAPHY 


662 


38. A Note on the Effect of Oil Screening Smokes on Resin- 
Impregnated Filters and the Stability of These Filters Under 
Tropical Conditions, Chemical Defence Experimental 
Station, Porton, England, May 12, 1943. 

39. Reference 1, p. 17. 

40. Development of MIT-El Canister Tester , W. B. Notting¬ 
ham, F. F. Diwoky, and D. W. Beaumont, MIT-MR-32, 
May 8, 1943. 

41. Canister and Charcoal Test Methods, Part I, Section M, 
Installation Operation, and Maintenance of Meter, Smoke 
Penetration, MIT-E1R1, CWS Pamphlet No. 2, Jan. 17, 
1944. 

42. Reference 1, pp. 31-32. 


43. Reference 1, pp. 11-12 and 39-40. 

44. Porton Report No. 2161; Porton Specification 1206. 

45. Evaluation of the British Sodium Flame Apparatus as a 
Filler Tester, C. A. Rinehart and J. H. Dinius, TDMR 
578, Feb. 26, 1943. 

46. Performance of Sodium Flame Penetrometer, M. W. Lister, 
Chemical Warfare Laboratories, Ottawa, Canada, 
Sept. 26, 1944. 

47. Standard Methods of Test (Chemical and Physical) Em¬ 
ployed in C. W. Investigations. 1(3 ) Tests on Particulate 
Filters, Porton Memorandum No. 17, Mar. 7, 1942. 

48. Aerosols, A Survey and Bibliography of Recent Literature, 
D. F. Jurgensen, MIT-MR-8, July 17, 1942. 


Chapter 25 


1. Screening Smokes, T. K. Sherwood, OSRD 436, Mar. 15, 

1942. Div. 10-502-M2 

2. Production of Smokes of Controlled Size by the Use of In¬ 
duction Nozzles, H. C. Hottel, OSRD 468, Jan. 12, 1942. 

Div. 10-501.2-MI 

3. Smoke Generator, I. Langmuir and V. J. Schaefer, OSRD 

487, Mar. 31, 1942. Div. 10-501.201-MI 

4. Screening Smokes, W. H. Rodebush, V. K. LaMer, 

I. Langmuir, T. K. Sherwood, OSRD 940, Oct. 5, 1942. 

Div. 10-502-M5 

5. Practical Considerations Involved in the Use of Screening 
Smokes, W. H. Rodebush, OSRD 1321, Apr. 9, 1943. 

Div. 10-502-M7 

6. Use of a Sulfur Boiler for Smoke Generation, W. K. Lewis, 

OSRD 1692, Aug. 9, 1943. Div. 10-501.2-M3 


7. Large Scale Screening Tests, Camp Sibert, Alabama, W. H. 

Rodebush and H. F. Johnstone, OSRD 1687, Aug. 10, 
1943. Div. 10-302.1-M10 

8. Study of Oil Smoke Plumes by Motion Pictures, H. F. 
Johnstone, OSRD 1697, Aug. 6, 1943. Div. 10-502-M8 

9. Smoke Experiments Carried Out At Camp Sibert, Alabama, 
T. S. Gilman and P. Hayward, OSRD 1712, Aug. 14, 1943. 

Div. 10-302.1-M11 

10. Reports on Special Smoke Project Amphibious Training 
Command, U. S. Atlantic Fleet, N. O. B. Norfolk, Va., 
1944-45. 

11. Cominch P-0J+ Smoke Screens for Amphibious Operations, 
Headquarter? of the Commander-in Chief, U. S. Fleet. 


Chapter 26 


1. Screening Smokes, T. K. Sherwood, OSRD 436, Mar. 15, 

1942. Div. 10-502-M2 

2. Production of Smokes of Controlled Size by the Use of In¬ 
duction Nozzles, H. C. Hottel, OSRD 468, Jan. 12, 1942. 

Div. 10-501.2-MI 

3. Smoke Generator, I. Langmuir and V. J. Schaefer, OSRD 

487, Mar. 31, 1942. Div. 10-501.201-MI 

4. Screening Smoke, W. H. Rodebush, V. K. LaMer, and 
I. Langmuir, OSRD 940, Oct. 5, 1942. Div. 10-502-M5 

5. The Pancake Effect in Gas Clouds, W. M. Latimer, OSRD 

1176, Feb. 3, 1943. Div. 10-401.123-MI 

6. Practical Considerations Involved in the Use of Screening 
Smokes, W. H. Rodebush, OSRD 1321, Apr. 9, 1943. 

Div. 10-502-M7 

7. Use of a Sulfur Boiler for Smoke Generation, W. K. Lewis, 

OSRD 1692, Aug. 9, 1943. Div. 10-501.2-M3 


8. Study of Oil Smoke Plumes by Motion Pictures, H. F. 
Johnstone, OSRD 1697, Aug. 6, 1943. Div. 10-502-M8 

9. Smoke Experiments Carried Out at Camp Sibert, Alabama, 

T. S. Gilman and P. Hayward, OSRD 1712, 
Aug. 14, 1943. Div. 10-302.1-M11 

10. Concentrations in Gas Clouds Under High Inversion Con¬ 

ditions, W. M. Latimer and S. Ruben, OSRD 1749, 
Aug. 31, 1943. Div. 10-302.1-M14 

11. The Evaporation of Small Drops of Thiodiglycol and Levin¬ 

stein Mustard, H. F. Johnstone, R. W. Parry, OSRD 2002, 
Nov. 9, 1943. Div. 10-501.12-Ml 

12. The Concentration of Vapor in H Aerosol Clouds, H. F. 
Johnstone and W. E. Winsche, OSRD 3284, Feb. 22, 1944. 

Div. 10-504-MI 

13. Statistical Considerations in the Use of DDT Aerosols, 
W. H. Rodebush, OSRD 4757, Mar. 5, 1945. 

Div. 10-602.21-M2 


Chapter 27 
Project C. E. 128 

Department of Physics, University of Manitoba 

1. III-1-789, Visual Aspects of the Screening Problem. Experiments. 

2. III-1-997, I. Determination of the Extinction Coefficient of III. Further Results on the Mechanism of 

Smoke. Obscuration. 

II. The Contrast IAmen in Smoke Chamber 3. III-1-1048, I. The Dependence of Cloud Brightness on the 


SECRET 



BIBLIOGRAPHY 


G63 


Amount of Smoke and on the Direction of Obser¬ 
vation in the Field. 

II. Brightness Meters. 

4. III-1-1230, Visibility of Targets in Relation to Night 

Screening. 

5. III-l-1298, The Brightness of HCE Clouds Under Different 

Viewing Conditions in Sunlight and Moonlight. 

6. III-1-1481, Smoke Screen Estimates. Part I. Flank Screen¬ 

ing Under Overcast Day Conditions. 

7. III-1-1851, Smoke Screen Estimates. V. Area Screening 

Under a Full Moon and a Cloudless Sky: Com¬ 
parison with Observed Data of C. D. Reports 


1098 and 1099, and Comments on Inferences 
Drawn in Those Reports. 

8. III-1-1893, Smoke Screen Estimates. Part VI. Area Screen¬ 

ing Under Cloudless Day Conditions Against 
Observation and Against Aimed Bombing At¬ 
tack. 

9. III-1-1939, A Survey of Visibility Limen Data. 

10. III-1-2001, The Probability of Detection and Recognition of 

Targets of Low Apparent Contrast which Varies 
with Time. 

11. III-1-2036, A Field Attenuation Meter for the Study of 

Flank Screening Problems. 


Chapter 29 


1. R. A. Castleman, Jr., Bur. Standards, J. Research, 6,1931, 
p. 369. 

2. J. Sauter, Forsch. Gebiete Ingenieurw., 1928, p. 312. 

3. Guy Littaye, Comptes rendus, 219, 1943, pp. 99, 340. 

4. S. Nukiyama and Y. Tanasawa, Trans. Soc. Mech. Engrs. 
(Japan), 4, 1938, pp. 14, 86; 4, 1938, pp. 15, 138; 5, 1939, 
pp. 18,63; 5, 1939, pp. 18, 68; 6,1940, pp.22, II-7; 6, 1940, 
pp. 23, 11-18. 

5. A Study of the Atomization of Liquids, H. C. Lewis, D. G. 

Edwards, M. J. Goglia, R. I. Rice, and L. W. Smith, 
OSRD 6345, November 1945. Div. 10-501.2-M6 

6. Chemical Engineers Handbook, 2nd Edition, McGraw-Hill 
Book Co., 1941, p. 842. 

7. Monthly Progress Reports of the Munitions Develop¬ 
ment Laboratory, Contract OEMsr-102, April to August 
1945. 

8. Chemical Engineers Handbook, 2nd Edition, McGraw- 
Hill Book Co., 1941, p. 1984. 

9. National Advisory Committee for Aeronautics, Report 
No.. 425, D. W. Lee, 1932. 

10. Mechanical Formation of Fogs, W. G. Brown, OSRD 325, 

Feb. 7, 1942. Div. 10-503.1-M2 

11. Use of Aqueous Solutions for Producing Screening Fogs or 
Smokes by Pneumatic Spray Nozzles, A. R. Olson and 
G. D. Gould, OSRD 537, Apr. 29, 1942. 

’ Div. 10-502-M4 

12. 7, Toxic Smoke Candle, and II, Screening Smoke Units, 
E. W. Comings, OSRD 1076, Dec. 1, 1942. 

Div. 10-504.12-M3 

13. Mechanical Formation of Smokes f G. G. Brown, OSRD 

153, Oct. 18, 1941. Div. 10-501-M2 

14. The Mechanical Formation of Screening Smokes Using Salt 
Solutions, G. G. Brow n, OSRD 980, October, 1942. 

Div. 10-502-M6 

15. The Formation of Screening Smokes, G. G. Brown, OSRD 

414, Feb. 26, 1942. Div. 10-502-MI 

16. The Assessment of Aerosols, H. F. Johnstone, NDRC 
10.4-48, Dec. 31, 1943; and Munitions Development 


Laboratory Biweekly Reports of November 10 and 24, 
1943. Div. 10-504.2-M3 

17. Memorandum on Airplane Vesicant Spray, T. K. Sher¬ 
wood, OSRD 2093, Dec. 2, 1943. Div. 11-203.522-MI 

18. The Break-Up of a Liquid Jet and Its Application to Air¬ 
craft, Porton Departmental Report No. 146. 

19. The Fragmentation of Liquid-C. W. Agents, Porton Re¬ 
port No. 2215, Serial No. 11, May 14, 1941. 

20. Munitions Development Laboratory Monthly Progress 
Report for October 1944. 

21. Munitions Development Laboratory Monthly Progress 
Report for December 1944. 

22. Supplementary Test of Improved Equipment and Tech¬ 
niques for Dissemination of DDT by Aircraft (Phase I and 
II); AAF Board, Orlando, Florida, Mar. 1, 1945; De¬ 
velopment and Test of Spray Equipment for L-5 Aircraft 
for Dissemination of Insecticide DDT, AAF Tactical 
Center and U. S. Department of Agriculture, Orlando, 
Florida, June 5, 1945. 

23. Final Test Report for DDT Insecticide Disseminator Units, 
Item 3, Navy Contract NOa(s) 7065, Cornell Aeronautical 
Laboratory (formerly Curtiss-Wright Corporation) June 
19, 1945. 

24. Chemical and Physical Methods for the Assessment of In¬ 
secticide Dispersal, C. W. Huffman, C. R. Naeser, and 
J. G. Hartnett, TDMR 1241, Mar. 29, 1946. 

25. The Mechanism of Dispersal of Liquids by Pressure Ex¬ 
plosion, R. Whytlaw r -Gray, Extramural Research Item 
No. 21, V. 727, University of Leeds, Dec. 20, 1940 to 
Mar. 17, 1941. 

26. Dispersal Under Various Conditions of a Mobile Liquid 
Filling by 20 mm SAP.CW Projectiles (20 mm Hispano 
HE Shell), B. A. Toms, Porton Report No. 2514, June 29, 
1943. 

27. The Break-Up of Liquids by Explosion, Part I, C. N. 
Davies, Porton Report No. 2425, Sept. 30, 1942. 

28. The Dispersal of Liquid Chargings from Bursting Weapons, 
A. W. Birnie, Technical Minute No. 37, Suffield Experi¬ 
mental Station, Oct. 4, 1943. 


Chapter 30 


1. Screening S?nokes, W. H. Rodebush, V. K. LaMer, I. 
Langmuir, T. K. Sherwood, OSRD 940, Oct. 5, 1942. 

Div. 10-502-M5 

2. Large Scale Screening Tests, Camp Sibert, Alabama, 


May 4-7, 1943, Part I — W. H. Rodebush, Part II — 
H. F. Johnstone, P. G. Roach, H. C. Weingartner, OSRD 
1687, Aug. 10, 1943. 

Div. 10-302.1-M10 


SECRET 




664 


BIBLIOGRAPHY 


3. The Concentration of Vapor in H Aerosol Clouds, H. F. 
Johnstone, W. E. Winsche, OSRD 3284, Feb. 22, 1944. 

Div. 10-504-MI 

4. The Evaporation of Small Drops of Thiodiglycol and Levin¬ 

stein Mustard , H. F. Johnstone and R. W. Parry, OSRD 
2002, Nov. 12, 1943. Div. 10-501.12-MI 

5. The Generation and Use of Concentrated Mustard Vapor 

Clouds, H. F. Johnstone and E. W. Comings, OSRD 3012, 
Dec. 14, 1943. Div. 10-504.1-MI 

6. Development of an Experimental Thermal Generator Pot 

for Dispersing Mustard Gas as an Aerosol, C. H. Adams, 
M. H. Raila, and E. W. Comings, OSRD 6431, Dec. 29, 
1945. Div. 10-504.1-M2 

7. Development of a Smoke Unit, E. W. Comings, OSRD 518, 

Apr. 23, 1942. Div. 10-504.12-M2 

8. The Development of the Thermal Generator Candle, E. W. 

Comings, E. D. Shippee, M. Forester, OSRD 3150, 
Jan. 18, 1944. Div. 10-504.12-M5 

9. 7. Toxic Smoke Candle, and II. Screening Smoke Units, 
E. W. Comings, OSRD 1076, Dec. 1, 1942. 

Div. 10-504.12-M3 

10. Smoke Production, E. W. Comings and E. D. Shippee, 

OSRD 109, June 27, 1941. Div. 10-504.4-MI 

11. Development of a Smoke Unit, E. W. Comings, OSRD 167, 

Nov. 5, 1941. Div. 10-504.4-M2 

12. Agent Decomposition in Toxic Smoke Candle, H. A. Fiess 
and E. W. Comings, Unpublished Report from OSRD 
Contract OEMsr-102, Aug. 26, 1942. 

13. Florida Trials with the Experimental H Generator, DPGSR 
34, Aug. 29, 1944. 

14. Development of a Thermal Generator Bomb for Dispersing 
Concentrated Mustard Aerosol, E. D. Shippee and E. W. 
Comings, OSRD 6574, Feb. 4, 1946. Div. 10-504.3-M3 

15. The Physiological Activity of the Cloud Produced by the 
Comings Thermal Generator, Suffield Report No. 98, 
Nov. 25, 1943. 

16. The Diffusive Properties of the Lower Atmosphere, an Ac¬ 
count of Investigations at Chemical Defense Experimental 
Station, Porton, Wilts, 1921-42, O. G. Sutton. 

17. Frossling Gerlands, Beitrage fur Geophysik, 52, 1938, 

p. 170. 

18. Estimating the Value of the Wind Gradient Parameter, “R,” 
A. Bleasdale, Porton Report No. 2408, Aug. 27, 1942. 

19. A Study of the Atomization of Liquids, H. C. Lewis, D. G. 

Edwards, M. Goglia, R. I. Rice, and L. W. Smith, OSRD 
6345, Nov. 23, 1945. Div. 10-501.2-M6 

20. The Dispersal of Liquid Chargings from Bursting Weapons, 
A. W. Birnie, Suffield Technical Minute No. 37, Oct. 4 
1945. 

21. Dugway Proving Ground Report for Week Ending De¬ 
cember 6, 1944, Report No. 85, Series 2. 

22. Dugway Proving Ground Report for Week Ending 

June 26, 1945, Report No. 114. 

23. Dugway Proving Ground Report for Week Ending 

August 28, 1945, Report No. 123. 

24. Dugway Proving Ground Report for Week Ending 

April 17, 1945, Report No. 104. 

25. Dugway Proving Ground Report for Week Ending 

April 24, 1945, Report No. 105. 

26. Fuel Blocks for Thermal Generators, R. W. Parry, M. H. 
Raila, R. C. Johnson, D. B. Ehrlinger, P. N. Rylander, 


C. H. Simonson, R. P. Connor, and E. W. Comings, 
OSRD 6636, Mar. 11, 1946. Div. I0-504.11-M3 

27. Telescoping Metal Tails for a Small Cluster Bomb ( Ther¬ 
mal Generator, 10-lb-E29Rl ), E. C. Manthei and J. A. 
Peck, OSRD 6121, Oct. 17, 1945. Div. 10-504.2-M9 

28. Development of a Colored Smoke Target Identification 

Bomb {Bomb, Target Identification, Smoke, Mk 72, Mod 2), 
C. H. Adams, E. H. Conroy, and E. W. Comings, OSRD 
6432, Dec. 29, 1945. Diy. 10-504.2-M11 

29. TCIF303. 

30. Letter (EW21/S77) from the Chief of the Bureau of 
Ordnance to the Chief, CWS, Apr. 7, 1945. 

31. Development of Oil Thermal Generator Floating Smoke Pot, 
E-23, M. F. Nathan, R. W. Davis, E. C. Manthei, and 
E. W. Comings, OSRD 6428. Dec. 29, 1945, 

Div. 10-501.21-M5 

32. Chicago Toxicity Laboratory Report, OSRD 4639. 

33. Letter from Commanding General, CWS Technical Com¬ 
mand to Chief, Technical Division, CWS, SPCVD 470.6 
(Smoke Candles) June 14, 1945. 

34. Letter from Commander Amphibious Training Com¬ 
mand, U. S. Atlantic Fleet, to Chief of the Bureau of 
Ordnance (Serial No. 0815), Feb. 9, 1945. 

35. Development of Training Oil Smoke Pot, E-21, M. F. 

Nathan, R. W. Davis, and E. W. Comings, OSRD 6211, 
Oct. 24, 1945. Div. 10-501.21-M4 

36. Letter from Chief, CWS Technical Division to Director, 
Munitions Development Laboratory (SPCVD 470.6 Uni¬ 
versity of Rlinois, October 25, 1944). 

37. Explosive Hazards of Oil Smokes in Confined Places, Test 
made at the Bureau of Mines, Pittsburgh, Pennsylvania, 
and reported by Lt, S. R. Purcell, CWS Pyrotechnics 
Division, in a trip report, July 11, 1945. 

38. Letter from Commanding Officer, CWS Technical Com¬ 
mand, Edgewood Arsenal to Chief, Technical Division, 
CWS, SPCVD 470.6 — Non-Toxic Oil Smoke Training 
Candle E-21, Dec. 21, 1945. 

39. Use of Sulfur Boiler for Smoke Generation, W. K. Lewis, 

OSRD 1692, Aug. 9, 1943. Div. 10-501.2-M3 

40. Sulfur Smoke Generator, designed by I. Bencowitz, Texas 
Gulf Sulphur Company — sketch dated Oct, 14, 1942. 

41. A Continuous Sulfur Smoke Generator, E. W. Comings and 
W. L. Lundy, OSRD 3213, Feb. 4, 1944. 

Div. 10-501.2-M4 

42. A Floating Colored Smoke Signal ( DS-4), D. G. Edwards, 

C. H. Adams, E. H. Conroy, and E. W. Comings, OSRD 
6375, Dec. 10, 1945. Div. 10-501.23-M4 

43. Testing of Daytime Distress Signals, V. K. LaMer, J. Q. 

Umberger, D. Sinclair, F. Buchwalter, and I. Johnson, 
OSRD 4539, Jan. 5, 1945. Div. 10-501.23-M3 

44. A New Daytime Distress Signal, I. Johnson and V. K. 
LaMer, NDRC 10.2-16, Oct. 23, 1944. 

Div. 10-501.23-M2 

46. Letter from Chief, Technical Command (SPCVD 412.41) 
May 16, 1945. 

47. Chemical Warfare Pocket Book (British), 1942, p. 45. 

48. Dugway Proving Ground Report No. 126, for two-week 
period ending Sept. 25, 1945. 

49. Cold Weather Trial of Comings H Thermal Generator, 
Suffield Report No. 136, A. W. Birnie, June 24, 1945. 


SECRET 



BIBLIOGRAPHY 


665 


50. Final Report of CWS Contract W-18-035-CWS-1232, velopment Laboratory, University of Illinois, for March, 

E. W. Comings, Jan. 31, 1946. April, and May 1944. 

51. Monthly Progress Reports of the NDRC Munitions De- 52. Monthly Progress Report of the NDRC Munitions De¬ 

velopment Laboratory, November 1944. 

Chapter 31 


1. Fuel Blocks for Thermal Generators , R. W. Parry, M. H. 
Raila, R. C. Johnson, D. Ehrlinger, C. H. Simonson, 
R. P. Connor, and E. W. Comings, OSRD 6636, Mar. 11, 
1946. Div. 10-504.11-M3 

3. Final Report of the Munitions Development Laboratory, 
CWS Contract W-18-035-CWS-1232, Jan. 31, 1946. 
An excerpt from this report covering the work on fuel 
blocks is included in OSRD 6636. Div. 10-504.11-M3 

4. Development of the British Type “M” Candle, CWD 
206A and 207A. Reported in Reference 5. 

5. The Nine-Pound DM Candle , EACD 241, Weaver, 1924. 

6. Low Temperature Fuels for Toxic Smokes, Finkelstein, 
TDMR 214, 1940. 

7. Laboratory Development of Nine-Pound HS-Sulfone 
Candle, TDMR 272, Finkelstein and Magram, 1941. 

8. Development of a New Fuel for the DM Candle, Maclntire, 
TDMR 479, 1942. 

10. Rocket Fundamentals, Allegheny Ballistics Laboratory 

SR-4, OSRD 3992, 1944. Div. 3-210-M3 

11. The 32°C Transition of NHJVOz, Kincaid and St. George, 

OSRD 1577, 1943. Div. 8-110.3-MI 


12. “Symposium on Gas Temperature Measurement,” Ri- 
baud, Laure, and Goudry, J. Inst. Fuel, 12, S18. 

14. Taylor and Neville, J. Amer. Chem. Soc., 43, 1921, 
p. 2055. 

15. “A Study of Carbon Combustibility by a Semi-Micro 
Method,” Blayden, Riley, and Shaw, Fuel in Science and 
Practice, 22, 1943, p. 2. 

16. Blayden, Riley, and Shaw, ibid., 22, 1943, p. 64. 

17. Blayden, Noble, and Riley, J. Inst. Fuel, 7, 1934, p. 139. 

18. Comprehensive Treatise on Inorganic and Theoretical 
Chemistry, Mellor, 2, 1922, p. 829. 

19. McCullough, R., and Long, Informal Conference at Day- 
ton, Ohio, July 26, 1945. 

21. Explosibility and Fire Hazard of NHJVOz, Davis, Circu¬ 
lar No. 719, U. S. D. A., 1945. 

22. The Reactivation in Oxygen of CWS Charcoals, T. F. 

Young, S. W. Weller, S. L. Simon, and M. G. Buck, 
OSRD 4104, Sept. 7, 1944. Div. 10-202.132-M2 

23. Grim and Roland, American Mineralogist, 27, 1942, 
pp. 746-760, 801-818. 

24. International Critical Tables, Vol. Ill and IV. 


Chapter 32 


1. The Vapor Pressure of FeClz-HfO Solutions and Its Rela¬ 
tion to Smoke Production, E. W. Comings and C. H. 
Adams, Report from OSRD Contract OEMsr-102, Jan. 6, 
1943 (unpublished). 

2. Screening Smokes, W. H. Rodebush, V. K. LaMer, I. 
Langmuir, and T. K. Sherwood, OSRD 940, Oct. 5, 1942. 

Div. 10-502-M5 

a. Ibid., Part V, T. K. Sherwood. 

3. Verification of Mie Theory — Calculations and Measure¬ 
ments of Light Scattering by Dielectric Spherical Particles, 
V. K. LaMer, OSRD 1857, Nov. 11, 1943. 

Div. 10-501.1-M2 

6. Kendrick, EACD No. 30, CWS. 

7. Development of the HC Smoke Mixtures, E. T. Lawrence, 

1925. 

8. Development of the Universal Type HS Smoke Candle, 
E2R3, L. J. Conkling. 

9. Investigation of Causes of Ignition of HC Smoke Pot, Smith 
and Hormats, TDMR No. 307, 1941. 

10. L. Finkelstein and Becker, TDMR 472, CWS. 

11. Al-ZnO-Hexachloroethane Filling, Barnard, TDMR 489, 
CWS, 1942. 

12. J. H. Ladd and Barnard, TDMR 544, CWS, 1943. 

13. New Chlorine Carriers for Metal Chloride Screening Smoke 

Mixtures, E. W. Comings, R. W. Parry, C. H. Adams, 
E. D. Shippee, and M. Forester, OSRD 3011, Dec. 14, 
1943 . Div. 10-502-M9 

14. H. F. Johnstone, H. C. Weingartner, and W. E. Winsche, 
Am. Chem. Soc., 54, 1942, p. 241. 

15. Textbook of Inorganic Chemistry, J. A. N. Friend, Charles 
Griffin and Company, 1925, 9, Part II, p. 102. 


16. F. W. J. Clendinnen, Jour. Chem. Soc. Trans., 123, 1923, 
p. 1340. 

17. G. Malquori, Gazz. C-him. Ital., 57, 1927, p. 665; 58, 1928, 
p. 891. 

19. Unpublished report by I. Bencowitz of the Texas Gulf 
Sulphur Co., 1942. 

20. Sulfur as a Screening Smoke, V. K. LaMer and S. Hoch- 
berg, OSRD Contract OEMsr-148, Jan. 5, 1943 (un¬ 
published). 

21. Use of Sulfur Boiler for Smoke Generation, W. K. Lewis, 

OSRD 1692, Aug. 9, 1943. Div. 10-501.2-M3 

22. Development of the Thermal Generator Candle, E. W. Com¬ 
ings, OSRD 3150, Jan. 18, 1944, p. 18. Div. 10-504.12-M5 
see also Part I, Toxic Smoke Candle, E. W. Comings, 
OSRD 1076, Dec. 1, 1942, p. 39. Div. 10-504.12-M3 

23. A Continuous Sulfur Smoke Generator, E. W. Comings and 
W. L. Lundy, OSRD 3213, Feb. 4, 1944. 

Div. 10-501.2-M4 

24. Development of the SN Screening Smoke Mixture, E. W. 

Comings, C. H. Adams, E. D. Shippee, and M. Forester, 
OSRD 1772, Sept. 4, 1943. Div. 10-501.21-M2 

25. The Aerosol Smoke Pot, W. D. Pye, Report No. 6 for 
period February 1-28, 1943 on OSRD Contract OEMsr- 
142, Apr. 16, 1943 (unpublished). 

26. The Aerosol Smoke Pot, W. D. Pye, Report No. 7 for 
period March 1-April 3, 1943 on OSRD Contract 
OEMsr-142, Apr. 16, 1943 (unpublished). 

28. The Development of a Portable Aerosol Smoke Pot, H. H. 
Champney, L. B. Counterman, R. Kamrath, J. G. Wis- 
ler, and R. M. Adams, OSRD 4565, Jan. 9, 1945. 

Div. 10-501.21-M3 


SECRET 




y 


6(56 


BIBLIOGRAPHY 


1 . 

3. 

4. 


6 . 

7. 

8 . 
9. 


1 . 


2 . 

3. 

4. 

5. 


6 . 


1 . 

2 . 

3. 

t/ A - 


6. 


Chapter 33 


Exhaust Type Airplane Unit, J. E. Cook and H. A. Rose- 
lund, Final Report of Contract OEMsr-578, covering 
period March 1942 to September 1943. 

Screening Smokes, W. H. Rodebush, V. K. LaMer, I. 
Langmuir, and T. K. Sherwood, OSRD 940, Oct. 5, 1942. 

Div. 10-502-M5 

Verification of Mie Theory — Calculations and Measure¬ 
ments of Light Scattering by Dielectric Spherical Particles, 
V. K. LaMer, OSRD 1857, Nov. 11, 1943. 

Div. 10-501.1-M2 

Graphical Method for Evaluating Relative Permanency of 
Fog Oils (SGF), Standard Oil Development Company, 
Feb. 23, 1943. 

Chemical Technology of Petroleum, Gruse and Stevens, 
McGraw-Hill Book Co., 1942. 

The Development of an Exhaust Smoke Generator for Mili¬ 
tary Aircraft, M. J. Goglia and H. F. Johnstone, OSRD 
5488, Aug. 25, 1945. Div. 10-501.203-M2 

NDRC Munitions Development Laboratory Monthly 
Progress Reports, August 1944 to April 1945. 

Tactical Evaluation of Exhaust Manifold Generated Oil 


Type, Smoke Screen Equipment, Naval Air Station, 
Patuxent River, Maryland, for January 29, 1945, Febru¬ 
ary 28, 1945, and March 15, 1945. 

10. Development of Exhaust Combustian Smoke Generator for 
the TBM-3 Airplane, Final Report on Contract OEMsr- 
1446, OSRD 6343, Nov. 23, 1945. Div. 10-501.203-M3 

11. Interrelation of Exhaust Gas Constituents, H. C. Gerish 
and F. Voss, N. A. C. A. Report No. 616, 1937. 

12. “Relation of Exhaust Composition to Air/Fuel Ratio,” 
B. A. D'Alleua and W. A. Lovell, S. A. E. Trans., 31, 
1936. 

13. NATC, Patuxent River, Maryland, confidential letter 
and report, Serial C-718 of July 9, 1945. 

14. Aircraft Oil Fog Generator, Mk. 4, Tests, Report of 
COTCLant/S77/(RD 214) Serial 03774 of October 29, 
1945. 

15. Use of Aircraft Oil Fog Generator, Mk. 4, for Laying Large 
Blanket Type Smoke Screens, COTCLant confidential 
letter, COTCLant/S77/(RD214) Serial 03815 of No¬ 
vember 10, 1945. 


Chapter 34 


The Development of a Light High Explosive Bomb for Dis¬ 
persing Toxic and Insecticidal Aerosols, H. F. Johnstone, 
R. L. LeTourneau, and H. C. Weingartner, OSRD 6565, 
Jan. 28, 1946. Div. 10-504.2-M12 

Development of a Small Base Ejection Air-Burst Bomb for 
Dispersing Liquid Agents, R. J. Kallal and R. W. Davis, 
OSRD 6300, Nov. 7, 1945. Div. 10-504.2-M10 

M. H. Davis and D. L. Woodbury, EATR 37, Edgewood 
Arsenal, Sept. 15, 1930. Div. 10-504.2-M10 

M-67 Bomb Modified for Improved Dispersion of H, E. K. 
Carver and G. Broughton, OSRD 2058. 

Weekly Report on the Research and Development Pro¬ 
gram, Dugway Proving Ground, week ending April 12, 
1944. 

Dugway Proving Ground Weekly Reports, Series 2, 
Nos. 116, 117, and 118; July 10, 17, and 24, 1945. 


7. Particle Size Measurements on Certain u AerosoV , Bombs 

for the Department of Agriculture, V. K. LaMer, NDRC 
10.2-14, Apr. 24, 1944. Div. 10-504.2-M4 

8. Special Summary on the Dispersal of Liquids by Gases, 
A. R. Olson, Progress Report Contract OEMsr-538, 
Mar. 16, 1943. 

9. Test of Bomb Developed by Professor A. R. Olson, W. S. 
Guthmann and T. M. North, DPGSR No. 6, June 1,1943. 

10. A Study of Aerosols Produced by the Olson Bomb, F. T. 
Gucker, Jr., NDRC 10.1-14, May 15, 1943. 

Div. 10-504.2-MI 

11. Field Methods of Dispersing Chemical Warfare Agents, 
A. R. Olson and K. J. Tong, OSRD 3578, May 4, 1944. 

Div. 10-504.2-M5 

12. Tests on C0 2 Spraying Devices, F. G. Straub and R. J. 
Kallal, OSRD 3577, May 4, 1944. Div. 10-501.2-M5 


Chapter 35 


Preliminary Field Tests on Powdered “W” Dispersed with 7. 
the E-5 Tail Ejection Bomb, Mangun, Skipper and Karel, 
TDMR 699, July 21, 1943. 8. 

Biweekly and Monthly Progress Reports of the Munitions 
Development Laboratory, 1943 and 1944. 

NDRC, Division 9, University of Chicago Toxicity Lab- 9. 
oratory Monthly Reports, 1943 and 1944. Div. 9-125-M2 
The Optical Characterization of Any Aerosol in the Labora- 10. 
tory or Field. The Production of Aerosols from Powdered 
Solid Materials, V. K. LaMer, NDRC Division 10 Final 11. 
Report, Oct. 31, 1944. 

Informal Monthly Progress Report on Toxicity and Irri¬ 
tancy of Chemical Agents, University of Chicago Tox- 12. 
icity Laboratory, Feb. 15, 1946. 

W. Sell, Forschungsheft, 1931, p. 347. 


Final Report on Preparation of W, Procter and Gamble 
Company, NDRC Division 9. 

The Preparation of Solid Materials for Dispersion as 
Aerosols, F. C. McGrew, OSRD 3902, July 17, 1944. 

Div. 10-504.3-M2 

Micromentics, The Technology of Fine Particles, J. M. 
Dallavalle, Pitman Co., 1943, p. 118. 

Dugway Proving Ground Medical Research Laboratory, 
Weekly Reports for 1944. 

The Deposition of Non-Volatile Aerosol Clouds in Open 
and Forested Areas, W. E. Winsche, NDRC 10.4-55, 
Mar. 1, 1944. Div. 10-501.12-M3 

Meteorological Aspects of Chemical Warfare, O. G. Sutton, 
H. Garnett, and P. A. Sheppard. Porton Report No. 2070, 
Jan. 16, 1939; 


SECRET 



BIBLIOGRAPHY 


667 


A Generalization of the Theory of Turbulent Atmospheric 
Diffusion, Porton Departmental Report No. 88, Aug. 31, 
1939; 

The Meteorology of Chemical Warfare, Porton Memoran¬ 
dum No. 6; 

The Diffusive Properties of the Lower Atmosphere (An Ac¬ 
count of Investigations at the Chemical Defence Experi¬ 
mental Station, Porton, Wilts, 1921-1942), O. G. Sutton. 

13. Some Theoretical Aspects of the Behavior of DDT Aerosols 

Dispersed from Aircraft, W. E. Winsche, R. L. Le Tour- 
neau, L. W. Smith, and H. F. Johnstone, OSRD 5710, 
Sept. 19, 1945. Div. 10-602.121-M5 

14. The Assessment of Aerosols, H. F. Johnstone, NDRC 

10.4-48, Dec. 31, 1943. Div. 10-504.2-M3 

15. The Cascade Impactor, K. R. May, Porton Report No. 
2463, Dec. 8, 1942. 

16. Memorandum to Suffield Experimental Station, W. L. 
Doyle, University of Chicago Toxicity Laboratory, Pub¬ 
lished as Appendix II of Suffield Report No. 137. 

17. The Efficiency of Dispersal of Agent IF as a Dry Powder 
and from Suspension by Different Munitions, Suffield 
Report No. 137, June 30, 1945. 

18. The Production of Particulate Clouds from Bombs — 
Part I. Comparison of Different Bursting Systems in 30-lb 
LC Bombs, E. Boyland, J. H. Gaddum, G. S. Hartley, 
and W. R. Lane, Porton Report 2391, Aug. 11, 1942; 
Experiments on Particulate Clouds, J. H. Gaddum, Ptn. 
1708 (S. 2507), Feb. 28, 1943; 


The Production of Particulate Clouds from Bombs, Part II. 
Comparison of Different Thicknesses of Burster and Case, 
J. H. Gaddum and R. W. Pittman, Porton Report 
No. 2397, July 18, 1942. 

19. Field Trials with W in Bombs, J. H. Gaddum, Porton. 

20. Gas Ejection Bombs for the Dispersal of Finely Divided 
Powders, C. A. Getz, J. C. Hesson, H. C. Weingartner, 
and H. F. Johnstone, OSRD 5489, Aug. 25, 1945. 

Div. 10-504.2-M8 

21. Development of Munitions for Dispersing Solid Particu¬ 
lates, H. F. Johnstone, OSRD 4166, Sept. 25, 1944. 

Div. 10-504.2-M6 

22. Munitions for Gas Dispersal, Munitions Development 

Laboratory Monthly Progress Report Contract OEMsr- 
102, March 1944. Div. 10-504-M2 

23. Studies of the Toxicity and Dispersibility of W in Muni¬ 
tions, Franklin, Lephin, Weingartner and Graef, MRL 
(DPG) Report No. 2, Project A1.12 and A10.3, July 19, 
1945. 

24. The Development of a Light High Explosive Bomb for Dis¬ 

persing Toxic and Insecticidal Aerosols, H. F. Johnstone, 
R. L. LeTourneau, and H. C. Weingartner, OSRD 6565, 
Jan. 28, 1946. Div. 10-504.2-M12 

25. Comparison of the Type F Bomb vs Plastic Bomb Both 
Charged “U” Slurry, H. Wolochow, Suffield Field Re¬ 
port No. 1011, May 18, 1945. 


Chapter 36 


1. Memorandum on Airplane Vesicant Spray, T. K. Sherwood, OSRD 2093, Dec. 2, 1943. Div. 11-203.522-Ml 


Chapter 37 


1. Munitions Development Laboratory Monthly Reports, 
October, November, and December 1943. 

2. Reports on Contract OEMsr-949 as follows: 

Tests on the Reinforced Phosphorus Fillings for Mortar 
Shells, Monthly Reports for July and August 1943; 

The Use of Carbon Black in WP Shells, NDRC 10.4-40, 
Nov. 11, 1943. Div. 10-504.21-MI 

I. Static Firing Tests on Tail-Ejection ( E-5) Bombs, 

NDRC 10.4-42, Dec. 7, 1943; Div. 10-504.21-M2 

Tests on M-69 Bombs Charged with Coated Precast Blocks 
ofWP, NDRC 10.4-56, Mar. 30, 1944. 

Div. 10-504.21-M4 

3. The Burning Properties and Anti-Personnel Effect of PWP, 
H. F. Johnstone, D. G. Edwards, M. F. Nathan, F. A. 
Orr, and M. M. Woyski, OSRD 4733, Mar. 3, 1945. 

Div. 10-504.21-M11 

4. The Development of Plasticized White Phosphorus (PWP), 
M. M. Woyski, E. A. Ford, C. E. Shoemaker, F. A. Orr, 

J. A. Mattern, R. D. Emmick, P. G. Roach, H. F. John¬ 
stone, and J. C. Bailar, Jr., OSRD 6566, Jan. 28, 1946. 

Div. 10-504.21-M13 

5. Plasticized White Phosphorus Process and Development, 
TDMR 1130, Nov. 26, 1945. 

6. Design of a Plant for Manufacturing and Loading Plasti¬ 

cized White Phosphorus, E. A. Ford, OSRD 6122, Oct. 17, 
1945 . Div. 10-504.21-M12 

7. Functioning and Comparison Tests of Smoke Bombs, 


M47A2, WP, WPT, and PWP Filled; HC Filled, J. P. 
Clay, E. H. Lewis, E. W. Marshall, and P. G. Roach, 
DPGMR No. 19. 

8. Report of CWS Participation in Combined Arms Test — 
Tactical Employment of 4-2-inch RCM, Camp Hood, 
Texas, July 15, 1945. 

9. Conf. letter 0.0.471.381/222(c) SPOTM — Art Amm Br 
of Feb. 27, 1945, Firing Tests of Shell, Smoke, PWP , 
60 mm M302(T6 ) and Shell, Smoke, PWP, 81 mm M57. 

10. ComPhibTraLant conf. ltr. FE25/S70-1/A9 Serial 
02310 of June 29, 1944: 4-5-inch Plasticized WP Smoke 
Rockets; Progress Report of Service Test. 

11. ComPhibTraLant conf. ltr. FE25/S77/L5/(RD30) Se¬ 
rial 03528 of Sept. 18, 1944 : 4-5-inch and 7.2-inch Smoke 
Rockets and 4-2-inch Chemical Mortar Smoke Shells; Serv¬ 
ice Tests and Tactical Use in Screening Landing Oper¬ 
ations. 

12. ComPhibTraLant conf. ltr. FE25/S70-1(RD30) Serial 
03417 of Sept. 9, 1944: Bombs M47A2, WP and PWP 
Filled, for Screening Landing Operations. 

13. ComPhibsPac conf. ltr. CAF/S76 Serial 059 of Jan. 
22, 1945: Demonstration of Smoke Munitions for Use in 
Amphibious Operations . 

14. Plasticized White Phosphorus in Small Munitions, OSRD 
4700, R. I. Rice et al, Feb. 16, 1945. Div. 10-504.21-M9 

15. Part I — Comparison of Anti-Personnel Effects of Plasti¬ 
cized WP and Solid WP in 4.2-inch CM Shells. Part II — 


SECRET 




0(58 


BIBLIOGRAPHY 


Evaluation of Flight Characteristics of ' h 2-inch CM Shell, 16. Burning Power and Harassing Effects of White Phosphorus, 

M2, Filled with Plasticized WP, — Dug way Proving Porton Report No. 2604. 

Ground Special Report No. 30. 17. Physics, Dillon and Johnson, 4, 1933, p. 225. 


Chapter 38 


1. “Particle Size in Relation to Insecticide Efficiency,” C. M. 
Smith and L. D. Goodhue, Industrial and Engineering 
Chemistry, 34, 1942, p. 490. 

2. Some Principles Governing the Production of Air Floated 
Oil Particles and Their Relation to the Toxicity of Contact 
Oil Sprays to Insects, R. C. Burdette, Bull. 632, New 
Jersey Agriculture Experimental Station, January 1938. 

3. “Relation of Viscosit}' to Drop Size and the Application 
of Oils by Atomization,” E. M. Searls and F. M. Snyder, 
Journal of Economic Entomology, 29, 1936, p. 1167. 

4. The Deposition of Spray Droplets on a Mosquito in Flight, 
H. A. Druett, H. L. Green, and R. M. A. Welchman, 
Porton 1641, June 1944. 

5. Particle Size Measurements on Certain Aerosol Bombs for, 

the Department of Agriculture, V. K. LaMer, S. Hochberg, 
B. Zimm, and B. Williamson, NDRC 10.2-14, Apr. 24, 
1944. Div. 10-504.2-M4 

6. Some Theoretical Aspects of the Behavior of DDT Aerosols 
Dispersed from Aircraft, H. F. Johnstone, W. E. Winsche, 

R. L. LeTourneau, and L. W. Smith, OSRD 5710, Na¬ 

tional Research Council Insect Control Committee 116, 
Sept. 19, 1945. Div. 10-602.121-M5 

7. Statistical Considerations in the Use of DDT Aerosols, 
W. H. Rodebush, OSRD 4757, OSRD Insect Control 
Committee Report 13, Mar. 5, 1945. 

Div. 10-602.21-M2 

8. Forschungsarbeiten Verein deutschen Ingenieuren, W. Sell, 
Verlag, Berlin, 1931. 

9. Deposition of Non-Volatile Aerosol Clouds in Open and 

Forested Areas, W. E. Winsche and H. F. Johnstone, 
NDRC 10.4-55, Mar. 1, 1944. Div. 10-501.12-M3 

10. Toxicity of DDT to Mosquitoes. Effect of Particle Size on 
the Efficiency of Oil Aerosols Bearing DDT, V. K. LaMer, 

S. Hochberg, K. Hodges, I. Wilson, and J. Adamo, 

OSRD 4447, Dec. 11, 1944. Div. 10-602.21-MI 

11. The Effect of Particle Size and Speed of Motion of DDT 

Aerosols of Uniform Particle Size in a Wind Tunnel on the 
Mortality of Mosquitoes, R. Latta, L. D. Anderson, E. E. 
Rogers, V. K. LaMer, S. Hochberg, H. K. Hodges, J. C. 
Rowell, and I. Johnson, OSRD 5566, National Research 
Council Insect Control Committee Report 119, Sept. 7, 
1945. Div. 10-602.21-M4 

12. Production, Analysis, and Use of Aerosols of Uniform 

Particle Size, V. K. LaMer and D. Sinclair, OSRD 119, 
Aug. 8, 1941. Div. 10-501-MI 

13. A Portable Optical Instrument for the Measurement of 
Particle Size in Smokes, the “ Owl ,” and the Improved 
Homogeneous Aerosol Generator, V. K. LaMer and D. 
Sinclair, OSRD 1668, Aug. 1943. Div. 10-501.11-M6 

14. Effect of Solvents on the Toxicity of DDT Aerosols, V. K. 

LaMer, S. Hochberg, H. Lauterbach, I. Johnson, R. 
Latta, L. D. Anderson, E. E. Rogers, OSRD 5936, Na¬ 
tional Research Council Insect Control Committee Report 
123, Aug. 31, 1945. Div. 10-601.1-M3 


15. “The Calculation of the Dosage Mortality Curve,” C. I. 
Bliss, Annals of Applied Biology, 22, 1935, p. 134. 

16. Toxicity to Drosophila (Fruit Flies ) of Aerosols of DDT of 

Uniform Droplet Size in Oil of High Boiling Point, V. K. 
LaMer, S. Hochberg, B. H. Zimm, B. Williamson, OSRD 
4796, Mar. 15, 1945. Div. 10-602.22-M2 

17. The Development of an Aerosol Generator for Dispersing 

DDT Solutions from the Exhaust of an Aircraft Engine, 
H. F. Johnstone, R. J. Kallal, and H. Adams, OSRD 
5309, OSRD Insect Control Committee Report 95, 
July 5, 1945. Div. 10-602.121-M2 

18. The Toxicity of DDT Films and Aerosol Deposits, H. F. 

Johnstone, W. H. Rodebush, R. L. LeTourneau, C. W. 
Kearns, J. S. Laughlin, and F. McKee, NDRC 10.4-74, 
Oct. 1, 1944. Div. 10-602.2-MI 

19. Toxicity to Drosophila (Fruit Flies) of DDT Deposited from 
Aerosols on the Surface of Certain Leaves and Grass, V. K. 
LaMer, S. Hochberg, B. Zimm, B. Williamson, and J. 
Betheil, NDRC 10.2-18, Dec. 7, 1944. 

Div. 10-602.22-MI 

20. The Deposition of Drops of a Non-Volatile Liquid Vesicant 
on Vertical and Horizontal Surfaces, W. E. Winsche and 
H. F. Johnstone, NDRC 10.4-49, Jan. 15, 1944. 

Div. 10-501.12-M2 

21. Mosquito Control by Ground Dispersal of DDT as Aerosol 

from Large Scale Generators, R. Ellis and V. K. LaMer, 
NDRC 10.2-19, OSRD Insect Control Committee Re¬ 
port 9, Dec., 1944. Div. 10-602.11-MI 

22. Salt Marsh and Anopheline Mosquito Control by Ground 

Dispersal of DDT Aerosols, V. K. LaMer, F. Brescia, I. 
Wilson, K. C. Hodges, J. C. Rowell, OSRD 5731, Na¬ 
tional Research Council Insect Control Committee Report 
122, Sept. 18, 1945. Div. 10-602.21-M5 

23. Efficacy of DDT and DNOC as Insecticides for Grasshop¬ 

pers when Dispersed by a Hochberg-LaMer Type Aerosol 
Generator, V. K. LaMer, NDRC 10.2-25, National Re¬ 
search Council Insect Control Committee Report 137, 
Oct, 25, 1945. Div. 10-602.23-M3 

24. “Insecticidal Aerosol Production. Spraying Solutions in 
Liquefied Gases,” L. D. Goodhue, Industrial and Engi¬ 
neering Chemistry, 34, 1942, pp. 1456-1459. 

25. Hochberg-LaMer Aerosol Generator Inventor’s Model, V. K. 
LaMer and S. Hochberg, OSRD 4901, OSRD Insect 
Control Committee Report 15, Apr. 15, 1945. 

Div. 10-602.11-M3 

26. Aerosol Generator for DDT Dispersal, Stewart-Warner 
Corp., December 1944. 

27. Visit to Stewart-Warner Corp., K. C. Hodges, and V. K. 
LaMer, Memorandum Report, Division 10, NDRC, 
November 1944. 

28. Conversion of Besler No. 374 Screening Smoke Generator to 
a Hochberg-LaMer Aerosol Generator for Insecticidal Pur¬ 
poses with Supplement on Conversion of Besler M-2 Gener¬ 
ator, V. K. LaMer, S. Hochberg, R. Ellis, F. E. Buch- 


SECRET 



BIBLIOGRAPHY 


669 


waiter, and J. C. Rowell, OSRD 4894, OSRD Insect 
Control Committee Report 53, Apr. 5, 1945. 

Div. 10-602.11-M2 

29. Disperser, Insecticide, Aerosol, Mechanical , TB CW 

32 War Department, November 1945. 

30. Test of Large Area Mosquito Control with Hochberg-LaMer 
Aerosol Generator in Lodge Village, British Guiana, K. C. 
Hodges and J. C. Rowell, OSRD 5310, OSRD Insect 
Control Committee Report 96, July 5, 1945. 

Div. 10-602.21-M3 

31. Reports on the Use in the South Pacific of the Nang Screen¬ 

ing Smoke Generator ( M374 ) Converted to an Insecticidal 
Aerosol Generator According to the Hochberg-LaMer Prin¬ 
ciple , F. Brescia and I. Wilson, OSRD 5730, National 
Research Council Insect Control Committee 121, May 7, 
1945. Div. 10-602.11-M4 

32. Field Tests of Hochberg-LaMer Aerosol Insecticide Gener¬ 

ator Against Salt Marsh Mosquitoes at Mantoloking , N. J., 
V. K. LaMer, S. Hochberg, J. Q. Umberger, I. Wilson, 
J. C. Rowell, J. Betheil, NDRC 10.2-23, National Re¬ 
search Council Insect Control Committee Report 134, 
Oct. 23, 1945. Div. 10-602.21-M6 

33. Cankerworms as Test Insects for DDT Field Tests of 
Models of the Hochberg-LaMer Insecticidal Aerosol Gener¬ 
ator at Hempstead Lake State Park, Long Island, New 
York, V. K. LaMer, S. Hochberg, J. Q. Umberger, J. 
Betheil, OSRD 6004, National Research Council Insect 
Control Committee Report 124, Sept. 28, 1945. 

Div. 10-602.23-MI 

34. Black Fly Control with DDT-Oil Aerosol Using the Hoch¬ 
berg-LaMer Generator with Notes on Spruce Bud Worm and 
Larch Case Bearer Control at Lake Placid, New York, V. K. 
LaMer, NDRC 10.2-26, National Research Council In¬ 
sect Control Committee Report 140, Nov. 8, 1945. 

Div. 10-602.23-M4 

35. Report of the Use of Hochberg-LaMer Aerosol Generator for 
Dispersing DDT to Control the Spruce Budworm, G. L. 
Osberg and B. W. Flaherty, Chemical Warfare Labora¬ 
tories, Ottawa, Research Section Report No. 59, No¬ 
vember 1945. 

36. Development of an Exhaust DDT Aerosol Generator for the 

1 /4-Ton 4x4 Truck (“Jeep”), H. F. Johnstone, R. L. 
LeTourneau, R. I. Rice, and H. F. Hrubecky, OSRD 
6301, National Research Council Insect Control Com¬ 
mittee 139, Nov. 7, 1945. Div. 10-602.122-M3 

37. Installation of an Exhaust DDT Aerosol Generator on 
the Cargo Carrier M29C (Weasel), H. F. Johnstone and 
R. I. Rice, NDRC 10.4-84, National Research Council 
Insect Control Committee Report 102, July 20, 1945. 

Div. 10-602.122-M2 

38. Development of an Experimental Thermal Generator Pot for 

Dispersing Mustard Gas as an Aerosol, E. W. Comings, 
C. H. Adams, and M. H. Raila, OSRD 6431, Dec. 29, 
1945. Div. 10-504.1-M2 

39. Tests with an Exhaust Aerosol DDT Generator on a 450 

H.P. Stearman Aircraft, H. F. Johnstone, R. L. LeTour¬ 
neau, C. W. Kearns, R. J. Kallal, C. H. Adams, and R. L. 
Metcalf, OSRD 4399, OSRD Insect Control Committee 
Report 51, Nov. 29, 1944. Div. 10-602.121-MI 

40. CWS Monthly Progress Report on Insect and Rodent 
Control, April to September 1945. 


41. Application of Sprays by Means of Portable Spray Unit 
from Cub Planes, Bureau of Entomology and Plant 
Quarantine, U. S. Department of Agriculture, CC-2-421, 
April 1944. 

42. A Study of the Atomization of Liquids, H. F. Johnstone, 
H. C. Lewis, D. G. Edwards, M. J. Goglia, R. I. Rice, 
and L. W. Smith, OSRD 6345, National Research Coun¬ 
cil Insect Control Committee Report 148, Nov. 23, 1945. 

Div. 10-501.2-M6 

43. Progress Report for Month of August 1945, Biology Sec¬ 
tion, Health and Safety Department, Tennessee Valley 
Authority, A. D. Hess, September 1945. 

44. The Development of an Exhaust Smoke Generator for Mili¬ 

tary Aircraft, H. F. Johnstone and M. J. Goglia, OSRD 
5488, Aug. 25, 1945. Div. 10-501.203-M2 

45. Operational Procedures for Airplane Dispersal of DDT' 
Aerosol by Type TBM-3 Aircraft, B. Commoner, J. C. 
Early, and M. H. Tuttle, U. S. Naval Air Test Center, 
Patuxent No. NA83/A16-3/C-760, BC/egd(TT), June 
1945. 

46. Development and Test of Airplane Dispersal of DDT 
Aerosol, B. Commoner, L. E. McDonald, and M. H. 
Tuttle, U. S. Naval Air Station, Patuxent River, Mary¬ 
land, NA83(TT), BC/egd, A16-3, January 1945. 

47. Exhaust Aerosol Generator for Dispersal of DDT Solution 

with SB2C-4 Airplane, J. H. Clark, OSRD 5487, National 
Research Council Insect Control Committee 114, Aug. 25, 
1945. Div. 10-602.121-M3 

48. Exhaust Aerosol Generator on the PBJ-1H for the Dispersal 

of DDT and Oil Smoke, J. H. Clark, OSRD 5510, National 
Research Council Insect Control Committee Report 115, 
Aug. 30, 1945. Div. 10-602.121-M4 

49. Tests of Exhaust Generator Spray Equipment on C-47 Air¬ 
craft, Army Air Force Board Project J4670. 

50. The Development of an Exhaust DDT Aerosol Generator for 

the Taylorcraft Light Airplane, R. I. Rice, OSRD 6344, 
National Research Council Insect Control Committee 

Report 144, Nov. 23, 1945. Div. 10-602.121-M6 

51. Considerations on the Design of a DDT Exhaust Generator 
for L-5 Aircraft, H. F. Johnstone and R. J. Kallal, 
NDRC 10.4-85, National Research Council Insect Con¬ 
trol Committee Report 165, December 1945. 

52. The Production of Aerosol Droplets Below 25 Microns 
Diameter for the Dispersal of Insecticides and CW Agents, 
H. F. Johnstone, R. L. LeTourneau, R. J. Kallal, and 
D. R. Powell, NDRC 10.4-60, Apr. 20, 1944. 

Div. 10-602-MI 

53. Monthly Progress Report from NDRC Munitions De¬ 
velopment Laboratory, University of Illinois, December 
1944. 

54. Test to Determine Suitability of Especially Designed Spray 
Equipment for the Dissemination of DDT from B-25 and 
C-47 Aircraft, Army Air Forces Board, Orlando, Florida, 
Project No. 4095BG725, April 1945. 

55. The Development of a Light High Explosive Bomb for Dis- 

persing Toxic and Insecticidal Aerosols , H. F. Johnstone, 
R. L. LeTourneau, H. C. Weingartner, D. R. Powell, 
P. N. Rylander, R. C. Johnson, and C. H. Simonson, 
OSRD 6565, Jan. 28, 1946. Div. 10-504.2-M12 

56. Monthly Progress Report from NDRC Munitions De- 


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670 


BIBLIOGRAPHY 


velopment Laboratory, University of Illinois, H. F. 
Johnstone and R. L. LeTourneau, May 1945. 

57. Sun Oil Company Solvent Aro-Sol (151B) as a Practical 
Solvent for DDT, V. K. LaMer, S. Hochberg, and J. 
Betheil, NDRC 10.2-22, OSRD Insect Control Com¬ 
mittee Report 60, Apr. 30, 1945. Div. 10-601.1-M2 

58. The Solubility of DDT in Mixtures of Xylene and Lubri¬ 
cating Oil ( 10W ), The Density of These Solutions when 
Saturated with DDT , V. K. LaMer, S. Hochberg, and J. 
Betheil, NDRC 10.2-20, National Research Council In¬ 
sect Control Committee Report 112, April 1945. 

Div. 10-601.1-MI 

59. Formulas Utilizing DDT Concentrate, V. K. LaMer, F. 
Brescia, I. Wilson, K. C. Hodges, J. C. Rowell, I. Johnson, 
J. Betheil, OSRD 5729, National Research Council Insect 
Control Committee Report 120, Aug. 18, 1945. 

Div. 10-601.2-M2 

60. “Efficiency of DDT as a Residual-Type Spray Against 
Adult Disease-Carrying Mosquitoes — Laboratory 
Tests,” J. B. Gahan, B. V. Travis, and A. W. Lindquist, 
J. Economic Entomology, 38, 1945, pp. 236-240. 

61. Slope-o-Meter; an Instrument for the Rapid Determination 


Chap 

1. “The Preparation and Properties of Disulfur Deca- 
fluoride,” Kenneth G. Denbigh and Robert Whytlaw- 
Gray, J. Chem. Soc., 1934, p. 1346. 

2. Agent F5, C. B. Griffine, Jr., A Memorandum Report 
TDMR 971, Feb. 3, 1945. 

3. Report on Improved Methods of Preparation and Prelim¬ 
inary Study of Physical and Chemical Properties of Com¬ 
pound 1120, A. B. Burg, OSRD 179, Nov. 15, 1941. 

Div. 10-402.32-MI 

4. The Fluorides of Sulfur, Part III, J. H. Simons, OSRD 

Report, May 13, 1942. Div. 10-402.311-M2 

5. The Preparation and Properties of 1120 — II, A. B. Burg, 
OSRD 294, Serial No. 149, Dec. 30, 1941. 

Div. 10-402.32-MI 

6. The Fluorides of Sulfur, Part 1, J. H. Simons, The Penn¬ 
sylvania State College, Contract Report, Jan. 24, 1942. 

Div. 10-402.311-M2 

7. Final Report on Contract OEMsr-299, L. F. Audrieth and 
John C. Bailar, Jr., Aug. 1, 1945. 

8. A Study of the Preparation of Compound 1120 Through the 

Use of a Regenerative Chemical, G. L. Clark and P. M. 
Bernays, University of Illinois, Contract Report, Feb. 15, 
1942. Div. 10-402.32-M3 

9. The Fluorides of Sulfur, Part II, J. H. Simons, The Penn¬ 
sylvania State College, Contract Report, Mar. 13, 1942. 

Div. 10-402.311-M2 

10. “The Fluorides and Oxyfluorides of Sulfur,” M. Trautz 
and K. Ehrmann, J. prakt. Chem., 142, 1935, p. 79. 

11. The Chemistry of the Sulfur Fluorides, J. H. Simons, 

OSRD 1036, Oct, 21, 1942. Div. 10-402.2-M5 

12. Final Summary Report, Contract NDCrc-113, A. B. 

Burg, June 5, 1944. Div. 10-402.36-M8 

13. Heat of Formation of S 2 F 10 , H. M. Huffman, J. B. Hatcher, 
and E. L. Ellis, OSRD 776, July 29, 1942. 

Div. 10-402.36-M3 


of Particle Radius and Concentration in the Laboratory and 
Field, NDRC 10.2-15, V. K. LaMer, June 19, 1944. 

Div. 10-501.11-M9 

62. The Cascade Impactor, an Apparatus for Sampling Solid 
and Liquid Particulate Clouds, K. R. May, Ptn. Report 
No. 2463, December 1942. 

63. CWS Monthly Progress Report on Insect and Rodent 
Control, September 1945. 

64. Particulate Program — Comparison of Carbon Coated and 
Magnesium Oxide Coated Slides, D. Benedict, S. Black, 
K. P. DuBois, R. G. Herrmann, A. McGinnis, H. E. 
Landahl, J. Savit, and W. R. Schmitz, The University of 
Chicago Toxicity Laboratory Informal Progress Report 
NS-1, April 1945. 

65. Informal Progress Reports from University of Chicago 
Toxicity Laboratory NS-1 to NS-5, W. L. Doyle et al, 
April to August 1945. 

66. Comparison of Sample Methods for Measuring Aerosols 
Cts, Captain Charles R. Naeser, Report of Conference at 
Edgewood Arsenal, Maryland, CWS Technical Com¬ 
mand, June 26, 27, 28, 1945, July 1945. 


er 39 

Calorimetric Studies II. The Entropy and Free Energy of 
S 2 F l0 , H. M. Huffman, J. B. Hatcher, and G. B. Guthrie, 
OSRD 934, Oct. 10, 1942. Div. 10-402.36-M4 

Thermodynamic Data on S 2 F W , H. M. Huffman, OSRD 
1055, Nov. 21, 1942. Div. 10-402.36-M5 

14. The Chemical Detection of 1120 , D. S. Tarbell, OSRD 879, 

July 1, 1942. Div. 9-422.121-M3 

15. “The Determination of Fluorine bv Precipitation as 
Triphenyltin Fluoride,” N. Allen and N. Howell Furman, 
J. Am. Chem. Soc., 54. 1932, p. 4625. 

16. “Esters of Monofluophosphoric Acid,” W. Lange and 
G. v. Krueger, Ber. 65B, 1932, p. 1598. 

17. Progress Reports, L. F. Audrieth and J. C. Bailar, Jr. 
University of Illinois, June 16, 1942 and July 15, 1942. 

Div. 10-402.311-M4 
Div. 10-402.311-M5 

18. A Report on FIuophosphates and Related Compounds, L. F. 
Audrieth and J. C. Bailar, Jr., University of Illinois 
Contract Reports, Oct. 15, 1942 and Nov. 15, 1942. 

Div. 10-402.311-M13 

19. Report No. 5 on Fluophosphates, II. McCombie, British 
Report W-8285. 

20. A Report on Fluophosphates and Related Compounds, J. C. 

Bailar, Jr., M. M. Woyski, C. D. Wagner, and J. E. 
Husted, University of Illinois Contract Reports, Jan. 15, 
1943 and Feb. 15, 1943. Div. 10-402.311-M14 

21. A Report on Fluophosphates and Related Compounds , J. C. 
Bailar, Jr., M. M. Woyski, and J. E. Husted, University 
of Illinois Contract Reports, Mar. 15, 1943. 

Div. 10-402.311-M14 

22. “Action of Phosphorus Trichloride on Glycerine and 
Glycol,” Bull. soc. Chim. (3), 27, 1902, p. 268. 

23. “Brenzcatechyl-phosphorus Oxychloride and o-Phenylene 
Phosphate,” L. Anschutz and W. Brocker, J. prakt. 
Chem., 223, 1926-27, p. 379. 


SECRET 



BIBLIOGRAPHY 


071 


24. A Report on Fluophosphates and Related Compounds, J. C. 
Bailar, Jr., M. M. Woyski, and J. E. Husted, University 
of Illinois Contract Report, Apr. 15, 1943. 

Div. 10-402.311-M14 

25. Report No. 9 on Fluophosphates, H. McCombie, Y-3043, 
WA.579-5, B-2929. 

A Report on Fluophosphates and Related Compounds, J. C. 
Bailar, Jr., J. B. Ziegler, Jr., and M. M. Woyski, Uni¬ 
versity of Illinois Contract Report, October 1943. 

Div. 10-402.311-M13 

26. “The Fluorination of Phosphorus Trichloride,” H. S. 
Booth and F. B. Dutton, J. Am. Chem. Soc., 61, 1939, 
p. 2937. 

27. Final Report on Contract OEMsr-299, J. C. Bailar, Jr. and 
L. F. Audrieth, University of Illinois, Aug. 1, 1945. 

28. The Alkyl Difluophosphates and the Mono- and Difluo- 
thiophosphates, L. F. Audrieth and J. C. Bailar, Jr., 
University of Illinois Contract Report, Sept. 15, 1942. 

Div. 10-402.311-M12 

29. Fluosulfonic Acid and Its Alkyl Esters, L. F. Audrieth 


and J. C. Bailar, Jr., University of Illinois Contract Re¬ 
port, July 15, 1942. Div. 10-402.311-M 6 

30. “Fluosulfonic Acid,” T. E. Thorpe and Walter Kirman, 
J. Am. Chem. Soc., 61, 1892, p. 921. 

31. “Hydrofluoric Acid and Fluosulfonic Acid,” O. Ruff and 
H. J. Braun, Ber., 47, 1914, p. 646. 

32. “Esters of Fluosulfonic Acid,” J. Meyer and G. Schramm, 
Z. anorg. allgem. Chem., 206, 1932, p. 24. 

33. The Preparation of New Toxic Gases, A. B. Burg, OSRD 

4012, June 5, 1944. Div. 10-402.36-M8 

34. Studies Relating to Phosphorus Trifluoride, A. B. Burg, 

NDRC CLIX, July 27, 1942. Div. 10-402.311-M7 

35. New Toxic Gases IX, A. B. Burg, D. L. Armstrong, and 

R. N. Doescher, University of Southern California Con¬ 
tract Report, Apr. 15, 1943. Div. 10-402.311-M15 

36. The Preparation of Acyl Fluorides, J. H. Simons, NDRC 

LIV, Dec. 16, 1941. Div. 10-402.311-M 1 

37. Vapor Pressure of Arsine in Various Solvents, L. F. 
Audrieth and J. C. Bailar, Jr., University of Illinois 
Contract Report, June 17, 1942. 


Chapter 40 


1. The Generation of Fluorine, W. C. Schumb, E. L. Gam¬ 
ble, H. H. Anderson, and A. J. Stevens, NDRC CXCV, 
Oct. 17, 1942. 

The Generation of Fluorine , W. C. Schumb, OSRD 984, 
Nov. 3, 1942. Div. 10-402.31-MI 

2. Electrolytic Cell for Producing Fluorine, W. S. Calcott and 
A. F. Benning, E. I. duPont de Nemours and Co., United 
States Patent 2,034,458, Mar. 17, 1936. 

3. An Electrolytic Cell Designed for Fluorine Production, J. H. 
Simons, OSRD 4199, July 24, 1942. Div. 9-252-MI 

4. The Production of Fluorine by Electrolysis, R. C. McHar- 
ness, R. G. Benner, et al, E. I. duPont de Nemours and 
Company, OSRD 1114, Dec. 9, 1942. 

Div. 10-402.31-M3 

5. The Generation of Fluorine, W. C. Schumb, E. L. Gamble, 

H. H. Anderson, and A. J. Stevens, NDRC 10.3B-4, Jan. 
15, 1943. Div. 10-402.31-M2 

6. The Generation of Fluorine, W. C. Schumb, E. L. Gam¬ 
ble, H. H. Anderson, and A. J. Stevens, NDRC 10.3B-24, 


June 15, 1943; OSRD 1690, June 15, 1943. 

Div. 10-402.31-M4 

7. The Generation of Fluorine, W. C. Schumb, Massachu¬ 

setts Institute of Technology Contract Report, Nov. 15, 
1942. Div. 10-402.31-M2 

8. The Generation of Fluorine, W. C. Schumb, E. L. Gam¬ 

ble, H. H. Anderson, and A. J. Stevens, NDRC 10.3B-18, 
Apr. 15, 1943. Div. 10-402.31-M2 

9. The Generation of Fluorine , W. C. Schumb, E. L. Gamble, 

and A. J. Stevens, NDRC 10.3B-28, July 15, 1943. 

Div. 10-402.31-M2 

10. The Generation of Fluorine, W. C. Schumb, E. L. Gamble, 

H. H. Anderson, and A. J. Stevens, NDRC 10.3B-15, 
Mar. 15, 1943. Div. 10-402.31-M2 

11. The Generation of Fluorine, W. C. Schumb, E. L. Gamble, 

H. H. Anderson, and A. J. Stevens, NDRC 10.3B-22, 
May 15, 1943. Div. 10-402.31-M2 

12. The Generation of Fluorine, W. C. Schumb, OSRD 3227, 

Feb. 9, 1944. Div. 10-402.31-M4 


Chapter 41 


1. C. A. Wurtz, Ann. Chem. (Liebig), 79, 1851, p. 285. 

2. W. L. Jennings and W. B. Scott, J. Am. Chem. Soc., 41, 
1919, p. 1241. 

3. F. D. Chattaway and J. M. Wadmore, J. Am. Chem. Soc., 
81, 1902, p. 191. 

4. T. S. Price and S. J. Green, J. Soc. Chem. Ind., 39, 1920, 
p. 98T. 

5. W. M. Latimer, NDRC reports dated April 14 and 
August 14, 1942. 


6. Reports Under Contract No. W-285-CWS-4782, Ameri¬ 
can Cyanamid Co., October 1942 to December 1943. 

7. Monthly and Final Reports under Contracts OEMsr- 
1004, W-18-035-CWS-883, and W-18-035-CWS-1257, 
August 1943 through December 1946; A. B. Burg et al. 

8. Weekly Reports of Dugway Proving Ground, 1943-46. 

9. M. S. Kharasch, Reports under Contract No. OEMsr-394. 

10. J. H. Yoe, Reports under Contract No. OEMsr-139. 


Chapter 42 

1. Final Summary Report under Contract OEMsr-1004, 3. Monthly Reports under Contract No. W-18-035-CWS- 

Part (a), A. B. Burg. 883, A. B. Burg et al. 

2. Weekly Reports of Dugway Proving Ground. 


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672 


BIBLIOGRAPHY 


1 . 

2 . 

3. 


4. 


6 . 

7. 

8 . 
9. 

10 . 


1 . 

2 . 

3. 

4. 

5 . 


6 . 


7. 


8 . 


9. 


Chapter 43 


Scale Model Studies of the Movement of Smoke and Gas 
Clouds, H. Rouse, NDRC 10.3A-36, Oct. 10, 1943. 

Div. 10-302.1-M15 

Local Dissipation of Natural Fog , H. G. Houghton and 
W. H. Radford, Massachusetts Institute of Technology, 
1938. 

Wind-Tunnel Studies of the Diffusion of Heat from a Line 
Source , H. Rouse, M. L. Albertson, R. A. Jensen, and 

C. F. Schadt, NDRC 10.2-12, Mar. 18, 1944. 

Div. 10-401.121-MI 
Fog-Dispersal Recommendations for the Island of Shemya, 
H. Rouse, M. L. Albertson, R. A. Jensen, and C. F. 
Schadt, Informal Report to Division 10, NDRC, Dec. 26, 
1944. 

Fog-Dispersal Recommendations for the Island of Shemya, 
Supplementary letter of Jan. 15, 1945, from H. Rouse to 
W. A. Noyes, Jr. 

The Iowa Radiant Burner , H. O. Croft and J. M. Trummel, 
Informal Report to Division 10, NDRC, Apr. 30, 1945. 
Development of a Fog-Dispersal Burner for Gasoline and 
Fuel Oil , M. L. Albertson, Informal Report to Division 10, 
NDRC, June 15, 1945. 

Fuel Nozzle for Fog Dispersal Equipment , J. B. Hoffman, 
Informal Report to Division 10, NDRC, Oct. 1, 1945. 
Study of the Use of Air Curtains for Fog Dissipation , A. P. 
Kratz, E. C. Manthei, and C. F. Holley, Jr., OSRD 3775, 
June 13, 1944. Div. 10-503.2-M4 

Wind-Tunnel Studies of the Diffusion of Heat by Single 
Wind Curtains and Baffles, H. Rouse, M. L. Albertson, 
R. A. Jensen, and D. F. Schadt, OSRD 4334, Nov. 11, 
1944. Div. 10-401.121-M3 


11. Wind-Curtain Installations for Fog Dispersal, R. A. Jen¬ 
sen, Informal Report to Division 10 NDRC, July 16, 
1945. 

12. Report on a Design Adapting the Principles of the Aerofoil 
Ring to the Wind Curtain Installation at Areata, California, 
T. D. Gregg, Informal Report to Division 10, NDRC, 
Oct. 27, 1945. 

13. Wind-Tunnel Studies of the Diffusion of Gas in Schematic 
Urban Districts, H. Rouse, M. L. Albertson, R. A. Jensen, 
and C. F. Schadt, NDRC 10.3A-46, May 9, 1944. 

14. Wind-Tunnel Studies of Gas Diffusion in a Typical Japa¬ 
nese Urban District, A. A. Kalinske, R. A. Jensen, and 
C. F. Schadt, NDRC 10.3A-48, June 8, 1945. 

Div. 10-401.121-M4 

15. Correlation of Wind-Tunnel Studies with Field Measure¬ 
ments of Gas Diffusion, A. A. Kalinske, R. A. Jensen, and 
C. F. Schadt, NDRC 10.3A-48a, Sept. 29, 1945. 

Div. 10-401.121-M5 

16. Diffusion of Smoke and Gas by Wind, (motion picture pre¬ 
pared for the Chemical Warfare Service by the Iowa 
Institute of Hydraulic Research through Division 10, 
NDRC). 

17. Preliminary Wind-Tunnel Studies on Air Flow Over 
Mountainous Terrain, A. A. Kalinske, R. A. Jensen, and 
C. F. Schadt, Informal Report to Division 10, NDRC, 
July 25, 1945. 

18. Wind-Tunnel Studies on Effects of Vertical Distortion of 
Terrain Models, report by the Iowa Institute of Hydraulic 
Research for the Weather Service of the Army Air Forces, 
Jan. 14, 1946. 


Chapter 44 


Report on Aerosols, W. H. Rodebush, OSRD 77, Mar. 12, 
1941. Div. 10-500-MI 

Rapid Methods of Preparing Phosgene, J. H. Simons, 
OSRD 88, Apr. 21, 1941. Div. 10-402.36-MI 

The Development of Laboratory Methods of Detecting and 
Analyzing Gases Containing Radioactive Sulfur , D. M. 
Yost, OSRD 127, Aug. 25, 1941. Div. 10-402.35-M3 
The Measurement of Radioactive Hydrogen, E. O. Law¬ 
rence, OSRD 128, Aug. 26, 1941. Div. 10-402.35-M4 
A Brief Investigation of Removal of Arsine in Air-Arsine 
Mixtures by Charcoal Using the Radioactive Tracer 
Method, D. M. Yost, OSRD 361, Jan. 9, 1942. 

Div. 10-202.154-M12 
A Study of the Removal of Arsine by Whetlerite, E. O. 
Wiig, OSRD 462, Mar. 23, 1942. Div. 10-202.154-M 15 
The Distribution of the Catalyst in Whetlerite; The Location 
and the Identification of the Reaction Products in Whetlerite 
Treated with Arsine, H. F. Johnstone and G. L. Clark, 
OSRD 704, June 1, 1942. Div. 10-202.14-M10 

Investigation of the Mechanism of Removal of Phosgene 
from Phosgene-Air Mixtures, Using the Radioactive Tracer 
Method, D. M. Yost, OSRD 903, Sept. 25, 1942. 

Div. 10-202.155-M5 
I. Rapid Methods for Synthesizing War Gases; II. The 
Chemistry of the Sulfur Fluorides, J. H. Simons, OSRD 
1036, Oct, 21, 1942. Div. 10-402.2-M5 


10. A Study of the Removal of Arsine and of Poisoning by Hy¬ 
drogen Cyanide; Preparation of Phosgene from Materials 
which Could Contain Radio-Chlorine, Parts 2 and 3 of a 
Joint Report, B6-1, Mar. 25, 1941. 

11. The Preparation of Radioactive Chlorpicrin, J. H. Simons, 

NDRC IV, May 28, 1941. Div. 10-402.35-MI 

12. Preparation of Radioactive Cyanogen Chloride, J. H. 
Simons, NDRC VIII, July 22, 1941. Div. 10-402.35-M2 

13. Use of Radioactive Tracer Technique for Arsine Removal, 

D. M. Yost, NDRC XXXIII, Sept, 30, 1941. 

Div. 10-202.154-M 7 

14. Conclusions from Investigations on the Adsorption of SA 
and the Distribution of the Arsenic on the Charcoal Bed, 

E. O. Wiig, NDRC XXXVI, Oct, 14, 1941. 

Div. 10-202.15-M5 

15. Preparation of Radioactive Hydrocyanic Add, J. H. 
Simons, NDRC LIII, December, 1941. 

Div. 10-402.35-M5 

16. Phosgene and Mustard Gas Removal, D. M. Yost, NDRC 

LXXI, Jan. 26, 1942. Div. 10-202.155-M2 

17. Preparation of Radioactive Selenium Hexafluoride, J. H. 
Simons, NDRC LXXXI, Feb. 12, 1942. 

Div. 10-402.35-M6 

18. Location of Silver on Silvered Whetlerite and Charcoals, 

H. F. Johnstone and G. L. Clark, NDRC CXIII, May 11, 
1942 * Div. 10-202.143-M2 


SECRET 



MICROFILMED REPORTS 


DIVISION 10 

Other reports which have been microfilmed are included in the following listing. 


Progress Report for Division 10, [Informal Report No.] I, (n.a.), 
[1941 (?)] Div. 10-101-MI 

Monthly Summary Report of Projects 10.1 and 104 , Division 10, 
NDRC, for the period of June 15 to July 15, 1943, 
(n.a.), [July 1943.] Div. 10-101-M3 

Division 10 Meeting, Dumbarton Oaks, D. C. October 26 and 
October 27, 1943, (n.a.), [October 1943.] Div. 10-101-M4 
Division 10 Meeting, Evanston, Illinois, January 28 and Janu¬ 
ary 29, 1944 j (n.a.), [January 1944.] Div. 10-101-M5 
Division 10 Meeting, Edgewood Arsenal, June 14, 1944, (n.a.), 
[June 1944.] Div. 10-101-M6 

Monthly Summary Reports of Section 10.1 of Division 10, 
NDRC, (n.a.), Feb. 15 and Mar. 15, 1945. 

Div. 10-101-M7 

Report on Trip to England, W. A. Noyes, Jr., NDRC VI, 
[June 1941.] Div. 10-102-MI 

Monthly Summary Report of Section 10.1 and 10.4 of Division 
10, NDRC, for the period of August 15 to September 15, 
1943, (n.a.), Sept. 15, 1943. Div. 10-200-M6 

Monthly Summary Report of the Central Laboratory, Division 
10, NDRC, (n.a.), Northwestern University, Apr. 15, 
1945. Div. 10-200-M8 

Canister Protection for Gases — A Survey, W. Conway Pierce 
and J. W. Zabor, Nov. 16, 1943. Div. 10-201.1-M21 
Accelerated Aging Studies, {[Part] IX, Supplement to Monthly 
Summary Report [of] August 15, 1944), T. Skei, C. 
Palmer, et al, Northwestern University, [Aug. 15, 1944.] 

Div. 10-201.1-M30 

Surveillance of Type ASC Whetlerite in M-10 %" Service 
Canisters, T. Skei, OEMsr-282, Service Project CWS-7, 
OSRD 4231, Northwestern University, Oct. 3, 1944. 

Div. 10-201.1-M31 

Summary of Investigations by the Engineering Pilot Group, 
([Paris] VII, IX, and XI to XVIII. Informal Reports 
10.4-23 and -31; 10.5-4, - 5, -8, -13, -16, -19, -27, and -31, 
for the period May 10 to August 10, 1943, and September 
10, 1943 to May 10, 1944), R- J- Kunz, J. C. Cooper, 
et al, OEMsr-282, Service Project CWS-7, North¬ 
western University. Div. 10-202.1-M10 

Accelerated Aging Studies, {[Study No.] Ill to IX for Decem¬ 
ber 15, 1943; January 15, February 15, March 15, April 
15, June 15, August 15, 1944), T. Skei, C. Palmer, et al, 
Northwestern University. Div. 10-202.16-M16 

Carbon Monoxide Removal, {Monthly Reports for the Period 
from July 15, 1943 to January 15, 1944), R- N. Pease, 
J. H. McLean, et al, NDCrc-131, Princeton University. 

Div. 10-202.2-M5 

Carbon Monoxide Removal and Drying Agents {Monthly Re¬ 
ports for March 15, June 15 {?), July 15, and August 15, 


1944), R. N. Pease, G. M. Brown, et al, NDCrc-131, 
Princeton University. Div. 10-202.2-M8 

Division 10 Meeting Northwestern Technological Institute, 
April 20 and April 21, 1943, Part I — Conference on 
Meteorology and Chemical Warfare, Part II — Protection 
Problems, Smoke Generators, and Development Problems, 
W. D. Walters and M. T. O’Shaughnessy, April 1943. 

Div. 10-300-MI 

Division 10 Meeting at National Academy of Sciences June 28 
and June 29, 1943, Part I — Conference on Practical 
Aspects of Division 10 Work in Relation to Chemical War¬ 
fare, Part II — Review of the Recent Work of Division 10, 
(n.a.), June 1943. Div. 10-300-M2 

Bibliography on Micrometeorology, 1927 to 1943 (as a supple¬ 
ment to the bibliography in Geiger’s Kima der boden- 
nahen luftschicht), I. Klotz, J. Colbert, G. J. Doyle, 
OEMsr-282, Northwestern University, Nov. 15, 1943. 

Div. 10-300-M3 

Progress Report for May, L. F. Audrieth and J. C. Bailar, Jr., 
letter to Dr. Noyes, University of Illinois, May 14, 1942. 

Div. 10-402.311-M3 

Preliminary Tube Tests with Various Substances, R. G. Dickin¬ 
son, NDCrc-137, California Institute of Technology, 
Aug. 5, 1942. Div. 10-402.11-M8 

The Preparation and Properties of 1120, ([Parts] IV, V, and 
VII), A. B. Burg, D. L. Armstrong, et al, [NDCrc-113,] 
University of Southern California, February 15, March 
20, and May 15, 1942. Div. 10-402.32-M4 

Calorimetric Studies of Compound 1120, H. B. Huffman, J. B. 
Hatcher, and E. L. Ellis, Cal. Inst, of Tech., Mar. 15, 

1942. Div. 10-402.32-M5 

Progress Report re 1120, J. H. Simons, letter to Dr. W. A. 

Noyes, Jr., Apr. 19, 1942. Div. 10-402.32-M6 

A Study of the Preparation of Compound 1120 Through the Use 
of a Regenerative Chemical, G. L. Clark, May 25, 1942. 

Div. 10-402.32-M7 

New Toxic Agents; Compound 1120, {Parts I to V, Progress 
Reports for the period [July 15] to December 21, 1942), 
A. B. Burg, D. L. Armstrong, and R. N. Doescher, 
NDCrc-113, Service Project CWS-26, University of Cali¬ 
fornia. Div. 10-402.32-M8 

Proceedings of Conference on Aerosols [at] Evanston, Illinois 
[from] February 25 to 27, 1943, (n.a.), February 1943. 

Div. 10-500-M2 

[Aerosols,] {Monthly Progress Reports for the months of Janu¬ 
ary 1944, and September 1944 lo June 1945), (n.a.), 
OEMsr-102, Service Project CWS-27, AC-108, and others, 
University of Illinois. Div. 10-500-M3 


SECRET 


673 


OSRD FORMAL REPORTS 


OSRD No. 

73 Production of Artificial Fog by Spraying Salt Solutions, 
W. G. Brown (W. K. Lewis), Jan. 17, 1941. 

Div. 10-503.1-MI 

77 Report on Aerosols, W. H. Rodebush, Mar. 12, 1941. 

Div. 10-500-MI 

80 Report on the Theory of Coagulation of Smokes in Closed 
Vessels, I. Langmuir, Mar. 27, 1941. Div. 10-501.1-MI 

84 A Preliminary Study of Adsorbents, Part I, H. F. John¬ 
stone and G. L. Clark; Part II, E. O. Wiig; Part III, 
F. T. Gucker, Jr.; Part IV, W. C. Pierce; Part V, T. F. 
Young; Part VI, P. H. Emmett, Apr. 24, 1941. 

Div. 10-202.151-MI 

88 Rapid Methods of Preparing Phosgene, J. H. Simons, 
Apr. 21, 1941. Div. 10-402.36-MI 

101 Filter Material, W. H. Rodebush, June 12, 1941. 

Div. 10-201.2-MI 

102 Cyanogen Chloride, W. M. Latimer, June 16, 1941. 

£)iv. 10-202.151-MI 

103 Investigations on the Adsorption of Hydrogen Cyanide and 
Arsine by Charcoals, E. O. Wiig, June 22, 1941. 

Div. 10-202.154-MI 

104 Methods of Studying the Removal of Selenium Hexaflu¬ 
oride, R. G. Dickinson, June 27, 1941. 

Div. 10-202.156-M2 

109 Smoke Production, E. W. Comings, June 27, 1941. 

Div. 10-504.4-MI 

111 The Removal of Ethylene I mine, P. A. Leighton, June 27, 
1941. Div. 10-402.2-MI 

119 Production, Analysis, and the Use of Aerosols of Uniform 
Particle Size, V. K. LaMer, Aug. 6, 1941. 

Div. 10-501-MI 

120 Aerosol Filter Materials, W. H. Rodebush, July 24, 1941. 

Div. 10-201.22-MI 

125 Studies on War Gas Detection and Analysis, J. H. Yoe, 
Aug. 24, 1941. Div. 10-402.2-M2 

127 The Development of Laboratory Methods of Detecting and 

Analyzing Gases Containing Radioactive Sulfur, D. M. 
Yost, Aug. 25, 1941. Div. 10-402.35-M3 

128 The Measurement of Radioactive Hydrogen, E. O. Law¬ 
rence, Aug. 26, 1941. Div. 10-402.35-M4 

132 The Deterioration of Thiocyanate Whetlerites, W. M. 
Latimer, Sept, 8, 1941. Div. 10-202.16-M2 

137 A Study of the Dispersion of Solids in Gases, R. Steven¬ 
son, Sept. 10, 1941. Div. 10-504.12-MI 

153 Mechanical Formation of Smokes, G, G. Brown, Oct, 18, 
1941. Div. 10-501-M2 

155 Analysis of Inhomogeneous Smoke, V. K. LaMer, Nov. 5, 
1941. Div. 10-501.11-MI 

167 Development of a Smoke Unit, E. W. Comings, Nov. 5, 

1941. Div. 10-504.4-M2 

168 Aerosol Filter Materials, W. H. Rodebush, Nov. 7, 1941. 

Div. 10-201.22-M3 

170 An Ultraviolet Photometer for the Detection and Quanti¬ 
tative Estimation of Very Small Concentrations of Noxious 
Gases in Air, M. Dole, Nov. 7, 1941. 

Div. 10-402.21-MI 


OSRD No. 

172 Studies on Impregnated Charcoal, H. F. Johnstone and 
G. L. Clark, Nov. 8, 1941. Div. 10-202.14-M4 

179 Improved Methods of Preparation and Preliminary Study 

of Physical and Chemical Properties of Compound 1120 , 
A. B. Burg, Nov. 15, 1941. Div. 10-402.32-MI 

180 Arsine Removal by Adsorbents, W. C. Pierce, Nov. 15, 

1941. Div. 10-202.154-M8 

181 The Effect of Particle Size on SA and A C Lives and on the 
Resistance of the Charcoal Bed, E. O. Wiig, Nov. 17, 1941. 

Div. 10-202.18-M2 

283 The Use of Gold Chloride and Potassium Permanganate 
as Arsine Breakpoint Indicators, E. O. Wiig, Dec. 18, 
1941. Div. 10-202.154-M10 

292 Studies of Particle Size in Smokes, H. Eyring, Dec. 8, 

1941. Div. 10-501.11-M2 
294 The Preparation and Properties of 1120 — II. A. B. 

Burg, Dec. 30, 1941. Div. 10-402.32-M2 

300 Preliminary Examination of 1120 Removal, R. G. Dickin¬ 
son, Dec. 18, 1941. Div. 10-202.156-M4 

304 The Removal of Hexamethylene Diamine, P. A. Leighton, 
Jan. 7, 1942. Div. 10-202.156-M6 

336 Sources of Mineral Fiber and Dispersion of Asbestos, 
Arthur D. Little, Inc., Nov. 3, 1942. 

Div. 10-201.22-M2 

361 A Brief Investigation of Removal of Arsine in Air-Arsine 
Mixtures by Charcoal Using the Radioactive Tracer 
Method, D. M. Yost, Jan. 7, 1942. 

Div. 10-202.154-M12 

362 Secondary Impregnation of Whetlerites with Mercury 
Compounds for the Production of Moisture-Resistant SA 
Catalysts, A. P. Colburn, Jan. 21, 1942. 

Div. 10-202.141-M5 

363 Cyanogen Chloride, II, W. M. Latimer, Jan. 21, 1942. 

Div. 10-202.152-M3 

364 Production of Smokes of Homogeneous Particle Size for 
Screening Tests and Development of Dyes from Thermally 
Dispersed Smokes, V. K. LaMer, Jan. 29, 1942. 

Div. 10-501.11-M3 

375 Mechanical Formation of Fogs, W. G. Brown, Feb. 26, 

1942. Div. 10-503.1-M2 
414 The Formation of Screening Smokes } G. G. Brown, 

Feb. 26, 1942. Div. 10-502-MI 

431 Asbestos Fibers of Small Diameter and Dispersion of 
Solids, A. D. Little, Inc., Mar. 2, 1942. 

Div. 10-201.22-M4 

436 Screening Smokes, T. K. Sherwood, Mar. 3, 1942. 

Div. 10-502-M2 

437 The Value of Soda Lime in Gas Adsorbents, W. C. Pierce, 
E. O. Wiig, P. A. Leighton, R. G. Dickinson, W. M. 
Latimer, M. Dole, and W. A. Noyes, Jr., Mar. 6, 1942. 

Div. 10-202.2-M2 

448 The Effect of Concentration and Temperature on the AC 
Life of Standard Whetlerite, E. O. Wiig, Feb. 29, 1942. 

Div. 10-202.16-M3 

449 Electrical Resistance and Temperature of Charcoals, M. 

Dole, Dec. 13, 1941. Div. 10-202.15-M7 


674 


SECRET 


BIBLIOGRAPHY 


675 


OSRD No. 

462 A Study of the Removal of Arsine by Whetlerite , E. O. 

Wiig, Mar. 23, 1942. Div. 10-202.154-M 15 

468 Production of Smokes of Controlled Size by the Use of In¬ 
duction Nozzles, H. C. Hottel, Jan. 21, 1942. 

Div. 10-501.2-MI 

472 A Search for New Reactants, F. E. Blacet, Mar. 12, 1942. 

Div. 10-202.141-M7 

487 Smoke Generator, I. Langmuir, Mar. 31, 1942. 

Div. 10-501.201-MI 

496 Studies of the Preparation and Evaluation of Gas Mask 
Adsorbents, A Summary of the Activities of Section B-6 
to March 13, 1942, W. L. McCabe, R. York, P. H. Em¬ 
mett, T. F. Young, H. F. Johnstone, J. C. Elgin, W. M. 
Latimer, W. C. Pierce, M. Dole, Mar. 13, 1942. 

Div. 10-202.1-M2 

518 Development of a Smoke Unit, E. W. Comings, Apr. 23, 
1942. Div. 10-504.12-M2 

533 Phosphorus Trifluoride Removal by Whetlerite and by 
Soda Lime — Whetlerite Admixtures, R. G. Dickinson, 
Apr. 6, 1942. Div. 10-202.156-M8 

537 Use of Aqueous Solutions for Producing Screening Fogs 
or Smokes by Pneumatic Spray Nozzles, A. R. Olson and 
G. D. Gould, Apr. 29, 1942. Div. 10-502-M4 

561 Hydrogen Cyanide Removal by Gas Mask Absorbent, E. O. 

Wiig, Apr. 6, 1942. Div. 10-202.154-M 16 

571 Stability of Cyanogen Chloride. Constants for Various 
Charcoals With Cyanogen Chloride, Preparation of 
Cyanogen and Nitrosyl Chloride, W. M. Latimer, 
Apr. 14, 1942. Div. 10-202.152-M4 

586 Studies on Impregnation, J. C. Elgin, Apr. 9, 1942. 

Div. 10-202.14-M7 

594 Effect of Water Upon the Removal of Arsine by Whetlerite, 
E. O. Wiig, May 20, 1942. Div. 10-202.154-M21 

616 Comparative Retentivities of Whetlerites and Type D Mix¬ 
ture for SeF o and for 1120, R. G. Dickinson, June 9, 1942. 

Div. 10-202.156-M12 
621 A Study of the Physical Variables in the Production of 
Whetlerite and Silvered Whetlerite, F. E. Blacet, June 9, 
1942. Div. 10-202.12-M3 

628 A Study of the Poisoning of Various Absorbents Toward 
Arsine by Hydrogen Cyanide, E. O. Wiig, June 6, 1942. 

Div. 10-202.154-M22 

629 The Use of Mercury Compounds in the Impregnation of 
Activated Charcoal, F. E. Blacet, May 25, 1942. 

Div. 10-202.141-M10 

703 Removal of Chloropicrin and the Nature of its Desorption 
Product. The Removal of Chloracetophenone as a Smoke at 
Low Temperature, G. P. Baxter, July 1, 1942. 

Div. 10-202.155-M3 

704 Part I. The Distribution of the Catalyst in Whetlerite; 

Part II. The Location and Identification of Reaction 
Products in Whetlerite Treated with Arsine, H. F. John¬ 
stone, June 1, 1942. Div. 10-202.14-M10 

710 Arsine and Hydrogen Cyanide, E. O. Wiig, July 1, 1942. 

Div. 10-202.154-M23 
720 I. Correlation of Canister Test Life with Human Tolerance 
for Cyanogen Chloride. II. The Cyanogen Chloride Pro¬ 
tection Afforded by Humidified Adsorbents, W. C. Pierce, 
June 29, 1942. Div. 10-201.1-M4 


OSRD No. 

759 The Effect of Organic Vapors on Service Lives of Whetler¬ 
ites and Type D. Mixtures, R. G. Dickinson, D. N. Yost, 
E. O. Wiig, W. M. Latimer, P. A. Leighton, July 29, 
1942. Div. 10-202.16-M9 

776 Heat of Formation of S 2 Fi Q , Hugh M. Huffman, July 29, 
1942. Div. 10-402.36-M3 

849 Rate of Sorption of Water Vapor from Humid Air Streams 
by Activated Carbons, A. P. Colburn, Sept. 1, 1942. 

851 Temperature in Canister and Tubes During SA Removal, 
M. Dole, I. Klotz, R. K. Brinton, Strodtz, J. B. Fehren- 
bacher, July 25, 1942. Div. 10-202.1-M5 

853 Impregnation of Activated Charcoals to Obtain High &A 
Lives, A. P. Colburn, September 1942. 

Div. 10-202.141-M 13 
865 Filtration of Aerosols and the Development of Filter Ma¬ 
terials, W. H. Rodebush, I. Langmuir, V. K. LaMer, 
Sept. 4, 1942. Div. 10-201.22-M5 

903 An Investigation of the Mechanism of Removal of Phosgene 
From Phosgene-Air Mixtures by Charcoal, Using the 
Radioactive Tracer Method, D. M. Yost, Sept. 25, 1942. 

Div. 10-202.155-M5 

934 Calorimetric Studies II, The Entropy and Free Energy of 
S 2 Fi 0 , H. M. Huffman, Oct. 10, 1942. 

Div. 10-402.36-M4 

940 Screening Smokes, W. H. Rodebush, V. K. LaMer, I. 
Langmuir, T. K. Sherwood, Oct. 5, 1942. 

Div. 10-502-M5 

956 Activation of Gas Charcoal by a New Jiggler Process, R. 

York, Jr., July 31, 1942. Div. 10-202.131-M3 

962 Studies and Investigations in Connection With the Disper¬ 
sion of Solids, A. D. Little, Inc., Oct. 31, 1942. 

Div. 10-201.22-M6 

970 A Summary of Tests on Soda Lime, W. C. Pierce, Oct. 21, 
1942. Div. 10-202.2-M3 

972 Adsorption Studies on Chloropicrin and Phosgene, Dole 
and Klotz, July 15, 1942. Div. 10-202.155-M4 

974 Interaction of Hydrogen Cyanide with Various Adsorbents, 
R. N. Pease, Oct, 21, 1942. Div. 10-202.151-M5 

980 The Mechanical Formation of Screening Smokes Using 
Salt Solutions, G. G. Brown, Oct. 29, 1942. 

Div. 10-502-M6 

984 The Generation of Fluorine, W. C. Schumb, Nov. 3, 1942. 

Div. 10-402.31-MI 

993 Studies on the Design of Collective Protectors, T. B. Drew, * 
Oct, 15, 1942. Div. 9-212.11-M3 

998 The Penetration and Persistence of Carbon Dioxide when 
Released in an Enclosed Court, F. E. Blacet, H. F. John¬ 
stone, Oct. 30, 1942. Div. 10-401.122-MI 

1002 Preparation of Wood Charcoal , W. L. McCabe, Oct. 21, 
1942. Div. 10-202.12-M6 

1028 Studies of the Preparation and Evaluation of Gas Mask 
Adsorbent — A Summary of the Activities of Section B-6 
August 7, 1942, F. E. Blacet, M. Dole, H. F. Johnstone, 
Kunz, W. M. Latimer, W. C. Pierce, T. F. Young, 
Aug. 8, 1942. Div. 10-202-MI 

1036 I. Rapid Methods for Synthesizing Certain War Gases. 
II. The Chemistry of the Sulfur Fluorides t J. H. Simons, 
Oct, 21, 1942. Div. 10-402.2-M5 


SECRET 





BIBLIOGRAPHY 


(576 


OSRD No. 

1048 Preparation of Superfine Organic Fibers from Cellulose 
Esters, Tennessee Eastman Corporation, Oct. 26, 1942. 

Div. 10-201.22-M7 

1053 Thermodynamic Data on S*F ]0 , H. M. Huffman, Oct. 21, 
1942. Div. 10-402.36-M5 

1055 Variation of the CG Life of Various Humidified Adsorbents 
with Decreasing Temperature, W. C. Pierce, Oct. 26, 
1942. Div. 10-202.16-M10 

• 1072 Retentivity Tests with Hydrogen Fluoride, R. G. Dickin¬ 
son, Dec. 8, 1942. Div. 10-202.156-M17 

1076 I, Toxic Smoke Candle and II, Screening Smoke Units, 

E. W. Comings, Dec. 1, 1942. Div. 10-504.12-M3 

1081 Studies of Canister Performance at High Humidities and 

Flow Rates, W. C. Pierce, Dec. 7, 1942. 

Div. 10-201.1-M11 

1090 Animal and Chemical Tests on Cyanogen in Effluent Air 
Stream After Adsorption of HCN, W. C. Pierce, Dec. 7, 
1942. Div. 10-202.152-M8 

1106 Preliminary Tube Tests with COCIF, R. G. Dickinson, 
Dec. 8, 1942. Div. 10-202.152-M9 

1114 The Production of Fluorine by Electrolysis, E. I. duPont 
de Nemours & Co., Dec. 9, 1942. Div. 10-402.31-M3 

1125 Third Report on the Comparison of Impregnated Charcoals, 

F. E. Blacet, Dec. 9, 1942. Div. 10-202.14-M18 

1126 Experiments with Type A *8 Whetlerites at Fostoria, Co¬ 
lumbus, and Zanesville, Ohio, F. E. Blacet, Dec. 9, 1942. 

Div. 10-202.1-M 7 

1133 Studies of the Adsorption Wave for PS on Carbon, J. E. 
Elgin, Dec. 9, 1942. Div. 10-202.157-M6 

1143 A Study of the Impregnated Charcoal by X-Ray Diffrac¬ 

tion Methods, H. F. Johnstone and G. L. Clark, Dec. 9, 
1942. Div. 10-202.143-M4 

1144 Determination of the Vapor Pressure of HS, W. C. Pierce, 

Dec. 9, 1942. Div. 10-402.2-M6 

1169 Summary of the Work on Division 10 Projects During the 
Period from November 16 to December 16, 1942, W. C. 
Pierce, W. H. Rodebush, D. M. Yost, H. F. Johnstone. 

Div. 10-101-M2 

1175 Analytical Methods for Whetlerites and Whetlerizing So¬ 
lutions, F. E. Blacet, Feb. 3, 1943. 

Div. 10-202.14-M21 

1176 The “Pancake” Effect in Gas Clouds, W. M. Latimer, 

Feb. 3, 1943. Div. 10-401.123-MI 

1182 Summary of Results in Section B-6, December 1941 to 
August 1942, W. A. Noyes, Jr., Feb. 6, 1943. 

Div. 10-200-M5 

1193 An Intermittent Flow Canister Test Machine, W. C. 

Pierce, Jan. 28, 1943. Div. 10-201.1-M 12 

1194 Performance of the M10 Canister Against HS Under 
Humid Tropical Conditions, W. C. Pierce, Feb. 3, 1943. 

Div. 10-201.1-M 13 

1201 Composition of Gas Evolved from Drying Whetlerites, 
F. E. Blacet, Jan. 4, 1943. 

1268 Summary of a Review on Hydrogen Cyanide, Cyanogen, 
Cyanogen Chloride Removal by Gas Mask Absorbents, 
E. O. Wiig, Mar. 22, 1943. Div. 10-202.154-M31 

1280 The Preparation of Wood Charcoal Suitable for Activation, 
W. L. McCabe, Mar. 24, 1943. Div. 10-202.12-M8 


OSRD No. 

1321 Practical Consideration Involved in the Use of Screening 
Smokes, W. H. Rodebush, Apr. 24, 1943. 

Div. 10-502-M7 

1349 Changes in Properties of PCI Charcoal and Whetlerite 
During Activation, F. E. Blacet, Apr. 24, 1943. 

Div. 10-202.13-M12 

1350 The Vulnerability of United States, Canadian and British 

Canisters Toward CC at High Humidities, W. C. Pierce, 
Apr. 28, 1943. Div. 10-201.32-MI 

1351 Study of the Partial Vapor Pressures of the Volatile Con¬ 

stituents in Whetlerizing Solutions, F. E. Blacet, Apr. 20, 
1943. Div. 10-202.19-M3 

1352 The Preparation and Surveillance of Hexamethylenetetra¬ 
mine-impregnated Charcoals, F. E. Blacet, Apr. 28, 1943. 

Div. 10-202.14-M23 

1447 I. Nitrobenzene as a Compound to Simulate HS. II. Dis- 
tribution of Nitrobenzene Vapors in a Closed Room, M. 
Dole, July 5, 1943. Div. 10-402.2-M9 

1453 The Gas Protection of the M10 Canister, W. C. Pierce, 

June 3, 1943. Div. 10-201.1-M 14 

1454 ASCM Whetlerite, E. O. Wiig, June 7, 1943. 

Div. 10-202.1-M 11 

1455 ASM Whetlerite, E. O. Wiig, May 25, 1943. 

Div. 10-202.12-M9 

1456 A Comparison of Canadian and American Light-Type 
Canisters, W. C. Pierce, June 7, 1943. 

Div. 10-201.32-M2 

1477 Thermal Data on KB-14 and KB-16, H. F. Huffman, 

June 8, 1943. Div. 10-402.36-M7 

1521 Further Development of a Laboratory Type Jiggler for 
Activating Gas Charcoal, and Tentative Results of Gasifi¬ 
cation Rate Studies, R. York, Jr., June 25, 1943. 

Div. 10-202.131-M4 

1526 Micro meteorological Observations at U. S. Army Smoke 
Tests in the Los Angeles Area, March 17-18-19 , and 
April 20, 1943, R. G. Dickinson, June 19, 1943. 

Div. 10-302.1-M8 

1527 An Investigation of the Possible Explosion Hazard Pre¬ 

sented by Silver Whetlerizing Solutions and Residues, 
F. E. Blacet, June 26, 1943. Div. 10-202.14-M26 

1569 Persistence Experiments with Sulfur Dioxide in a Wooded 
Area, F. E. Blacet, July 13, 1943. Div. 10-302.2-MI 

1626 Additional Study of the Partial Vapor Pressures of the 
Volatile Constituents in Whetlerizing Solutions, F. E. 
Blacet, June 21, 1943. Div. 10-202.14-M27 

1667 Dissipation of Water Fog by Intense Sound of Audible 
Frequency, V. K. LaMer and D. Sinclair, Aug. 17, 1943. 

Div. 10-503.2-MI 

1668 A Portable Optical Instrument for the Measurement for the 

Particle Size in Smokes, the “ Owl ”, and an Improved 
Homogeneous Aerosol Generator, V. K. LaMer, D. 
Sinclair, Aug. 24, 1943. Div. 10-501.11-M6 

1686 Application of the Electron Microscope to the Study of 
Charcoal, H. F. Johnstone and G. L. Clark, Aug. 7,1943. 

Div. 10-202.143-M5 

1687 Large Scale Screening Tests, Camp Sibert, Alabama, 
May 4~7, 1943, Part I — Rodebush, Part II, Johnstone, 
Roach, Weingartner, Aug. 26,1943. Div. 10-302.1-M10 

1690 The Generation of Fluorine, W. C. Schumb, Aug. 17, 1943. 

Div. 10-402.31-M4 


SECRET 




BIBLIOGRAPHY 


677 


OSRD No. 

1691 CG Aging for Type and ASC Whetlerites; Fourth 

Comparison Chart, F. E. Blacet, W. C. Pierce, Aug. 17, 
1943. Div. 10-202.16-M12 

1692 Use of Sidfur Boiler for Smoke Generation, W. K. Lewis, 

Aug. 31, 1943. Div. 10-501.2-M2 

1693 Type ASM Whetlerite Prepared in Rotary Drier, E. O. 

Wiig, Aug. 6, 1943. Div. 10-202.12-M10 

1697 A Study of Oil Smoke Plumes by Motion Pictures, H. F. 

Johnstone, Aug. 19, 1943. Div. 10-502-M8 

1712 Smoke Experiments Carried out at Camp Sibert, Ala¬ 
bama, T. S. Gilman, P. Hayward, Aug. 25, 1943. 

Div. 10-302.1-M11 

1746 Effect of Activation Time on Properties of PCI Charcoal 
and Corresponding Whetlerites (Second Report), F. E. 
Blacet, W. C. Pierce, T. Skei, Sept. 9, 1943. 

Div. 10-202.11-M6 

1747 Penetration and Persistence of Gases in an Enclosed 

Court, F. E. Blacet, M. Dole, H. F. Johnstone, Sept. 6, 
1943. Div. 10-401.122-M3 

1748 The Persistence and Penetration of Gas in a House, F. E. 

Blacet, Sept. 13, 1943. Div. 10-401.124-MI 

1749 Concentrations in Gas Clouds Under High Inversion Con¬ 
ditions, W. M. Latimer, Sept. 6, 1943. 

Div. 10-302.1-M 14 

1771 Use of Aminated Phenol-Formaldehyde Xerogels as Gas 
Adsorbents, G. F. Mills, Sept. 4, 1943. 

Div. 10-202.21-M6 

1772 Development of the SN Screening Smoke Mixture, E. W. 

Comings, C. H. Adams, E. D. Shippee, M. Forester, 
Sept. 20, 1943. Div. 10-501.21-M2 

1777 Adsorption and Surface Area Measurements on Whetler¬ 
ites and Charcoal Samples, P. H Emmett, Sept. 14, 1943. 

Div. 10-202.15-M18 

1778 Design and Construction of the Whetlerization Pilot Plant 

at the NDRC Division 10 Central Laboratory , R. J. Kunz, 
Sept, 14, 1943. Div. 10-202.14-M29 

1780 Analyses of Base Charcoals , E. O. Wiig, J. F. Flagg, 
Sept. 22, 1943. Div. 10-202.11-M7 

1856 The Preparation of Wood Charcoal Suitable for Activa¬ 

tion, W. L. McCabe, L. Byman, F. P. Williams, J. E. 
Jenkins, Oct, 9, 1943. Div. 10-202.12-M 11 

1857 Verification of Mie Theory — Calculations and Measure¬ 
ments of Light Scattering by Dielectric Spherical Particles, 

V. K. LaMer, Nov. 11, 1943. Div. 10-501.1-M2 

1872 A Meter for the Calibration of Breather Pumps, W. C. 
Pierce, J. W. Zabor, D. P. Smith, Oct. 12, 1943. 

Div. 10-201.1-M 16 

1873 Surveillance of Types ASC and ASCM Whetlerites, E. O. 

Wiig, Nov. 12, 1943. Div. 10-202.16-M15 

1912 Preparation and Properties of A*SF Whetlerites, E. O. 
Wiig, Oct. 24, 1943. Div. 10-202.12-M12 

1982 Apparatus for Evaluating the Maximum Inspiratory and 
Expiratory Resistances of Gas Masks During Wearing, 

W. C. Pierce, J. W. Zabor, D. P. Smith, Nov. 11, 1943. 

Div. 10-201.1-M20 

1983 A Study of Smoke Clouds in a Coastal Area; Field Ex¬ 
periments Near Brownsville, Texas, D. M. Yost, C. 
Croneis, T. S. Gilman, Nov. 12, 1943. 

Div. 10-302.1-M 16 


OSRD No. 

1984 Apparatus and Method for Determining Gas Mask Outlet 
Valve Leakage Under Conditions of Use, D. P. Smith, 

J. W. Zabor, Nov. 11, 1943. Div. 10-201.1-M19 

2002 The Evaporation of Small Drops of Thiodiglycol and Levin¬ 
stein Mustard, H. F. Johnstone, R. W. Parry, Nov. 12, 

1943. Div. 10-501.12-M 1 
2050 Filter Penetration by Aerosols of Very Small Particle Size, 

W. H. Rodebush, C. E. Holley, Jr., B. A. Lloyd, Jan. 4, 

1944. Div. 10-201.22-M13 
2086 Correlation of Gas Concentrations With Meteorological 

Data, W. M. Latimer, K. S. Pitzer, S. Ruben, W. D. 
Gwinn, T. W. Norris, Jan. 3, 1944. Div. 10-302.1-M18 
2088 Present Status of Development of Toxic Gases, W. A. 
Noyes, Jr., Dec. 10, 1943. Div. 10-402.2-M14 

3011 New Chlorine Carriers for Metal Chloride Screening 
Smoke Mixtures, E. W. Comings, Dec. 31, 1943. 

Div. 10-502-M9 

3012 The Generation and Use of Concentrated Mustard Vapor 
Clouds, H. F. Johnstone, E. W. Comings, Dec. 12, 1943. 

Div. 10-504.1-MI 

3048 The Hot Wire Analyser for Gas Concentrations, W. M. 
Latimer, S. Ruben, T. H. Norris, W. D. Gwinn, Dec. 3, 

1943. Div. 10-401.11-MI 

3049 Concentrations From Gas Bombs in the Mt. Shasta Forest 

Region, W. M. Latimer, S. Ruben, W. D. Gwinn, T. H. 
Norris, Jan. 3, 1944. Div. 10-302.2-M3 

3058 Performance of Canisters After Wearing Tests at Camp 

Sibert, Alabama, W. C. Pierce, J. W. Zabor, H. S. Joseph, 
Jan. 8, 1944. Div. 10-201.1-M22 

3059 Gas Concentrations from Line Sources and CW Bombs on 
a Beach Area, W. M. Latimer, W. D. Gwinn, Dodson, 
Houston, Leininger, Winklemen, Jan. 10, 1-943. 

Div. 10-302.2-M4 

3071 Catalysts for the Oxidation of Carbon Monoxide in Air, 
R. N. Pease, N. C. Robertson, W. J. Shelburne, Jr., 
Jan. 12, 1944. Div. 10-202.2-M6 

3130 Picoline as Impregnant for Gas Mask Absorbent, E. O. 
Wiig, H. Scoville, Jr., Jan. 21, 1944. 

Div. 10-202.141-M17 
3150 The Development of the Thermal Generator Candle, E. W. 

Comings, Jan. 22, 1944. Div. 10-504.12-M5 

3213 A Cordinuous Sulfur Smoke Generator, E. W. Comings, 
W. L. Lundy, Feb. 11, 1944. Div. 10-501.2-M3 

3227 The Generation of Fluorine , W. C. Schumb, Feb. 10, 1944. 

Div. 10-402.31-M5 

3284 The Concentration of Vapor in H Aerosol Clouds, H. F. • 
Johnstone, W. E. Winsche, Feb. 26, 1944. 

Div. 10-504-MI 

3320 Studies of the Adsorption Wave on Two Types of Charcoal, 
R. H. Wilhelm, S. F. Williams, J. C. Whitwell, Mar. 10, 

1944. Div. 10-202.157-M7 

3460 Smokes and Filters — Supplement to Section I, I. Lang¬ 
muir, K. B. Blodgett, Apr. 25, 1944. 

Div. 10-201.22-M14 

3461 Aqueous Hydrolysis of CNCl, T. M. Klotz, Apr. 25, 1944. 

Div. 10-202.152-M10 
3463 Development and Testing of a Pump-type Autovent for 
Nitrogen Elimination in Navy High Altitude Rebreather, 
D. S. Martin, J. E. Seegmiller, Apr. 25, 1944. 

Div. 10-203-M3 


SECRET 




678 


BIBLIOGRAPHY 


OSRD No. 

3577 Tests on CO 2 Spraying Devices, F. G. Straub, R. J. 

Ka-llal, May 20, 1944. Div. 10-501.2-M5 

3578 Field Methods of Dispersing Chemical Warfare Agents, 
A. R. Olson, Karl Jan Tong, May 20, 1944. 

Div. 10-504.2-M5 

3714 A Remote Indicating Cup Anemometer with Magnetic 
Coupling, R. G. Dickinson, D. L. Kraus, July 7, 1944. 

Div. 10-301.1-M2 

3774 Factors in Canisters Design and Tube Testing; Critical 

Bed Depth and the Nature of Gas Flow Through Charcoal, 
I. M. Klotz, June 23, 1944. Div. 10-201.1-M26 

3775 Study of the Use of Air Curtains for Fog Dissipation, 
A. P. Kratz, E. C. Manthei, C. E. Holley, June 13, 1944. 

Div. 10-503.2-M4 

3776 Charcolite: A Calcium Chloride Impregnated Charcoal 
Drying Agent, R. N. Pease, June 15, 1944. 

Div. 10-202.142-M2 

3859 Wind-Tunnel Studies of the Diffusion of Gas in Schematic 
Urban Districts, H. Rouse, July 5, 1944. 

Div. 10-401.121-M2 

3902 The Preparation of Solid Materials for Dispersion as 
Aerosols, F. C. McGrew, July 17, 1944. 

Div. 10-504.3-M2 

3975 Use of Aminated Phenol-Formaldehyde Xerogels as Gas 
Adsorbents, G. F. Mills, Aug. 4, 1944. 

Div. 10-202.21-M8 

4011 Activation of Charcoal in a Boiling-Bed Furnace, R. 

York, Jr., Aug. 12, 1944. Div. 10-202.13-M21 

4012 The Preparation of New Toxic Gases, A. B. Burg, Aug. 12, 

1944. Div. 10-402.36-M8 

4013 Compilation of N 0 and X c Values for Miscellaneous Whet- 
lerites Before and After Aging, T. Skei et al, Aug. 12,1944. 

Div. 10-202.16-M17 

4014 Performance of M10 and MIXA2 Canisters After Regular 
Use at Camp Sibert, Ala., T. Skei et al, Aug. 12, 1944. 

Div. 10-201.1-M28 

4015 Additional Surveillance Tests on Canisters Used in the 
First Sibert Surveillance Study, T. Skei, Aug. 12, 1944. 

Div. 10-201.1-M29 

4104 The Reactivation in Oxygen of CJFS Charcoals, T. F. 
Young, Sept. 7, 1944. Div. 10-202.132-M2 

4112 Whetlerization and Surveillance Studies on PCI Charcoal 
at Varying Stages of Activation (Third Report), T. Skei, 
Sept, 9, 1944. Div. 10-202.13-M23 

4129 Summary of Pilot Studies on the Preparation of ASC 
Whetlerite, R. J. Kunz, Sept, 14, 1944. 

Div. 10-202.12-M14 

4157 Pilot Plant Study of the Processing of Plasticized White 
Phosphorus, H. Adler, Sept, 21, 1944. 

Div. 10-504.21-M8 

4166 Development of Munitions for Dispersing Solid Particu¬ 
lates, H. F. Johnstone, Sept, 25, 1944. 

Div. 10-504.2-M6 

4231 Surveillance of Type ASC Whetlerite in M10-%" Service 
Canisters, T. Skei, Oct. 3, 1944. Div. 10-201.1-M31 

4232 Surveillance Tests on ASC, Ell, and E13 Whetlerites, 

T. Skei, Oct. 12, 1944. Div. 10-202.16-M 19 

4283 Activation of Charcoal by the Jiggler Process. A Summary 
of Results Obtained in the Fourth (Metal Tube) Pilot 
Mode, R. J. Kunz, Oct. 23, 1944. Div. 10-202.131-M13 


OSRD No. 

4324 Zinc Chloride Activated Wood Charcoal, G. W. Heise, 
J. A. Slyh, et al, Sept. 30, 1944. Div. 10-202.13-M24 

4334 Wind-Tunnel Studies of the Diffusion of Heat by Singh 
Wind Curtains and Baffles, H. Rouse, Nov. 11, 1944. 

Div. 10-401.121-M3 

4346 Surveillance Studies on Whetlerites at Northwestern Uni¬ 
versity — A Summary of Work from 1942-1944, T. Skei, 
Nov. 15, 1944. Div. 10-202.16-M20 

4377 Combustion Gas Type Fog Generator for Shipboard In¬ 
stallation 400-500 GPH Capacity Machine No. H-202, 
J. W. Hession, V. K. LaMer, Nov. 30, 1944. 

Div. 10-501.202-M2 

4378 Asbestos Bearing Filter Paper, T. L. Wheeler, E. Staf¬ 
ford, Nov. 23, 1944. Div. 10-201.22-M15 

4399 Tests with an Exhaust Aerosol DDT Generator on a 450 
H. P. Stearman Aircraft, R. L. LeTourneau, C. W. 
Kearns, R. J. Kallal, C. H. Adams, R. L. Metcalf, 
Nov. 20, 1944. Div. 10-602.121-MI 

4447 Toxicity of DDT to Mosquitoes. Effect of Particle Size on 
the Efficiency of Oil Aerosols Bearing DDT, V. K. LaMer, 
S. Hochberg, K. Hodges, Dec. 11, 1944. 

Div. 10-602.21-MI 

4539 Testing of Daytime Distress Signals, V. K. LaMer, J. Q. 
LYnberger, D. Sinclair, et al, Jan. 5, 1945. 

Div. 10-501.23-M3 

4565 The Development of a Portable Aerosol Smoke Pot, H. H. 
Champney, L. B. Counterman et al, Jan. 9, 1945. 

Div. 10-501.21-M3 

4700 Plasticized White Phosphorus in Small Smoke Munitions, 
H. F. Johnstone, R. I. Rice, M. F. Nathan, F. A. Orr, 
C. E. Shoemaker, Feb. 16, 1945. Div. 10-504.21-M9 

4733 The Burning Properties and Anti-Personnel Effect oj 
PWP, H. F. Johnstone, D. D. Edwards, M. F. Nathan, 
F. A. Orr, M. M. Woyski, Sept. 15, 1944. 

Div. 10-504.21-Mil 

4757 Statistical Considerations in the Use of DDT Aerosols, 
W. H. Rodebush, Jan. 1, 1945. Div. 10-602.21-M2 

4796 Toxicity of Drosophila (Fruit Flies) of Aerosols of DDT 
of Uniform Droplet Size in Oil of High Boiling Point, 
V. K. LaMer, Seymore Hochberg, Bruno H. Zimm, 
Byron Williamson, Oct. 31, 1944. Div. 10-602.22-M2 

4848 The Temperature of the Liquid Contents of Munitions Ex¬ 
posed to Sunlight, G. C. Gross, D. L. Armstrong, A. B. 
Burg, Jan. 2, 1945. Div. 10-504.2-M7 

4894 Conversion of Besler No. 374 Screening-Smoke Generator 
to a Hochberg-LaMer Aerosol Generator for Insecticidal 
Purposes — with Supplement on Conversion of Besler 
M-2 Generator, V. K. LaMer, S. Hochberg, R. Ellis, 
F. Buchwalter, J. C. Rowell, Apr. 2, 1945. 

Div. 10-602.11-M2 

4895 Gel-Type Hopcalite and Some Granular Reagents for 
Carbon Monoxide, R. N. Pease, Apr. 5, 1945. 

Div. 10-202.151-M6 

4896 Results of Canister Tests Against Carbon Monoxide, 
R. N. Pease, C. Orenyo, Apr. 5, 1945. 

Div. 10-201.1-M34 

4897 Further Investigation of Drying Agents, R. N. Pease, 

J. H. McLean, Apr. 5, 1945. Div. 10-202.142-M3 

4898 Protection Against Carbon Monoxide, R. N. Pease, 

Apr. 5, 1945. Div. 10-202.2-M8 


SECRET 




BIBLIOGRAPHY 


679 


OSRD No. 

4901 The Hochberg-LaMer Aerosol Generator, V. K. LaMer, 
S. Hochberg, Oct, 31, 1944. Div. 10-602.11-M3 

4904 The Optical Characterization of Any Aerosol in the Labora¬ 
tory or Field. The Production of Aerosols from Powdered 
Solid Materials, V. K. LaMer, J. Q. Umberger, D. Sin¬ 
clair, F. E. Buchwalter, Oct. 31, 1944. 

Div. 10-601.2-MI 

4928 Performance of M10, MWAl, and MlAl Canisters After 

Use in the Southwest Pacific Area, J. B. Fehrenbacher, 
Betty Roake, Marion Walker, Betty Mortenson, Mar. 3, 
1945. Div. 10-201.1-M35 

4929 Gas Protection Afforded by German Canisters, J. B. 

Fehrenbacher, Mar. 7, 1945. Div. 10-201.31-M3 

4930 Gas Protection of Australian Coconut Charcoal, J. B. 

Fehrenbacher, Mar. 12, 1945. Div. 10-202.01-M2 

4959 Part I: Water Isotherms and Rales of Adsorption and De¬ 
sorption: Part II: Macro Pore Measurements, P. H. 
Emmett et al, Apr. 20, 1945. Div. 10-202.17-M9 

5065 Adsorption and Surface Area Measurements on Whetler- 
ites and Charcoal Samples, P. H. Emmett et al, May 30, 
1945. Div. 10-202.15-M19 

5114 Surveillance of ASC-Ni Whetlerites With CK, R. J. 

Grabenstetter, May 9, 1945. Div. 10-202.16-M21 

5115 The Effect of Air Carbonization in the PCC Charcoal 
Process Upon the Whetlerite Qualities of the Adsorbent, 

B. A. White, C. R. Bierman, G. L. Pratt, May 24,1945. 

Div. 10-202.14-M30 

5116 Studies of the Preparation of Activated Charcoal Suitable 
for Whetlerization from Coconut Shells, B. A. White, 

C. R. Bierman, G. L. Pratt, May 1, 1945. 

Div. 10-202.134-M5 

5117 Magnetic Studies on Impregnated Charcoal, H. G. Cut- 
forth, I. M. Klotz, Apr. 27,1945. Div. 10-202.14-M32 

5139 A Summary of Work by the University of California 
Group, W. M. Latimer, June 20, 1945. 

Div. 10-302.1-M21 

5234 Effect of Preliminary Particle Size in the Processing of 
Pittsburgh Coke and Chemical Company Type Charcoal, 
B. A. White et al, May 22, 1945. Div. 10-202.18-M4 

5235 Determination of Ammonia in Low Concentration Evolved 
from Canisters, W. B. Lewis, May 21, 1945. 

Div. 10-201.1-M36 

5236 Retentivity of Charcoals — A Study urith Methyl Ethyl 

Ether, Neopentane and Methanol, D. H. Volman, G. J. 
Doyle, Apr. 23, 1945. Div. 10-202.15-M20 

5237 Leaching and Rewhetlerization of Impregnated Charcoals, 
R. J. Grabenstetter, L. C. Weiss, Apr. 26, 1945. 

Div. 10-202.1-M13 

5238 Gas Protection Afforded by Japanese Canisters, J. B. 

Fehrenbacher, May 30, 1945. Div. 10-201.31-M4 

5239 Factors in Canister Design and Tube Testing: II and III. 
Critical Bed Depths and Mechanisms of Removal of Six 
Gases, W. L. McCabe, I. Klotz, W. E. Roake, H. G. 
Cutforth, B. White, Nov. 28, 1944 to June 7, 1945. 

Div. 10-202.156-M20 

5240 The Effect of Treating Activated Charcoal with Air or 
Air-Steam Mixtures at Elevated Temperatures, C. R. 
Bierman, G. L. Pratt, B. White, June 14, 1945. 

Div. 10-202.13-M25 


OSRD No. 

5241 Preparation and Properties of Aerosols, F. T. Wall, 
June 21, 1945. Div. 10-500-M4 

5277 Miscellaneous Impregnants, R. J. Grabenstetter, May 31, 

1945. Div. 10-202.141-M 19 

5278 Gas and Chemical Activation of Charcoal, R. York, Jr., 

July 30, 1945. Div. 10-202.13-M26 

5309 The Development of an Aerosol Generator for Dispersing 
DDT Solutions from the Exhaust of an Aircraft Engine, 
H. F. Johnstone, R. J. Kallal, C. H. Adams, June 1,1945. 

Div. 10-602.121-M2 

5310 Mosquito Control With Hochberg-LaMer Aerosol Gener¬ 

ator in British Guiana, K. C. Hodges, J. C. Rowell, 
July 5, 1945. Div. 10-602.21-M3 

5343 The Protection of United States and Enemy Canisters 

against Nitrogen Dioxide, W. B. Lewis, J. W. Thomas, 
May 22, 1945. Div. 10-201.32-M3 

5344 Operational Manual for Dickinson Field Conductivity 
Meter, R. K. Brinton, J. W. Otvos, June 25, 1945. 

Div. 10-402.3-MI 

5354 Summary of Investigations of the Physical Chemistry of 
the Activation of Charcoal, T. F. Young, July 21, 1945. 

Div. 10-202.13-M27 

5487 Exhaust Aerosol Generator for Dispersal of DDT Solutions 
With SB2C-4 Airplane, Solar Aircraft Co., Aug. 3, 1945. 

Div. 10-602.121-M3 

5488 The Development of an Exhaust Smoke Generator for Mili¬ 

tary Aircraft, H. F. Johnstone, M. J. Goglia, July 20, 
1945. Div. 10-501.203-M2 

5489 Gas Ejection Bombs for the Dispersal of Finely Divided 
Powders, C. A. Getz and J. C. Hesson, Aug. 25, 1945. 

Div. 10-504.2-M8 

5499 A Sensitive Photoelectric Smoke Penetrometer, F. T. 

Gucker, Jr., H. B. Pickard, C. T. O’Konski, July 30, 
1945. Div. 10-201.22-M16 

5500 Survey of Pore Structure in Charcoal, A. Juhola, June 

20, 1945. Div. 10-202.111-M5 

5501 A Particle-Counting Smoke Penetrometer, F. T. Gucker, 
Jr., Aug. 31, 1945. 

5510 Exhaust Aerosol Generator on the PBJ-1H for the Dis¬ 
persal of DDT and Oil Smoke, J. H. Clark, Aug. 30, 1945. 

Div. 10-602.121-M4 

5563 Final Report on Contract OEMsr-282, F. E. Blacet, 
Aug. 20, 1945. Div. 10-101-M8 

5566 The Effect of Particle Size and Speed of Motion of DDT 
Aerosols of Uniform Particle Size in a Wind Tunnel on 
the Mortality of Mosquitoes, V. K. LaMer, R. Latta, 
July 30, 1945. Div. 10-602.21-M4 

5710 Some Theoretical Aspects of the Behavior of DDT Aerosols 
Dispersed from Aircraft, H. F. Johnstone, W. E. 
Winsche, R. L. LeTourneau, L. W. Smith, Sept. 19, 1945. 

Div. 10-602.121-M5 

5729 Formulas Utilizing DDT Concentrate, V. K. LaMer, 

Sept. 18, 1945. Div. 10-601.2-M2 

5730 Reports on the Use in the South Pacific of the Navy Screen¬ 
ing Smoke Generator ( M374 ) Converted to an Insecticidal 
Aerosol Generator According to the Hochberg-LaMer 
Principle, F. Brescia, I. Wilson, Sept. 18, 1945. 

Div. 10-602.11-M4 

5731 Salt Marsh and Anopheline Mosquito Field Control Tests 
with the Hochberg-LaMer Insecticidal Generator Using 


SECRET 






680 


BIBLIOGRAPHY 


OSRD No. 

Oil-DDT Aerosols, V. K. LaMer, R. Latta, F. Brescia, 

I. Wilson, K. Hodges, J. Rowell, Sept. 18, 1945. 

Div. 10-602.21-M5 

5936 Effect of Solvents on the Toxicity of DDT Aerosols, V. K. 
LaMer, R. Latta, Aug. 31, 1945. 

Div. 10-601.1-M3 

6004 Cankerworms as Test Insects, V. K. LaMer, S. Hochberg, 

J. Q. Umberger, J. Betheil, Sept. 28, 1945. 

Div. 10-602.23-MI 

6088 Meteorological Instruments, S. W. Grinnell, Oct. 15, 1945. 

Div. 10-301-M3 

6121 Telescoping Metal Tails for a Small Cluster Bomb {Ther¬ 

mal Generator, 10-lb-E29Rl), E. 0. Manthei, J. A. Peck, 
Sept, 1, 1945. Div. 10-504.2-M9 

6122 Design of a Plant for Manufacture and Loading Plasti¬ 
cized White Phosphorus, E. A. Ford, Sept, 15, 1945. 

Div. 10-504.21-M12 

6172 An Alternative Circuit for the Portable Continuous Gas 

Concentration Meter, J. W. Otvos, R. G. Dickinson, 
Dec. 31, 1944. Div. 10-401.111-M5 

6173 A Mercury Contact Wind Direction Vane, R. G. Dickin¬ 
son, R. L. Mills, H. S. Johnston, Dec. 31, 1944. 

Div. 10-301.11-M4 

6174 Portable Instruments for Use in the Study of Micrometeor¬ 
ology and Microclimatology of the Southwest Pacific Area, 
R. L. Mills, R. G. Dickinson, Aug. 1, 1945. 

Div. 10-301-M4 

6211 Development of a Training Oil Smoke Pot, E21, M. F. 
Nathan, R. W. Davis, E. W. Comings, Oct. 1, 1945. 

Div. 10-501.21-M4 

6300 Development of a Small Base Ejection Air-Burst Bomb for 

Dispersing Liquid Agents, R. J. Kallal, R. W. Davis, 
Sept. 30, 1945. Div. 10-504.2-M10 

6301 Development of an Exhaust DDT Aerosol Generator for the 
K Ton, 4 x 4 Truck {Jeep), R. L. LeTourneau, R. I. 
Rice, H. F. Hrubecky, Oct, 1, 1945. 

Div. 10-602.122-M3 

6341 I. Wind-Tunnel Studies of Fog-Dispersal Methods, 
II. Wind-Tunnel Studies of Gas Diffusion in Urban Dis¬ 
tricts, III. Wind-Tunnel Studies of Air Flow Over Moun¬ 
tainous Terrain , H. Rouse, Nov. 19, 1945. 

Div. 10-401.121-M6 


OSRD No. 

6343 Development of Exhaust Combustion Smoke Generator for 

the TBM-3 Airplane, Solar Aircraft Company, Nov. 23, 
1945. Div. 10-501.203-M3 

6344 The Development of an Exhaust DDT Aerosol Generator 

for the Taylorcraft Light Airplane, R. I. Rice, Oct. 20, 
1945. ' Div. 10-602.121-M6 

6345 A Study of the Atomization of Liquids, H. C. Lewis, D. G. 

Edwards, M. J. Goglio, R. I. Rice, L. W. Smith, Oct. 10, 
1945. Div. 10-501.2-M6 

6373 Final Report on Contract OEMsr-102 {Including Contract 
OEMsr-599 ), H. F. Johnstone, E. W. Comings, Oct. 30, 
1945. Div. 10-500-M5 

6375 Development of a Floating Colored Smoke Signal ( DS-4), 

D. G. Edwards, C. H. Adams, E. H. Conroy, Oct. 20, 

1945. Div. 10-501.23-M4 
6428 Development of Oil Thermal Generator Floating Smoke 

Pot, E23, M. F. Nathan, R. W. Davis, E. C. Manthei, 

E. W. Comings, Nov. 15, 1945. Div. 10-501.21-M5 

6431 Development of an Experimental Thermal Generator Pot 
for Dispersing Mustard Gas as an Aerosol, C. H. Adams, 
M. H. Raila, E. W. Comings, Oct. 15, 1945. 

Div. 10-504.1-M2 

6432 Development of a Colored Smoke Target Identification 

Bomb {Bomb, Target Identification, Smoke, Mk 72, 
Mod. 2), C. H. Adams, E. H. Conroy, E. W. Comings, 
Oct, 20, 1945. Div. 10-504.2-M11 

6565 The Development of a Light High Explosive Bomb for 
Dispersing Toxic and Insecticidal Aerosols, H. F. John¬ 
stone, R. L. LeTourneau, H. C. Weingartner, Jan. 28, 

1946. Div. 10-504.2-M12 

6566 The Development of Plasticized White Phosphorus {PWP), 

M. M. Woyski, P. G. Roach, H. F. Johnstone, J. C. 
Bailar, Jr., Jan. 28, 1946. Div. 10-504.21-M13 

6574 Development of a Thermal Generator Bomb for Dispersing 
Concentrated Mustard Aerosol, E. D. Shippee, M. H. 
Raila, E. W. Comings, Feb. 4, 1946. 

Div. 10-504.3-M3 

6636 Fuel Blocks for Thermal Generators, R. W. Parry, M. H. 
Raila, R. C. Johnson, D. Ehrlinger, C. H. Simonson, 
R. P. Connor, E. W. Comings, J. C. Bailar, Jr., Mar. 11, 
1946. Div. 10-504.11-M3 


SECRET 




NDRC INFORMAL REPORTS 


SECTION B-6 a 


I. Heats of Wetting and Surface Areas; A Study of the Removal 

of Arsine and of Poisoning by Hydrogen Cyanide; The 
Preparation of Phosgene from Materials which Could Con¬ 
tain Radio Chlorine; Preliminary Investigations of Vari¬ 
ation of Electrical Resistance of Charcoal Due to Adsorp¬ 
tion; Progress Report on Project No. 50, Mar. 25, 1941. 

Div. 10-101-MI 

II. Summary of English Report, J. F. Kincaid, (n.d.). 

Div. 10-102-M2 

III. Report on Activities of Section L-ll, W. A. Noyes, Jr., 

Apr. 25, 1941. Div. 10-202.156-Ml 

IV. The Preparation of Radioactive Chlorpicrin, J. H. Simons, 

May 28, 1941. Div. 10-402.35-MI 

V. On the Structure of Charcoal, T. F. Young, June 18, 1941. 

Div. 10-202.11-MI 

VI. Report on Trip to England, W. A. Noyes, Jr., July, 1941. 

Div. 10-102-MI 

VII. Study of the Preparation of Whetlerite and of Promoted 
Whetlerites, J, C. Elgin, July 16, 1941. 

Div. 10-202.12-MI 

VIII. Preparation of Radioactive Cyanogen Chloride, J. H. 

Simons, July 22, 1941. Div. 10-402.35-M2 

IX. Memorandum from H. F. Johnstone, Aug. 8, 1941. 

Div. 10-202.16-MI 

X. Comments on Report by F. N. Matthews’ Diffraction of 

X-rays by Impregnated Charcoal, H. F. Johnstone, Aug. 12, 
1941. Div. 10-202.143-MI 

XI. Outline of the Problem of Canister Design, W. A. Noyes, 

Jr., Aug. 15, 1941. Div. 10-201-MI 

XII. Summary of Lister’s Report, J. F. Kincaid, (n.d.). 

Div. 10-202.15-M21 

XIII. Report on Adsorption of HCN by Various Materials, 

R. N. Pease, Aug. 28, 1941. Div. 10-202.154-M4 

XIV. Report on Research Performed in Section B-6, NDRC, 

W. A. Noyes, Jr., Sept. 3, 1941.' Div. 10-200-MI 

XV. Problem of Gas Removal, L. S. Kassel, (n.d.). 

Div. 10-202.15-M22 

XVI. Notes on the Kassel Report, J. F. Kincaid, Sept. 16, 1941. 

Div. 10-202.157-M2 

XVII. Agenda for Meeting, Pittsburgh, (SECRET), W. A. 

Noyes, Jr., Sept. 19, 1941. Div. 10-201-M2 

XVIII. Report on Impregnation, A. P. Colburn, E. O. Krae- 
mer, Aug. 25, 1941. Div. 10-202.15-MI 

XIX. Removal of EN, P. A. Leighton, Aug. 26, 1941. 

Div. 10-202.156-M3 

XX. Effect of Osmium in Whetlerites, F. E. Blacet, Aug. 26, 

1941. Div. 10-202.154-M2 

XXI. Impregnation of Charcoals with Liquid Ammonia Solu¬ 
tions, F. E. Blacet, Aug. 26, 1941. Div. 10-202.154-M3 

XXII. Summary of Work, W. C. Pierce, Aug. 26, 1941. 

Div. 10-202.15-M2 

XXIIT. Summary of Work (Location of Cu in whetlerite, 
Nature of Red Coating, Attempts to increase Cu content 


a This series was discontinued in August 1942 when Division 10 was 

organized. 


and arsine life of whetlerites by means of vacuum and 
pressure, note on ash determination), T. F. Young, 
Aug. 28, 1941. Div. 10-202.141-MI 

XXIV. Removal of HiS; Project for Studying the Removal of 
CoCh, D. M. Yost, Aug. 28, 1941. Div. 10-202.15-M3 

XXV. Conclusions from Results of Investigations on the Ad¬ 
sorption of Hydrogen Cyanide and Arsine by Impregnated 
Charcoals, E. O. Wiig, Aug. 29,1941. Div. 10-202.154-M5 

XXVI. The Increase in Weight of Charcoal at the Break-Point. 
Summary of work on (a) electrical resistance of charcoal, 

(b) rise of temperature of charcoal on adsorption of PS, 

(c) ultraviolet absorption apparatus, M. Dole, Aug. 29, 

1941. Div. 10-202.11-M2 

XXVII. Study of Impregnation, J. C. Elgin, Aug. 30, 1941. 

Div. 10-202.14-MI 

XXVIII. Study of Adsorption Wave, J. C. Elgin, Aug. 30, 
1941. Div. 10-202.157-MI 

XXIX. The Efficiency of Charcoal toward Chloracetophenone at 

Low Temperatures, The Removal of Chlorpicrin, G. P. 
Baxter, September 1941. Div. 10-202.15-M4 

XXX. Hydrogen Cyanide and Arsine Lives of Equilibrated 
Charcoals, E. O. Wiig, Sept. 10, 1941. 

Div. 10-202.154-M6 

XXXI. Brief Summary of Information Relative to the Mecha¬ 

nisms of Removal of Various War Gases, W. A. Noyes, Jr., 
Oct, 6, 1941. Div. 10-202.156-M21 

XXXII. Work on Contract B-71, Selenium Hexafluoride, R. G. 

Dickinson, Oct. 15, 1941. Div. 10-202.15-M23 

XXXIII. Use of Radioactive Tracer Technique for Arsine Re¬ 
moval, D. M. Yost, Sept. 30, 1941. Div. 10-202.154-M7 
XXXIV. Report on Activities of Section B-6, (SECRET), 
W. A. Noyes, Jr., Oct. 29, 1941. Div. 10-202.12-M2 
XXXV. Informal Progress Report on Project B-6, 54, Impreg¬ 
nation, (SECRET), J. C. Elgin, Oct. 22, 1941. 

Div. 10-202.14-M2 

XXXVI. Conclusions from Investigations on the Adsorption of 
SA and the Distribution of the Arsenic on the Charcoal Bed, 
E. O. Wiig, Oct. 14, 1941. Div. 10-202.15-M5 

XXXVII. Studies on Impregnation, A. P. Colburn, Oct. 31, 
1941. Div. 10-202.14-M3 

XXXVIII. Hydrogen Cyanide and Carbon Monoxide, R. N. 

Pease, Oct. 16, 1941. Div. 10-202.15-M6 

XXXIX. The Effect of Particle Size on the SA and AC Lives 
and on the Resistance of the Charcoal Bed, E. O. Wiig, 
Nov. 9, 1941. 

XL. Studies on Arsine Protection, W. C. Pierce, Oct. 25, 1941. 
XLI. Mesh Size and Arsine Saturation Values, W. C. Pierce, 
Nov. 10, 1941. Div. 10-202.18-MI 

XLII. Effect of Intermittent versus Continuous Running on 
the SA Life of Copper Whetlerite, J. C. Elgin, Nov. 19, 
1941. Div. 10-202.154-M9 

XLIII. Substitutes for Gas Mask Absorbents. The Use of Wyo- 
lite as an Inert Carrier for Absorbents, G. F. Smith, 
Nov. 27, 1941. Div. 10-202.2-MI 

XLIV. Ultraviolet Photometer for War Gases, M. Dole, 
Nov. 19, 1941. Div. 10-402.21-M2 


SECRET 


681 



682 


BIBLIOGRAPHY 


XLV. A Study of the Penetration of Charcoal by Chloropicrin 
by Means of the Ultraviolet Photometer, M. Dole, Dec. 3, 
1941. 

XLVI. Investigations on Ad- and Desorption Processes in 
Cranular Stream-Penetrated Beds of Adsorbents, E. Wicke 
(translated by M. Dole), (n.d.). Div. 10-202.15-M24 
XLVII. Nature of the Impregnant and New Absorbents, H. F. 
Johnstone and G. L. Clark, Dec. 5, 1941. 

Div. 10-202.141-M2 

XLVIII. The Use of Cold Chloride and Potassium Permanga¬ 
nate as Arsine Breakpoint Indicators , E. O. Wiig, Dec. 6, 
1941. 

XLIX. Removal of HCN by Whetlerite, R. N. Pease, Dec. 29, 
1941. Div. 10-202.154-M 11 

L. Nature of Impregnant and New Absorbents, H. F. Johnstone 
and G. L. Clark, Dec. 26, 1941. Div. 10-202.01-MI 

LI. The Effect of Particle Size on the SA Lives of Equilibrated 
Charcoals, E. O. Wiig, Dec. 17, 1941. 

Div. 10-202.18-M3 

LII. Adsorption, Surface Area and Pore Size Studies on Acti¬ 
vated Charcoals and Whetlerite, P. II. Emmett, Dec. 22, 
1941. Div. 10-202.13-M3 

LIII. Preparation of Radioactive HCN, J. H. Simons, Dec. 11, 
1941. Div. 10-402.35-M5 

LIV. Preparation of Acyl Fluoride, J. H. Simons, Dec. 16, 
1941. Div. 10-402.311-MI 

LV. Study of Impregnation, J. C. Elgin, Dec. 22, 1941. 

Div. 10-202.14-M19 

LVI. Adsorption Wave Studies, J. C. Elgin, Dec. 22, 1941. 

Div. 10-202.157-M3 

LVII. Distribution of Copper in Whetlerites, Mechanism of 
Whetlerization, T. F. Young, Dec. 26, 1941. 

Div. 10-202.14-M5 

LVIII. Activation of Charcoal, W. L. McCabe, Dec. 23, 1941. 

Div. 10-202.13-M2 

LIX. Removal of Chloracetophenone at Low Temperatures, 
G. P. Baxter, Dec. 29, 1941. Div. 10-202.156-M5 

LX. The Removal of EN, P. A. Leighton, Dec. 23, 1941. 

Div. 10-202.156-M22 
LXI. A Search far Promoter Activity in Whetlerites, F. E. 

Blacet, Dec. 26, 1941. Div. 10-202.141-M3 

LXII. Impregnations from Liquid Ammonia from the Liquid 
Phase and with Cupric Acetyl Acetonate, F. E. Blacet, 
Dec. 22, 1941. Div. 10-202.13-MI 

LXIII. Substitutes for Gas Mask Canister Soda Lime, G. F. 

Smith, Dec. 20, 1941. Div. 10-202.15-M25 

LXIV. A Study of the Penetration of Charcoal by Chlorpicrin 
by Means of the Ultraviolet Photometer, M. Dole, Dec. 13, 
1941. Div. 10-202.155-Ml 

LXV. Summary of Data on Protection toward Various Gases, 
W. A. Noyes, Jr., Feb. 4, 1942. Div. 10-202.151-M2 
LXVI. Behavior of Hopcalite, Certain Whetlerites, Some 
Resins, and Whetlerite-Soda Lime Mixtures toward Cyan¬ 
ogen Chloride, W. M. Latimer, Jan. 15, 1942. 

Div. 10-202.152-M2 

LXVII. Activation of Charcoal: Comparison of Jiggler and 
Pilot Plant Operation, W. L. McCabe, Jan. 15, 1942. 

Div. 10-202.131-MI 

LXVIII. Adsorptions and Surface Areas of Certain Charcoals 
and Whetlerites, P. H. Emmett, Jan. 18, 1942. 

Div. 10-202.15-M8 


LXIX. Study of Impregnation: Iodic Acid, J. C. Elgin, Jan. 15, 
1942. Div. 10-202.141-M4 

LXX. The Effect of Impregnation on the Removal of Ethylene 
I mine. Break times for di-, tri-, and pentamethylene imines, 
P. A. Leighton, Jan. 15, 1942. Div. 10-202.14-M33 
LXXI. Phosgene and Mustard Gas Vapor Removal, D. M. 

Yost, Jan. 26, 1942. Div. 10-202.155-M2 

LXXI I. Summary of Protection Data on Ethylene I mine, P. A. 

Leighton, Jan. 23, 1942. Div. 10-202.156-M7 

LXXIII. Steam Activation on Samples from Various Sources, 
W. L. McCabe, Jan. 20, 1942. Div. 10-202.13-M4 

LXX1V. Nature of Reaction Product of >SM on Whetlerite, H. F. 

Johnstone, Feb. 3, 1942. Div. 10-202.1-MI 

LXXV. Heat of Wetting and Apparent Density, T. F. Young, 
Feb. 4, 1942. Div. 10-202.15-M9 

LXXVI. Part I. Summary of Present Knowledge Concerning 
the Value of Soda Lime for a Canister Filling, W. C. 
Pierce, Feb. 4, 1942. Part II. The Effect of Soda Lime on 
Protection, W. A. Noyes, Jr., Feb. 19, 1942. 

LXXVII. The Effect of Concentration and Temperature on the 
AC Life of Standard Whetlerite, E. O. Wiig, Feb. 19, 1942. 
LXXVIII. Performance Data on Some Recent Samples, W. A. 

Noyes, Jr., Feb. 17, 1942. Div. 10-202.14-M6 

LXXIX. Studies of CC and CNBr, W. L. Latimer, Feb. 15, 
1942. Div. 10-202.15-M 10 

LXXX. Removal of HCN by Whetlerite; Substitute Absorbents; 
Pyrolysis of Cotton Cellulose; and Protection Against Car¬ 
bon Monoxide, R. N. Pease, Feb. 15, 1942. 

Div. 10-202.154-M 13 
LXXXI. Preparation of Radioactive Selenium Hexafluoride, 
J. H. Simons, Feb. 12, 1942. Div. 10-402.35-M6 

LXXXI I. Substitutes for Gas Mask Absorbents, G. F. Smith, 
Feb. 10, 1942. Div. 10-202.2-MI 

LXXXIII. Variation of SA Life with Temperature and Poison¬ 
ing of AC toward SA Lives, E. O. Wiig, Mar. 15, 1942. 

Div. 10-202.16-M4 

LXXXIV. Removal of HCN by Whetlerite: Pyrolysis of Cotton 
Cellulose: Protection against Carbon Monoxide, R. N. 
Pease, Mar. 15, 1942. Div. 10-202.154-M14 

LXXXV. Adsorption and Surface Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, Mar. 15, 
1942. Div. 10-202.15-M 11 

LXXXVI. Activation of Charcoal and of Anthracite, R. York, 
(W. L. McCabe), Mar. 15, 1942. Div. 10-202.13-M5 
LXXXVI I. Sorption Time Data for Water Vapor on Whetler¬ 
ite, A. P. Colburn, Mar. 16, 1942. Div. 10-202.17-M5 
LXXXVIII. Studies of Adsorbents, P. A. Leighton, Mar. 15, 
1942. Div. 10-202.151-M3 

LXXXIX. X-Ray Studies: (1 ) Humidified Charcoals at Low 
Temperature, (2) Silvered and E6 Whetlerites, H. F. John¬ 
stone and G. L. Clark, Apr. 2, 1942. 

Div. 10-202.17-M2 

XC. Resume of Data on World War Work, A. Patterson, 
June 1919. Div. 10-202.141-M6 

XCI. Phosphorus Trifluoride Removal by Whetlerite and by 
Soda Lime —Whetlerite Mixtures, R. G. Dickinson, 
Apr. 6, 1942. 

XCII. Protection against Carbon Monoxide at Low Concentra¬ 
tions; Removal of Hydrogen Cyanide by Whetlerite, R. N. 

Pease, Apr. 15, 1942. Div. 10-202.156-M9 


SECRET 



BIBLIOGRAPHY 


683 


XCIII. The Adsorption of PS and CG, M. Dole, Apr. 15, 1942. 

Div. 10-202.156-M11 
XCIV. Adsorption and Surface Area Measurements on Whet¬ 
lerite and Charcoal Samples, P. H. Emmett, Apr. 15, 1942. 

Div. 10-202.15-M11 

XCV. Comparative AC Retentivities of Whetlerite and Type D 
Mixture, E. O. Wiig, Apr. 22, 1942. Div. 10-202.15-M 13 
XCVI. The Effect of Initial Concentration on the Arsine 
Life (I); SA Testing (II), E. O. Wiig, Apr. 15, 1942. 

Div. 10-202.154-M17 
XCV II. Substitutes for Gas Mask Absorbents. The Use of 
Wyolite as an Inert Carrier for Absorbent, G. F. Smith, 
Apr. 15, 1942. Div. 10-202.2-MI 

XCVIIT. Summary. Protection Against Two Gases, prepared 
by W. D. Walters, April, 1942. Div. 10-202.151-M7 
XCIX. The Behavior of Mixtures of Charcoal and Inert Ma¬ 
terial, W. C. Pierce, Apr. 10, 1942. Div. 10-201.2-M2 
C. The Nature of the Product Desorbed from Charcoal Brought 
Half Way to the Breakpoint with Chlorpicrin, G. P. Baxter, 
Apr. 14, 1942. Div. 10-202.15-M 12 

Cl. The Rate of Water Absorption of Charcoals and Whetler- 
ites, A. P. Colburn, Apr. 23, 1942. Div. 10-202.17-M3 
CII. Stability of Cyanogen Chloride; Constants for Various 
Charcoals with Cyanogen Chloride: Preparation of Cy¬ 
anogen and Nitrosyl Chloride, W. M. Latimer, Apr. 14, 
1942. 

CIII. Studies on the Reaction Product of Arsine on Charcoal 
and Whetlerite, H. F. Johnstone and G. L. Clark, Apr. 10, 
1942. Div. 10-202.154-M 18 

CIV. Flow Rate Studies on the E20R48 Miniature Canister, 
W. C. Pierce, Apr. 22, 1942. Div. 10-201.1-MI 

CV. Absorbent Performance Data for Use in Canister Design¬ 
ing, W. C. Pierce, Apr. 23, 1942. Div. 10-201.1-M2 
CVI. EN: Polymerization, Thermal Effects, Effect of Oxygen, 
Effect of Drying, Miscellaneous Gases, Especially A mines, 
P. A. Leighton, Apr. 15, 1942. Div. 10-202.156-M 10 
CVII. Variation of Life with Relative Humidity for Equi¬ 
librated Charcoals, E. O. Wiig, May 15, 1942. 

Div. 10-202.17-M4 

CVIII. Italian Canister (large size) D.z.g.c. 3-1934, E. O. 

Wiig, May 15, 1942. Div. 10-201.31-MI 

CIX. Summary of Test Data on E-6 Whetlerite, W. C. Pierce, 
May 9, 1942. Div. 10-202.16-M5 

CX. Central Laboratory Report of May 16, 1942, W. C. Pierce 
et al. Div. 10-200-M2 

CXI. The Adsorption of CG, M. Dole, May 15, 1942. 

Div. 10-202.157-M4 

CXII. Efficiency of Whetlerite Containing Considerable Pro¬ 
portions of Water Against Chlorpicrin, G. P. Baxter, 
May 15, 1942. Div. 10-202.16-M6 

CXIII. I. X-Ray Studies of Various Materials, II. Carbon¬ 
ization of Resins, III. Electron Microscope Studies, IV. Lo¬ 
cation of Silver on Silvered Whetlerites and Charcoals, 
V. The Irreversible Adsorption of Asffdz from Alcohol by 
Whetlerite, H. F. Johnstone and G. L. Clark, May 11, 
1942. Div. 10-202.143-M2 

CXIV. Protection against Carbon Monoxide, R. N. Pease, 
May 15, 1942. 

CXV. Mechanism of Removal of HCN by Whetlerite, R. N. 
Pease, May 15, 1942. Div. 10-202.154-M20 


CXVI. Calorimetric Studies on Arsine Removal, H. M. Huff¬ 
man, May 14, 1942. Div. 10-202.154-M 19 

CXVII. Problems Relating to CC , W. M. Latimer, May 15, 
1942. Div. 10-202.141-M8 

CXVIII. The Design of a Pilot Plant Jiggler for Charcoal 
Activation, R. York, May 15, 1942. Div. 10-202.131-M2 
CXIX. A Comparison of Impregnated Charcoals, F. E. Blacet 
and T. Skei, May 5, 1942. Div. 10-202.14-M8 

CXX. The Adsorption of Silver on Charcoal from Whetlerizing 
Solutions, F. E. Blacet and D. Volman, May 18, 1942. 

Div. 10-202.14-M9 

CXXI. The Use of Mercury Compounds in the Impregnation 
of Activated Charcoal, F. E. Blacet and R. J. Graben- 
stetter. 

CXXII. Preliminary Study of Hexamine Impregnation, F. E. 
Blacet and J. G. Roof, May 22, 1942. 

Div. 10-202.141-M9 

CXXIII. Adsorption and Surface Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, May 15, 
1942. Div. 10-202.15-M11 

CXXIV. Flow Resistance of Axial and Radial Canisters, W. C. 

Pierce, May 15, 1942. Div. 10-201.1-M3 

CXXV. Substitutes for Gas Mask Absorbents. The Use of 
Wyolite as an Inert Carrier for Absorbents, G. F. Smith, 
May 15, 1942. Div. 10-202.2-Ml 

CXXVI. The Effect of Preliminary Passage of Air-Hexane 
Mixtures on the SA and AC Life of CWSE-1 TE-1 and 
Type D Mixture, E. O. Wiig, May 28, 1942. 

Div. 10-202.156-M 13 
CXXVIL Study of the Adsorption Wave, J. C. Elgin, May 15, 
1942. Div. 10-202.157-M5 

CXXVIII. I. The Effect of Various Vapors on the SA Life of 
Absorbents; II. A Continuation of the Study of the Effect of 
AC on the SA Life and the Effect of &A on the AC Life of 
Absorbents; III. Variation of $A Life with Relative Humid¬ 
ity for Dry arid Equilibrated Whetlerites, E. O. Wiig, 
June 15, 1942. Div. 10-202.16-M7 

CXXIX. Design of a Lightweight Canister, W. C. Pierce, 
July 18, 1942. Div. 10-201-M3 

CXXX. I. Correlation of Canister Test Life with Human Toler¬ 
ance for Cyanogen Chloride; II. The Cyanogen Chloride 
Protection Afforded by Humidified Adsorbents, W. C. 
Pierce, May 29, 1942. 

CXXXI. I. Carbonization of Resins and Other Plastics; II. Na¬ 
ture of Reaction Product from Arsine on Whetlerite; 
III. X-Ray Studies, H. F. Johnstone and G. L. Clark, 
June 11, 1942. Div. 10-202.1-M3 • 

CXXXII. Calorimetric Studies on Arsine Removal, H. M. 

Huffman, June 15, 1942. Div. 10-202.154-M 19 

CXXXIII. Rale of Humidification of Charcoals and Whetler¬ 
ites, A. P. Colburn, June 17, 1942. Div. 10-202.17-M5 
CXXXIV. Adsorption and Surface Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, June 15, 
1942. Div. 10-202.15-M 11 

CXXXV. Production of Primary Charcoal by the Carlisle 
Process, W. L. McCabe, June 16, 1942. Div. 10-202.12-M4 
CXXXVI. A Laboratory Study of Activation, R. York, Jr., 
June 15, 1942. Div. 10-202.13-M6 

CXXXVII. Behavior of Sulfur Dioxide and of Several Other 
Gases on Whetlerite, P. A. Leighton, June 15, 1942. 

Div. 10-202.156-M 14 


SECRET 




684 


BIBLIOGRAPHY 


CXXXVIII. Part I. Summary to Date on Resins: Part II. 
Aminated Phenol-Formaldehyde Xerogels as Absorbents, 
P. A. Leighton, June 15, 1942. Div. 10-202.21-MI 

CXXXIX. Substitutes for Gas Mask Absorbents. The Use of 
Wyolite as an Inert Carrier for Absorbents, G. F. Smith, 
June 15, 1942. Div. 10-202.2-MI 

CXL. Vapor Pressure of Arsine Dissolved in Thionyl Chloride, 
etc., L. F. Audrieth and J. C. Bailar, Jr., June 17, 1942. 

Div. 10-401.1-MI 

CXLI. The Dialkylmonofluophosphates, L. F. Audrieth and 
J. C. Bailar, Jr., June 16, 1942. Div. 10-402.311-M4 
CXLII. Protection against Carbon Monoxide, R. N. Pease, 
June 15, 1942. Div. 10-202.2-M3 

CXLIII. Optimum Concentrations of Copper, Ammonia, and 
Carbon Dioxide for Whetlerizing Solutions, F. E. Blacet 
and D. Volman, June 22, 1942. Div. 10-202.14-M 11 
CXLIV. Preliminary Study of Whetlerites from: I. Different 
Size Extruded Charcoals: II. Charcoals Activated at Dif¬ 
ferent Temperatures, F. E. Blacet and D. Volman, 
June 23, 1942. Div. 10-202.1-M4 

CXLV. Diffusion of the Limiting Factor for Critical Bed 
Length, M. Dole, June 25, 1942. Div. 10-202.19-MI 
CXLVI. Final Report on Arsine and Hydrogen Cyanide, E. O. 
Wiig, July 1, 1942. 

CXLVII. Second Report on the Comparison of Impregnated 
Charcoals, F. E. Blacet, T. Skei, June 29, 1942. 

Div. 10-202.14-M 12 

CXLVIII. Tube Tests with Hydrogen Fluoride, R. G. Dickin¬ 
son, June 29, 1942. Div. 10-402.2-M3 

CXLIX. Adsorption of Cyanogen by Charcoal. A mine-Impreg¬ 
nated Charcoals, W. M. Latimer, June 15, 1942. 

Div. 10-202.152-M5 

Cli Cyanogen in Effluent Air Stream after the Absorption of 
HCN by Whetlerites, E. O. Wiig, July 15, 1942. 

Div. 10-202.154-M24 
CLI. Comparison of the Effect of Water, AC, and Other Poisons 
on the SA Lives of Silvered and Unsilvered Whetlerites, 
E. O. Wiig, July 15, 1942. Div. 10-202.16-M8 

CLII. The Use of Non-Persistent Gases, W. A. Noyes, Jr., 
July 17, 1942. Div. 10-402.1-MI 

CLIII. I. Study of Foreign Canister Materials. II. X-Ray Re¬ 
sults from Various Materials. III. Preparation of Char¬ 
coals from Resins and Other Materials. IV. Adsorption of 
AS-iOz from Alcohol by Charcoal andWhetlerites, H. F. John¬ 
stone and G. L. Clark, July 15, 1942. Div. 10-200-M3 
CLIV. Studies of CC on Absorbents; Stability of Cyanogen; 
Cyanogen in the Effluent from AC Tube Tests, W. M. 
Latimer, July 14, 1942. Div. 10-202.152-M6 

CLV. Leakage of Facepieces, D. M. Yost, July 31, 1942. 

Div. 10-201.1-M5 

CLVI. Adsorption and Surface Area Measurements on Whet¬ 
lerites and Charcoal Samples, P. H. Emmett, July 15,1942. 

Div. 10-202.15-M11 

CLVII. Fluophosphates and Related Compounds, L. F. Audri 
eth and J. C. Bailar, Jr., July 15,1942. Div. 10-402.311-M5 
CLVIII. Fluorosulfonic Acid and Its Alkyl Esters, L. F. 
Audrieth and J. C. Bailar, Jr., July 15, 1942. 

Div. 10-402.311-M6 

CLIX. Studies Relating to Phosphorus Trifluoride, A. B. Burg, 
July 15, 1942. Div. 10-402.311-M7 


CLX. Oxygen Treatment of Charcoal. Heats of Combustion of 
Charcoals, T. F. Young, June 15 to July 15, 1942. 

Div. 10-202.13-M7 

CLXI. The Preparation and Preliminary Study of (CH-^zNPF-t, 
A. B. Burg, July 24, 1942. Div. 10-402.36-M2 

CLXII. Temperatures in Canisters and Tubes during SA Re¬ 
moval, M. Dole, July 25, 1942. Div. 10-201.1-M6 

CLXIII. Iodine, Halogen Acids and their Salts as Charcoal 
Impregnants, F. E. Blacet, July 27, 1942. 

Div. 10-202.141-M11 
CLXIV. Activation of Charcoal, R. York, Jr., July 15, 1942. 

Div. 10-202.13-M8 

CLXV. The Preparation of Crude Char, W. L. McCabe, 
July 16, 1942. Div. 10-202.12-M5 

CLXVI. The Protection of Ml and MIXAl Canisters against 
Sulfur Dioxide, W. C. Pierce, July 29, 1942. 

Div. 10-201.1-M8 

CLXVII. Retention of HCl by the MIXAl Canister, W. C. 

Pierce, July 29, 1942. Div. 10-201.1-M7 

CLXVIII. I. The Effects of Cuprous Copper and Nitrate Ions 
in Whetlerizing Solutions; II. The Minimum Silver Re¬ 
quirement for Different Activated Charcoals, F. E. Blacet, 
July 15, 1942. Div. 10-202.14-M13 

CLXIX. Study of the Adsorption Wave, J. C. Elgin, July 16, 
1942. Div. 10-202.157-M5 

CLXX. Relative Protection of Dewey and Almy Super Soda 
Limes and High Copper Whetlerite in the M10 Canister, 
R. K. Brinton and W. C. Pierce, Aug. 5, 1942. 

Div. 10-201.1-M9 

CLXXI. Foreign, Canisters and Canister Fillings, F. T. 

Gucker, Jr., Aug. 1, 1942. Div. 10-201.31-M2 

CLXXII. Adsorption Studies on Chloropicrin and Phosgene, 
M. Dole, July 15, 1942. 

CLXXIII. Further Experiments with Cyanogen. Stability of 
CC, W. M. Latimer, Aug. 14, 1942. Div. 10-402.34-MI 
CLXXIV. A Preliminary Study of the Performance of Double 
Layer Absorbents, W. C. Pierce, J. W. Zabor, and T. Skei, 
Aug. 17, 1942. Div. 10-202.151-M4 

CLXXV. A Study of HCN and ( CN) 2 Concentrations in the 
Effluent from Various Absorbents Exposed to HCN under 
Several Conditions. Lowering the Vapor Pressure of Arsine, 
E. O. Wiig, Aug. 15, 1942. Div. 10-202.154-M25 

CLXXVI. One-Step Impregnation with Whetlerizing Solutions 
Containing Copper, Silver, and either Molybdenum, Vana¬ 
dium, or Tungsten, F. E. Blacet and R. J. Grabenstetter, 
Aug. 5, 1942. Div. 10-202.141-M 12 

CLXXVII. I. The Solubility of Silver Thiocyanate in Whetler¬ 
izing Solution. II. The Adsorption of Silver Ions and 
Thiocyanate Ions by Charcoal from Solutions, F. E. Blacet 
and D. Volman, Aug. 3, 1942. Div. 10-202.14-M 14 
CLXXVIII. I. X-Ray Studies of Basic Copper Carbonate in 
Whetlerites. II. X-Ray Studies of some Hopcalites. III. 
X-Ray Studies on Hexamethylene Tetramine and NaOH- 
treated Charcoals and Whetlerites. IV. Preparation of Char¬ 
coals from Resins, H. F. Johnstone and G. L. Clark, 
Aug. 15, 1942. Div. 10-202.143-M3 

CLXXIX. Adsorption and Surface Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, Aug. 15, 
1942. Div. 10-202.15-M 11 

CLXXX. Vapor Pressures of Diethyl Fluophosphate, Ethyl 
Difluophosphaie, Dimethyl Fluophosphate, Ethyl Fluo- 


SECRET 



BIBLIOGRAPHY 


685 


sulfonate, and Trimeric Phosphonitrilic Chloride, L. F. 
Audrieth and J. C. Bailar, Jr., Aug. 15, 1942. 

Div. 10-402.311-M9 

CLXXXI. I. Alkyl Fluosulfonates; II. Phosphonitrilic Flu¬ 
oride, L. F. Audrieth and J. C. Bailar, Jr., Aug. 15, 1942. 

Div. 10-402.311-M10 
CLXXXII. Tube and Canister Test Methods Used at the B6 
Central Laboratory, W. C. Pierce, Aug. 30, 1942. 

Div. 10-201.1-M10 

CLXXXIII. The Carbonization of Pres-to-logs, W. L. McCabe 
Aug. 13, 1942. Div. 10-202.134-MI 

CLXXXIV. The Absorption of HCN by Whetlerite and Other 
Absorbents, E. O. Wiig, Sept. 15, 1942. 

Div. 10-202.154-M26 
CLXXXY. /nteraction of Hydrogen Cyanide with Various Ad¬ 
sorbents, R. N. Pease, Aug. 28, 1942. 

CLXXXVI. Sampling Methods for Field Experiments, W. M. 

Latimer, Sept. 15, 1942. Div. 10-402.2-M4 

CLXXXVII. Protection against Cyanogen, W. M. Latimer, 
Sept. 15, 1942. Div. 10-202.154-M27 

CLXXXVII I. The Alkyl Difluophosphates and the Mono- and 
Difluothiophosphates, L. F. Audrieth and J. C. Bailar, Jr., 
Sept. 15, 1942. Div. 10-402.311-M12 

CLXXXIX. Phosphonitrilic Fluoride; Diethyl Sulfamyl Flu¬ 
oride, L. F. Audrieth and J. C. Bailar, Jr., Sept. 14, 1942. 

Div. 10-402.311-M 11 
CXC. Calorimetric Studies on the Removal of Arsine, H. M. 

Huffman, Sept. 15, 1942. Div. 10-202.154-M 19 

CXCI. Respirators for Civilian Use, W. C. Pierce, Sept. 9, 
1942. Div. 10-200-M4 

CXCII. Drying Agents for Use with Hopcalite, R. N. Pease, 
Sept. 15, 1942. Div. 10-202.142-MI 

CXCIII. The Penetration and. Persistence of Carbon Dioxide 
when Released in an Enclosed Court, F. E. Blacet and 
H. F. Johnstone, Aug. 28, 1942. 

CXCIV. Prevention of Wall Leakage in Axial Canisters, W. C. 

Pierce, Oct. 14, 1942. Div. 10-201-M4 

CXCV. The Generation of Fluorine, W. C. Schumb, Oct. 17, 
1942. 

CXCVI. One-Step Impregnation with Whetlerizing Solutions 
Containing Copper, Silver, and Chromium, F. E. Blacet, 
Oct, 15, 1942. Div. 10-202.141-M14 

CXCVII. Summary of Results in Section B-6, December 194.0 
to August 1942, W. A. Noyes, Jr., Aug. 31,1942. 

CXCVIII. Calorimetric Studies on the Removal of H. M. 

Huffman, Oct. 15, 1942. Div. 10-202.156-M15 

CXCIX. Adsorption and Surfax'e Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, Oct. 16, 
1942. Div. 10-202.15-M11 

CC. Variation of theCG Life of Various Humidified Adsorbents 
with Decreasing Temperature, W. C. Pierce, Nov. 4, 1942. 
CCI. An Ultraviolet Photometer for Routine Analysis, M. 

Dole, Nov. 5, 1942. Div. 10-402.21-M3 

CCII. I. Study of Commercial Whetlerite; II. Work on Char¬ 
coal, H. F. Johnstone and G. L. Clark, Oct. 15, 1942. 

Div. 10-202.1-M6 

CCII1. I. The Adsorption of HCN, C 2 N 2 , and SA by Whetler¬ 
ite and Other Adsorbents; II. The Effect of Temperature on 
the HCN Life of Whetlerite; III . Desorption and Recovery 
of Adsorbents after Adsorption of HCN on C 2 N 2 , E. O. 
Wiig, Oct. 15, 1942. Div. 10-202.154-M28 


CCIV. The Effects of Reactivation on the Properties of Certain 
Activated Charcoals, T. F. Young, Oct. 21, 1942. 

Div. 10-202.132-MI 

CCV. Studies on Canister Performance at High Humidities and 
Flow Rates, W. C. Pierce, Nov. 16, 1942. 

CCVI. Preliminary Tube Tests with COCIF, R. G. Dickinson, 

Oct. 21, 1942. Div. 10-202.156-M16 

CCVII. Retentivity Tests with Hydrogen Fluoride, R. G. Dick¬ 
inson, Oct, 10, 1942. Div. 10-202.15-M 14 

CCVIII. Properties of Cyanogen: Toxicity, Adsorption by 
Charcoal, Detection and Estimation, D. M. Yost, Sept. 15, 
1942. Div. 10-202.152-M7 

CCIX. Animal and Chemical Tests on Cyanogen in Effluent Air 
Stream after Adsorption of HCN, W. C. Pierce, Nov. 1,1942. 
CCX. A Study of Thiocyanate-Treated Whetlerites, F. E. 

Blacet, Sept. 17, 1942. Div. 10-202.14-M15 

CCXI. Further Studies on the Characteristics and Impregnation 
of Aminated Phenol-Formaldehyde Xerogels, P. A. Leigh¬ 
ton, Nov. 15, 1942. Div. 10 202.21-M2 

CCXII. Wind Velocities and Gustiness, D. M. Yost, Nov. 

15, 1942. Div. 10-302.1-M 1 

CCXIII. The Preparation from Wood of Charcoal Suitable for 
Activation, W. L. McCabe, Nov. 15, 1942. 

CCX1V. Experiments with CC and C 2 N 2 , W. M. Latimer, 
Nov. 15, 1942. Div. 10-402.34-M2 . 

CCXV. The Fixed Oxygen Content of Charcoal, R. N. Pease, 
Nov. 20, 1942. Div. 10-202.11-M4 

CCXVI. Adsorption and Surface Area Measurements on 
Whetlerite and Charcoal Samples, P. H. Emmett, Nov. 16, 
1942. Div. 10-202.15-M 11 

CCXVII. The i ‘Pan-Cake ,, Effect in Gas Clouds, W. M. 
Latimer, Dec. 15, 1942. 

CCXVIII. The Removal of HCN and C 2 N 2 by Absorbents, 

E. O. Wiig, Nov. 23, 1942. Div. 10-202.154-M29 

CCXIX. Analytical Methods for Whetlerites and Whetlerizing 
Solutions, F. E. Blacet, Dec. 8, 1942. Div. 10-202.14-M28 
CCXX. Third Report on the Comparison of Impregnated Char¬ 
coals, F. E. Blacet, Dec. 10, 1942. 

CCXXI. Effect of Moisture on 8,4, AC, and CC Tube Lives for 
Two Type ASC Whetlerites, F. E. Blacet, Dec. 10, 1942. 
CCXXII. Second Report on the Use of Copper, Silver, and 
Chromium Solutions as Charcoal Impregnants, F. E. 
Blacet, Dec. 21, 1942. Div. 10-202.141-M 16 

CCXXIII. Adsorption of Constituents from a Standard Whet¬ 
lerizing Solution, F. E. Blacet, Nov. 5, 1942. 

Div. 10-202.12-M7 

CCXXIV. Miscellaneous Experiments with National Char- . 
coals; The Minimum Silver Requirements of CWSN-Cl 
Charcoal, F. E. Blacet, Nov. 10,1942. Div. 10-202.14-M17 
CCXXV. One-Step Impregnation with Copper, Silver, and 
Either Molybdenum, Vanadium, or Zinc, F. E. Blacet, 
Nov. 10, 1942. Div. 10-202.141-M 15 

CCXXVI. A Study of the Physical Variables in the Production 
of Type A and Type AS Whetlerites from CWSN-44, 
CWSNC-1, and CWSPCI-1 Charcoals, F. E. Blacet, 
Nov. 5, 1942. Div. 10-202.11-M3 

CCXXVII. A Study of Impregnated Charcoal by X-Ray Dif¬ 
fraction Methods, H. F. Johnstone and G. L. Clark, 
Aug. 31, 1942. (Also published as a formal report identi¬ 
fied as Division B Serial No. 468, OSRD No. 1143.) 

Div. 10-202.143-M4 


SECRET 




DIVISION 10 NDRG INFORMAL REPORTS 


Report a No. 
10.1-1 

Date 

12/15/42 

Investigator 

P. H. Emmett 

10.1-2 

12/21/42 

E. O. Wiig 

10.1- 3* 

10.1- 4* 

10.1- 5 

1/28/43 

1/4/43 

1/16/43 

W. C. Pierce 

F. E. Blacet 

F. E. Blacet 

10.1-6 

2/24/43 

F. T. Gucker, Jr 

10.1-7* 

3/19/43 

F. E. Blacet 

10.1-8* 

3/12/43 

F. E. Blacet 

10.1-9 

4/3/43 

W. C. Pierce 

10.1-10 

10.1-11 

10.1-12 

4/5/43 

4/12/43 

4/30/43 

F. E. Blacet 

W. C. Pierce 

D. M. Yost 

10.1- 13 

10.1- 14 

5/14/43 

5/15/43 

F. E. Blacet 

F. T. Gucker, Jr 

10.1- 15 

10.1- 16* 

6/3/43 

6/9/43 

F. E. Blacet 

F. E. Blacet 

10.1-17 

6/11/43 

F. E. Blacet 

10.1-18 

10.1-19 

6/15/43 

6/10/43 

F. E. Blacet 

F. E. Blacet and 
W. C. Pierce 

10.1-20 

6/25/43 

F. E. Blacet 

10.1-21 b 

8/2/43 

F. E. Blacet 

10.1-22 

7/27/43 

F. E. Blacet 

10.1-23* 

8/10/43 

F. E. Blacet and 
W. C. Pierce 

10.1-24 

8/12/43 

W. C. Pierce 

10.1- 25 

10.1- 26* 
10.1-27 

8/10/43 

6/11/43 

9/7/43 

F. E. Blacet 

E. O. Wiig 

F. T. Gucker, Jr. 

10.1-28* 

9/2/43 

E. O. Wiig 

10.1-29 

9/22/43 

F. E. Blacet 

10.1-30 

9/15/43 

D. M. Yost 


Title 

Adsorption and Surface Area Measurements on Whetlerite and 
Charcoal Samples Div. 10-202.15-M11 

I. Variation of HCN Life with Layer Depth for Type ASC Whet¬ 
lerite; II. The Effect of Particle Size on the C 2 N 2 Life 

Div. 10-202.154-M30 

An Intermittant Flow Canister Test Machine Div. 10-201.1-M12 
Composition of Gas Evolved from Drying Whetlerites 
Determination of Ammonia Concentrations in Field Tests 

Div. 10-402.2-M7 

A Colorimetric Method of Determining the Mass Concentration of 
Triphenyl Phosphate Smokes Div. 10-201.22-M11 

A Study of the Partial Vapor Pressures of the Volatile Constituents 
in Whetlerizing Solutions Div. 10-202.14-M22 

Changes in Properties of PCI Charcoal and Whetlerite During 
Activation Div. 10-202.13-M10 

An Accelerated Flow Method for Humidifying Small Samples of 
Adsorbents for Plant Control Tests Div. 10-202.17-M7 

Surveillance of Whetlerites Div. 10-202.16-M11 

Mesh Size Studies, I Div. 10-201.21-MI 

Some Mathematical Theories for Charcoal Tube Testing 

Div. 10-202.1-M9 

Methods of Analysis for the Freons in Air Div. 10-401.1-M2 
A Study of Aerosols Produced by the Olson Bomb 

Div. 10-504.2-MI 

G. L. Cabot Carbon Black Charcoals Div. 10-202.1-M12 

Additional Study of the Partial Vapor Pressures of the Volatile 
Constituents in Whetlerizing Solutions Div. 10-202.14-M27 

Reactions Involving Chromium which Occur when ASC Whetler¬ 
izing Solution Is in Contact with Charcoal Div. 10-202.14-M25 
The Non-Uniform Activation of Charcoals Div. 10-202.13-M14 
I. Protection afforded by ASC Whetlerites of Varying Copper Con¬ 
tent; II. Surveillance of ASC Whetlerites of Varying Copper 
Content Div. 10-202.14-M24 

Action of Nitrogen Dioxide on Activated Charcoals, Whetlerites, 
and other Substances Div. 10-202.156-M18 

Analytical Methods for Whetlerites and Whetlerizing Solutions 

Div. 10-202.14-M28 

Changes in Properties of Barnebey-Cheney Company Pecan Char¬ 
coal and Whetlerite During Activation Div. 10-202.11-M5 
Effect of Activation Time on Properties of PCI Charcoal and Cor¬ 
responding ASC Whetlerites (Second Report) 

Div. 10-202.11-M6 

Preparation and Properties of a New Modification of the Starch- 
Pyridine-Iodine CC Indicator for Canister Testing 

Div. 10-201.1-M 15 

The Surveillance of Base Charcoals Div. 10-202.16-M13 

Analyses of Base Charcoals Div. 10-202.11-M7 

Polarization Relationships in Homogeneous and Inhomogeneous 
Smokes; “Owl” Settings for DOP Smokes Div. 10-501.11-M7 
Preparation and Properties of ASV Whetlerite 

Div. 10-202.12-M12 

Preliminary Report on the Aging of ASC Whetlerite under Various 
Atmospheres in Sealed Systems 
Nitrogen Elimination in the Navy High Altitude Rebreather 

Div. 10-203-M2 


a Asterisk indicates that the NDRC informal report has also been published as an OSRD (Div. 10, NDRC) formal report. 
b This report supersedes B-6 Report CCXIX as revised May 10, 1943. 


686 


SECRET 



BIBLIOGRAPHY 


687 


Report No. 

Date 

Investigator 

10.1-31 

9/15/43 

W. C. Schumb 

10.1-32 

10/14/43 

W. C. Pierce 

10.1-33 

10/15/43 

D. M. Yost 

10.1-34 

10/15/43 

W. C. Schumb 

10.1-35 

11/15/43 

D. M. Yost 

10.1-36 

11/12/43 

F. E. Blacet 

10.1-37 

11/15/43 

W. C. Schumb 

10.1-38* 

12/21/43 

E. O. Wiig 

10.1-39 

1/28/44 

W. C. Pierce 

10.1-40 

2/11/44 

W. C. Pierce 

10.1-41 

2/7/44 

F. E. Blacet 

10.1-42 

3/30/44 

W. C. Pierce 

10.1-43 

3/29/44 

W. C. Pierce 

10.1-44 

5/12/44 

W. C. Pierce 

10.1-45* 

5/18/44 

I. M. Klotz 
(Central Lab.) 

10.1-46 

) 

6/28/44 

T. Skei et al 
(Central Lab.) 

10.1-47 

6/15/44 

R. N. Pease 

10.1-48* 

7/10/44 

T. Skei et al 
(Central Lab.) 

10.1-49* 

7/24/44 

T. Skei 

(Central Lab.) 

10.1-50* 

7/22/44 

T. Skei et al 
(Central Lab.) 

10.1-51* 

8/12/44 

T. Skei et al 
(Central Lab.) 

10.1-52* 

9/6/44 

T. Skei et al 
(Central Lab.) 

10.1-53* 

9/12/44 

T. Skei et al 
(Central Lab.) 

10.1-54 

9/18/44 

L. C. Weiss 

10.1-55 

10/14/44 

I. M. Klotz with 
F. E. Blacet 

10.1-56 

11/16/44 

L. C. Weiss 

10.1-57 

11/28/44 

I. M. Klotz 

10.1-58 

1/24/45 

A. J. Juhola with 
F. E. Blacet 

10.2-1 

3/28/43 

V. K. LaMer 

10.2-2 

8/26/42 
(pub. 8/43) 

V. K. LaMer 

10.2-3 

7/23/43 

V. K. LaMer 


Title 

The Generation of Fluorine Div. 10-402.31-M2 

Canister Surveillance Studies, I Div. 10-201.1-M17, M18 

Nitrogen Elimination in the Navy High Altitude Rebreather 

Div. 10-203-M2 

The Generation of Fluorine Div. 10-402.31-M2 

Nitrogen Elimination in the Navy High Altitude Rebreather 

Div. 10-203-M2 

Second Report on the Aging of ASC and ASCP Whetlerite Contain¬ 
ing Various Amounts of Water in Sealed Systems 

Div. 10.202.17-M8 

The Generation of Fluorine Div. 10-402.31-M2 

Picoline as Impregnant for Gas Mask Absorbents 

Div. 10-202.141-M17 

The State of Impregnants on ASC Charcoal: Magnetic Suscepti¬ 
bility Studies Div. 10-202.141-M 18 

The Effect of Pore Size and Pore-Size Distribution on the Perform¬ 
ance of ASC Whetlerites at High Humidities Div. 10-202.111-M2 
An Exploratory Study of Carbon Monoxide Protection on Charcoal 
and Other Carriers Div. 10-202.153-MI 

Canister Protection at High Concentrations Div. 10-201.1-M25 
Canister Efficiency of CC Removal at Varied Breathing Rates 

Div. 10-201.1-M24 

Determination of Pyridine and Ammonia in Whetlerite and Whet- 
lerizing Solutions Div. 10-202.14-M30 

Factors in Canister Design and Tube Testing: Critical Bed Depth 
and the Nature of Gas Flow Through Charcoal 

Div. 10-201.1-M2p 

A Study of Pore Development and ASC Whetlerite Performance of 
Charcoals Prepared from Briquetted Coal Div. 10-202.1-M3 
Volume Requirements for a Carbon Monoxide Canister for Use 
with Diluter-demand Regulator Equipment Div. 10-201.1-M27 
Compilation of N 0 and X c Values for Miscellaneous Whetlerites be¬ 
fore and after Aging Div. 10-202.16-M17 

Additional Surveillance Tests on Canisters Used in the First Sibert 
Surveillance Study Div. 10-201.1-M29 

Performance of M10 and MIXA2 Canisters after Regular Use at 
Camp Sibert, Ala. Div. 10-201.1-M28 

Whetlerization and Surveillance Studies on PCI Charcoal at Vary¬ 
ing Stages of Activation (Third Report) Div. 10-202.13-M23 
Surveillance of Type ASC Whetlerite in M10-*j^" Service Canisters 

Div. 10-201.1-M31 

Surveillance Tests on ASC, Ell, and E13 Whetlerites 

Div. 10-202.16-M 19 

Leaching and Rewhetlerization: Their Effect on Whetlerite Quality 

Div. 10-202.16-M 18 

Diffusion Coefficients and Molecular Radii of PS, CG, AC and CC 

Div. 10-202.156-M19 

The Use of Pyridine and Picoline in Gas Mask Charcoal 

Div. 10-201.1-M32 

I. Factors in Canister Design and Tube Testing, II. Critical Bed 
Depths in Removal of CC by the E3 (or Mil) Canister 

Div. 10-201.1-M33 

Determination of Pore Diameters in Charcoal 

Div. 10-202.111-M4 

The Efficient Generation of Chlorosulphonic Acid Smokes for 
Screening Purposes Div. 10-502-M3 

Unipolar Smoke and Filter Penetration Div. 10-201.22-M12 

Characteristics of Different Models of the “Owl” 

Div. 10-501.11-M4 


SECRET 





BIBLIOGRAPHY 


688 

Report No. 

10.2- 4 

10.2- 5 

10 . 2 - 6 

10.2- 7 

10 . 2 - 8 

10.2- 9 

10.2- 10 
10.2-11 

10 . 2-12 

10.2- 13 

10.2- 14 

10.2- 15 

10.2- 16 

10.2- 17 

10.2- 18 

10.2- 19 

10 . 2 - 20 

10 . 2-21 

10.2-22 

10.2- 23 

10.2- 24 

10.2- 25 

10.2- 26 

10.3A-1 

10.3A-2 

10.3A-3 


Date 

7/28/43 

Investigator 

V. K. LaMer 

9/23/43 

V. K. LaMer 

10/15/43 

V. K. LaMer 

10/18/43 

V. K. LaMer 

10/18/43 

V. K. LaMer 

11/12/43 

V. K. LaMer 

12/10/43 

1/20/44 

E. I. duPont 
de Nemours & Co. 
V. K. LaMer 

3/18/44 

H. Rouse 

4/13/44 

V. K. LaMer 

4/24/44 

V. K. LaMer 

6/19/44 

V. K. LaMer 

10/23/44 

9/19/44 

V. K. LaMer 

V. K. LaMer 

12/7/44 

V. K. LaMer 

Dec. 1944 

V. K. LaMer 

Apr. 1944 

V. K. LaMer 

Aug. 1945 

V. K. LaMer 

Apr. 1945 

V. K. LaMer 

8/24/45 

V. K. LaMer 

10/23/45 

V. K. LaMer 

10/25/45 

V. K. LaMer 

11/8/45 

V. K. LaMer 

12/15/42 

D. M. Yost 

1/14/43 

1/15/43 

F. T. Wall 

D. M. Yost 


Title 

Determination of the Particle Size Distribution in Smokes by 
Analysis of the Scattered Light Div. 10-501.11-M5 

Thermal Forces as a Means of Determining Particle Size and Size 
Distribution of Aerosols Div. 10-501.11-M8 

Large Horn for the Concentration of Sound from a “Victory” 

Siren for Use in Fog Dissipation Div. 10-503.2-M2 

Properties of Oils with Special Reference to Their Use in Smoke 
Generators Div. 10-501.22-Ml 

Comparison of S.G.F. No. 1 Oil (Texas Company) with Other Oils 
for Use in Oil Fog Generators Div. 10-501.22-M2 

Dispersal and Persistence Properties of Solid Aerosols 

Div. 10-504.3-Ml 

A Method for Determining Dispersibility of Powdered Solids by 
High Explosive Bursts Div. 10-504.2-M2 

“Wetness” in Screening Smokes and a Comparison of the Quality 
of Smoke from the Hession and Besler Units at Edge wood 
Arsenal, Nov. 9 and 10, 1943 Div. 10-501.201-M2 

Wind-tunnel Studies of the Diffusion of Heat from a Line Source 

Div. 10-401.121-MI 

Report of Tests of Sonic Dissipation of Fog in California 

Div. 10-503.2-M3 

Particle Size Measurements on Certain “Aerosol” Bombs for the 
Department of Agriculture Div. 10-504.2-M4 

The Slope-O-Meter: An Instrument for the Rapid Determination 
of Particle Radius and Concentration in the Laboratory and 
Field Div. 10-501.11-M9 

A New Daytime Distress Signal Div. 10-501.23-M2 

Field and Laboratory Testing of Smoke Signals with Special Refer¬ 
ence to Floating Distress Signals for Air-Sea Rescue 

Div. 10-501.23-MI 

Toxicity to Drosophila (Fruit Flies) of DDT Deposited from 
Aerosols on the Surface of Certain Leaves and Glass 

Div. 10-602.22-Ml 

Mosquito Control by Ground Dispersal of DDT as Aerosol from 
Large Scale Generator Div. 10-602.11-MI 

The Solubility of DDT in Mixtures of Xylene and Lubricating Oil 
(10W); The Density of These Solutions when Saturated with 
DDT Div. 10-601.1-MI 

The Suitability of Vertical Slides as a Particle Size Measurement 
Method Div. 10-501.11-M10 

Sun Oil Company Solvent Aro-Sol (151B) as a Practical Solvent 
for DDT Div. 10-601.1-M2 

Field Tests of Hochberg-LaMer Aerosol Insecticide Generator 
Against Salt Marsh Mosquitoes at Mantoloking, New Jersey 

Div. 10-602.21-M6 

Laboratory Experiments Testing Effects of DDT on Wood Tick 
Dermacentor Variabilis Div. 10-602.23-M2 

Efficacy of DDT and DNOC as Insecticides for Grasshoppers 
when Dispersed by a Hochberg-LaMer Type Aerosol Generator 

Div. 10-602.23-M3 

Black Fly Control with DDT-Oil Aerosols Using the Hochberg- 
LaMer Generator with Notes on Spruce Bud Worms and Larch 
Case Bearer Control at Lake Placid, New York 

Div. 10-602.23-M4 

Meteorological Instruments; Wind Velocity Measurements 

Div. 10-301.11-M 1 

Movement of Smoke in the Atmosphere Div. 10-302.1-M2 

Report of Meteorological Observations Made During U. S. Army 
Smoke Tests at Sault Ste. Marie, Michigan, December 28-30, 
1942 - Div. 10-302.1-M3 


SECRET 



BIBLIOGRAPHY 


689 


Report No. 

Dale 

Investigator 

10.3A-4 

1/15/43 

D. M. Yost 

10.3A-5 

1/15/43 

D. M. Yost 

10.3A-6 

2/15/43 

W. M. Latimer 

10.3A-7 

2/10/43 

H. F. Johnstone 

10.3A-8 

2/8/43 

R. G. Dickinson 

10.3A-9 

2/24/43 

R. G. Dickinson 

10.3A-10 

2/15/43 

D. M. Yost 

10.3A-11* 

2/15/43 

M. Dole 

10.3A-12 

3/15/43 

R. G. Dickinson 

10.3A-13 

4/15/43 

R. G. Dickinson 

10.3A-14 

4/15/43 

W. M. Latimer and 

10.3A-15 

4/16/43 

S. Ruben; K. Pitzer 
H. F. Johnstone 

10.3A-16* 

5/3/43 

R. G. Dickinson 

10.3A-17 

4/17/43 

M. D. Thomas 

10.3A-18* 

6/15/43 

Amer. Smelting & 
Refining Co. 

F. E. Blacet, 

10.3A-19 

6/21/43 

M. Dole, and 

H. F. Johnstone 

R. G. Dickinson 

10.3A-20 

6/10/43 

W. M. Latimer 

10.3A-21 

5/26/43 

H. F. Johnstone 

10.3A-22* 

6/15/43 

H. F. Johnstone 

10.3A-23* 

7/10/43 

F. E. Blacet 

10.3A-24* 

7/14/43 

W. M. Latimer and 

10.3A-25 

6/20/43 

S. Ruben; K. Pitzer 
D. M. Yost and 

10.3A-26 

7/20/43 

R. G. Dickinson 

D. M. Yost 

10.3A-27 

6/18/43 

D. M. Yost 

10.3A-28 

8/22/43 

D. M. Yost 

10.3A-29 

8/12/43 

D. M. Yost 

10.3A-30 

8/25/43 

D. M. Yost 

10.3A-31 

8/27/43 

I). M. Yost 


Title 

Testing Charcoal Fines by the ‘‘Spotted Dick” Test 

Div. 10-202.15-M15 

Suggested Field Laboratory Method of Testing Permeable Fabrics 
for Resistance to Penetration by Mustard Vapor 

Div. 10-202.19-M2 

Meteorological Instruments Div. 10-301-Ml 

Dispersion of Gases in a Closed Court and the Design of Wind 
Obstacles Div. 10-401.122-M2 

Determination of CG in Air, using Silica Gel Div. 10-402.2-M8 
A Portable Continuous Gas Concentration Meter 

Div. 10-401.111-MI 

Micro-Meteorological Measurements Made During the Smoke 
Screening Tests at the Portsmouth (Va.) Navy Yard on Febru¬ 
ary 3 and 8, 1943 Div. 10-302.1-M4 

I. Nitrobenzene as a Compound to Simulate HS; II. Distribution 
of Nitrobenzene Vapors in a Closed Room Div. 10-402.2-M9 
Measurement of CC with the Portable Continuous Gas Concen¬ 
tration Meter Div. 10-401.111-M2 

Measurements on AC, CC and Mixtures of the Two with the 
Portable Continuous Gas Concentration Meter 

Div. 10-401.111-M3 

I. Meteorological Instruments; II. Observations in the Field 

Div. 10-301-Ml 

Meteorological Observations in Connection with the Study of 
Smokes and Gases Div. 10-302.1-M5 

Micrometeorological Observations at United States Army Smoke 
Tests in the Los Angeles Area, March 17, 18, and 19 and April 20 ; 
1943 Div. 10-302.1-M8 

Temperature Gradients and R Values in Relation to the Smoke 
Conditions in the Salt Lake Valley Div. 10-302-MI 

The Penetration and Persistence of Gases in an Enclosed Court 

Div. 10-401.122-M3 

Some Observations at Rosamond Dry Lake on Parameters Used in 
the Treatment of Gas and Smoke Clouds Div. 10-302.1-M9 
Tabulations of Data on Concentrations in Gas Clouds under Vari¬ 
ous Meteorological Conditions Div. 10-302.1-M6 

Large-Scale Screening Tests with Esso Smoke Generators 

Div. 10-501.201-M2 

A Study of Oil Smoke Plumes by Motion Pictures Div. 10-502-M8 
The Persistence and Penetration of Gas in a House 

Div. 10-401.124-MI 

Concentrations in Gas Clouds under High Inversion Conditions 

Div. 10-302.1-M14 

Experiments on the Accumulation of Sulfur Dioxide in Fox Holes 

Div. 10-402.2-M11 

Experiments on the Measurement of Air Temperatures with 
Thermocouples Div. 10-301.2-MI 

Report on the Preliminary Investigation of the Micrometeorologi¬ 
cal Conditions at Rancho Grande, Calif. Div. 10-302.1-M7 
Experiments at the Rancho Grande, July 28 and 29, 1943, on 
(1) the “Doughnut” Effect, and (2) the Influence of Terrain on 
the Flow of Gas Clouds Div. 10-302.1-M 12 

A Short Photographic Record of the Motion of a Bidirectional 
Vane ' Div. 10-301.11-M2 

Measurements on the Widths of Smoke Clouds 

Div. 10-302.1-M13 

Further Experiments on the Accumulation of Sulfur Dioxide in 
Fox Holes Div. 10-402.2-M12 


SECRET 





690 


BIBLIOGRAPHY 


Report No. 

Date 

10.3A-32 

8/27/43 

10.3A-33 

8/31/43 

10.3A-34 

8/31/43 

10.3A-35 

9/14/43 

10.3A-36 

10/10/43 

10.3A-37* 

9/1/43 

10.3A-38 

10/26/43 

10.3A-39 

12/10/43 

10.3A-40 

11/1/43 

10.3A-41 

1/25/44 

10.3A-42 

4/1/44 

10.3A-43 

4/1/44 

10.3A-44* 

4/10/44 

10.3A-45 

4/11/44 

10.3A-46* 

5/9/44 

10.3A-47 

1/3/45 

10.3A-48 

6/8/45 

10.3A-48a 

9/29/45 

10.3B-1 

12/15/42 

10.3B-2 

12/15/42 

10.3B-3 

12/21/42 

10.3B-4 

1/15/43 

10.3B-5 

1/15/43 

10.3B-6 

1/15/43 

10.3B-7 

2/15/43 

10.3B-8 

2/19/43 

10.3B-9 

2/16/43 

10.3B-10 

2/15/43 

10.3B-11 

3/15/43 

10.3B-12 

2/15/43 

10.3B-13 

3/15/43 

10.3B-14 

3/15/43 

10.3B-15 

3/15/43 

10.3B-16* 

4/15/43 

10.3B-17 

4/15/43 

10.3B-18 

4/15/43 

10.3B-19 

4/15/43 


Investigator 
D. M. Yost 
D. M. Yost 

D. M. Yost 

W. M. Latimer and 
S. Ruben 
H. Rouse 

D. M. Yost 

R. G. Dickinson 

W. M. Latimer 
D. M. Yost 
R. G. Dickinson 


F. E. Blacet 

F. E. Blacet 

R. G. Dickinson 

R. G. Dickinson 

H. Rouse 

R. G. Dickinson 

A. A. Kalinske 

A. A. Kalinske 

W. C. Schumb 
J. C. Bailar, Jr. 

A. B. Burg 
W. C. Schumb 
J. C. Bailar, Jr. 

D. M. Yost 

W. C. Schumb 
A. B. Burg 
H. M. Huffman 
D. M. Yost 

H. M. Huffman 
J. C. Bailar, Jr. 

J. C. Bailar, Jr. 

A. B. Burg 
W. C. Schumb 
H. M. Huffman 
A. B. Burg 
W. C. Schumb 
D. M. Yost 


Title 

Thermocouple Experiments Div. 10-301.2-M2 

Measurements on S0 2 and NH a with the Portable Continuous Gas 
Concentration Meter Div. 10-401.111-M4 

Chemical Analysis of Mixtures of NH 3 and Air and S0 2 and Air 

Div. 10-402.2-M13 

Gas Concentrations from Line Sources in a Forested Area 

Div. 10-302.2-M2 

Scale Model Studies of the Movement of Smoke and Gas Clouds 

Div. 10-302.1-M15 

A Study of Smoke Clouds in a Coastal Area; Field Experiments 
near Brownsville, Texas Div. 10-302.1-M 16 

A Comparison of Three Types of Cup Anemometers at Low 
Velocities Div. 10-301.1-M 1 

Dugway Trials with the Hot Wire Meter Div. 10-302.1-M 17 
Graphically Recording Bi-Directional Vanes Div. 10-301.11-M3 
Micro-meteorological Conditions at Prisoner’s Harbor on Santa 
Cruz Island, California (June 24-July 13, 1943) 

Div. 10-302.1-M19 

Determination of CC and CG Concentrations in Field Tests 

Div. 10-402.2-M15 

Determination of S0 2 Concentrations in Field Tests 

Div. 10-402.2-M 16 

A Remote Indicating Cup Anemometer with Magnetic Coupling 

Div. 10-301.1-M2 

An Apparatus for Temperature Profile Measurement 

Div. 10-301.2-M3 

Wind-Tunnel Studies of the Diffusion of Gas in Schematic Urban 
Districts Div. 10-401.121-M2 

Micrometeorological Observations in Connection with DDT 
Operations in Panama Div. 10-302.1-M20 

Wind-Tunnel Studies of Gas Diffusion in a Typical Japanese Urban 
District Div. 10-401.121-M4 

Correlation of Wind-Tunnel Studies With Field Measurements of 
Gas Diffusion Div. 10-401.121-M5 

The Generation of Fluorine Div. 10-402.31-M2 

Fluophosphates and Related Compounds, VI 

Div. 10-402.311-M 14 

New Toxic Gases, V 

The Generation of Fluorine Div. 10-402.31-M2 

A Report on Fluophosphates and Related Compounds, VII 

Div. 10-402.311-M 14 

Nitrogen Elimination in High Altitude Rebreather 

Div. 10-203-MI 

The Generation of Fluorine Div. 10-402.31-M2 

New Toxic Gases, VII Div. 10-402.311-M 15 

Thermal Data on KB-16 

Nitrogen Elimination in High Altitude Rebreather 

Div. 10-203-MI 

Thermal Data on KB-16 

Fluophosphates and Related Compounds, VIII 

Div. 10-402.311-M 14 

Fluophosphates and Related Compounds, IX 

Div. 10-402.311-M 14 

New Toxic Gases, VIII Div. 10-402.311-M 15 

The Generation of Fluorine Div. 10-402.31-M2 

Thermal Data on KB-14 and KB-16 Div. 10-402.36-M7 

New Toxic Gases, IX Div. 10-402.311-M15 

The Generation of Fluorine Div. 10-402.31-M2 

Nitrogen Elimination in High Altitude Rebreather 

Div. 10-203-Ml 


SECRET 



BIBLIOGRAPHY 


691 


Report No. 

10.3B-20 

10.3B-21 

Date 

5/5/43 

4/15/43 

Investigator 

D. M. Yost 

J. C. Bailar, Jr. 

10.3B-22 

10.3B-23 

5/15/43 

6/15/43 

W. C. Schumb 

D. M. Yost 

10.3B-24* 

10.3B-25 

6/15/43 

7/15/43 

W. C. Schumb 

A. B. Burg 

10.3B-26 

6/17/43 

G. P. Baxter 

10.3B-27 

7/15/43 

D. M. Yost 

10.3B-28 

10.3B-29 

7/15/43 

8/15/43 

W. C. Schumb 

D. M. Yost 

10.3B-30 

8/15/43 

A. B. Burg 

10.3B-31 

10.4-1 

8/15/43 

12/17/42 

W. C. Schumb 
Chemical Process Co. 

10.4- 2 

10.4- 3 

12/18/42 

12/15/42 

A. D. Little, Inc. 

R. J. Kunz 

10.4-4 

1/15/43 

R. J. Kunz 

10.4- 5 

10.4- 6 

10.4- 7* 

1/15/43 

1/15/43 

1/15/43 

Chemical Process Co. 
A. D. Little, Inc. 

W. L. McCabe 

10.4-8 

2/10/43 

R. J. Kunz 

10.4-9 

2/10/43 

A. D. Little, Inc. 

10.4-10 

2/10/43 

Chemical Process Co. 

10.4-11 

3/12/43 

R. J. Kunz 

10.4-12 

3/11/43 

Chemical Process Co. 

10.4-13 

3/10/43 

A. D. Little, Inc. 

10.4-14 

4/1/43 

R. York, Jr. 

10.4-15 

4/15/43 

R. J. Kunz 

10.4-16 

4/9/43 

A. D. Little, Inc. 

10.4- 17 

10.4- 18 

4/13/43 

5/1/43 

G. F. Mills 

Chemical Process Co. 
R. York, Jr. 

10.4-19 

5/10/43 

R. J. Kunz 

10.4-20* 

4/1/43 

R. York, Jr. 

10.4- 21 

10.4- 22* 

5/15/43 

6/1/43 

E. W. Comings 

H. F. Johnstone and 
G. L. Clark 


Title 

Nitrogen Elimination in High Altitude Rebreather Div. 10-203-MI 
Fluophosphates and Related Compounds, X 

Div. 10-402.311-M14 

The Generation of Fluorine Div. 10-402.31-M2 

Nitrogen Eliminator for High Altitude Oxygen Rebreather 

Div. 10-203-M1 

The Generation of Fluorine Div. 10-402.31-M4 

I. Flame-Damping of Hydrogen Cyanide; II. Stabilization of 
Cyanogen Chloride Div. 10-402.33-MI 

Preparation of Certain Extremely Pure Strontium Salt 

Div. 10-402.2-M10 

Nitrogen Elimination in High Altitude Rebreather 

Div. 10-203-M 1 

The Generation of Fluorine Div. 10-402.31-M2 

Nitrogen Elimination in Navy High Altitude Rebreather 

Div. 10-203-M2 

Flame-Damping of Hydrogen Cyanide, II; Stabilization of Cyan¬ 
ogen Chloride, III. Div. 10-402.33-MI 

The Generation of Fluorine 

Preparation and Use of Amine Resins for Gas Adsorption 

Div. 10-202.21-M3 

Dispersion of Fine Fibers and Solids Div. 10-201.22-M8 

Summary of Investigations at the Activation Laboratory, I 

Div. 10-202.13-M9 

Summary of Investigations at the Activation Laboratory, II 

Div. 10-202.13-M9 

Studies of Adsorbent Resins Div. 10-202.21-M4 

Asbestos Impregnated Filter Papers Div. 10-201.22-M9 

The Preparation of Wood Charcoal Suitable for Activation 

Div. 10-202.12-M8 

Summary of Investigations at the Activation Laboratory, III 

Div. 10-202.13-M9 

Dispersion of Asbestos Fibers (Filter Paper Products) 

Div. 10-201.22-M10 

Preparation and Use of Amine Resins for Gas Adsorption 

Div. 10-202.21-M3 

Summary of Investigations of Activation Laboratory, IV 

Div. 10-202.13-M9 

Development of Amine Resin Adsorbents for Gas Adsorption and 
other Purposes Div. 10-202.21-M5 

Dispersion of Asbestos Fibers (Filter Paper Products) 

Div. 10-201.22-M 10 

Weight and Size Losses During Laboratory Activation of PCI Char 

Div. 10-202.13-M11 

Summary of Investigations at the Activation Laboratory, V 

Div. 10-202.13-M9 

Dispersion of Asbestos Fibers (Filter Paper Products) 

Div. 10-201.22-M 10 

Development of Amine Resin Adsorbents for Gas Adsorption and 
Other Purposes Div. 10-202.21-M5 

Activation of Charcoal in a “Boiling Bed” Furnace 

Div. 10-202.13-M 13 

Summary of Investigations at the Activation Laboratory, VI 

Div. 10-202.13-M9 

Further Development of a Laboratory Jiggler for Activating Gas 
Charcoal, and Tentative Results on Gasification Rate Studies 

Div. 10-202.131-M4 

Smoke Investigations Div. 10-501.2-M2 

Application of the Electron Microscope to the Study of Charcoal 

Div. 10-202.143-M5 


SECRET 






BIBLIOGRAPHY 


692 


Report No. 

Date 

Investigator 

10.4-23 

6/10/43 

R. J. Kunz 

10.4-24 

6/15/43 

E. W. Comings 

10.4-25* 

6/24/43 

G. F. Mills 

Chemical Process Co. 

10.4-26 

5/27/43 

P. H. Emmett 

10.4-27 

7/10/43 

R. J. Kunz 

10.4-28 

7/5/43 

L. B. Counterman 
Hercules Powder Co. 

10.4-29 

7/8/43 

P. H. Emmett 

10.4-30 

8/1/43 

R. York, Jr. 

10.4-31 

8/10/43 

R. J. Kunz 

10.4-32 

8/2/43 

Hercules Powder Co. 

10.4-33 

9/6/43 

Hercules Powder Co. 

10.4-34 

9/15/43 

A. B. Burg 

10.4-35* 

8/1/43 

H. F. Johnstone 

10.4-36 

10/4/43 

Hercules Powder Co. 

10.4-37 

10/14/43 

A. B. Burg 

10.4-38* 

10/20/43 

H. F. Johnstone 

E. W. Comings 

10.4-39 

11/15/43 

A. B. Burg 

10.4-40 

11/11/43 

Victor Chemical Works 

10.4-41 

11/8/43 

Hercules Powder Co. 

10.4-42 

12/7/43 

Victor Chemical Works 

10.4-43 

12/3/43 

E. W. Comings 

10.4-44 

12/14/43 

A. B. Burg 

10.4-45 

1/3/44 

Hercules Powder Co. 

10.4-46 

1/20/44 

Chemical Process Co. 

10.4-47 

1/15/44 

A. B. Burg 

10.4-48 

12/31/43 

H. F. Johnstone 

10.4-49 

1/15/44 

H. F. Johnstone 

10.4-50 

2/14/44 

A. B. Burg 

104-51 

2/7/44 

Hercules Pow r der Co. 

10.4-52 

3/13/44 

A. B. Burg 

10.4-53 

2/1/44 

J. C. Bailar, Jr. and 

H. F. Johnstone 

10.4-54 

3/6/44 

Hercules Powder Co. 

10.4-55 

3/1/44 

H. F. Johnstone 

10.4-56 

3/30/44 

Victor Chemical Works 


Title 

Summary of Investigations by the Engineering Pilot Group, VII 

Div. 10-202.1-M10 

Smoke Investigations 

Use of Aminated Phenol-Formaldehyde Xerogels as Gas Adsorbents 

Div. 10-202.21-M6 

Adsorption and Surface Area Measurements on Whetlerite and 
Charcoal Samples Div. 10-202.15-M16 

Summary of Investigations by the Engineering Pilot Group, VIII 

Div. 10-202.13-M15 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Chemisorption of Gases on Charcoals and Type A Whetlerites 

Div. 10-202.15-M 17 

Composition of Gases Evolved during Activation Div. 10-202.13-M16 
Summary of Investigations by the Engineering Pilot Group, IX 

Div. 10-202.1-M 10 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Flame-Damping of Hydrogen Cyanide III; Stabilization of Cyan¬ 
ogen Chloride IV Div. 10-402.33-Ml 

The Evaporation of Small Drops of Thiodiglycol and Levinstein 
Mustard Div. 10-501.12-MI 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-Ml 

Flame-Damping of Hydrogen Cyanide IV; Stabilization of Cyan¬ 
ogen Chloride V Div. 10-402.33-Ml 

The Generation and Use-of Concentrated Mustard Vapor Clouds 

Div. 10-504.1-M 1 

Flame-Damping of Hydrogen Cyanide V; Stabilization of Cyano¬ 
gen Chloride VI Div. 10-402.33-Ml 

The Use of Carbon Black in WP Shells Div. 10-504.21-MI 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

I. Static Firing Tests on Tail-ejector (E-5) Bombs; II. Notes on 
WP in Anti-personnel Role Div. 10-504.21-M2 

Improvements in the Fuel Block for the Thermal Vapor Generator 

Div. 10-504.11-M 1 

Flame-Damping of Hydrogen Cyanide VI; Stabilization of Cyano¬ 
gen Chloride, VII Div. 10-402.33-Ml 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-M 1 

Use of Amine Resins as Gas Adsorbents Div. 10-202.21-M7 

Stabilization of Cyanogen Chloride, VIII Div. 10-402.34-M3 

The Assessment of Aerosols Div. 10-504.2-M3 

The Deposition of Drops of a Non-volatile Liquid Vesicant on 
Vertical and Horizontal Surfaces Div. 10-501.12-M2 

Stabilization of Cyanogen Chloride, IX Div. 10-402.34-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Stabilization of Cyanogen Chloride, X Div. 10-402.34-M3 

Preparation of Plasticized Phosphorus Mixtures 

Div. 10-504.21-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

The Deposition of Non-volatile Aerosol Clouds in Open and 
Forested Areas Div. 10-501.12-M3 

Tests on M-69 Bombs Charged with Coated Precast Blocks of WP 

Div. 10-504.21-M4 


SECRET 



BIBLIOGRAPHY 


693 


Report No. 

10.4- 57 

10.4- 58 

Date 

4/10/44 

4/15/44 

10.4-59 

4/3/44 

10.4-60 

4/20/44 

10.4-61 

5/14/44 

10.4-62 

5/8/44 

10.4-63 

5/1/44 

10.4-64 

6/5/44 

10.4-65 

6/30/44 

10.4- 66 

10.4- 67 

6/15/44 

7/4/44 

10.4- 68 

10.4- 69 

7/15/44 

8/7/44 

10.4- 70 

10.4- 71 

8/14/44 

9/4/44 

10.4- 72 

10.4- 73 

9/15/44 

9/1/44 

10.4-74 

10/1/44 

10.4- 75 

10.4- 76 

10.4- 77 

9/15/44 

10/14/44 

9/25/44 

10.4- 78 

10.4- 79 

10.4- 80 

10.4- 81 

11/15/44 

12/14/44 

1/13/45 

2/20/45 

10.4-82 

6/15/45 

10.4-83 

5/1/45 

10.4-84 

7/20/45 

10.5- 1 

10.5- 2 

9/1/43 

9/10/43 

10.5-3 

9/11/43 

10.5-4 

10/15/43 

10.5-5 

11/15/43 

10.5-6 

11/12/43 


Investigator 
J. C. Bailar, Jr. 

A. B. Burg 

Hercules Powder Co. 

H. F. Johnstone 
R. L. LeTourneau 

A. B. Burg 

Hercules Powder Co. 

H. F. Johnstone 
E. W. Comings 
Hercules Powder Co. 

J. C. Bailar, Jr. 

A. B. Burg 
Hercules Powder Co. 

A. B. Burg 
Hercules Powder Co. 

A. B. Burg 
Hercules Powder Co. 

A. B. Burg 
J. C. Bailar, Jr. 

H. F. Johnstone 
W. H. Rodebush 
H. F. Johnstone 
A. B. Burg 

Munitions Dev. Lab. & 
TVA Health and 
Safety Department 
A. B. Burg 
A. B. Burg 
A. B. Burg 
H. F. Johnstone 
E. A. Ford 
P. A. Pitt 

R. I. Rice 
H. F. Hrubecky 
R. I. Rice 

R. York, Jr. 

R. J. Kunz 

P. H. Emmett 

R. J. Kunz 

R. J. Kunz 

R. York, Jr. 


Title 

Plasticized White Phosphorus (PWP) Div. 10-504.21-Mo 

Stabilization of Cyanogen Chloride and Hydrogen Cyanide, XI 

Div. 10-402.34-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-Ml 

The Production of Aerosol Droplets below Twenty-five Micron 
Diameter for the Dispersal of Insecticides and CW Agents 

Div. 10-602-M1 

Flame-Damping of Hydrogen Cyanide, VII; Stabilization of 
Cyanogen Chloride XII Div. 10-402.33-Ml 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Fuel Blocks for the Model G-8 Thermal Generator Bomb 

Div. 10-504.11-M2 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Factors Affecting the Thermal Stability of Plasticized Phosphorus 

Div. 10-504.21-M6 

Stabilization of Cyanogen Chloride, XIII Div. 10-402.34-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-Ml 

Stabilization of Cyanogen Chloride, XIV Div. 10-402.34-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-Ml 

Stabilization of Cyanogen Chloride, XV Div. 10-402.34-M3 

The Development of a Filling Mixture for Smoke Pots, Grenades, 
and Floats Div. 10-501.21-MI 

Stabilization of Cyanogen Chloride, XVI Div. 10-402.34-M3 

The Development of Plasticized White Phosphorus, IV 

Div. 10-504.21-M7 

The Toxicity of DDT Films and Aerosol Deposits 

Div. 10-602.2-MI 

The Burning Properties and Anti-Personnel Effect of PWP 
Stabilization of Cyanogen Chloride, XVII Div. 10-402.34-M3 
Tests with an Exhaust Aerosol DDT Generator on a 450 H. P. 
Stearman Aircraft 


Stabilization of Cyanogen Chloride, XVIII 
Stabilization of Cyanogen Chloride, XIX 
Stabilization of Cyanogen Chloride, XX 
The Apparent Viscosity of PWP 


Div. 10-402.34-M3 
Div. 10-402.34-M3 
Div. 10-402.34-M3 
Div. 10-504.21-M10 


The Tailpipe Combustion Unit to Increase the Rate of Smoke 
Production of TBM-3 Exhaust Generator Div. 10-501.203-MI 
Directions for Installation and Operation of Exhaust-Type Aerosol 
Generator on “Jeep” Div. 10-602.122-Ml 

Installation of an Exhaust DDT Aerosol Generator on the Cargo 
Carrier M29C (Weasel) Div. 10-602.122-M2 

Activation of Carbonized Pres-to-Logs Div. 10-202.134-M2 

Summary of Investigations by the Engineering Pilot Group, X 

Div. 10-202.131-M5 


Adsorption of Nitrogen on CWSN Base Charcoals 

Div. 10-202.11-M8 

Summary of Investigations by the Engineering Pilot Group, XI 

Div. 10-202.1-M10 

Summary of Investigations by the Engineering Pilot Group, XII 

Div. 10-202.1-M 10 

Activation of Charcoal in a Boiling-Bed Furnace (second report) 

Div. 10-202.13-M13 


SECRET 





694 


BIBLIOGRAPH \ 


Report No. 

10.5- 7 

10.5- 8 

10.5- 9 

10.5- 10 

10.5- 11 
10.5*12 

10.5- 13 

10.5- 14 

10.5- 15 

10.5- 16 

10.5- 17 

10.5- 18 

10.5- 19 

10.5- 20 

10.5- 21 

10.5- 22 

10.5- 23 

10.5- 24 

10.5- 25 

10.5- 26 

10.5- 27 

10.5- 28 

10.5- 29 

10.5- 30 

10.5- 31 

10.5- 32 

10.5- 33 

10.5- 34 


Date 

Investigator 

Title 

12/1/43 

R. York, Jr. 

The Effect of the Activation Process on the Nitrogen Adsorption 
and Whetlerite Properties of PCI and Carlisle Chars 

Div. 10-202.11-M9 

12/10/43 

R. J. Kunz 

Summary of Investigations by the Engineering Pilot Group, XIII 

Div. 10-202.1-M 10 

12/15/43 

R. York, Jr. 

Activation of Carbonized Peach Pits and Black Walnut Shells in 
PCI Retorts Div. 10-202.134-M3 

1/15/44 

R. J. Kunz 

Preliminary Design and Cost Estimate for Five-Ton-per-Day 


(written 7/1/43) 


12/10/43 

11/12/43 

1/10/44 

National Carbon Co., 
P. H. Emmett 

R. J. Kunz 

2/1/44 

R. York, Jr. 

1/10/44 

2/10/44 

National Carbon Co. 
R. J. Kunz 

2/10/44 

3/1/44 

National Carbon Co. 
R. York, Jr. 

3/10/44 

R. J. Kunz 

3/1/44 

P. H. Emmett 

3/14/44 

R. J. Kunz 

3/10/44 

3/9/44 

3/25/44 

National Carbon Co. 
R. J. Kunz 

R. J. Kunz 

3/20/44 

R. J. Kunz 

4/24/44 

4/10/44 

R. J. Kunz and 

D. G. Anderson 

R. J. Kunz 

3/15/44 

R. J. Kunz 

4/10/44 

5/6/44 

National Carbon Co. 
R. J. Kunz 

5/10/44 

R. J. Kunz 

5/10/44 

National Carbon Co. 

5/23/44 

R. York, Jr. 

6/10/44 

National Carbon Co. 


Activation Plant Based on Jiggler Process Div. 10-202.131-M6 
Inc. Study of Zinc Chloride Carbon, I Div. 10-202.133-Ml 

Pore Size Alteration of Charcoal Div. 10-202.111-MI 

Summary of Investigations by the Engineering Pilot Group on 
Carbonization, Activation, and Whetlerization, XIV 

Div. 10-202.1-M10 

An Hypothesis of the Activation Mechanism in Charcoal 

Div. 10-202.13-M17 

Study of Zinc Chloride Carbon, II Div. 10-202.133-Ml 

Summary of Investigations by the Engineering Pilot Group on 
Carbonization, Activation, and Whetlerization, XV 

Div. 10-202.1-M10 

Zinc Chloride-Activated Wood Charcoal, III Div. 10-202.13-M 18 
A Modified Boiling-bed Furnace for Charcoal Activation by 
Steam, III Div. 10-202.13-M20 

Summary of Investigations by the Engineering Pilot Group on 
Carbonization, Activation, and Whetlerization, XVI 

Div. 10-202.1-M10 

Nitrogen Surface Area Measurements on a Series of PCI Samples 
Subjected to Steam Activation for Various Periods of Time 
(to Nov. 11, 1943) • Div. 10-202.13-M 19 

A Study of the Effect of Uniformity of Activation of Sieve Fractions 
on CC Canister Performance for Mixtures of PCI Charcoals 
Zinc Chloride-Activated Wood Charcoal, IV Div. 10-202.13-M 18 
Reclamation of Type A Whetlerite Div. 10-202.19-M4 

The Effect of Time and Temperature of Activation on the Proper¬ 
ties of PCI Charcoal Activated in the Jiggler Pilot Plant 

Div. 10-202.131-M8 

Activation of Charcoal by the Jiggler Process. A Summary of the 
Results Obtained in the First Two Pilot Models 

Div. 10-202.131-M7 

A Systematic Study of Pressure Drop in Beds of Charcoal 

Div. 10-202.11-M 10 

Summary of Investigations by the Engineering Pilot Group on 
Carbonization, Activation, and Whetlerization, XVII 

Div. 10-202.1-M 10 

An Investigation of the Applicability of ASC-type Whetlerizing 
Equipment to the Preparation of ASM Whetlerite 

Div. 10-202.12-M13 

Zinc Chloride-Activated Wood Charcoal, V Div. 10-202.13-M 18 
The Effect of Backfeeding on the Quality of ASC Whetlerite 

Div. 10-202.19-M5 

Summary of Investigations by the Engineering Pilot Group on 
Carbonization, Activation, and Whetlerization, XVIII 

Div. 10-202.1-M 10 

Zinc Chloride-Activated Wood Charcoal, VI 

Div. 10-202.13-M 18 

A Modified Boiling-bed Furnace for Charcoal Activation by 
Steam, IV 

Zinc Chloride-Activated Wood Charcoal, VII 

Div. 10-202.13-M 18 


SECRET 



BIBLIOGRAPHY 


695 


Report No. 
10.5-35 

Date 

7/14/44 

10.5-36 

7/10/44 

10.5-37 

6/30/44 

10.5-38 

7/10/44 

10.5-39 

7/15/44 

10.5-40* 

8/4/44 

10.5-41* 

8/15/44 

10.5-42 

8/14/44 

10.5-43 

8/10/44 

10.5-44* 

8/15/44 

10.5-45* 

8/15/44 

10.5- 46 

10.5- 47* 

9/10/44 

9/30/44 

10.5-48 

11/20/44 

10.5-49 

11/24/44 


Investigator 
R. J. Kunz 

R. J. Kunz 
R. J. Kunz 

National Carbon Co. 
R. J. Kunz 
T. F. Young 
R. J. Kunz 
R. J. Kunz 
National Carbon Co. 
R. J. Kunz 

R. J. Kunz 

National Carbon Co. 
National Carbon Co. 

T. B. Drew et al 

B. White et al 


Title 

Activation of Charcoal by the Jiggler Process. Factors other than 
Time-Temperature Affecting Product Quality and Yield 

Div. 10-202.131-M11 

Design, Construction, and Operating Characteristics of the Third 
Pilot Jiggler Activator Div. 10-202.131-M 10 

The Effect of Time and Temperature of Activation upon the 
Properties of Barnebey-Cheney and Carlisle Charcoals Processed 
in the Jiggler Pilot Activator Div. 10-202.131-M9 

Zinc Chloride-Activated Wood Charcoal, VIII 

Div. 10-202.13-M18 

Carbonization of Peach Pits and Their Preparation into ASC 
Whetlerite Div. 10-202.134-M4 

The Reactivation in Oxygen of CWS Charcoals 

Div. 10-202.132-M2 

Summary of Pilot Studies of the Preparation of ASC Whetlerite 

Div. 10-202.12-M14 

A Study of the Steam Activation of Various Charcoals in a Small 
Horizontal Rotary Retort Div. 10-202.13-M22 

Zinc Chloride Activated Wood Charcoal, IX 

Div. 10-202.13-M 18 

Activation of Charcoal by the Jiggler Process. A Summary of 
Results Obtained in the Fourth (Metal Tube) Pilot Model 

Div. 10-202.131-M 13 

Final Design and Cost Estimate for a Two-Ton-per-Day Activator 
Using the “Jiggler” Process Div. 10-202.131-M12 

Zinc Chloride-Activated Wood Charcoal, X Div. 10-202.13-M 18 
Zinc Chloride-Activated Wood Charcoal, Final Report 

Div. 10-202.13-M24 

I. The Adsorption Wave. II. Study of the Adsorption Wave. 
III. Plotting of the Schumann-Furnas Graphs for Low Values 
of the Concentration Div. 10-202.157-M8 

A Study of the Carbonization of Coal Materials 

Div. 10-202.12-M 15 


SECRET 




OSRD APPOINTEES 


DIVISION 10 

Chief 

W. A. Noyes, Jr. 


Members 

F. E. Blacet 
H. F. Johnstone 

V. K. LaMer 

W. M. Latimer 

Technical Aides 

M. T. O’Shaughnessy 
W. C. Pierce 

W. J. Wyatt 


W. L. McCabe 
W. C. Pierce 
W. H. Rodebush 
D. M. Yost 


C. D. Wagner 
W. D. Walters 


Special Advisors 

L. M. K. Boelter 

M. K. Fahnestock 
E. P. Heckel 

Consultants 


F. E. Bartell 
A. F. Benton 
W. D. Bonner 

W. E. Brinker, Jr. 

L. O. Borckway 
W. G. Brown 

G. L. Clark 
A. P. Colburn 

E. W. Comings 
C. Croneis 

M. Dole 
T. B. Drew 
J. C. Elgin 

H. W. Elley 
P. H. Emmett 

F. T. Gucker, Jr. 
W. D. Harkins 
L. F. Hawley 

J. H. Hillman, III 
H. G. Houghton 
W. C. Johnson 
L. S. Kassel 
C. A. Kraus 
F. J. Kunz 


I. M. Johnston 
R. D. Madison 
A. C. Willard 


A. B. Lamb 

V. K. LaMer 
I. Langmuir 

P. A. Leighton 

G. N. Lewis 

H. H. Lowry 

W. L. McCabe 

R. B. Montgomery 
A. R. Olson 
M. T. O’Shaughnessy 
K. S. Pitzer 
A. B. Ray 
H. A. Roselund 
P. W. Schutz 
T. K. Sherwood 

D. Sinclair 
A. F. Spilhaus 
M. D. Thomas 
F. T. Wall 

E. O. Wiig 
R. E. Wilson 
W. P. Yant 
T. F. Young 

F. W. H. Zachariasen 


SECTION L-l 

Chairman 

W. H. Rodebush 


H. Eyring 
V. K. LaMer 


Members 

L. Pauling 
R. Stevenson 

I. Langmuir 


Considtants 


W. G. Brown 


E. W. Comings 


696 


SECRET 


OSRD APPOINTEES 


697 


W. M. Latimek 

SECTION L-ll 

Chairman 

W. A. Noyes, Jr. 

V ice-Chairmen 

W. L. McCabe 

A. F. Benton 

Members 

F. T. Gucker, Jr. 

A. B. Burg 


H. F. Johnstone 

A. P. Colburn 


R. N. Pease 

T. B. Drew 


W. C. Pierce 

P. H. Emmett 


E. O.Wiig 

F. E. Bartell 

T. F. Young 

Consultants 

W. D. Harkins 

S. Brunauer 


L. S. Kassel 

T. H. Chilton 


A. R. Olson 

G. L. Clark 


A. B. Ray 

R. G. Dickinson 


T. D. Stewart 

H. Eyring 

W. P. Yant 

Technical Aide 

W. D. Walters 

SECTION B-5 

Chairman 

W. H. Rodebush 

Members 

I. Langmuir 

V. K. LaMer 


L. Pauling 

F. T. Gucker, Jr. 

Technical Aides 

M. T. O’Shaughnessy 

W. W. Duecker 

W. D. Walters 

Special Advisors 

M. T. O’Shaughnessy 

W. A. Noyes, Jr. 

Consultant 

N. K. Chaney 

SECTION B -6 

Chairman 

D. M. Yost 

H. F. Johnstone 

Vice-Chairmen 

W. L. McCabe 

W. M. Latimer 


W. C. Pierce 

F. E. Blacet 

Members 

F. T. Gucker, Jr. 

M. Dole 


H. F. Johnstone 

J. C. Elgin 


P. A. Leighton 

P. H. Emmett 


W. C. Pierce 

R. B. Montgomery 

T. F. Young 

Special Advisors 

A. F. Spilhaus 

F. E. Bartell 

Consultants 

W. D. Harkins 

A. F. Benton 


L. F. Hawley 

W. D. Bonner 


L. S. Kassel 

W. E. Brinker, Jr. 


H. H. Lowry 

S. Brunauer 


A. B. Ray 

R. J. Cashman 


C. E. Reed 

T. H. Chilton 


T. D. Stewart 

T. B. Drew 


J. Turkevich 


W. P. Yant 

Technical Aide 

W. D. Walters 



SECRET 




CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS 


Contract No. 

Contractor 

NDCrc-13 

NDCrc-18 

NDCrc-28 

Massachusetts Institute 
of Technology 

The College of the 

City of New York 
Princeton University 

NDCrc-33 

NDCrc-47 

Columbia University 
University of Illinois 

NDCrc-49 

NDCrc-65 

NDCrc-70 

NDCrc-71 

NDCrc-76 

NDCrc-104 

NDCrc-106 

NDCrc-108 

NDCrc-109 

University of Illinois 
University of Chicago 
University of Delaware 
University of Chicago 
University of Rochester 
General Electric Company 
Princeton University 
Princeton University 
Northwestern University 

NDCrc-112 

NDCrc-113 

NDCrc-115 

NDCrc-119 

Harvard University 
University of 

Southern California 
California Institute 
of Technology 

Johns Hopkins University 

NDCrc-122 

Stanford University 

NDCrc-124 

Carnegie Institute 
of Technology 

NDCrc-126 

Universitj' of California 

NDCrc-131 

Princeton University 

NDCrc-133 

NDCrc-135 

University of California 
University of California 


NDCrc-137 California Institute 
of Technology 


Subject 

Special fuels for jet propulsion, colored smokes and related pyrotechnic problems. 

The study of dispersion of solids in gases. 

The preparation of smokes of predetermined particle size and determination of 
particle size. 

The study of physical properties of smokes. 

The formation of smokes. 

Supplement 1: To conduct large scale tests of the smokes developed. 

The study of dispersion of solids in gases. 

Gas absorbents. A study of the structure of gas absorbents. 

Impregnating agents for gas adsorbents. 

The mechanical formation of fogs and smokes. 

Mechanism of adsorption of gases. 

The preparation of smokes and experimental study of their properties. 

Impregnating agents for gas adsorbents. 

The absorption wave in gas adsorbents. 

Gas absorbents. 

Supplement 1: To conduct studies and experimental investigations in connection 
with thermal effects in gas absorbents. 

The removal of chloropicrin and phosgene. 

The preparation of new toxic gases. 

The development of laboratory methods of gas detection, using radioactive 
elements as tracers. 

The determination of pore size and surface adsorbents. 

Supplement 1: The determination of pore size and surface adsorbents, and the 
specific absorption capacity of active charcoal. 

Supplements 2 , 3, J+: Extension of time and addition of funds. 

The removal of ethylene imine. 

Supplement 1: The removal of ethylene imine, and investigations of certain 
synthetic resins as possible gas absorbents. 

Supplement 2: Extension of time and addition of funds. 

Supplement 3: (i) The removal of ethylene imine, (ii) investigations of certain 
synthetic resins as possible gas absorbents, and (iii) the meteorological condi¬ 
tions effecting the use of chemical warfare agents. 

Production and activation of gas charcoal. 

Supplement 1: Conduct studies and investigations in connection with (i) the 
production and activation of charcoal, (ii) the pre-impregnation of charcoal 
with metallic compounds prior to activation, and (iii) the activation of such 
pre-impregnated charcoal. 

The removal of cyanogen chloride and its action as an adsorbent poison. 

Supplement 1: Extension of time. 

Supplement 2: The removal of cyanogen chloride and its action as an adsorbent 
poison, and a study of the form and effectiveness of gas clouds. 

Supplements 3, /+, 5 , 6 , 7: Extension of time and addition of funds. 

Protection against carbon monoxide; absorbent properties of synthetic resins. 

Supplement 1: The study and experimental investigations in connection with 
synthetic gases, and removal of carbon monoxide. 

Supplement 2: (i) Protection against carbon monoxide, (ii) adsorbent properties 
of syntheticresins, and (iii) the removal of carbon monoxide at low partial 
pressures. 

New solid reactants. 

Development of apparatus and method for using radioactive hvdrogen as a 
tracer. 

The adsorption of selenium hexafluoride by charcoal. 

Supplement 1: The adsorption of selenium hexafluoride by charcoal and the use 
of halogen compounds and certain inorganic substances as chemical warfare 
agents. 

Supplement 2: (i) The adsorption of selenium hexafluoride by charcoal and the 
use of halogen compounds and certain inorganic substances as chemical war¬ 
fare agents, and (ii) the factors affecting the travel of gas clouds and the 
development of devices for the analysis of gas clouds. 


098 


SECRET 












Contract No. 


NDCrc-138 


NDCrc-152 


NDCrc-154 

NDCrc-166 

NDCrc-167 

NDCrc-171 

NDCrc-208 

OEMsr-16 

OEMsr-22 

OEMsr-28 

OEMsr-59 

OEMsr-83 

OEMsr-102 


OEMsr-103 


OEMsr-108 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued ) 
_ Contractor _ Subject 


University of California 
University of Illinois 


University of Illinois 
University of Virginia 
Pennsylvania State College 
Harvard University 
University of Michigan 
University of California 
Northwestern University 

California Institute 
of Technology 
Harvard University 
Arthur D. Little, Inc. 
University of Illinois 


California Institute 
of Technology 

University of Illinois 


Supplements 3, 4, 5: Extension of time and addition of funds. 

Supplement 6: Delivery of models of such devices as may be developed. 

To maintain and operate a cyclotron. 

Supplement 1: To prepare, by the use of the cyclotron, radioactive materials, 
and to furnish artificially radioactive substances. 

Development of X-ray or other techniques for studying reactive agents in 
adsorbents, and the development of new adsorbents. 

Supplement 1: Development of X-ray or other techniques for studying reactive 
agents in adsorbents, and the development of new adsorbents, and the X-ray 
of metallic catalysts and the reaction products on the surface of these catalysts 
or other adsorbents. 

The development of substitutes for activated carbon. 

Methods of detection of gases. 

Rapid methods of making war gases for tests of adsorbents. 

To furnish artificially radioactive substances produced by means of the cyclotron. 

Experimental investigations of screening smokes. 

New solid reactants, new impregnants, and new methods of impregnation. 

The development of an ultra-violet absorption apparatus for the analysis of 
war gases in a gas stream. 

Adsorption of war gases by means of radioactive tracers. 

Use of cyclotron for the preparation of radioactive sulfur and arsenic. 

Sources of mineral fibers and the dispersion of asbestos. 

Development of equipment for the formation of smokes. 

Supplement 1: Studies and experimental investigations in connection with the 
development of equipment for the formation of smokes and methods of gener¬ 
ating toxic smokes in the field. 

Supplements 2 , 3: Extension of time. 

Supplement 4- (i) The design of munitions for chemical warfare, (ii) the con¬ 
struction and testing of models which are developed hereunder, (iii) the re¬ 
production of developed munitions in sufficient quantity for testing by the 
Services, (iv) investigation of new physical and chemical combination as 
fillings for chemical warfare munitions existing or developed under this con¬ 
tract, (v) the behavior of gas and smoke clouds in built-up city areas and 
woods. 

Supplements 5, 6 } 7: Extension of time. 

Supplement 8: (i) The design of munitions for chemical warfare, for screening 
and signal smokes, for the dissemination of insecticides, and for related pur¬ 
poses, (ii) the construction and testing of models which are developed here¬ 
under, (iii) the reproduction of developed munitions in sufficient quantity for 
testing by the Services, (iv) investigation of new physical and chemical com¬ 
bination as fillings for chemical warfare munitions existing or developed 
under this contract, and (v) the development of equipment for the generation 
of aerosols from airplanes, for screening, insecticidal and other purposes. 

Supplements 9, 10, 11, 12, 13, 14, 15: Extension of time and addition of funds. 

Development of an instrument for the rapid determination of particle size 
distribution of smokes. 

Supplement 1: Extension of time and addition of funds. 

Dispersion of solids in gases and of smoke filtration. 

Supplement 1: Extension of time. 

Supplement 2: Dispersion of solids and liquids in gases and removal of suspended 
solid or liquid particles from gases by filtration or by other means. 

Supplement 3: (i) Properties of aerosols and filter materials for aerosols, par¬ 
ticularly with the radioactive tracer technique, and (ii) the behavior and 
use of screening smokes, with reference to weather and terrain. 

Supplement 4- (i) Properties of aerosols and filter materials for aerosols, par¬ 
ticularly with the radioactive tracer technique, and (ii) the behavior and use 
of screening smokes, and the rendering of assistance to the Services in the 
study thereof, and (iii) the use of aerosols for special purposes, including in¬ 
sect control. 

Supplement 5: (i) Properties of aerosols and filter materials for aerosols, par¬ 
ticularly with the radioactive tracer technique, and (ii) the behavior and use 
of screening smokes, and the rendering of assistance to the Services in the 
study thereof, and (iii) the use of aerosols for special purposes, including in¬ 
sect control, and (iv) the dispersal of DDT as an aerosol and on the effective¬ 
ness of aerosols of DDT as insecticide. 

Supplement 6: Extension of time. __ 


SECRET 


699 















CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued ) 


Contract No. 


Contractor 


Subject 


OEMsr-116 

OEMsr-131 


OEMsr-142 


OEMsr-148 


OEMsr-199 

OEMsr-219 


OEMsr-221 

OEMsr-226 

OEMsr-236 

OEMsr-251 

OEMsr-272 

OEMsr-282 


Carnegie Institute 
of Technology 
General Electric Company 


Servel, Inc. 


Columbia University 


California Institute 
of Technology 
Arthur D. Little, Inc. 


United Gas Improvement 
Company 

University of Illinois 

University of California 
University of Michigan 

Tennessee Eastman 
Corporation 

Northwestern University 


Preparation of wood charcoal suitable for activation. 

Supplement 1: Extension of time. 

The preparation of smokes and experimental study of their properties. 
Supplement 1: The preparation of smokes and experimental study of their 
properties, and to produce field units for production of screen smokes, and 
to carry out related field tests. 

Supplement 2: (i) The preparation of smokes and experimental study of their 
properties, (ii) to produce field units for production of screen smokes and to 
carry out related field tests, and (iii) study in connection with the determina¬ 
tion of the screening power of certain smokes under moonlight and starlight 
illumination and the investigation of the ability of the normal eye to detect 
contrast under such conditions. 

Supplement 3: Extension of time and addition of funds. 

Supplement 1+: The removal of aerosols from air by filtration. 

Supplements 5 , 6: Extension of time. 

Development of a practical device for the production of screening smokes. 
Supplement 1: Development qf a practical device for the production of screening 
smokes, this development to be based on a laboratory device now in existence. 
Supplement 2: Development of a practical device for the production of screening 
smokes, this development to be based on a laboratory device now in existence, 
and also the development of a smoke bomb. 

Supplement 3: Extension of time. 

Measurement of particle size and particle size distribution in aerosols and the 
production of screening smokes. 

Supplement 1: (i) Measurement of particle size and particle size distribution in 
aerosols, (ii) the production of screening smokes, and (iii) the production of 
suitable smokes for special screening purposes. 

Supplement 2: (i) Measurement of particle size and particle size distribution in 
aerosols, (ii) the production of screening smokes, and (iii) the production of 
suitable smokes for special screening purposes, and (iv) the development of 
devices for the production of screening smokes. 

Supplement 3: (i) Further studies on aerosols, and studies and experimental 
investigations in connection with, (ii) the evaluation of screening smokes and 
the development of instruments for their evaluation, (iii) the dispersion of 
toxic solids as aerosols and the evaluation of the aerosols so produced, and 
(iv) the development of screening smoke generators. 

Supplement 4- Extension of time. 

Supplement 5: Investigations in connection with (i) aerosols, (ii) the evaluation 
of screening smokes and the development of instruments for their evaluation 
in the field, (iii) the dispersion of toxic solids as aerosols and the evaluation 
of the aerosols so produced, (iv) the development of screening smoke gener¬ 
ators, (v) the evaluation and improvement of colored smoke signals, (vi) the 
application of aerosols to insecticidal uses and other miscellaneous uses of 
military importance. 

Heats of removal of war gases on adsorbents. 

Supplements 1, 2: Extension of time and addition of funds. 

The dispersion of solids. 

Supplement 1: Addition of funds. 

Supplement 2: The dispersion of asbestos in paper or other materials. 

Supplement 3: The dispersion of asbestos in paper and other materials, and the 
fabrication of particulate filters from sheet materials thus produced. 
Supplements 4, 6: Extension of time and addition of funds. 

Inorganic fibers suitable for filters. 

A study of the preparation of compound 1120, particularly through the use of a 
regenerative chemical. 

The production and stabilization of smokes and fogs. 

Mechanical formation of smokes, including the formation of toxic smokes and 
screening smokes by means of large-scale, high-pressure sprays. 

Preparation of superfine organic fibers of 1 or 2 microns diameter. 

The study of properties of absorbents for certain toxic gases and of the behavior 
of absorbents, and other studies, and to equip, staff, and operate a laboratory 
for these purposes. 

Supplement 1: Conducting studies and experimental investigations in connection 
with (i) the properties of absorbents for certain toxic gases and the behavior 


700 


SECRET 













Contract No. 




OEMsr-299 


OEMsr-345 

OEMsr-349 


OEMsr-376 


OEMsr-405 


OEMsr-414 


OEMsr-539 


OEMsr-548 


OEMsr-578 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued) 


Contractor 


Subject 


University of Illinois 


Owens-Corning 
Fiberglas Corp. 
Columbia University 

American Viscose 
Corporation 
Massachusetts Institute 
of Technology 
E. I. Du Pont de Nemours 


University of California 


University of Rochester 


DeVilbiss Company 


of absorbents, (ii) the preparation of certain toxic gases, (iii) the development 
of oxygen-breathing equipment and carbon impregnated clothing, (iv) the 
assembly and operation of a small pilot jiggler activation unit, (v) the opera¬ 
tion of a small-scale pilot plant for the experimental production of crude char 
from domestic raw materials, with special emphasis on color as part or all of 
the raw material, (vi) the determination of factors affecting the field use of 
chemical warfare agents, and (vii) the behavior, productive value, and design 
of canisters. 

Supplement 2: Extension of time. 

Supplement 3: (viii) Method of impregnation of charcoal on a pilot plant scale. 

Supplement 4' Extension of time. 

Supplement 5: (i) The properties and preparation of activated charcoals and 
whetlerites, (ii) rebreathers, and (iii) the field use of chemical warfare agents. 

Supplement 6: (i) The preparation and properties of charcoals and whetlerites, 
(ii) canister testing and design, (iii) field use of chemical warfare agents. 

Supplement 7: Extension of time. 

Supplement 8: (i) The preparation and properties of charcoals and whetlerites, 

(ii) canister testing and design, (iii) field use of chemical warfare agents, and 
delivery of models of such equipment as may be developed and samples of 
such absorbents as may be produced. 

Supplements 9 , and 10: Extension of time. 

A study of the preparation of compound 1120, particularly through the use of a 
regenerative chemical. 

Supplements 1 , 2: Extension of time. 

Supplement 3: (i) The preparation of a certain compound and derivatives for 
use as war gas, and (ii) modified fillings for smoke munitions. 

Supplement 4- Extension of time. 

Electrical dispersion of oil, clay, and other materials to produce a screening 
smoke. 

Analysis of adsorption wave in gas adsorbents. 

Supplement 1: Extension of time. 

The development of very fine filaments for use as gas mask filters. 

Supplement 1: Extension of time and addition of funds. 

Methods of formation of toxic smokes. 

Supplement 1: Extension of time. 

Development of an electrolytic fluorine generator that will produce one pound 
of fluorine per hour. 

Supplement 1: Addition of funds. 

The production of screening smokes and fogs without the use of large com¬ 
pressors, and the stabilization of such smokes and fogs under field conditions. 

Supplement 1: The production of screening smokes and fogs without the use of 
large compressors, and the stabilization of such smokes and fogs under field 
conditions, and the stability and persistence of toxic smokes or simulated 
agents. 

Supplements 2, 3: Extension of time. 

Supplemerd 4' (i) The production of screening smokes and fogs without the use 
of large compressors, (ii) the stabilization of such smokes and fogs under 
field conditions, (iii) the stability and persistence of toxic smokes or simulated 
agents, and (iv) field methods of dispersing chemical warfare agents. 

Supplement 5: Extension of time. 

The use of two gases simultaneously or in sequence in chemical warfare. 

Supplement 1: The use of two gases simultaneously or in sequence in chemical 
warfare, (ii) the performance of whetlerite against cyanogen chloride. 

Supplement 2: (i) The use of two gases simultaneously or in sequence in chemical 
warfare, (ii) the performance of whetlerite against cyanogen chloride, and 

(iii) new methods of impregnation of charcoal. 

Development of stationary oil smoke generators. 

Supplement 1: (i) Development of stationary oil smoke generators, (ii) the 
development of motor truck smoke generators. 

Supplement 2: Extension of time. 

Supplement 3: (i) Stationary oil smoke generators, (ii) small portable oil smoke 
generators, (iii) exhaust-type oil smoke generators for aircraft, and (iv) modi¬ 
fication of the color of the smoke produced by oil smoke generators of any type. 

Supplement 4: (i) Stationary oil smoke generators, (ii) small portable oil smoke 
generators, (iii) exhaust-type oil smoke generators for aircraft, (iv) modifica- 


SECRET 


701 














CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued ) 


Contract No. 


OEMsr-580 


OEMsr-586 

OEMsr-587 

OEMsr-588 


OEMsr-599 


OEMsr-603 


OEMsr-660 

OEMsr-676 

OEMsr-713 


OEMsr-861 


OEMsr-889 


OEMsr-917 

OEMsr-948 


OEMsr-963 


OEMsr 1004 


OEMsr-1021 


Contractor 


Carnegie Institute 
of Technology 


University of Chicago 

Massachusetts Institute 
of Technology 
Massachusetts Institute 
of Technology 

University of Illinois 


Distillation Products, Inc. 


University of Rochester 
Chemical Process Company 

Gaertner Scientific 
Corporation 

California Institute 
of Technology 


Williams Oil-O-Matic 
Company 


Harvard University 
Victor Chemical Works 


E. I. du Pont de Nemours 
and Company 


University of California 


Hercules Powder 
Company 


Subject 

tion of the color of the smoke produced by oil smoke generators of any type, 
and (v) smoke generators operated by steam. 

Supplement 5: Extension of time. 

Methods of production and activation of gas charcoal. 

Supplement 1: (i) Methods of production and activation of gas charcoal, (ii) the 
pre-impregnation of charcoal with metallic compounds prior to activation, 
and (iii) the activation of such pre-impregnated charcoal. 

Supplement 2: Extension of time and addition of funds. 

The physical chemistry of the activation of charcoal. 

Supplements 1, 2, 3, 4y 5: Extension of time. 

The use of sulfur to produce screening smokes. 

Supplements 1, 2: Extension of time. 

The development of fluorine generators and their use in the preparation of 
certain mechanical compounds. 

Supplement 1: Extension of time. 

The physical form of activated charcoal and whetlerite with the use of the 
X-ray and the electron microscope. 

Supplement 1: (i) The physical form of activated charcoal and whetlerite with 
the use of the X-ray and the electron microscope, and (ii) the behavior of 
smoke and gas clouds in built-up sections of cities. 

Supplement 2: (i) The physical activated charcoal and whetlerite with the use 
of X-ray and electron microscope, (ii) the determination of factors affecting 
the preparation and performance of whetlerite, and (iii) the behavior of 
smoke and gas clouds in built-up city areas and woods. 

(i) The design of generators for production of screening smokes, (ii) vapor 
pressures of oils suitable for liquid smokes, and (iii) additives to increase the 
persistence of liquid smokes. 

The interpretation of data on absorbents. 

The preparation of resins as gas absorbents. 

Supplements 1 , 2: Extension of time. 

Construction of 4 models of an instrument to determine the particle size of 
smoke. 

Supplements 1, 2: Extension of time. 

To conduct field studies of agents and weapons for chemical warfare including 
meteorological investigations to determine the conditions for the use of chemi¬ 
cal warfare agents, and to develop such instruments as may be necessary for 
conducting such studies. 

Supplements 1, 2, 3, 4, 5: Extension of time. 

The development of smoke generator using a minimum amount of strategic 
materials, and such oils as are available to produce a smoke which may be 
darkened for use in night screening operations. 

Supplements 1, 2: Extension of time. 

The preparation of certain extremely pure inorganic chemicals. 

The improvement of the performance of WP munitions. 

Supplements 1 , 2: The improvement of WP munitions by physical and chemical 
modification of the WP loadings. Construction and operation of a pilot plant 
for preparing 1200 pounds to 1500 pounds per day of PWP shell filling (as 
developed under Contract OEMsr-102, University of Illinois) and for loading 
munitions with this material. 

The dispersion of finely powdered solid materials, especially surface treated 
materials as aerosols, both by jet dispersion and explosion, and the evaluation 
by physical and physical-chemical tests of the properties of the aerosols 
produced. 

Supplement 1: The preparation of aerosols of solid materials, and the reduction 
of solid organic materials to suitable particle size for aerosol formation. 

Supplements 2 , 3, 4- Extension of time. 

The methods of (i) lowering the inflammability of hydrogen cyanide, (ii) stabi¬ 
lizing cyanogen chloride, and (iii) preparing special inorganic compounds. 

Supplement 1: Addition of funds. 

Supplement 2: The methods of (i) lowering the inflammability of hydrogen 
cyanide, (ii) stabilizing cyanogen chloride and hydrogen cyanide, and (iii) pre¬ 
paring special inorganic compounds. 

(i) The development of a filling for smoke pots, grenades, floats, etc., consisting 
of a combustible mixture such as black powder intimately mixed with either 
high-boiling oil or granulated sulfur, (ii) the development of containers in which 
this mixture can be burned efficiently, and (iii) the development of a process 
for manufacture of the mixture in quantity. 


702 


SECRET 








CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued) 


Contract No. 

OEMsr-1150 

OEMsr-1200 

OEMsr-1243 


OEMsr-1277 


OEMsr-1334 

OEMsr-1388 

OEMsr-1446 


Contractor 


The Heil Company 

National Carbon 
Company, Inc. 

Iowa Institute 

of Hydraulic Research 


Delco Appliance, 
Division of 
General Motors 
Corporation 


E. I. du Pont de Nemours 
and Company 
Columbia University 


Solar Aircraft 


Subject 

Supplements 1, 2, 3, 4, 5: Extension of time. 

(i) Improvement in design and performance of the DeVilbiss model SCE smoke 
generator, and (ii) engineering development work on other smoke generators. 

The improvement of activated charcoals (particularly the zinc chloride type) 
and whetlerite. 

Supplement 1: Extension of time. 

Studies and experimental investigations in connection with the circulation of air 
in situations such as would be encountered (i) in the application of certain 
methods for the dissipation of fog over airfields, and(ii)in the use of gas warfare. 

Supplement 1: Extension of time and addition of funds. 

Supplement 2: (i) Circulation of air in situations such as would be encountered 
in the application of certain methods for the dissipation of fog over airfields, 
and in the use of gas warfare, (ii) the improvement of equipment used in the 
dissipation of fog over airfields. 

Supplement 3: Extension of time. 

Supplement 4 ’ (i) Circulation of air in situations such as would be encountered 
in the application of certain methods for the dissipation of fog over airfields, 
and in the use of gas warfare, (ii) the improvement of equipment used in the 
dissipation of fog over airfields, and (iii) local winds and cloud cover over 
selected Japanese target areas using small-scale models in a wind tunnel. 

Supplement 5: Extension of time and addition of funds. 

(i) Development of, from partially completed models supplied by Columbia 
University under Contract OEMsr-148, one or more finished designs of light¬ 
weight, combustion-type oil smoke generators of approximately 50 gal/hr 
capacity, eliminating if possible the use of water as an operating fluid, (ii) fabri¬ 
cate 3 or more replicas of the preferred design for tests by the Armed Services, 
and (iii) conduct research on further smoke generators or other related equip¬ 
ment. 

Supplements 1, 2, 3, 4, 3, 6, 7: Extension of time. 

Ultra fine cellulose acetate fiber-batt and the production of 100 sq ft thereof. 

(i) The production and evaluation of aerosols for killing insects, (ii) a method of 
evaluating smoke generated by smoke signals, and (iii) the production of 
colored smokes. 

Supplements 1 , 2, 3, 4 , 5 , 6, 7: Extension of time and addition of funds. 

The development of devices for the generation and dispersion of screening 
smoke and insecticidal aerosols on the service-type airplanes. 

Supplements 1, 2, 3: Extension of time. 


SECRET 


703 










SERVICE PROJECT NUMBERS 



The projects listed below were transmitted to the Executive Secretary, 

National Defense Research Committee, NDRC, from the War or Navy 

Department through either the War Department Liaison Office for the 

NDRC or the Office of Research and Inventions (formerly the Co¬ 
ordinator of Research and Development), Navy Department. 

Service Project No. 

Subject 

AC-108 

AC-125 

CWS-1 

Spraying Equipment for DDT. 

Japanese Weather Model Studies. 

Aerosols, Generation, and Precipitation. Collection of fundamental scientific information on the dis¬ 
semination of particulate clouds from solid materials, and carrying out of experimental work 
upon which to base further improvement of munitions employed to generate smokes and the 
development of improved protective devices used for the removal of smoke particles from the air. 

Extended to include dispersion of fogs. 

Extended to include Dispersal of Insecticides and Rodenticides. 

Extended to include Development of a Smoke Generator incorporating either a preheating system 

CWS-7 

for the oil or a secondary combustion system for the exhaust gases. 

Fundamental Study of Gas Mask Absorbents. The collection, evaluation, and testing of all avail¬ 
able information influencing the design of gas mask canisters. The formulation of rules from 
the data collected with a view to simplifying the manufacture of such equipment. 

CWS -8 

The Generation of Colored Smokes. The study and development of more efficient means of dis¬ 
seminating colored smoke clouds, particularly black and orange, for certain marking purposes. 

CWS-15 

Improved Filter Materials. To devise detailed methods of improving the manufacture of existing 
types of filter materials, especially with the view of reducing the effect of high humidity upon 
the filter and for increasing the filtration of liquid smoke particles. 

CWS-16 

Improved Filter Design. To redesign the filter of the gas mask canister so as to provide for the 
maximum filter surface with the best filter material. 

CWS-17 

Production and Stabilization of a Fog. 

Part a: Extended to include a project to color the smoke produced by the unit developed by 

Dr. I. Langmuir. 

Part a: Transferred to NS-123. 

CWS-24 

Development of Protective Cloth. To develop a charcoal impregnating cloth with a binding 
agent other than rubber or synthetic rubber which will give better protection against chemical 
agents for which the present clothing does not give good protection of the present clothing against 

CWS-26 

the agents for which there is now ample protection. 

Meteorology Applied to Chemical Warfare. The accumulation and evaluation of micrometeoro- 
logical data and the determination of the behavior of chemical warfare agents under various 
climatological and terrain conditions and the development of suitable instruments. 

CWS-27 

NA-106 

Simple and Unusual Munitions for Setting up Field Concentrations of Chemical Warfare Agents. 
Oxygen Breathing Apparatus. Development of oxygen breathing apparatus for use with liquid 
oxygen. Studies and experimental investigations in connection with the development of indicating 
instruments for determining low concentrations of noxious gases in air. 

NA-164 

NE-104 

NL-B 1 

Dissipation of Fog Over Airfield Runways, Development of Means of. 

Development of an Accurate Method of Evaluating Smoke Generated by Smoke Signals. 

Problems Related to the Manufacture and Use of Potassium Peroxide in Oxygen Breathing Equip¬ 
ment. 

a. The production of K 2 O 4 from Potassium compounds, avoiding the use of metallic potassium or 
sodium. 

b. Sources of cheap metallic potassium. 

c. Vapor-liquid equilibrium data for sodium-potassium. 

d. Development of an alloy to withstand liquid alkalies at 600-800°. 

e. Nitrogen fixation at — 30°C for elimination of nitrogen from oxygen breathing equipment at 
high altitudes. 

f. Development of an instrument for the measurement of oxygen partial pressures. 

g. Reactant to remove carbon dioxide and water vapor from air at — 30°C. 


704 


SECRET 










SERVICE PROJECT NUMBERS ( Continued) 

Service Project No. 

Subject 

NL-B11 

NL-B26 

h. Reactant evolving heat on contact with carbon dioxide or water vapor at low temperatures by 
Trigger reactant for K 2 0 4 . 

i. Physiological performance tests of oxygen rebreather equipment development of improved 
masks. 

Colored Smokes. 

Analytical Methods and Technique for Determining the Protective Properties of Gas Mask 
Canisters Against Mustard Gas, Phosgene, Chloropicrin, Hydrogen Cyanide, Arsin, and such 
other Gases as may possibly be used in Chemical Attack. 

Replaced by NS-338. 

XL-B28 

Development of a Better Chemical than “Whetlerite” for Filtering of Neutralizing Toxic War 


Gases Particularly Under Conditions of High Temperature and Humidity Combined with Salt 

Spray. 

NL-B29 

Replaced by NS-338. 

Check the Efficiency of the New Charcoal Developed by the Chemical Warfare Service in Com¬ 
parison with Coconut Shell Charcoal with Particular Consideration of Conditions of High Tem¬ 
perature and Humidity Combined with Salt Spray. 

Replaced by NS-338. 

NL-B34 

Improved Methods of Measurement for Study of Protection Given by Filters Against Smokes at 

High Humidities. 

Replaced by NS-338. 

NM-100 

NO-276 

NO-292 

NS-123 

NS-150 

Dispersal of DDT. 

Colored Smokes for Target Identification and Sea Markers. 

Consulting Service on Design and Construction of PWP Loading Plant. 

The Coloring of Smoke from a Langmuir Unit. 

Combustion Gas Type Smoke Generator. Desired to fulfill the following requirements: 

1. Burn as fuel a liquid which is in common use by the Navy. 

2. Make optimum smoke at a combustion rate of about 300 to 400 gallons per hour. 

NS-338 

Investigation of Respiratory Protection. To cover work not only on gas absorbents, but also on 
canisters, facepieces, speech diaphragms, outlet valves, filters, and methods of protection against 

SG-6 

any new type of agent. 

Investigation of the Chemistry of Insecticides and Repellants. Devise analytical procedures for 
determining the constituents present in DDT, to isolate, characterize and synthesize these con¬ 
stituents so that their relative toxicity can be determined and to study practical methods of 
purification. Other insecticides and repellants will be included in the scope of the investi¬ 
gation. 


SECRET 


705 














INDEX 


1 he subject indexes of all STR volumes are combined in a master index printed in a separate volume. 

For access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


Absorption properties of colored parti¬ 
cles, 332 

Absorption vs. adsorption, 9 
Acids as war gases, 152-165 
Acoustical forces as precipitation fac¬ 
tors 

see Aerosol coagulation by sound vi¬ 
bration 

Activated charcoal 

hydrogen and oxygen content, 36 
packet structure, 35 
pore structure, 35 
substitutes, 84-87 

Activated charcoal, manufacture, 23-39 
Cabot Co. carbon black processes, 
29-30 

coconut charcoal, 31 
commercial manufacture, 31-32 
history, 23 

Jiggler method of activation, 37 
Kimberly-Clark Co., 30-31 
Pittsburgh Coke and Chemical Co., 
27-28 

Prest-o-log process, 28-29 
Saran charcoal, 31 
summary, 23-24 
Activated charcoal, properties 
see Charcoal characteristics, measure¬ 
ment; Charcoal structure 
Activated charcoal, raw ingredients, 
24-26 

bituminous coal, 25 
coconut, 25 

esoteric materials not needed, 26 
lignin, 25 
nut shells, 25 

requirements for materials, 24 
sawdust, 25 
synthetic materials, 25 
tests for raw material, 26 
Activation of charcoal by chemicals, 
38-39 

chemical method requirements, 38 
mechanism of activation, 39 
zinc chloride process, 38-39 
Activation of charcoal by steam, 31-37 
activation rate, 37 
carbonization, 33-34 
crushing and briquetting, 32-33 
final step, 34 
process variables, 34-35 
summary, 23-24 

surface complex formed during acti¬ 
vation, 131-132 
temperature control, 35 
weight loss, internal vs. external, 36 


Acyl chlorides as war gases, 609 
Adamsite smoke, 362 
Adiabatic lapse rate 
effect on stability, 383 
influenced by convection, 219 
normal rate, 213 
saturated rate, 214 
super-lapse, 215 

Adsorption, relation to molecular struc¬ 
ture, 134-140 

adsorption data for gases, 135 
entropy term estimated, 136-137 
experimental data, 138-139 
integral heat of adsorption, calcula¬ 
tion, 137-140 
molecular size, 108-109 
pressure of adsorbate, 135-136 
temperature of adsorption, 135 
thermodynamic equation, adsorption 
of gas on solid, 136 

Adsorption heat, acid on charcoal sur¬ 
face, 142 

Adsorption isotherms, surface area 
measurements, 97-99 
adsorption as function of relative 
pressure, 98-99 
adsorption data equation, 97 
applications of method, 98-99 
Harkins and Jura’s work, 98 
Adsorption method, porous area meas¬ 
urements, 97-99 

Adsorption of vapors by charcoal, 140- 
142 

carbon tetrachloride adsorption, 141— 
142 

chloropicrin adsorption, 140 
isopiestic technique in adsorption 
studies, 141 

4-picoline adsorption, 141 
pyridine adsorption, 141 
Adsorption of water vapor from char¬ 
coal, 102-108 

adsorption vs. capillary condensa¬ 
tion, 105-107 

density of water in charcoal, 107 
equilibration, charcoal with water 
vapor, 105 

freezing method studies of adsorbed 
water, 107 
hysteresis, 103, 106 
nature of water adsorption, 105- 
108 

nature of water in capillaries, 107- 
108 

nitrogen adsorption studies, 107-108 
oxygen surface complexes, 128 


rate of adsorption, 104-105 
water adsorption isotherms, 102-104 
Adsorption vs. absorption, 9 
Adsorption wave, 169-182 
canister life equations, 181-182 
curvature, adsorption isotherm, 173 
factors affecting break time, 174-180 
reasons for study of wave, 169-170 
speed of adsorption, 170 
steps in removal of toxic gas from 
air, 169-170 
summary, 182 
symbols used in study, 182 
Adsorption wave theories, 170-174 
diffusion as rate-controlling step, 
171-173 

effluent concentration curve, 170 
general differential equation, 170-171 
removal rate determined by more 
than one step, 173 

surface reaction as rate-controlling 
step, 172-173 

theories compared with experiment, 
173-174 

variables effecting removal rate, 171 
Aedes aegypti, DDT test mosquitoes, 
581-583 

Aerograms (thermodynamic graphs) 214 
Aerosol cloud evaporation, 412-419 
boundary curves of concentration in 
cloud, 417 

effect of nonvolatile impurities, 414- 
415, 418-419 

effect of temperature on vapor con¬ 
centration, 413 

evaporation equations, 415-417 
maximum drop size for saturation 
maintenance, 413-414, 417-418 
nomenclature, 418-419 
persistence dependent on saturation, 
412-413 

smoke cloud evaporation, 386-387 
Aerosol coagulation, 305-308 
see also; Aerosol settling 
Brownian motion, 305-306 
concentration gradient, 305-306 
homogeneous aerosol coagulation, 306 
law of atmosphere, 305-306 
stirred settling and coagulation com¬ 
bined, 306-308 
summary, 297 

Aerosol coagulation by sound vibration, 
309-313 

attraction of particles due to air mo¬ 
tion, 311-312 

laboratory experiments, 312 


SECRET 


707 


708 


INDEX 


motion of particles relative to each 
other, 310-311 
summary, 302 
theory summarized, 312 
vortex motion, air around particles, 
312 

Aerosol dispersal, liquid droplets, 524- 
533 

DDT dispersing plastic bomb, 524- 
527 

dissolved gases under pressure in 
liquids, 530-533 

ejection-airburst bomb, 527-530 
Aerosol dispersal, solid particles, 534- 
545 

air bomb, 542 

concentration in aerosol clouds, 536- 
537 

dispersibility of powders, 535-536 
effective toxicity of aerosol, 535 
gas ejection bomb, 539-543 
impactability of aerosol particles, 
534-535 

munitions testing, 537-539, 543-545 
plastic bomb, 543 
Aerosol electrical properties 
effect of filtration, 313 
homogeneous smoke charge, 308 
summary, 299 
unipolar smoke charge, 309 
Aerosol filtration, 190-193, 354-359 
clogging, 358 

diffusion mechanism vs. inertial ef¬ 
fects, 356-357 
direct interception, 354 
effect of aerosol electrical properties, 
313 

effect of particle size, 313 
electrostatic action, 191, 358-359 
force resisting motion of particle, 355 
foreign filters, 190 
impingement of small particles, 356 
Stokes’ law deposition, 355 
summary, 299-300 
theory, 356-357 
velocity effect, 357 
Aerosol filtration, materials 
asbestos, 192-193 
fiber content, 191 
fiber diameter, 354-356 
glass wool fibers, 191, 357 
organic fibers, 192 
rock wool, 191, 357-358 
synthetic fibers, 358 
Aerosol formation, 314-317 
air-jet dispersion, 315-317 
condensation in vapor jets, 314-315 
fogs, 298 

gas ejection bomb, 317 
mechanical dispersion, 298 
particle size control, 314 


smoke produced by combustion, 299 
summary, 298-299 
vapor condensation, 299 
Aerosol optical properties 
see Aerosol scattering of light 
Aerosol particle motion 
see also Aerosol stability 
deposition in centrifugal fields, 308 
in thermal gradient, 309 
pressure exertion, 305-306 
Aerosol particle size, 334-353 
amplitude and phase of vibration de¬ 
termined by size, 310 
gravity settling measurement meth¬ 
ods, 339-343 

logarithmic probability distribution, 
304-305 

median weight diameter, 305 
microscopic examination, 334-335 
optical measurement methods, 343- 
353 

range of particle sizes, 301 
Aerosol particle size sampling, 335-339 
centrifugal separator, 335-336 
gravity settling, 337 
mass concentration, 338 
optical mass-concentration meter, 
338-339 

thermal precipitator, 336-337 
Aerosol scattering of light, 318-333 
absorbing particles, 332-333 
optical properties of aerosols, 300 
single spherical particles, 318-321 
solid particles, 330-332 
spherical particles, nonuniform size, 
327-330 

spherical particles, uniform size, 321- 
327 

Aerosol settling, 302-305, 339-343 
coagulation and stirred settling com¬ 
bined, 306-308 
convection currents, 303 
differential settler, 341-343 
gravity settling slide, 337 
homogeneous smoke settler, 339 
logarithmic-probability distribut ion 
of sizes, 304-305 

stirred settling, homogeneous parti¬ 
cles, 303-305 

stirred settling measurements, 343 
Stokes’ law, 302-303 
tranquil settling, homogeneous parti¬ 
cles, 302-303 
Aerosol stability, 301-305 
acoustical forces, 302 
adhesion vs. separation, 302 
Browmian movement, effect on sta¬ 
bility, 301 

centrifugal forces, 302 

density variation with height, 305-306 

diffusion and evaporation, 297 


precipitation, 297 

settling, heterogeneous aerosols, 302- 
305 

summary, 297 

thermal and electrical forces, 302 
Air circulation in streets and court¬ 
yards, 281-283 
Air mass effects, 223-224 
Air motions, 219 

Air-burst vesicant bomb, 527-530 
advantages, 527 
hexagonal bomb, 528-529 
round bomb, 529-530 
Airplane bombs for insecticide dis¬ 
persal, 598 

Airplane exhaust generator, 507-523 
atomization, 509 
combustion units, 517-521 
combustion within short space, 516 
evaporation capacity of exhaust 
gases, 507-509 
for high speed planes, 523 
heat transfer, 509 
hydraulic system, 511 
smoke generators, 510-511 
smoke output increase, 515 
summary, 395 
tactical uses, 522-523 
test cell performance, 520 
Venturi section, 510 
Airplane exhaust generator, DDT dis¬ 
persal, 593-596 

combination equipment, smoke gen¬ 
erator and DDT disperser, 595 
diameter of jets, 594 
early installation in Stearman planes, 
594 

nozzle design, 594 
summary, 602 
Venturi atomizer, 594 
Airplane exhaust generator, installa¬ 
tions 

B-26 installations, 507 
TBM-3 installation, 521-522 
test installation, 516-517 
Venturi unit, installation on TBM 
plane, 509 

Airplane exhaust generator, perform¬ 
ance, 512-515 

effect on airplane performance, 
513 

evaporation capacity, 512-513 
smoke screen effectiveness, 513-515 
Airplane fields, fog dispersal, 624-633 
burner studies, 626-630 
dispersal methods, 624 
English fogs, 626 
heat diffusion analysis, 627-629 
wind curtains, 630-633 
Airplane rockets for smoke screen lay¬ 
ing, 564-565 


SECRET 



INDEX 


709 


Airplane sprays, atomization of liquids, 
406-408 

break-up of liquids in spray, 406 
DDT dispersal, 407-408 
Venturi air scoop, 406-408 
Albedo effect, reflected solar radiation, 
218-219 

Albumen, toxic agent simulant,535-536 
suitability for testing, 535 
treatments to improve dispersibility, 
536 

use in bomb dispersal tests, 541 
Alkali activation of charcoal, 466-467 
Alkyldifluorophosphates, 608 
Alkylmonofluorothiophosphates, 608 
American Cyanamid Co., cyanogen 
chloride 

see Cyanogen chloride stabilization 
Amines, mechanism of removal, 166 
Ammonia 

adsorption, 128 

evolved from aminated resins, 87 
impregnated charcoal, 40 
mechanism of removal, 165 
vapor evolved from moist whetler- 
ites, 78 

Ammonium dichromate, thermal gen¬ 
erator fuel, 477-480 
Ammonium ferric chloride complexes, 
smoke screen use, 492 
Ammonium nitrate, thermal generator 
fuel, 466-468 

crystalline modifications, 468 
hygroscopic nature, 468 
moisture content, 467-468 
particle size, 467 

Ammonium picrate-sodium nitrates, 
bomb propellants, 483-484 
Anabatic winds, 223 
Anemometers, 239-246 
British anemometer, 245 
cup systems, 241 
hot wire anemometer, 246 
magnetic cup anemometer, 239-244 
mercury cup anemometer, 244 
wiring arrangements, 244 
Angle of rise, smoke clouds, 386 
Anopheles quadrimnculatus, DDT test 
mosquito, 583-584 
“Apparent density” of gas, 21 
Aquadag, colloidal graphite, 610-611 
Arsenic trifluoride, 157 
Arsine 

absorption by charcoal, 56 
as war gas, 609 

mechanism of removal, 166-168 
rapid oxidation reaction, 167 
reaction with whet lerites, 46-47,167- 
168 

Asbestos, aerosol filter material, 192- 
193 


Atmospheric diffusion, 380, 384 
Atmospheric radiation, 217 
Atomization of liquids by explosions, 
408-410 

atomization mechanism, 408-409 
drop size distribution, 409-410 
explosive bursts, 524-526 
German bursters, 408 
Atomization of liquids by nozzles, 398- 
406 

drop size distribution, 399-402 
droplet formation process, 398 
hydraulic nozzles, 405 
nozzle types, 399 
pneumatic nozzles, 399-402 
smoke screen production, 405-406 
Venturi atomizer, 402-405 
Atomization of liquids in airplane 
sprays, 406-408 

break-up of liquids in spray, 406 
DDT dispersal, 407-408 
Venturi air scoop, 406-408 
Atmospheric stability, 213-214 
adiabatic lapse rate, 213 
effect on area covered by gas cloud, 
277-278 

effect on gas cloud efficiency, 260 
moist air stability, 214 
“potential temperature,” 214 
temperature dependence on altitude, 
213-214 

Austausch coefficient, 219 
Australian ionization penetrometer, 
363 

B-26 exhaust smoke generator, 507 
Ballistic stability of PWP (plasticized 
white phosphorus), 557-558 
Beach area, gas cloud behavior, 264 
Bisdimethylamine phosphoryl fluoride, 
609 

Bituminous coal, activated charcoal 
material, 25 

Blanket smoke screens, 375-376 
Blasting powder, smoke pot mixture, 
501 

Bombs 

carbon dioxide pressurized, 530-533 
chemical, 429-432 

colored smoke, target identification, 
455-458 

DDT dispersing, plastic, 524-527 
ejection-airburst, 527-530 
gas cloud dispersing, 269-281 
gas ejection, aerosol dispersing, 539- 
543 

Olsen pressurized, 530-533 
Boron trifluoride acetonitrile, 157 
“Break time,” gas masks, 174-180 
“break point,” defined, 12 
critical bed depth, 177-180 


effect of bed depth, 175-177 
effect of charcoal’s capacity, 180 
nature of flow in charcoal, 174-175 
Reynolds number, flow of fluids 
measurement, 174-175 
Breather pumps, human breathing 
simulators 
construction, 15 
flow rate, 15 
test precision, 21 

Breathing resistance to gas masks, 186- 
189 

Breezes, land and sea, 223-224, 383 
Briquetting process, activation of char¬ 
coal, 32—33 

British 

carbon-smoke penetrometers, 364 
gas mask filters, 190 
munitions for solid aerosol dispersal, 
539 

orchard heater, 375 
Brownian motion of aerosols 
displacement, 305 

effect on disappearance rate, 305- 
306 

effect on stability, 301 
Bursters, German, 408 
Butyl carbitol 

atomization when pressurized, 531 
carbon dioxide solvent, 531 

Cabot Co. activated charcoal manu¬ 
facture, 29-30 
Candles, DDT thermal, 592 
Canisters for gas masks 
see Gas mask canisters 
Capillary condensation theory of water 
adsorption on charcoal, 105-107 
Capillary condensation vs. multilayer 
adsorption, 109-111 
Carbon dioxide 

behavior in smoke cloud, 380 
in atmosphere, 215-216 
solubility in butyl carbitol, 531 
solubility in mustard gas, 530 
Carbon dioxide pressurized bomb, 530- 
533 

impracticality, 530-531 
ineffective for saturated aerosol pro¬ 
duction, 531-533 

multiple tube ejection bomb, 531-533 
spinning tubes, 531 
Carbon monoxide protection, 203-206 
canister, 205 
catalysts, 205-206 
charcalite drier, 203-204 
Hopcalite, 203-205 
physiological effects of exposure, 
203 

silver permanganate catalyst, 205 
silver peroxide catalyst, 205 


SECRET 




710 


INDEX 


Carbon monoxide reaction with ami- 
nated resins, 86 

Carbon tetrachloride adsorption by 
charcoal, 141 

Carbons for gas mask filters 
see Activated charcoal 
Carbon-smoke penetrometer, 373 
Cardox gas-ejection bomb, 542 
Cascade impactor, collection of insecti¬ 
cide samples, 599 

Catalytic actions of activated charcoal, 
52-53 

Centrifugal forces, aerosol coagulation, 
302 

Centrifugal separation, 335-336 
Charcalite drier, 203-204 
Charcoal, activated 
see Activated charcoal 
Charcoal as thermal generator fuel 
see Thermal generator fuel blocks 
Charcoal characteristics, measurement, 
97-149 

adsorption and molecular structure, 
134-140 

adsorption of vapors, 140-142 
adsorption of water vapor, 102-108 
chemisorption of gases by whetler- 
ites, 144 

heats of adsorption and immersion, 
142-143 

influence of pore size on performance, 
117-121 

oxygen surface complexes, 125-132 
pore size alteration, 121-125 
pore size and distribution, 108-117 
retentivity, 143-144 
summary, 147-149 
surface coatings, 132-134 
Charcoal impregnation, 40-87 
absorbent resins as activated char¬ 
coal substitutes, 84-87 
catalytic reactions, 52-53 
compounds used as impregnants, 53- 
55 

copper-silver-chromium impregnants, 
64-81 

hexamine impregnation, 48-50 
iodic acid impregnation, 56 
mercury impregnation, 56 
molybdenum and vanadium impreg¬ 
nation, 57-64 

organic base impregnations, 81-84 
reactions during adsorption process, 
53 

thiocyanate impregnations, 50-52 
vapor phase impregnation, 56 
whetlerites, 40-41 

Charcoal pore size, alteration, 121-125 
chromium oxide treatment, 124-125 
hydrogenation without impregna¬ 
tion, 123 


influence of impregnants on alter¬ 
ation, 124-125 

iron oxide treatment, 124-125 
nickelous oxide treatment, 125 
partial oxidation without impreg¬ 
nation, 124 

steaming without impregnation, 123 
Charcoal pore size, influence on per¬ 
formance, 117-121 
free volume of pore as efficiency cri¬ 
terion, 118-119 

macropore volume and cyanogen 
chloride activity, 119 
pore measurements and cyanogen 
chloride lives, 118-119 
pore measurements and noxious 
gases, 120-121 
terminology, 117 

Charcoal pore size, measurement, 108- 

117 

Kelvin equation, 109-112 
mercury forced into charcoal, pres¬ 
sure measured, 114-117 
molecular size as criterion, 108-109 
surface area changes from water 
take-up, 113-114 

water adsorption and desorption iso¬ 
therms, 112-113 
Charcoal structure, 145-147 
chemical behavior, 146 
cylindrical capillaries, 146 
electron microscope observations, 146 
expansion during adsorption, 146 
microscopic study, 145 
platelet arrangement of carbon in 
charcoal, 145 
pore shape, 145 

speculative nature of studies, 145 
true density of carbon in charcoal, 
146-147 

X-ray study, 145 

Charcoal surface area measurement, 
97-102 

adsorption method of measurement, 
97-99 

methods, 99-101 

performance predictions from meas¬ 
urements, 101-102 

Chemical activation of charcoal, 38- 
39 

Chemical behavior of charcoal, 146 
Chemical bombs, 424-441 
see also E29R1 chemical bomb 
basic dosage equation, 430 
choice of size and dosage, 430 
dosage distribution, 430-432 
effect of meteorological conditions, 
430-431 

integrated cross wind dosage, 430 
munitions’ effectiveness, 431-432 


target area covered by given dos¬ 
age, 429-430 

Chemical removal of gases, 150-168 
acid-forming gases, 152-165 
base-forming gases, 165-166 
gases retained by physical adsorp¬ 
tion, 151-152 

purpose of investigation, 150 
readily oxidizable gases, 166-168 
readily reducible gases, 168 
steps in removal process, 169-170 
Chemisorption of gases by whetlerites, 
144 

Chloride smoke screen mixtures, 488- 
494 

anhydrous ferric chloride manufac¬ 
ture, 491-492 

chloride complexes, 492-493 
chlorine carriers, 490-491 
chloropropane, 494 
development of mixtures, 488-490 
ferric chloride and aluminum mix¬ 
ture, 491-492 

high efficiency mixtures, 493-494 
stability of mixtures, 491 
Chlorine surface complexes on charcoal, 
133 

Chloropicrin 

adsorption on charcoal, 140 
canister protection against chloro¬ 
picrin, 200 

effect of gas mixture’s humidity, 151 
nature of desorbed product, 151 
rate of removal, 179 
reaction with base charcoal and 
whetlerites, 151 
Chloropicrin gas test 
disadvantages, 19 
operation, 18 
use, 13 

Chloropropane, smoke screen use, 494 
Chromium adsorption from whetlerite 
solutions, 73-74 

copper chromate removal of cyano¬ 
gen chloride, 73-74 
precipitate formation, 73 
valence state of impregnant, 73-74 
Chromium impregnated charcoal, 62 
Chromium oxide as charcoal impreg¬ 
nant, 124-125 

Clausius-Clapeyron equation, applied 
to whetlerite solutions, 68 
Clouds of smoke 
see Smoke clouds 
Clouds of toxic gases 
see Gas clouds 

Coal, use in maufacture of activated 
charcoal, 25 

Coconuts, gas mask charcoal mate¬ 
rial 

deficiencies, 23 


SECRET 



INDEX 


711 


improvement process, 31 
performance, 25 

Color of light transmitted through fog, 
350 

Colored particles as light scatterers, 
332-333 

absorption characteristics, 332 
calculation tables, 333 
color distribution, 321-322 
color of transmitted light, 333 
dye smoke particle size, 333 
multiple scattering, 333 
optical density of pure dye smoke, 
333 

Colored smoke identification bomb, 
455-458 

components, 456-457 
dyes, 458 

flaming control, 457-458 
fuel block formulas, 461 
nylon parachute, 457 
operation, 456 

Colored smoke signal, 451-455 
construction, 453-454 
development, 451-452 
dye chamber, 454-455 
fuel block formulas, 461 
operation, 454 
proposed design, 454 
specifications, 451 
theory, 452 

Contrast limen, smoke screens, 389-392 
conditions approaching extinction, 
390 

light extinction by fog, 389-390 
light extinction by screening smoke, 
390 

visibility dependent on concentra¬ 
tion, 390 

visibility formula, 390-392 
visibility in natural fog, 389 
Convection, vertical air movement, 
219-220, 385-386 

Convection currents in aerosol settling 
process, 303 

Convective ceiling, smoke clouds, 385 
Copper Carbonite, 41 
Copper compounds, effect of dehydra¬ 
tion and evaporation, 41 
Copper impregnated charcoal 
see Whetlerites 

Copper-silver-chromium whetlerites, 
64-81 

ammonia evolution, 78 
compared with molybdenum whetler¬ 
ites, 61-62, 64 

conversion, one whetlerite to another, 
81 

effect of base charcoal, 74 
leaching and rewhetlerization, 79-80 
metallic constituents, 67 


removal of gases, mechanism of, 74- 
76 

Copper-silver-chromium whetlerites, 
aging, 75-76 

aging under field conditions, 76 
canister design, effect on aging, 76 
charcoal surface, effect on aging, 
75-76 

nature of aging process, 75-76 
organic base additions, 82-84 
pH factor, effect on aging, 75 
storage in closed containers, 75 
Copper-silver-chromium whetlerites, 
production, 76-78 
air flow, 77 
back feeding, 78 
charge temperature, 77 
drier, 68, 77 
flue gas, 78 
impregnator, 76 
temperature schedule, 77 
Copper-silver-chromium whetlerites. 
solutions, 64-74 

ammonia and carbon dioxide con¬ 
centration, 66 

chromium adsorption, 73-74 
copper and chromium concentra¬ 
tions, 64-66 
heats of solution, 71 
laboratory impregnation, 68 
metallic constituents, 66-67 
preparation, 67 
vapor pressure, 68 
volatile constituents, 71 
Coronae measurements, light beam in 
fog, 347-348 

“Critical bed depth,” gas, 177-182 
approximation methods of determi¬ 
nation, 181-182 

depth due to diffusion, 177-178 
depth due to granular processes, 178 
mechanism of removal, 179-180 
nature of adsorbent, 180 
variation with velocity of flow, 
178 

Cunningham correction coagulation 
equation, 306 

CWS-MIT-E1 canister tester, 372 
CWS-MIT-E2 photoelectric smoke 
penetrometer, 367 
Cyanogen chloride 

canister protection, 198-199 
conductimetric analysis, 285 
lives of gas masks, 92, 118-121 
properties and reactions, 55-56 
protection of hexamine impregnated 
adsorbents, 50 

protection of thiocyanate impreg¬ 
nated whetlerites, 51 
reaction with organic bases, 81-82 
surveillance, 91 


Cyanogen chloride removal mechanism, 
161-164 

complexity of mechanism, 161 
copper oxide role in reaction, 161 
hydrolysis, 163-164 
metal oxides, 162 
oxidation, 163-164 
physical adsorption process, 161 
removal from whetlerites, 74 
whetlerites for cyanogen chloride 
protection, 162-163 
Cyanogen chloride stabilization, 613- 
617 

acidity determination, 616 
deterioration mechanism, 615-616 
deterioration products, 617 
polymerization tendency, 613 
research history, 613-614 
substances harmful to cyanogen 
chloride, 614 

substances inert to cyanogen chlor¬ 
ide, 614-615 

substances stabilizing cyanogen 
chloride, 615 
summary, 617 

temperature, effect on deterioration, 
616 

water content determination, 617 
Cyclohexyl monofluorophosphate, 607 

DDT dispersal, 577-603 
atomization by sprays, 407-408 
conclusions and summary, 601-603 
formulations, 598-599 
mathematical symbols, 602-603 
nonvolatile solvent required, 598 
recommendations for use, 601-603 
research recommendations, 601 
DDT dispersal, aircraft equipment, 
593-598 

airplane exhaust generators, 593- 
596 

historical summary, 593 
insecticide bombs, 598 
plane’s downwash, effect on dis¬ 
persal, 587-588 
spray devices, 596-598 
summary, 602 

DDT dispersal, assessment methods, 
599-601 

airborne dosage of particle size, 600- 
601 

entomological results as final evalu¬ 
ation, 601 

samples collected by impaction, 599- 
600 

samples collected on slides, 599-600 
samples collected on vertical wires, 
601 

DDT dispersal, ground equipment, 
588-593 


SECRET 





712 


INDEX 


exhaust generators for motor vehi¬ 
cles, 591-592 
Freon bomb, 588 

Hochberg-LaMer type generators, 
588-591 

thermal candles, 592 
DDT dispersal, optimum particle size, 
578-588 

contact-kill particle size, 578-583 
deposition on insect, wind tunnel 
studies, 582-583 
dosage-mortality graphs, 581 
foliage density as dosage determi¬ 
nant, 586-588 

meteorological conditions as dosage 
determinant, 584-586 
pre DDT research, 578 
residual kills, 583-584 
resting vs. flying mosquito, 578-580 
summary, 601 

uniform particle size aerosols, 581 
DDT dispersing bomb, 524-527 

atomization of liquids by explosive 
bursts, 524-526 

design and manufacture, 526-527 
droplet spectra from chargings, 525 
Desorption isotherms, charcoal pore 
size measurements, 109-113 
adsorption vs. desorption on nitro¬ 
gen, 109-112 
Kelvin equation, 112-113 
Desorption tests, gas masks, 19 
Dialkylmonofluorophosphates, 606-608 
cyclic esters, 607 
isopropyl ester, 607 
preparation, 606-608 
properties, 608 
toxicity tests, 607 

Diaphragm pump sampler, gases, 286- 
287 

Dichlorobenzene, Olsen bomb use, 532 
Differential settler, smoke measuring 
instrument, 341-343 
Diffraction rings, light beam through 
fog, 347-348 
Diffusion 

as rate-controlling step in toxic gas 
removal, 171-172 
atmospheric diffusion, 380, 384 
control of “critical bed depth” of 
gases, 177-178 
eddy diffusion, 380 
gas diffusion, 173, 633-638 
kinetic vs. thermal diffusion, 297 
Dimethylaminophosphorusdifluoride, 
609 

1,2-dinitro-tetrafluoro-ethane, 157 
Dioctylphthalate, smoke material, 361 
Diol fog, light beam observations, 326 
Diol-sawdust-chlorate smoke mixtures, 
497-499 


Diphenylchloro arsine tests, 362 
Disulfur decafluoride, 604-606 

action of fluorides on sulfur com¬ 
pounds, 605 
chemical detection, 606 
controlled reaction of fluorine and 
sulfur, 604-605 

fluorination of sulfur chlorides, 605 
preparation, 604-605 
properties, 605-606 
thermal stability, 605 
Droplet dispersing bombs, 524-533 
bombs containing dissolved gas in 
liquids, 530-533 

DDT dispersing, plastic bomb, 524- 
527 

drop size distribution, 399-402 
ejection-airburst bomb, 527-530 
Droplet formation by nozzles, 398 
Drosophila melanogaster t DDT test 
flies, 582-583 

DS-4 colored smoke signal, 451-455 
Dugway recording instruments, 255- 
259 

Dust 

particle size, 301 
properties; see Aerosol 
retention in lungs, 535 
Dye smokes 

colored smoke screens, 392 
floating, smoke signals, 454-455 
optical density, pure dye smoke, 
333 

particle size, 333 

requirements for colored smoke 
munition, 458 

E-20 nonfloating oil smoke pot, 445- 
446 

E-21 training oil smoke pot, 446-447 
E-23 floating oil smoke pot, 441-445 
E29R1 chemical bomb, 424-441 
bomb size choice, 429-432 
chemical efficiency, 428-429 
feeding of agent to gas stream, 433 
field test, 440 

50-lb nonclustering bomb, 432 
fuel block formulas, 461 
high-velocity vaporizer, 433-435 
recommendations for improvement, 
440 

thermal generator characteristics, 

424- 425 

thermal generator cluster, 432 
E29R1 chemical bomb, construction, 

425- 428, 435-439 
agent feed system, 436 
bomb body, 425-426 
bomb tail, 427 

booster tube powder, 435-436 
centrifugal arming fuze, 428 


cloth streamer tail, 436 

clustering bands, 436 

coating on agent compartment, 436- 

437 

folding metal tail, 437 
fuel block, 426-427 
metal telescoping tail, 427-428, 438- 
439 

sealing of fuel and ignition system, 
439 

streamer tail with shroud line, 437- 

438 

Earth temperature, 216-218 
albedo effect, 218-219 
black-body temperature, 217 
diurnal variation, 218 
ocean temperature, 218 
radiation of solar energy, 216-217 
soil below earth’s surface, 218 
surface moisture effect, 218 
Eddy currents, 637-638 
Eddy diffusion, 380 
Eddy velocity, 220 

Edgewood Arsenal, E3 canister tester, 
371-372 

“Effective scattering area” of drop, 390 
Egg albumen, toxic agent simulant, 
535-536 

suitability for testing, 535 
treatments to improve dispersibility, 
536 

use in bomb dispersal efficiency 
tests, 541 

Ejection-airburst vesicant bomb, 527- 
530 

advantages, 527 
hexagonal bomb, 528-529 
round bomb, 529-530 
EK-1 vesicant dispersing bomb, 528- 

529 

EK-4 vesicant dispersing bomb, 529- 

530 

Electrical properties of aerosols 
effect of filtration, 313 
homogeneous smoke charge, 308 
summary, 299 
unipolar smoke charge, 309 
Electron microscope, 335 
Entropy term, gas adsorption, 136-137 
Esterline-Angus meters, wind recorders, 
256-257 

Ethylenimine, mechanism of removal, 
166 

Evaporation capacity of exhaust gases, 
507-509 

enthalpy of oil and vaporization, 509 
equilibrium saturation temperature, 
508 

weight of oil per exhaust gases, 508 
Evaporation of aerosols 

see Aerosol cloud evaporation 


SECRET 



INDEX 


713 


Evaporation of vapor drops, 386-387 

Exhaust generator for airplanes 
see Airplane exhaust generator 

Exhaust generators for motor vehicles, 
591-592 

Explosions, atomization of liquids, 408- 
410 

atomization mechanism, 408-409 
drop size distribution, 409-410 
explosive bursts, 524-526 
German bursters, 408 

F-7 thermal generator candle, insecti¬ 
cide use, 592 

F7A mustard generator pot, 419-425 
condensate composition, 422-423 
experimental models, 421-422 
field tests, 423-424 
fuel block formulas, 461 
operation, 420-421 

Ferric chloride mixtures, smoke screen 
use, 491-493 

Fibers used in aerosol filters, 191-193 
asbestos, 192-193 
glass wool, 191 
organic fibers, 192 
rock wool, 191 
summary, 5 

Field canister tester, 292-293 

Field conductivity analyzer, gases, 289- 
291 

Filtration of aerosols, 190-193, 354-359 
clogging, 358 

diffusion mechanism vs. inertial 
effects, 356-357 
direct interception, 354 
effect of aerosol electrical properties, 
313 

effect of particle size, 313 
electrostatic filters, 191, 358-359 
force resisting motion of particle, 355 
foreign filters, 190 
impingement of small particles, 356 
Stokes’ law deposition, 355 
summary, 299-300 
theory, 356-357 
velocity effect, 357 

Filtration of aerosols, materials 
asbestos, 192-193 
fiber content, 191 
fiber diameters, 354-355 
glass wool, 191, 357 
organic fibers, 192 
rock wool, 191, 357-358 
synthetic fibers, 358 

Flies, DDT test subjects, 582-584 

Flow of fluids through granular solids, 
174-175 

Flow rate in gas mask testing, 14-15 
breather pumps, 15 
British vs. U. S. tests, 15 


human breathing, 14-15 
intermittent flow testing, 14-15 
tube tests, 15 
Fluid motion studies 
see Wind tunnel studies 
Fluorides, mechanism of removal, 156- 
158 

arsenic trifluoride, 157 
boron trifluoride acetonitrile, 157 
1,2-dinitro-tetrafluoro-ethane, 157 
phosphorous trifluoride, 156 
phosphoryl trifluoride, 157-158 
sulfur pentafluoride, 157 
sulfuryl chloro-fluoride, 156-157 
Fluorine and sulfur reactions, 604-605 
action of fluorine on sulfur com¬ 
pounds, 605 

controlled reaction, 604-605 
nonelectrolytic method, fluorine 
preparation, 605 

sulfur chlorides, fluorination by 
heavy metal fluorides, 605 
sulfur hexafluoride reactions, 605 
Fluorine preparation, 610-612 
baths at high temperatures, 611 
baths at medium temperatures, 610- 
611 

baths at room temperature, 610 
hydrogen fluoride-less baths, 611 
metal fluorides, decomposition, 610 
polarization and anode effect, 611- 
612 

Fluorophosphates, 606-608 
alkyldifluorophosphates, 608 
alkylmonofluorothiophosphates, 608 
cyclohexyl monofluorophosphate, 

607 

dialkylmonofluorophosphates, 606- 

608 

Fluorosulfonates, 608 
Fog 

defined, 301 
Diol fog, 350 
effect on light, 389-390 
English fogs, 626 
naturally-occurring fogs, 298 
oleic acid fogs, 321-322 
particle size, 298, 301 
production by mechanical atomiza¬ 
tion, 405-406 
properties; see Aerosol 
stearic acid fogs, 321-322 
Fog dispersal, wind tunnel studies, 624- 
633 

burner construction, 629-630 
burner studies, 626-630 
dispersal methods, 624 
heat diffusion analysis, 627-629 
relative cost, burners vs. wind cur¬ 
tains, 633 

wind-curtains, 630-633 


Forest 

foliage, DDT lethal dosage determi¬ 
nant, 586-588 
temperatures, 234-236 
thermal turbulence, 236 
“Free volume,” charcoal pore volume, 
117 

Freon insecticide bomb, 588 
Frossling’s measurements, vaporization 
rate of droplets, 416 
Froude number, measure of gravita¬ 
tional influence, 621-622 
Fuch’s evaporation equation, 386-387 
Fuel blocks for thermal generators, 
459-484 

ammonium picrate-sodium nitrate 
fuels, 483-484 
cast fuel mixtures, 479-482 
fuel mixture formulas, 461 
liquid fuels, 484 

pressed charcoal fuel mixtures, 462- 
477 

pressed fuel mixtures without carbon, 
477-480 

smokeless powder fuels, 482-483 
surge tester, 464 
volume tester, 463-464 

Gas adsorption process 
see Adsorption wave 
Gas clouds, 260-283 

atmospheric stability, effect on effi¬ 
ciency of cloud, 260 
gravity effects, 268-269 
munition efficiency, 260 
toxic dosage for given munition, 260 
wind speed effect on efficiency, 260 
Gas clouds, in urban areas, 281-283 
cul-de-sacs, danger from, 283 
flow of air in sewers, 282 
wind circulation in courtyards, 282 
wind circulation in streets, 281-282 
Gas clouds, release, 260-264 
beach area behavior, 264 
cloud travel data, 263 
forest area behavior, 263 
“line source” release, 260-264 
open terrain release, 260-263 
Gas clouds, travel theory, 264-268 
application to bombs, 266-267 
basic formulas, 264-266 
disadvantages, 267-268 
gas concentration slide rule, 266 
Gas clouds from bombs, 269-281 
500 lb bombs, 270 
1,000 lb bombs, 269-270 
2,000 and 4,000 lb bombs, 271 
ammunition expenditure, 273-276 
casualty production, 272-273 
dosage variation with height, 271 
multiple bombs, area coverage, 271 


SECRET 




714 


INDEX 


multiple bombs in line, 271 
munition requirements for desired 
casualty effects, 272-273 
munition requirements for surprise 
effects, 276 

munition requirements for wooded 
areas, 281 
surprise areas, 272 
surprise attack objectives, 272-273 
uniform coverage of target area, 273 
Gas clouds from mortar shells, 277-281 
atmospheric stability, 277-278 
dosage effect, 278 
wind velocity effect, 277 
wooded area performance, 279-281 
Gas concentration slide rule, 266 
Gas diffusion, wind tunnel studies, 633- 
638 

comparison of field measurement and 
wind tunnel predictions, 636- 
638 

contour patterns of gas released over 
Japanese village, 637 
diffusion after pancake bursts, 637 
diffusion as time function, 633 
motion pictures of eddy currents, 
637-638 

relative concentration contours, 634 
urban districts, schematic models, 
634-636 

Gas ejection bomb, 539-543 
air bomb, 542 

ammunition expenditures, 273-276 
Cardox bomb, 542 
compared with plastic bomb, 541 
development, 539-542 
dispersion test, 542 
line distribution vs. upwind distribu¬ 
tion, 274-276 

Gas evolution from charcoals during 
heating, 128-132 

Gas mask canister lives, 175-177, 181— 
182 

break time equation, 181 
“critical bed depth”, 177-182 
effected by moisture, 88-89 
life-thickness curves, 175-177 
Mecklenburg equation, 176 
Gas mask canister tests, 18-22 

see also Gas mask canisters, aging 
programs; Smoke filter testing 
desorption tests, 19 
field tests, 20 
flow rate tests, 18 
human tests, 19-20 
minican tests, 20 

tester simulating breathing cycle, 
292-293 

types of tests, 18-19 
Gas mask canisters, aging programs, 
89-90 


canisters aged in carriers, 95 
cyclic chamber simulation of tem¬ 
perature changes, 89-90 
field tests, 90 

simulation of climatic conditions at 
Edgewood Arsenal, 89 
Gas mask canisters, design, 183-189 
amount of protection, 183-184 
breathing resistance, 186-189 
effect on whetlerite deterioration, 76 
lack of ruggedness, 189 
mesh size, effect on resistance and 
protection, 188-189 
radial-flow design, 185 
relation of resistance to canister size, 
188 

relation of weight and protection, 
185-186 

Gas mask canisters, filters 

see Aerosol filtration; Aerosol filtra¬ 
tion, materials 

Gas mask canisters of World War II, 
9-10, 184-185 
CBI theater use, 93-94 
facepiece canisters, 185 
hosetube canisters, 184-185 
Ml; 10 

MIXA1; 9, 10 
M9A2; 9 
M10; 9-10 
Mil; 10 

New Guinea use, 92-93 
radial flow canisters, 9 
relative merits of canister types, 184 
Gas mask carbon 
see Activated charcoal 
Gas mask filters 

see Aerosol filtration; Aerosol filtra 
tion, materials 

Gas mask protection, 194-206 
carbon monoxide, 203-206 
chloropicrin, 200 
cyanogen chloride, 198-199 
foreign canisters, 194 
gas penetration theory, 12-13 
hydrogen cyanide, 199 
nitrogen dioxide, 201 
phosgene, 196-198 
Gas mask tests, 12-22 
canister tests, 18-22 
chloropicrin test, 18 
concentration of test gas, 16-17 
deficiencies of test methods, 21-22 
field testing, necessity for, 208 
flow rate, 14-15 
hardness test, 20 
heat of wetting, 20 
humidity, 13-14 
indicators, 15-16 
layer depth studies, 20 
rough handling resistance, 21 


screen analysis, 21 
temperature, 17 
test gases, 13 
tube tests, 17-18 
Gas masks, 7-22, 194-209 
chin type combat mask, 9 
combat mask requirements, 8 
development during World War II, 
summary, 207-208 
diaphragm masks, 8 
face pieces, 8 
M2A1, service mask, 8 
M2-1-1 training mask, 8 
M3-light, service mask, 8 
M5-combat mask, 8 
Navy mask, 9 
optical masks, 8 

pre-World War II development, 7 
recommendations for future research, 
208-209 

status in 1945; 11 

Gas penetration theory, 12-13 
Gases, war 
see War gases 

Geiger counter, measurement of radio¬ 
active elements, 640-642 
Generators, thermal 
see Thermal generator 
German bursters, 408 
German gas mask filter research, 190 
Glass wool, aerosol filter, 191, 357 
Graphs, thermodynamic, 214 
Gravity effects on gas clouds, 268-269 
Gravity winds, 222-223 
Guanidine nitrate, thermal generator 
fuel, 477-480 

Gunpowder smoke pot mixtures 

see Smoke pot mixtures, oil and gun¬ 
powder 

Gustiness, air motion, 220 
Gustiness, vanes for measuring, 253- 
254 

Harkins and Jura’s work on surface 
area measurements, 98 
Heat conductivity of earth’s surface, 
217-218 

Heat diffusion, 627-629 
Heat of immersion, charcoals, 142- 
143 

Heat of wetting, charcoals, 20, 143 
Herbicide dispersal, 546-550 
areas of high concentration, 548 
maximum areas covered by given 
dosage, 549 

munitions for dispersal, 547-548 
particle densities, 547 
particle size distribution, 546-547 
terminal velocities, 547 
travel of solid particles, 546 


SECRET 



INDEX 


715 


Hexachlorethane, smoke screen use, 
488-490 

Hexamine impregnation of whetlerites, 
48-50 

application process, 49 
cyanogen chloride, 50 
disadvantages, 49 

pH factor, effect on impregnants, 49 
salt additions, 49-50 
X-ray studies, 50 

Hill’s photoelectric smoke penetrom¬ 
eter, 363 

Hochberg-LaMer DDT generators, 
588-591 

formulas for DDT concentrates, 598- 
599 

meteorological factors affecting use, 
589 

operation principle, 588 
procedures for use, 590 
pumps, 589 
summary, 602 
Hopcalite, catalyst, 203-205 
gel type, 204-205 
pre-drying by charcalite, 203-204 
thermal activity, 205 
Humidity 

detrimental to canister performance, 
88-89 

in gas mask testing, 13-14 
micrometeorological measurements, 
255 

Hydrocarbons, as antiflash agents, 
619-620 

Hydrogen chloride, catalyst in cyano¬ 
gen chloride deterioration, 615- 
616 

Hydrogen cyanide, 618-620 
adsorption by whetlerites, 46-47 
canister protection, 199 
conductimetric analysis, 285 
flame inhibitors, 619 
hydrocarbons as antiflash agents, 
619-620 

inflammability, 619 
removal mechanism, 74-75, 158-161 
stabilization, 618-619 
Hydrostatic head pump, gas sampler, 
284-285 

advantages, 285 

concentration vs. time curve, 285 
construction, 284 
cyanogen chloride analysis, 285 
hydrogen cyanide analysis, 285 
operation, 284 
phosgene analysis, 285 

Impregnated charcoal 
see Charcoal impregnation 
Indicators for gas mask testing, 15-16 
break point conditions, 16 


choice of test indicator, 15 
physical vs. chemical indicators, 16 
Insecticides 
see DDT dispersal 

Integral heat of adsorption for gases, 
137-140 

Iodic acid impregnated charcoal, 56 
Ionization penetrometer, Australian, 
363 

Iowa Institute fog dispersal studies, 
626-633 

Iron oxide as charcoal impregnant, 124- 
125 

Japanese gas mask filters, 190 
Jiggler method of charcoal activation, 
37 

Katabatic wind, 222 
Kelvin equation, pore size measure¬ 
ment, 109-113 

adsorption vs. desorption isotherms, 
112 

applied to adsorbates other than 
water, 109-112 

applied to desorption isotherms, 112— 
113 

capillary condensation vs. multimo- 
lecular adsorption, 109 
drawbacks of method, 109-111 
nitrogen adsorption near saturation, 
111-112 

Kimberly-Clark Co. 
activated charcoal manufacture, 30- 
31 

nephelometer, 364-365 
sulfur smoke generator, 449-450 
Koenig’s equation, force components 
in sound field, 311-312 

Land breezes, 223-224, 383 
Larsonite, ammonia impregnated char¬ 
coal, 40 

Leaching of whetlerites, 78-80 
Life-thickness curves of canisters, 175- 
177 

Light beam through fog, 347-348 
Light extinction by fog and smoke, 
389-390 

Light scattered by aerosols 
see Scattering of light 
Lignin, raw material for activated 
charcoal, 25 

“Line source” release of gas clouds, 
260-264 

beach area release, 264 
forest area release, 263 
open terrain release, 260-263 
Liquid droplet dispersing bombs, 524- 
533 


bombs containing gases dissolved in 
liquid, 530-533 

DDT dispersing, plastic bomb, 524- 
527 

ejection-airburst bomb, 527-530 
Logarithmic-probability distri button, 
aerosol size, 304-305 
Lungs, retention of dust particles, 535 

M2-1-1 gas mask, 8 
M2A1 gas mask, 8 
M3 gas mask, 8 
M5 gas mask, 8 
MIXA1 gas mask canister, 9 
M9A2 gas mask canister, 9 
M10 gas mask canister, 9 
Mil gas mask canister, 10 
M47A2 bomb filled with plasticized 
white phosphorus, 561-564 
Mach number, measure of elastic 
effects, 621-622 
Macropores, definition, 117 
Mass median diameter (MMD) 
aerosol powders, 535, 537-538 
droplets, 401 

Mass-concentration meter, 338-339, 
362-363 

“Mechanical goat,” canister tester, 
292-293 

Mecklenburg equations for canisters, 
176 

Mercury cup anemometer, 244 
Mercury impregnated charcoal, 56, 
114-115 

Mesh size of canisters, 188-189 
Meteorological principles, 213-238, 
382-386 

see also Micrometeorology in wooded 
areas 

air motions, 219 
air-mass effects, 224-225 
atmospheric stability, 213-214 
breezes, land and sea, 223-224, 383- 
384 

convection, 219-220, 385-386 
DDT lethal dosage, 584-586 
ground layer of air, 214 
ground temperatures, 217-218 
gustiness, 219-220 
radiation effects, 215-217 
stability conditions over water, 
382 

stability relations at land-water 
boundaries, 383-384 
thermal gradient as stability deter¬ 
minant, 383 
thermal stability, 382 
turbulence, 219-220, 382 
wind fluctuations, 220—224 
Methylene blue smoke filter tests, 
~ 362 


SECRET 



716 


INDEX 


Micrometeorological instruments, 239- 
259 

anemometers, 239-246 
circuits used in field, 259 
for assessment of munition samples, 
255-256 

frequency meter, relay-type, 256-257 
humidity measurements, 255 
instruments for field use, 255-259 
keep-alive circuit, 257-259 
photocell illumination recorder, 255 
recording instruments, 256 
selection of instruments, 255-256 
smoke puffer, 254 
temperature apparatus, 247-253 
use in continuous observations, 
225-229 

vanes for gustiness, 253-254 
wind direction recorders, 246-247, 
259 

Micrometeorology in wooded areas, 
230-238 

forest temperatures, 234-236 
low canopy jungle conditions, 237- 
238 

turbulence in forest, 236 
wind direction, 232-233 
wind speed, 230-232 
Micropores defined, 117 
Microscopic examination of aerosol par¬ 
ticles, 334-335 
electron microscope, 335 
light microscope, 334 
suspension of water droplet in castor 
oil, 334 

Mie theory of light scattering by par¬ 
ticles, 318-321 

angular distribution of intensity, 321 
intensity of scattered light, 318 
plane-polarized components, 321 
scattering coefficient, 318-320 
total scattering by one particle, 318 
MIT-E1 canister tester, 372 
MIT-E1R1 optical mass-concentration 
meter, 363 

MIT-E1R7 smoke generator, 361 
MIT-E2 smoke penetrometer, 367 
MIT-Freeport Sulfur Co. generator, 
448 

MMD (mass median diameter) 
aerosol powders, 535, 537-538 
droplets, 401 

Molybdenum whetlerites, 57-64 
aging characteristics, 61 
compared with copper-silver-chro¬ 
mium whetlerites, 61-62, 64 
drying process, 59-60 
heat treatment temperature, 57-58 
mixed impregnations, 58 
optimum concentrations of compo¬ 
nents, 59 


organic acid additions, 58 
pilot plant experiments, 61-62 
rotary vs. static oven driers, 60 
simultaneous impregnation, molyb¬ 
denum and chromium, 62 
surveillance quality, 95-96 
zinc impregnations, 57 
Mortar shells for gas cloud dispersal, 
277-281 

atmospheric stability, 277-278 
dosage effect, 278 
wind velocity effect, 277 
wooded area performance, 279-281 
Mosquito exterminating bomb, 524- 
527 

atomization of liquid by explosive 
bursts, 524-526 

design and manufacture, 526-527 
droplet spectra from chargings, 525 
Mosquitoes, DDT test subjects, 578- 
588 

aedes aegypti, 581-583 
anopheles quadrimaculat us, 583-584 
males less resistant than females, 
581 

rate of paralysis, mosquitoes vs. 
flies, 584 

research history, 578 
resting vs. flying mosquitoes, 578- 
580 

toxic dosage, mosquitoes vs. flies, 582 
Motion, fluid 
see Wind tunnel studies 
Munitions 
see also Bombs 

airplane exhaust generator, 5C7-523, 
593-596 

atomization of liquids by explosions, 
408-410 

atomization of liquids by nozzles, 
398-406 

atomization of liquids in airplane 
sprays, 406-408 
herbicide dispersing, 547-548 
mustard gas generator pot, 419-425 
PWP (plasticized white phosphorus) 
munitions, 555-565 
smoke munitions, 395-396 
smoke pots, 441-448, 485-506 
thermal generators, 411-484 
Munitions for dispersing liquid aero¬ 
sols, 524-530 

Munitions for dispersing solid aerosols, 
537-545 

British developmental work, 539 
Cardox bomb, 542 
chamber tests, 540-541 
compressed air bomb, 542 
conclusions, 545 

DDT dispersing plastic bomb, 524- 
527 


dissolved gases under pressure in 
liquids, 530-533 

ejection-airburst bomb, 527-530 
field tests, 543-545 
gas-ejection bomb, 539-542 
particle size distribution assessment, 
538-539 

plastic bomb, 543 
tests, 537-538 

Mustard gas as toxic agent, 151 
Mustard gas generator pot, 419-425 
condensate composition, 422-423 
experimental models, 421-422 
field tests, 423-424 
fuel block formulas, 461 
operation, 420-421 

Nasal penetration by aerosols, 534 
NDRC balanced smoke filter, 365 
NDRC optical mass-concentration 
meter, 362 

NDRC photoelectric smoke filter pene¬ 
trometer, 365 

NDRC-E1R2 smoke penetrometer, 
365-367 

Nephelometer, filter tester, 364-365 
Newton’s law, bodies in turbulent mo¬ 
tion, 308 

Nickelous oxide as charcoal impreg- 
nant, 125 

Nitrate and sulfur smoke screen mix¬ 
tures 

see Sulfur-nitrate smoke screen mix¬ 
tures 

Nitrogen adsorption isotherms, 121- 
122 

Nitrogen adsorption on charcoal, 107- 
108, 111-112 
Nitrogen dioxide 

canister protection, 201 
mechanism of removal, 155 
Nitrogen surface complex on charcoal 
132-133 

Nitrogen trifluoride as war gases, 609 
Nonpersistent gases, sampling meth¬ 
ods, 284-294 
air injector, 293 

diaphragm pump sampler, 286-287 
field canister tester, 292-293 
field conductivity analyzer, 289-291 
hot wire analyzer, 287-289 
hydrostatic head pump sampler, 284- 
285 

radio control of samplers, 293 
rotary distributor sampler, 291-292 
snap sampler, 293 

suggestions, selection of methods, 
294 

summary, 294 
tape recorder, 293 
ultraviolet photometer, 293 


SECRET 





INDEX 


717 


Nozzle atomization of liquids, 398, 406 
hydraulic nozzle performance, 405 
pneumatic nozzle performance, 399- 
402 

smoke screen production, 405-406 
types of nozzles, 399 
Venturi atomizer, 402-405 
NRL smoke generator, 361 
NRL-E2 smoke penetration meter, 367 
NRL-E3 smoke penetration meter, 
372-373 

Nukiyama and Tanasawa studies 
atomizing nozzle equations, 593-594 
pneumatic nozzle, 399-402 
Nut shells, activated charcoal raw ma¬ 
terials, 25 

Nylon parachute for target identifica¬ 
tion bomb, 457 

Ocean temperature, diurnal variations, 
218 

Oil smoke generation by airplane ex¬ 
haust, 507-523 
Oil smoke pots, 441-448 
floating pot, 441-445 
fuel block formula, 461 
nonfloating pot, 445-446 
training pot, 446-447 
Oil vapor smoke generators, 377-378 
Oil-gunpowder smoke mixtures 

see Smoke pot mixtures, oil and gun¬ 
powder 

Oleic acid fogs, illuminated for color 
studies, 321-322 

Olsen bomb, pressurized liquid disper¬ 
sal, 530-533 

atomization of butyl carbitol, 531 
dichlorobenzene dispersal from spin¬ 
ning tubes, 532 
impracticality, 530-531 
ineffective for saturated aerosol pro¬ 
duction, 531-533 

multiple tube ejection bomb, 531-533 
solubility of carbon dioxide in butyl 
carbitol, 531 

solubility of carbon dioxide in mus¬ 
tard gas, 530 
spinning tubes, 531 

Optical measurements of particle size, 
343-353 

color of transmitted light, 350-353 
coronae, 347-348 
Owl instrument, 343-347 
Slope-o-meter, 348-350 
Orchard heater, British smoke screen 
layer, 375 

Organic base impregnations .of char¬ 
coals, 81-84 

pyridine and picoline impregnations, 
82-84, 96 


reactions of bases with cyanogen 
chloride, 81-82 

Owl, smoke observation instrument, 
343-347 

Oxygen surface complexes on charcoals, 
125-132 

complex formed during steam activa¬ 
tion, 131-132 

complexes present on charcoal, 126 
degassing experiments, 129, 131 
displacement of complex by adsorp¬ 
tion of vapors, 131 
effect of exposure to air, 130 
gas evolution from charcoals during 
heating, 128-132 

heat of binding, oxygen and carbon, 
128 

influence on adsorption of ammonia, 
128 

influence on adsorption of water 
vapor, 128 

influence on base and acid adsorptive 
properties, 127 

oxygen pickup by charcoals, 126 
whetlerizability, 131 

Paper as aerosol filter material, 357 
PCC activated charcoal manufacture, 
27-28 

Penetrometers for smoking testing 
see Smoke penetrometers 
pH factor 

effect on copper-silver-chromium 
whetlerites, 75 

effect on hexamine impregnants, 49 
Phenol-formaldehyde resins, 84-87 
Phosgene 

canister protection, 196-198 
conductimetric analysis, 285 
reaction with unimpregnated char¬ 
coal, 152-153 

reaction with whetlerites, 152-154 
removal mechanism, 152-154 
Phosphorus, plasticized white 

see PWP (plasticized white phospho¬ 
rus) 

Phosphorus trifluoride, 156, 608 
Phosphoryl trifluoride, 157-158 
Photocell illumination recorder, 255 
Photoelectric smoke penetrometers 
see Smoke penetrometers, photo¬ 
electric 

Photometer for gas sampling, 293 
Picoline impregnated charcoals, 82-84, 
96 

Pittsburgh Coke and Chemical Co., 
activated charcoal manufacture, 
27-28 

Plastic bomb, aerosol dispersal, 524-527 
atomization of liquids by explosive 
bursts, 524-526 


compared with gas-ejection bomb, 
541 

design and manufacture, 526-527 
droplet spectra from various charg¬ 
ings, 525 

liquid droplet dispersal, 524-527 
solid particulate dispersal, 543 
Polanyi relationship, adsorption tem¬ 
perature and adsorbate, 135 
Polarization 

in fluorine preparation, 611-612 
photometer, 345 

solid particles illumined by polarized 
light, 330 

uniform size particles, 322-323 
Pore size, charcoal 
see Charcoal pore size 
Pore structure, activated charcoal, 32 
Porous materials, measurement of sur¬ 
face, 97-99 

adsorption as function of pressure, 
98-99 

adsorption data equation, 97-98 
small pore structures, 98-99 
Powder dispersion, 535-536 
aggregates in aerosol cloud, 536 
British bombs for solid powder dis¬ 
persal, 539 

dispersibility of various powders, 
535-536 

egg albumen, 535, 541 
gas-ejection bomb, 539-543 
Precipitation of aerosols, 297 
Prest-o-log process, activated charcoal 
manufacture, 28-29 
PS (chloropicrin)gas test 
disadvantages, 19 
operation, 18 
use, 13 

PWP (plasticized white phosphorus), 
551-574 

antipersonnel effects, 565-568 
recommendations for future work, 
573-574 

temperature rise, 552 
white phosphorus, 551 
PWP (plasticized white phosphorus), 
manufacture, 552-555, 572-573 
granulators, batch, 553 
granulators, continuous, 553 
labor, 556 

mixing of constituents, 555 
phosphorus granulation, 553 
power and services, 556 
rubber, variations in types, 572-573 
rubber solution preparation, 553-555 
solvents, variant types, 573 
PWP (plasticized white phosphorus), 
manufacturing specifications, 
568-572 

apparent viscosity, 569-571 


SECRET 





718 


INDEX 


moisture, 569 
particle size, 568-569 
specific gravity, 569 
thermal stability, 569 
viscosity of rubber solution, 571-572 
PWP (plasticized white phosphorus), 
munitions, 555-565 
ballistic stability, 557-558 
comparison with white phosphorus 
munitions, 561-564 
filling weight, 557 
loading, 555 
moisture control, 556 
screening efficiency, Army bombs, 
561-564 

screening efficiency, Navy munitions, 
564-566 

PWP (plasticized white phosphorus), 
stability, 557-561 
ballistic stability, 557-558 
effect of aging on viscosity, 563 
effect of particle size, 559-560 
“instability factor”, 559 
stability, PWP containing vegetable 
oil, 562 

summary, surveillance tests, 559- 
561 

thermal stability, 569 
Pyridine adsorption on charcoal, 141 
Pyridine impregnated charcoals, 82-84, 
96 

Radiation and atmospheric effects, 216- 
217 

absorption of water vapor, 215 
atmospheric counterradiation, 217 
black-body temperature of earth, 
216-217 

radiation, clear vs. cloudy sky, 217 
reflected radiation, 215 
sky radiation, 216-218 
Radioactive smoke test, 362 
Radioactive tracer technique in gas 
studies, 640-643 
apparatus, 641 

concentration of agent in gas stream, 
641 

distribution, toxic agent in charcoal 
bed, 642-643 

location of catalyst in whetlerite, 643 
location of reaction product in whet¬ 
lerite, 643 

reaction products in gas stream, 642 
smoke filter study, 643 
war gases containing radioactive ele¬ 
ments, 640-641 

Rankinites, copper impregnated char¬ 
coals, 41 

Rayleigh theory of scattered light, 318 
Reflection of solar radiation by atmos¬ 
phere, 215-217 


Research recommendations 
atomization theory, 602 
DDT dispersal, 601 
E29R1 chemical bomb, 440 
gas masks, 208-209 
physiological effects of canister 
breathing resistance, 187 
PWP (plasticized white phosphorus), 
573-574 

Resins, absorbent, 84-87 
animated resins, 84 
chemical absorption vs. physical 
adsorption, 85 
effect of impregnants, 86-87 
evolution of ammonia, 87 
impregnation, 86 
preparation, 85-86 
volume changes with humidity, 
85-86 

Reynolds number 

flow of fluids measurement, 174-175 
viscous influence upon flow, measure¬ 
ment of, 621-622 
wind tunnel studies, 638-639 

Richardson number, relation to gas 
cloud travel, 263 

Rock wool as aerosol filter, 191, 357- 
358 

Rockets for smoke screen laying, 564- 
565 

“Rotary distributor sampler,” gases, 
291-292 

Rubber, PWP (plasticized white phos¬ 
phorus) constituent, 553-555 

St. Clair’s aerosol coagulation work, 
310-312 

Sampling methods for nonpersistent 
gases 

see Nonpersistent gases, sampling 
methods 

Saran charcoal 
characteristics, 25 
of theoretical interest, 31 
preparation process, 31 

Sawdust, activated charcoal raw mate¬ 
rial, 25 

Sawdust-chloride smoke pot mixtures, 
497-499 

Scattering of light by colored particles, 
332-333 

absorption characteristics, 332 
calculation tables, 333 
color of transmitted light, 333 
dye smoke particle size, 333 
multiple scattering, effect on color, 
333 

optical density, pure dye smoke, 
333 

Scattering of light by nonuniform size 
particles, 327-330 


heterogeneous aerosol without coagu¬ 
lation, 328-329 

scattered intensity vs. particle ra¬ 
dius, 328 

scattering analysis, 329-330 
transmission in settling, 328-329 
Scattering of light by single particles, 
318-321 

angular distribution of intensity, 
321 

intensity of scattered light, 318 
Mie theory, 318-321 
plane-polarized components, 321 
scattering coefficient, 318-320 
total scattering, one particle per unit 
intensity, 318 

Scattering of light by solid particles, 
330-332 

effective density, 331-332 
effective refractive index, 331-332 
polarization, 330 
scintillating particles, 330-331 
transmission in settling, 331-332 
Scattering of light by uniform size par¬ 
ticles, 321-327 

angular color distribution, 321-322 
polarization, 322-323 
scattering by large particles, 327 
total scattering, 323-326 
transmission, 326 
Screening by smoke 
see Smoke screens 
Sea breezes 

effect on gas cloud travel, 264 
meteorological characteristics, 223, 
383-384 
on islands, 224 
Selenium hexafluoride, 156 
Sell’s calculations of particle impacta- 
bility, 534-535 

Settling of aerosols under gravity 
see Aerosol settling 

Shemya installations, fog dispersal 
studies, 629 

Silver adsorption by whetlerizing solu¬ 
tions, 44 

Silver permanganate, carbon monoxide 
catalyst, 205 

Silver peroxide, carbon monoxide cata¬ 
lyst, 205 

Slide rule for gas concentration calcula¬ 
tion, 266 

Slope-o-meter, 348-350 
construction, 348-350 
light transmission as wavelength 
function, 348 
limitations, 350 
operation, 350 
Smoke 

coverage for stated area, 376 
defined, 301 


SECRET 





INDEX 


719 


electrical charge, homogeneous 
smoke, 308 

general properties; see Aerosol 
partible size, 301 
production by combustion, 299 
production by condensation, 315 
stability, 297 

unipolar charged smoke, 309 
Smoke clouds, behavior under mete¬ 
orological conditions, 384-386 
see also Smoke clouds, travel 
angle of rise, 386 
convective pattern, 385-386 
stable conditions, 384-385 
unstable conditions, 385 
Smoke clouds, disappearance, 386-388 
see also Aerosol cloud evaporation 
concentration of cloud, 386 
deposition rate, 387 
evaporation, 386-387 
inertial effects, 388 
Smoke clouds, travel, 380-384 
atmospheric diffusion, 380 
atmospheric diffusion theory, 384 
effect of temperature on density, 380 
formation, 380 

land-water boundary conditions, 
383-384 

thermal gradient, 383 
thermal stability, 382 
turbulence, 382 

wind speed and direction, 381-382 
Smoke filter testing, 360-374 
apparatus required, 360 
chemical test-smoke generators, 361 
flow rate selection, 360 
materials for test smoke, 361 
smoke generators, 361 
Smoke filter testing during production, 
371-374 

carbon-smoke penetrometer, 373 
Edgewood Arsenal E3 canister tester, 
371-372 

MIT-E1 canister tester, 372 
XRL-E3 smoke penetrometer, 372- 
373 

particle-counting canister tester, 373 
sodium-flame penetrometer, 373 
Smoke filter testing in laboratory, 361- 
371 

adamsite tests, 361 
Australian ionization penetrometer, 
363 

diphenylchloro arsine tests, 362 
methylene blue tests, 362 
optical smoke penetrometers, 362- 
363 

penetrometers, comparative tests, 
368-371 

photoelectric smoke penetrometers, 
363-368 


radioactive smoke test, 362 
Smoke formation 
see Aerosol formation 
Smoke from color dyes, 332-333 
absorption properties, 332 
color of transmitted light, 333 
colored smoke clouds, 392 
optical density, 332-333 
particle sizes, 333 
Smoke generators for airplanes 
see Airplane exhaust generator 
Smoke observation instrument, Owl, 
343-347 

Smoke particle sampler, 336-337 
advantages, 336 
construction, 336 

lithopone and zinc oxide deposits on 
slides, 337 

method of sampling, 336-337 
variety of particle shapes, 337 
Smoke penetrometers, 362-371 
comparative tests, 368-371 
MIT-E1R1 mass-concentration me¬ 
ter, 363 

NDRC mass-concentration meter, 
362 

optical, 362-363 

particle-counting smoke penetrome¬ 
ter, 368-371 

Smoke penetrometers, photoelectric, 
363-368 

British carbon-smoke penetrometers, 

364 

CWS-MIT-E2 penetrometer, 367 
Hill penetrometer, 363 
Kimberly-Clark nephelometer, 364- 

365 

NDRC balanced smoke filter, 365 
NDRC-E1R2 penetrometer, 365-367 
NRL-E2 penetrometer, 367 
Smoke pot, floating, 441-448 
control of oil feed rate, 443 
design and construction, 442-443 
floating stability, 445 
fuel block formula, 461 
operational principles, 441-442 
specifications, 441 
toxicity, 444-445 
Smoke pot mixtures, 485-506 
applications, 485 
availability of ingredients, 486 
continuous smoke generators, 485 
diol-sawdust-chloride mixtures, 497- 
499 

metal chloride mixtures, 488-494 
stability, 488 

substitute specifications, need for, 485 
sulfur-nitrate mixtures, 494-497 
toxicity, 488 

Smoke pot mixtures, oil and gun¬ 
powder, 499-506 


blasting powder, 501 
composition of charges, 501-503 
conclusions from experiments, 500 
containers, 503-505 
internal pressure measurements, 505- 
506 

jellied oil, vapor producing materials, 
501 

non-jellied mixtures, 502 
primers, 506 
requirements, 499-500 
temperatures in pots, 505 
transition mixtures, 503 
Smoke pot mixtures, screening power, 
486-488 

effect of smoke particle size, 487 
hygroscopic nature of mixtures, 486 
volatility and dilution, 487-488 
Smoke protection 

see Gas mask protection 
Smoke puffer, wind detector, 254 
Smoke screens, 375-379 

blanket vs. curtain screens, 375 
colored smoke screens, 392 
coverage, 376 

laid by airplane exhaust smoke gen¬ 
erators, 513-515 

laid by airplane rockets, 564-565 
laying methods, 378 
mechanical atomization production, 
405-406 

meteorological conditions, effect of, 
375 

obscuring power, 300 
oil vapor smoke generators, 377-378 
Smoke screens, materials, 376-377 
see also Smoke pot mixtures 
coagulation period, 376-377 
inflammability, 377 
particle size, oil smokes, 376-377 
requirements, 376 
sulfur, 376 

Smoke screens, tactical uses, 522-523 
area screening of an anchorage, 522- 
523 

defensive screens, 379 
individual ship screen, 523 
offensive screens, 379 
task force under way, screening of, 
522-523 

Smoke screens, visibility, 389-392 
amount of smoke required for obser¬ 
vation, 391-392 

conditions approaching extinction, 
390 

contrast limen, 389 
dependence on concentration, 390 
light extinction by fog, 389-390 
light extinction by screening smoke, 
390 

visibility formula, 390-392 


SECRET 




720 


INDEX 


visibility in natural fog, 389 
Smoke settler, differential, 341-343 
Smoke settler, homogeneous, 339 
Smoke signals, floating, 451-455 
colored signals, proposed design, 
454 

construction, 453-454 
development, 451-452 
dye chamber, 454-455 
fuel block formulas, 461 
specification, 450 
theory, 452 

Smokeless powder, thermal generator 
fuel, 482-483 

Smoluchowski expression, collisions be¬ 
tween particles, 307 
“Snap sampler,” gases, 293 
Soda lime, whetlerite component, 48 
Sodium-flame penetrometer, 373 
Soil, 217-218 
albedo effect, 218-219 
diurnal variations in temperature, 
218 

heat conductivity, 218 
temperature below earth’s surface, 
217-218 

temperature on earth’s surface, 217- 
218 

thermometer, 250 
Solar radiation, 215-217 
albedo effect, 218-219 
atmospheric counterradiation, 217 
influence on earth temperature, 215- 
216 

reflection, 215 

water vapor absorption, 215 
Solenoid production, 214 
Sound vibrations causing aerosol coag¬ 
ulation, 309-313 

attraction of particles due to air 
motion, 311-312 
laboratory experiments, 312 
motion of particles relative to each 
other, 310-311 
theory summarized, 312 
vortex motion, air around particles, 
312 

Stability of aerosols, 301-305 
acoustical forces, 302 
adhesion vs. separation, 302 
Brownian movement, effect on sta¬ 
bility, 301 

centrifugal forces, 302 
density variations with height, 305- 
306 

diffusion and evaporation, 297 
precipitation, 297 

settling of heterogeneous aerosols, 
303-305 

settling of homogeneous aerosols, 
302-303 


summary, 297 

thermal and electrical forces, 302 
Steam activation of charcoal 

see Activation of charcoal by steam 
Stearic acid fogs, illuminated for color 
studies, 321-322 

Stearman planes, DDT dispersing 
equipment, 594 

Stokes’ law, fall of small spheres, 303 
Stokes’ law deposition, rate of fall of 
particle during filtration, 355 
Stokes-Cunningham velocity of fall of a 
particle, 307 

Sulfite processed into gas mask char¬ 
coal, 30-31 

Sulfur and fluorine reactions, 604-605 
action of fluorine on sulfur com¬ 
pounds, 605 

controlled reaction, 604-605 
fluorination by heavy metal fluo¬ 
rides, 605 

nonelectric method of fluorine prepa¬ 
ration, 605 

sulfur hexafluoride, defluorination, 
605 

Sulfur as smoke screen material, 376 
Sulfur dioxide, mechanism of removal, 
155-156 

Sulfur pentafluoride, 157 
Sulfur smoke generators, 448-450 
Kimberly-Clark generator, 449-450 
MIT-Freeport Sulfur Co. generator, 
448 

Texas Gulf Sulphur Co. generator, 
448 

Sulfur surface coatings on charcoal, 
134 

Sulfur-nitrate smoke screen mixtures, 
494-497 

composition, 497 

fuel gas-sulfur vapor mixture, 495 
safety precautions, 497 
screening power, 496 
suggestions for improvement, 496 
sulfur smoke production, 494-495 
summary, 494 

Sulfuryl chloro-fluoride, 156-157 
Summary, NDRC, Division 10 activi¬ 
ties, 5, 7 

Surface area measurements, charcoals, 
97-102 

adsorption method of measurement, 
97-99 

methods applicable to charcoals, 99- 
101 

Surface coatings on charcoal, 132-134 
chlorine coatings, 133 
nitrogen coatings, 132-133 
sulfur coatings, 134 
Surging in fuel blocks, 471-476 
description, 471-472 


laboratory analysis, surge-producing 
charcoal, 473-475 
mechanism of surging, 475-476 
summary, surging experiments, 476 

Tanasawa’s pneumatic nozzle studies, 
399-402 

Tape recorder, gas sampler, 293 
Target identification bomb of colored 
smoke, 455-458 
components, 456-457 
dyes, 458 

flaming control, 457-458 
fuel block formulas, 461 
nylon parachute, 457 
operation, 456 

Task force under way, screening of, 
522-523 

TBM-3 exhaust smoke generator, 509, 
521-522 

combustion generator installation, 

521 

DDT dispersal use, 595 

plane design suited for generator, 509 

standardization of equipment, 521- 

522 

test results, 522 

Telescoping tail, E291U bomb, 438-439 
Temperature gradient measurement, 
383 

Temperature in forests, 234-236 
Temperature measurers, 247-253 
aspirated thermocouple systems, 
247-251 

recording resistance thermometers, 
251-252 

surface thermometers, 252 
Temperature of ground, 216-218 
albedo effect, 218-219 
as solar energy radiator, 216-217 
black-body temperature, 217 
diurnal variation, 218 
heat conductivity, surface materials, 
217-218 

ocean temperature, 218 
soil below earth’s surface, 217 
surface moisture effect, 218 
Texas Gulf Sulphur Co. generator, 448 
Thermal generator 

aerosol cloud evaporation, 415-419 
aerosol persistence, 412-415 
carrier gas from fuel, 412 
design requirements, 411-412 
heat from fuel gases, 411-412 
heat transfer, 412 
thermal stability of agent, 411 
vapor transfer, 412 

Thermal generator fuel blocks, 459-484 
alkali activation of charcoal, 466-467 
ammonium nitrate variables, 466- 
468 


SECRET 



INDEX 


721 


burning characteristics, 460 
. burning condition variables, 470-471 
effect of charcoal particle size, 465- 
466 

factors influencing reactivity, 467 
formula variations, effect on burning 
rate, 470 

lacquering variables, 469-470 
mixing variables, 468 
physical characteristics, 460 
pressing variable, 468-469 
testing of blocks, 463-464 
Thermal generator fuel blocks, surging, 

471- 476 

description, 471-472 

gas analysis of surging blocks, 474- 

475 

mechanism of surging, 475-476 
summary, surging experiments, 

476 

surging vs. nonsurging charcoals, 

472- 474 

Thermal generator fuels 

ammonium picrate-sodium nitrate 
fuels, 483-484 
liquid fuels, 484 

smokeless powder fuels, 482-483 
Thermal generator fuels, cast mixtures, 
479-482 

cast vs. pressed mixtures, 479-480 
formula variations, 481-482 
manufacturing process, 480 
mixture formulas, 461 
pH of mixture, 482 
properties, 480 
storage, 482 

suggestions for improvement, 482 
Thermal generator fuels, pressed mix¬ 
tures, 462-480 
block properties, 462-463 
cast vs. pressed mixtures, 479-480 
control of block characteristics, 464- 
471 

manufacturing procedure, 463 
mixture formulas, 461 
noncarbon mixtures, 477-480 
storage difficulties, 476-477 
Thermal generator mustard pot, 419- 
425 

conclusions, 424-425 
condensate composition, 422-423 
experimental models, 421-422 
field tests, 423-424 
fuel block formulas, 461 
operation, 420-421 
Thermal generator types 411-484 
colored smoke munitions, 451-458 
E29R1 bomb, 424-441 
F7A mustard pot, 419-425 
oil smoke pots, 441-448 
sulfur smoke generators, 448-450 


“Thermal precipitator,” smoke particle 
sampler, 336-337 
advantages, 336 
construction, 336 

lithopone and zinc oxide deposits on 
slides, 337 

method of sampling, 336-337 
variety of particle shapes, 337 
Thermal stability of atmosphere, 382 
Thermal turbulence in forest, 236 
Thermocouple systems, aspirated, 247- 
251 

aspirator, 249-250 
electrical system, 250-251 
mast, 248 

observational procedure, 251 
radiation shields, 247 
Thermodynamic atmosphere graphs, 
214 

Thermometer, earth surface temper¬ 
ature measurements, 252 
Thermometer, recording resistance, 
251-252 

Thiocyanate impregnations of whet- 
lerites, 50-52 
ammonia odor evolved, 51 
cyanogen chloride life, 51 
disadvantages, 49 
storage effect, 51 

Tobacco smoke, illustration of Ray¬ 
leigh’s theory, 322 

Tokyo Bay wind velocity and turbu¬ 
lence studies, 638 
Toxic gas adsorption 

see Adsorption wave theories 
Toxic gas clouds 
see Gas clouds 

Toxic gases, inorganic, 604-609 
alkyldifluorophosphates, 608 
alkylmonofluorothiophosphates, 608 
dialkylmonofluorophosphates, 606- 
608 

disulfur decafluoride, 604-606 
fluorosulfonates, 608 
miscellaneous gases, 608-609 
Tricresyl phosphate smoke material, 361 
Triphenyl phosphate smoke material, 
361 

Turbulence 

caused by irregular air motion, 219- 
220 

caused by wind speed, 382 
in forest, 236 

thermal instability, turbulence cause, 
382 

Ultraviolet photometer, gas sampler, 
293 

Vanadium whetlerites, 62-64 

cyanogen chloride life increase, 57 


heat treatment temperature, 57 
impregnating solution, 62-63 
preparation, 63-64 
storage lines, 63 
surveillance quality, 95-96 
Vapor condensation during aerosol 
formation, 299 

Vapors adsorbed by charcoals 

see Adsorption of vapors by charcoal 
Venturi 

air scoop for atomization, 406-409 
airplane exhaust generator, 510 
atomizer, 402-405, 594 
vaporizer, modifications for E29R1 
bomb, 433-435 

Vesicant dispersing air-burst bomb, 
527-530 
advantages, 527 
hexagonal bomb, 528-529 
round bomb, 529-530 
Visibility through fog and smoke, 389- 
392 

conditions approaching extinction, 
390 

contrast limen, 389 
dependence on particle size, 390 
formulae, 390-392 
light extinction by fog, 389-390 
light extinction by smoke, 390 
natural fog, 389 

War gases 

acid forming, 152-165 
acyl chlorides, 609 
amines, 166 
ammonia, 165 
arsine, 166-168, 609 
base-forming, 165-166 
carbon monoxide, 203-206 
chloropicrin, 151 
cyanogen chloride, 161-164 
fluorides, 156-158 
fluorophosphates, 606-608 
general conclusions, 164-166 
hydrogen cyanide, 158-161, 618-620 
inorganic gases, 604-609 
mustard gas, 419-425 
nitrogen dioxide, 155, 201 
nonpersistent gases, 284-294 
phosgene, 152-154, 196-198 
readily oxidizable, 166-168 
retained by physical adsorption, 151— 
152 

sulfur dioxide, 155-156 
Water adsorption from charcoal 

see Adsorption of water vapor from 
charcoal 

Whetlerite type A, 40-44 
canister performance, 41 
copper impregnant analyzed, 41 
distinct from “whetlerite A,” 40 


SECRET 



722 


INDEX 


preparation conditions, 44 
preparation process, 41 
Whetlerite type AS 
plant production, 43 
preparation conditions, 44 
preparation process, 43-44 
Whetlerites, 40-48 

catalyst located by radioactive trac¬ 
ers, 643 

chemisorption of gases, 144 
definition, 40 
early development, 40-41 
reaction product located by radio¬ 
active tracers, 643 
type D mixture, 48 
Whetlerites, aging studies, 91-95 
accelerated aging data, 92 
canisters field use, 92-95 
cyanogen chloride protection, 91 
dry storage, 91 
moist storage, 91 
rate of aging, 91 

Whetlerites, gas adsorption, 46-48 
arsine adsorption, 46-47 
basic vapors adsorption, 47 
hydrogen cyanide adsorption, 46-47 
“poisoning effect”, 47 
various vapors adsorption, 47-48 
Whetlerites, hexamine impregnated, 
48-50 

cyanogen chloride protection, 50 
disadvantages, 49 
hexamine application process, 49 
pH factor, effect on impregnants, 49 
salts added to impregnant, 49-50 
X-ray studies, 50 

Whetlerites, molybdenum impregnated 
see Molybdenum whetlerites 
Whetlerites, surveillance, 88-96 
see also Whetlerites, aging studies 
canister aging programs, 89-90 
early studies, whetlerite stability, 89 
effect of moisture on canister lives, 
88-89 

molybdenum whetlerites, 95-96 
picoline impregnants, 96 


pyridine impregnants, 96 
vanadium whetlerites, 95-96 
Whetlerites, thiocyanate impregnated, 
50-52 

ammonia odor evolved, 51 
application to whetlerite type A, 50 
application to whetlerite type AS, 51 
cyanogen chloride life, 51 
disadvantages, 49 
effect of storage, 51 
Whetlerizing solutions, 44-46 

adsorption of constituents from 
solution, 44 
concentrations, 44 
gases evolved during drying, 46 
heat of solution, 46 
silver adsorption, 44 
vapor pressure, 45 
X-ray studies, 45 

Whytlaw-Gray powder dispersing 
bomb, 539 

Wind curtains, 630-633 
Wind direction 

effect on smoke cloud travel, 381-382 
in wooded area, 232-233 
Wind direction recorders, 246-247 
CIT type vane, 246 
8-point commercial vane, 247 
field use, 259 

relay-type frequency meter, 256-257 
Wind fluctuations, 219-224 
anabatic winds, 223 
convection, 219-220 
eddy velocity, 220 
gradient wind, 220 
gravity winds, 222-223 
gustiness, 220 
katabatic wind, 222 
land and sea breezes, 223-224 
surface wind, 220 
thermal belts, 223 
turbulence, 219-220 
Wind speed 

at various heights, 222 
effect on area covered by gas 
clouds, 277 


effect on efficiency of gas cloud, 
260 

effect on gustiness, 220 
effect on 1,000 lb gas bombs, 269-270 
effect on smoke cloud travel, 381- 
382 

in wooded areas, 230-232 
measurements, 221-222 
turbulence cause, 382 
Wind tunnel studies, 621-639 
experimentation technique, 623-624 
flow measurement instruments, 623 
flow over terrain models, 638-639 
flow pattern around irregular bound¬ 
aries, 638 

fluid mechanics, fundamental rela¬ 
tionships, 621-622 
fog dispersal, 624-633 
gas diffusion, 633-638 
model method of study, 622 
wind tunnel construction, 623-624 
Wooded areas, micrometeorology, 230- 
238 

forest temperatures, 234-236 
low canopy jungle conditions, 237- 
238 

turbulence in forest, 236 
wind direction, 232-233 
wind speed, 230-232 

X-ray studies 

charcoal structural characteristics, 
145 

copper content of whetlerites, 45 
hexamine impregnated whetlerites, 
50 

Zinc chloride process, charcoal activa¬ 
tion, 38-39 

calcination, primary and secondary, 
39 

development, 38 
manufacturing process, 38-39 
mechanism of activation, 39 
reaction of mixer, 39 
Zinc impregnated charcoals, 57-58 



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